omena-transform-cst 0.3.0

//! Transform IR: node arena with epochs, edit transactions, and identity round-trip printing.

use omena_parser::{
    ParsedCssModuleComposesFactKind, ParsedCssModuleValueFactKind, ParsedIcssFactKind,
    ParsedStyleFacts, StyleDialect, TypedCstNode, facts_from_cst, parse_only,
};
use omena_syntax::{SyntaxKind, SyntaxNode};
use serde::Serialize;
use std::collections::BTreeSet;

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize)]
#[serde(transparent)]
pub struct IrNodeIdV0(pub usize);

impl IrNodeIdV0 {
    pub const fn index(self) -> usize {
        self.0
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IrTargetV0 {
    Node {
        node_id: IrNodeIdV0,
        observed_epoch: u64,
    },
}

impl IrTargetV0 {
    pub const fn node(node_id: IrNodeIdV0, observed_epoch: u64) -> Self {
        Self::Node {
            node_id,
            observed_epoch,
        }
    }

    pub const fn node_id(self) -> IrNodeIdV0 {
        match self {
            Self::Node { node_id, .. } => node_id,
        }
    }

    pub const fn observed_epoch(self) -> u64 {
        match self {
            Self::Node { observed_epoch, .. } => observed_epoch,
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum IrNodeKindV0 {
    StyleRule,
    AtRule,
    Declaration,
    Selector,
    Value,
    UrlValue,
}

impl IrNodeKindV0 {
    pub const fn as_label(self) -> &'static str {
        match self {
            Self::StyleRule => "style-rule",
            Self::AtRule => "at-rule",
            Self::Declaration => "declaration",
            Self::Selector => "selector",
            Self::Value => "value",
            Self::UrlValue => "url-value",
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum NodeTextOriginV0 {
    Original {
        source_id: String,
        source_span_start: usize,
        source_span_end: usize,
    },
    Synthesized {
        pass_id: String,
        parent_node_ids: Vec<IrNodeIdV0>,
    },
}

impl NodeTextOriginV0 {
    pub const fn is_original(&self) -> bool {
        matches!(self, Self::Original { .. })
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub struct IrBlockSpanV0 {
    pub prelude_start: usize,
    pub open_brace_start: usize,
    pub body_start: usize,
    pub body_end: usize,
    pub rule_end: usize,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct IrNodeV0 {
    pub node_id: IrNodeIdV0,
    pub kind: IrNodeKindV0,
    pub parent: Option<IrNodeIdV0>,
    pub children: Vec<IrNodeIdV0>,
    pub source_span_start: usize,
    pub source_span_end: usize,
    pub origin_index: usize,
    pub global_order: usize,
    pub dirty: bool,
    pub deleted: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub canonical_text: Option<String>,
    #[serde(skip_serializing)]
    pub block_span: Option<IrBlockSpanV0>,
    #[serde(skip_serializing)]
    pub owner_block_span: Option<IrBlockSpanV0>,
}

impl IrNodeV0 {
    pub fn source_span_len(&self) -> usize {
        self.source_span_end.saturating_sub(self.source_span_start)
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrKindIndexV0 {
    pub kind: IrNodeKindV0,
    pub node_ids: Vec<IrNodeIdV0>,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrParentIndexV0 {
    pub parent: Option<IrNodeIdV0>,
    pub node_ids: Vec<IrNodeIdV0>,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrIndexesV0 {
    pub by_kind: Vec<TransformIrKindIndexV0>,
    pub by_parent: Vec<TransformIrParentIndexV0>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrParseErrorSpanV0 {
    pub source_span_start: usize,
    pub source_span_end: usize,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct IrEditRegionV0 {
    pub source_span_start: usize,
    pub source_span_end: usize,
}

impl IrEditRegionV0 {
    pub const fn full(source_byte_len: usize) -> Self {
        Self {
            source_span_start: 0,
            source_span_end: source_byte_len,
        }
    }

    pub const fn contains_span(self, source_span_start: usize, source_span_end: usize) -> bool {
        self.source_span_start <= source_span_start && source_span_end <= self.source_span_end
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrV0 {
    pub schema_version: &'static str,
    pub product: &'static str,
    pub source_id: String,
    pub dialect: &'static str,
    pub source_byte_len: usize,
    pub parser_error_count: usize,
    pub parse_error_spans: Vec<TransformIrParseErrorSpanV0>,
    pub root_nodes: Vec<IrNodeIdV0>,
    pub nodes: Vec<IrNodeV0>,
    pub origins: Vec<NodeTextOriginV0>,
    pub indexes: TransformIrIndexesV0,
    pub original_node_count: usize,
    pub synthesized_node_count: usize,
    #[serde(skip_serializing)]
    ir_epoch: u64,
    #[serde(skip_serializing)]
    structural_block_spans: Vec<IrBlockSpanV0>,
    source_text: String,
}

impl TransformIrV0 {
    pub const fn ir_epoch(&self) -> u64 {
        self.ir_epoch
    }

    pub fn all_nodes_original(&self) -> bool {
        self.nodes.iter().all(|node| {
            !node.dirty
                && !node.deleted
                && self
                    .origins
                    .get(node.origin_index)
                    .is_some_and(NodeTextOriginV0::is_original)
        })
    }

    pub fn source_text(&self) -> &str {
        self.source_text.as_str()
    }

    pub fn structural_block_spans(&self) -> &[IrBlockSpanV0] {
        self.structural_block_spans.as_slice()
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum TransformIrPrintErrorV0 {
    MissingNodeOrigin {
        node_index: usize,
    },
    InvalidOriginalSpan {
        node_index: usize,
        source_span_start: usize,
        source_span_end: usize,
        source_byte_len: usize,
    },
    MissingSynthesizedText {
        node_index: usize,
    },
    CannotMaterializeParseErrorSpans {
        parser_error_count: usize,
    },
    MissingRenderedSpan {
        node_index: usize,
    },
    UnprojectableDirtyChild {
        node_index: usize,
        child_index: usize,
    },
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct TransformIrIdentityRoundTripV0 {
    pub schema_version: &'static str,
    pub product: &'static str,
    pub source_id: String,
    pub dialect: &'static str,
    pub source_byte_len: usize,
    pub printed_byte_len: usize,
    pub node_count: usize,
    pub original_node_count: usize,
    pub synthesized_node_count: usize,
    pub parser_error_count: usize,
    pub all_nodes_original: bool,
    pub byte_identical: bool,
    pub printed_css: String,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum IrTransactionValidationErrorV0 {
    DanglingNode {
        node_index: usize,
        dangling_node_index: usize,
    },
    ParentChildLinkMismatch {
        node_index: usize,
        parent_index: usize,
    },
    DeclarationWithoutRuleOwner {
        node_index: usize,
    },
    DuplicateGlobalOrder {
        global_order: usize,
    },
    MissingProvenance {
        node_index: usize,
        origin_index: usize,
    },
    EditOutsideDeclaredRegion {
        node_index: usize,
        region: IrEditRegionV0,
    },
    EditInsideParseErrorRegion {
        node_index: usize,
        parse_error_span: TransformIrParseErrorSpanV0,
    },
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum IrTransactionErrorV0 {
    UnknownNode {
        node_index: usize,
    },
    InvalidSourceSpan {
        node_index: usize,
        source_span_start: usize,
        source_span_end: usize,
    },
    NodeKindMismatch {
        node_index: usize,
        expected: IrNodeKindV0,
        actual: IrNodeKindV0,
    },
    Validation(IrTransactionValidationErrorV0),
}

pub struct IrTransactionV0<'ir> {
    ir: &'ir mut TransformIrV0,
    working: TransformIrV0,
    pass_id: String,
    declared_region: IrEditRegionV0,
    changed_node_ids: Vec<IrNodeIdV0>,
}

struct IrSubtreeCopyStateV0<'inserted, 'mapping, 'copied> {
    inserted_ir: &'inserted TransformIrV0,
    anchor_id: IrNodeIdV0,
    canonical_text_overrides: &'inserted [(IrNodeIdV0, String)],
    node_mapping: &'mapping mut [Option<IrNodeIdV0>],
    next_global_order: &'mapping mut usize,
    copied_nodes: &'copied mut Vec<IrNodeIdV0>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
struct CandidateNodeV0 {
    kind: IrNodeKindV0,
    source_span_start: usize,
    source_span_end: usize,
    block_span: Option<IrBlockSpanV0>,
    owner_block_span: Option<IrBlockSpanV0>,
}

pub fn lower_transform_ir_from_source(
    source: &str,
    dialect: StyleDialect,
    source_id: impl Into<String>,
) -> TransformIrV0 {
    let source_id = source_id.into();
    let parse = parse_only(source, dialect);
    let cst = parse.cst();
    let facts = facts_from_cst(source, &parse);
    let mut candidates = Vec::new();

    candidates.extend(
        cst.rules()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::StyleRule, node)),
    );
    candidates.extend(
        cst.at_rules()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::AtRule, node)),
    );
    candidates.extend(css_module_value_statement_candidates(&facts, cst.root()));
    candidates.extend(css_module_composes_declaration_candidates(
        &facts,
        cst.root(),
    ));
    candidates.extend(icss_module_block_candidates(&facts, cst.root()));
    candidates.extend(
        cst.declarations()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::Declaration, node)),
    );
    candidates.extend(
        cst.selectors()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::Selector, node)),
    );
    candidates.extend(
        cst.values()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::Value, node)),
    );
    candidates.extend(
        cst.url_values()
            .into_iter()
            .map(|node| candidate_from_typed_node(IrNodeKindV0::UrlValue, node)),
    );

    let block_spans = collect_structural_block_spans(cst.root());
    for candidate in &mut candidates {
        assign_candidate_block_spans(candidate, block_spans.as_slice());
    }

    candidates.sort_by_key(|candidate| {
        (
            candidate.source_span_start,
            std::cmp::Reverse(candidate.source_span_end),
            kind_order(candidate.kind),
        )
    });
    candidates.dedup();

    let mut nodes = candidates
        .iter()
        .enumerate()
        .map(|(index, candidate)| IrNodeV0 {
            node_id: IrNodeIdV0(index),
            kind: candidate.kind,
            parent: None,
            children: Vec::new(),
            source_span_start: candidate.source_span_start,
            source_span_end: candidate.source_span_end,
            origin_index: index,
            global_order: index,
            dirty: false,
            deleted: false,
            canonical_text: None,
            block_span: candidate.block_span,
            owner_block_span: candidate.owner_block_span,
        })
        .collect::<Vec<_>>();

    let origins = candidates
        .iter()
        .map(|candidate| NodeTextOriginV0::Original {
            source_id: source_id.clone(),
            source_span_start: candidate.source_span_start,
            source_span_end: candidate.source_span_end,
        })
        .collect::<Vec<_>>();

    assign_parent_links(&mut nodes);
    let root_nodes = nodes
        .iter()
        .filter(|node| node.parent.is_none())
        .map(|node| node.node_id)
        .collect::<Vec<_>>();
    let indexes = build_indexes(&nodes);
    let original_node_count = origins.iter().filter(|origin| origin.is_original()).count();

    TransformIrV0 {
        schema_version: "0",
        product: "omena-transform-cst.transform-ir",
        source_id,
        dialect: dialect_label(dialect),
        source_byte_len: source.len(),
        parser_error_count: parse.errors().len(),
        parse_error_spans: parse
            .errors()
            .iter()
            .map(|error| TransformIrParseErrorSpanV0 {
                source_span_start: error.range.start().into(),
                source_span_end: error.range.end().into(),
            })
            .collect(),
        root_nodes,
        nodes,
        origins,
        indexes,
        original_node_count,
        synthesized_node_count: 0,
        ir_epoch: 0,
        structural_block_spans: block_spans,
        source_text: source.to_string(),
    }
}

fn css_module_value_statement_candidates(
    facts: &ParsedStyleFacts,
    root: &SyntaxNode,
) -> Vec<CandidateNodeV0> {
    facts
        .css_module_values
        .iter()
        .filter(|value| {
            matches!(
                value.kind,
                ParsedCssModuleValueFactKind::Definition
                    | ParsedCssModuleValueFactKind::ImportSource
            )
        })
        .filter_map(|value| {
            let fact_start = value.range.start().into();
            let fact_end = value.range.end().into();
            let (source_span_start, source_span_end) =
                syntax_node_span_containing(root, fact_start, fact_end, |kind| {
                    matches!(
                        kind,
                        SyntaxKind::CssModuleExportBlock | SyntaxKind::CssModuleImportBlock
                    )
                })?;
            Some(CandidateNodeV0 {
                kind: IrNodeKindV0::AtRule,
                source_span_start,
                source_span_end,
                block_span: None,
                owner_block_span: None,
            })
        })
        .collect()
}

fn css_module_composes_declaration_candidates(
    facts: &ParsedStyleFacts,
    root: &SyntaxNode,
) -> Vec<CandidateNodeV0> {
    facts
        .css_module_composes
        .iter()
        .filter(|composes| {
            matches!(
                composes.kind,
                ParsedCssModuleComposesFactKind::Target
                    | ParsedCssModuleComposesFactKind::ImportSource
            )
        })
        .filter_map(|composes| {
            let fact_start = composes.range.start().into();
            let fact_end = composes.range.end().into();
            let (source_span_start, source_span_end) =
                syntax_node_span_containing(root, fact_start, fact_end, |kind| {
                    kind == SyntaxKind::CssModuleComposesDeclaration
                })?;
            Some(CandidateNodeV0 {
                kind: IrNodeKindV0::Declaration,
                source_span_start,
                source_span_end,
                block_span: None,
                owner_block_span: None,
            })
        })
        .collect::<BTreeSet<_>>()
        .into_iter()
        .collect()
}

fn icss_module_block_candidates(
    facts: &ParsedStyleFacts,
    root: &SyntaxNode,
) -> Vec<CandidateNodeV0> {
    facts
        .icss
        .iter()
        .filter(|icss| {
            matches!(
                icss.kind,
                ParsedIcssFactKind::ExportName
                    | ParsedIcssFactKind::ImportLocalName
                    | ParsedIcssFactKind::ImportRemoteName
                    | ParsedIcssFactKind::ImportSource
            )
        })
        .filter_map(|icss| {
            let fact_start = icss.range.start().into();
            let fact_end = icss.range.end().into();
            let (source_span_start, source_span_end) =
                syntax_node_span_containing(root, fact_start, fact_end, |kind| {
                    matches!(
                        kind,
                        SyntaxKind::CssModuleExportBlock | SyntaxKind::CssModuleImportBlock
                    )
                })?;
            Some(CandidateNodeV0 {
                kind: IrNodeKindV0::StyleRule,
                source_span_start,
                source_span_end,
                block_span: None,
                owner_block_span: None,
            })
        })
        .collect::<BTreeSet<_>>()
        .into_iter()
        .collect()
}

fn syntax_node_span_containing(
    root: &SyntaxNode,
    fact_start: usize,
    fact_end: usize,
    accepts_kind: impl Fn(SyntaxKind) -> bool,
) -> Option<(usize, usize)> {
    root.descendants()
        .filter(|node| accepts_kind(node.kind()))
        .filter_map(|node| {
            let range = node.text_range();
            let start = usize::from(range.start());
            let end = usize::from(range.end());
            (start <= fact_start && fact_end <= end).then_some((start, end))
        })
        .min_by_key(|(start, end)| end.saturating_sub(*start))
}

pub fn print_transform_ir_css(ir: &TransformIrV0) -> Result<String, TransformIrPrintErrorV0> {
    validate_node_origins(ir)?;
    if ir.all_nodes_original() {
        return Ok(ir.source_text.clone());
    }

    let mut output = String::new();
    let mut cursor = 0;
    for node_id in sorted_root_nodes(ir) {
        let node = &ir.nodes[node_id.index()];
        if node.source_span_start > cursor {
            output.push_str(source_slice(
                ir,
                node.node_id.index(),
                cursor,
                node.source_span_start,
            )?);
        }
        output.push_str(render_node_css(ir, node.node_id)?.as_str());
        cursor = cursor.max(node.source_span_end);
    }
    if cursor < ir.source_text.len() {
        output.push_str(source_slice(ir, 0, cursor, ir.source_text.len())?);
    }
    Ok(output)
}

pub fn materialize_transform_ir_printed_source(
    ir: &mut TransformIrV0,
) -> Result<String, TransformIrPrintErrorV0> {
    if ir.parser_error_count > 0 && ir.parse_error_spans.is_empty() {
        return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
            parser_error_count: ir.parser_error_count,
        });
    }

    let rendered = render_transform_ir_css_with_node_spans(ir)?;
    let printed_css = rendered.css;
    let source_id = ir.source_id.clone();
    let deleted_subtree_nodes = deleted_subtree_flags(ir);
    let materialized_spans = ir
        .nodes
        .iter()
        .map(|node| {
            rendered
                .node_spans
                .get(node.node_id.index())
                .and_then(|span| *span)
                .or_else(|| deleted_subtree_nodes[node.node_id.index()].then_some((0, 0)))
                .ok_or(TransformIrPrintErrorV0::MissingRenderedSpan {
                    node_index: node.node_id.index(),
                })
        })
        .collect::<Result<Vec<_>, _>>()?;
    let remapped_parse_error_spans = remap_parse_error_spans_after_materialization(
        ir,
        printed_css.as_str(),
        materialized_spans.as_slice(),
        deleted_subtree_nodes.as_slice(),
    )?;
    let mut origins = Vec::with_capacity(ir.nodes.len());

    for node in &mut ir.nodes {
        let (source_span_start, source_span_end) = materialized_spans[node.node_id.index()];
        let origin_index = origins.len();
        origins.push(NodeTextOriginV0::Original {
            source_id: source_id.clone(),
            source_span_start,
            source_span_end,
        });
        node.source_span_start = source_span_start;
        node.source_span_end = source_span_end;
        node.origin_index = origin_index;
        node.dirty = false;
        node.deleted = deleted_subtree_nodes[node.node_id.index()];
        node.canonical_text = None;
    }

    ir.source_text = printed_css.clone();
    ir.source_byte_len = ir.source_text.len();
    ir.origins = origins;
    ir.parser_error_count = remapped_parse_error_spans.len();
    ir.parse_error_spans = remapped_parse_error_spans;
    refresh_ir_block_spans(ir);
    refresh_transform_ir_metadata(ir);
    Ok(printed_css)
}

struct RenderedTransformIrCssV0 {
    css: String,
    node_spans: Vec<Option<(usize, usize)>>,
}

fn render_transform_ir_css_with_node_spans(
    ir: &TransformIrV0,
) -> Result<RenderedTransformIrCssV0, TransformIrPrintErrorV0> {
    validate_node_origins(ir)?;
    let mut css = String::new();
    let mut node_spans = vec![None; ir.nodes.len()];
    let mut cursor = 0;

    for node_id in sorted_root_nodes(ir) {
        let node = &ir.nodes[node_id.index()];
        if node.source_span_start > cursor {
            css.push_str(source_slice(
                ir,
                node.node_id.index(),
                cursor,
                node.source_span_start,
            )?);
        }
        render_node_css_with_spans(ir, node.node_id, &mut css, node_spans.as_mut_slice())?;
        cursor = cursor.max(node.source_span_end);
    }
    if cursor < ir.source_text.len() {
        css.push_str(source_slice(ir, 0, cursor, ir.source_text.len())?);
    }

    Ok(RenderedTransformIrCssV0 { css, node_spans })
}

impl<'ir> IrTransactionV0<'ir> {
    pub fn new(
        ir: &'ir mut TransformIrV0,
        pass_id: impl Into<String>,
        declared_region: IrEditRegionV0,
    ) -> Self {
        Self {
            working: ir.clone(),
            ir,
            pass_id: pass_id.into(),
            declared_region,
            changed_node_ids: Vec::new(),
        }
    }

    pub fn replace_node(
        &mut self,
        node_id: IrNodeIdV0,
        canonical_text: impl Into<String>,
    ) -> Result<(), IrTransactionErrorV0> {
        self.mark_node_synthesized(node_id, canonical_text.into(), false)
    }

    pub fn replace_node_covering_span(
        &mut self,
        node_id: IrNodeIdV0,
        canonical_text: impl Into<String>,
        source_span_start: usize,
        source_span_end: usize,
    ) -> Result<(), IrTransactionErrorV0> {
        self.mark_node_covering_span(
            node_id,
            canonical_text.into(),
            false,
            source_span_start,
            source_span_end,
        )
    }

    pub fn delete_node(&mut self, node_id: IrNodeIdV0) -> Result<(), IrTransactionErrorV0> {
        self.mark_node_synthesized(node_id, String::new(), true)
    }

    pub fn unwrap_node(&mut self, node_id: IrNodeIdV0) -> Result<(), IrTransactionErrorV0> {
        let Some(node) = self.working.nodes.get(node_id.index()).cloned() else {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: node_id.index(),
            });
        };
        let (promoted_children, retained_children): (Vec<_>, Vec<_>) = node
            .children
            .iter()
            .copied()
            .partition(|child_id| self.node_should_be_promoted_by_unwrap(node.kind, *child_id));
        self.mark_node_synthesized(node_id, String::new(), true)?;
        self.working.nodes[node_id.index()].children = retained_children;
        for child_id in &promoted_children {
            self.working.nodes[child_id.index()].parent = node.parent;
        }
        self.promote_nodes_after_anchor(node_id, &promoted_children);
        refresh_transform_ir_metadata(&mut self.working);
        Ok(())
    }

    pub fn insert_before(
        &mut self,
        anchor_id: IrNodeIdV0,
        kind: IrNodeKindV0,
        canonical_text: impl Into<String>,
    ) -> Result<IrNodeIdV0, IrTransactionErrorV0> {
        let Some(anchor) = self.working.nodes.get(anchor_id.index()).cloned() else {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: anchor_id.index(),
            });
        };
        let anchor_order = anchor.global_order;
        for node in &mut self.working.nodes {
            if node.global_order >= anchor_order {
                node.global_order += 1;
            }
        }
        let node_id = IrNodeIdV0(self.working.nodes.len());
        let origin_index = self.push_synthesized_origin([anchor_id]);
        let node = IrNodeV0 {
            node_id,
            kind,
            parent: anchor.parent,
            children: Vec::new(),
            source_span_start: anchor.source_span_start,
            source_span_end: anchor.source_span_start,
            origin_index,
            global_order: anchor_order,
            dirty: true,
            deleted: false,
            canonical_text: Some(canonical_text.into()),
            block_span: None,
            owner_block_span: None,
        };
        self.working.nodes.push(node);
        self.insert_node_in_parent(anchor_id, node_id);
        self.changed_node_ids.push(node_id);
        refresh_transform_ir_metadata(&mut self.working);
        Ok(node_id)
    }

    pub fn insert_ir_roots_before(
        &mut self,
        anchor_id: IrNodeIdV0,
        inserted_ir: &TransformIrV0,
    ) -> Result<Vec<IrNodeIdV0>, IrTransactionErrorV0> {
        let Some(anchor) = self.working.nodes.get(anchor_id.index()).cloned() else {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: anchor_id.index(),
            });
        };
        let root_ids = sorted_root_nodes(inserted_ir)
            .into_iter()
            .filter(|node_id| !inserted_ir.nodes[node_id.index()].deleted)
            .collect::<Vec<_>>();
        if root_ids.is_empty() {
            return Ok(Vec::new());
        }

        let insertion_count = root_ids
            .iter()
            .map(|root_id| active_subtree_node_count(inserted_ir, *root_id))
            .sum::<usize>();
        for node in &mut self.working.nodes {
            if node.global_order >= anchor.global_order {
                node.global_order += insertion_count;
            }
        }

        let mut copied_roots = Vec::with_capacity(root_ids.len());
        let mut copied_nodes = Vec::with_capacity(insertion_count);
        let mut node_mapping = vec![None; inserted_ir.nodes.len()];
        let mut next_global_order = anchor.global_order;
        let canonical_text_overrides =
            root_canonical_text_overrides(inserted_ir, root_ids.as_slice())?;
        let mut copy_state = IrSubtreeCopyStateV0 {
            inserted_ir,
            anchor_id,
            canonical_text_overrides: canonical_text_overrides.as_slice(),
            node_mapping: node_mapping.as_mut_slice(),
            next_global_order: &mut next_global_order,
            copied_nodes: &mut copied_nodes,
        };
        for root_id in root_ids {
            let copied_root =
                self.copy_ir_subtree_before_anchor(&mut copy_state, root_id, anchor.parent)?;
            copied_roots.push(copied_root);
        }
        for copied_root in &copied_roots {
            self.insert_node_in_parent(anchor_id, *copied_root);
        }
        self.changed_node_ids.extend(copied_nodes);
        refresh_transform_ir_metadata(&mut self.working);
        Ok(copied_roots)
    }

    pub fn rewrite_value(
        &mut self,
        node_id: IrNodeIdV0,
        canonical_text: impl Into<String>,
    ) -> Result<(), IrTransactionErrorV0> {
        let Some(node) = self.working.nodes.get(node_id.index()) else {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: node_id.index(),
            });
        };
        if node.kind != IrNodeKindV0::Value {
            return Err(IrTransactionErrorV0::NodeKindMismatch {
                node_index: node_id.index(),
                expected: IrNodeKindV0::Value,
                actual: node.kind,
            });
        }
        self.mark_node_synthesized(node_id, canonical_text.into(), false)
    }

    pub fn commit(mut self) -> Result<(), IrTransactionErrorV0> {
        refresh_transform_ir_metadata(&mut self.working);
        validate_transaction_commit(&self.working, &self.changed_node_ids, self.declared_region)
            .map_err(IrTransactionErrorV0::Validation)?;
        self.working.ir_epoch = self.ir.ir_epoch.saturating_add(1);
        *self.ir = self.working;
        Ok(())
    }

    fn mark_node_synthesized(
        &mut self,
        node_id: IrNodeIdV0,
        canonical_text: String,
        deleted: bool,
    ) -> Result<(), IrTransactionErrorV0> {
        if self.working.nodes.get(node_id.index()).is_none() {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: node_id.index(),
            });
        }
        let origin_index = self.push_synthesized_origin([node_id]);
        let node = &mut self.working.nodes[node_id.index()];
        node.origin_index = origin_index;
        node.dirty = true;
        node.deleted = deleted;
        node.canonical_text = Some(canonical_text);
        self.changed_node_ids.push(node_id);
        refresh_transform_ir_metadata(&mut self.working);
        Ok(())
    }

    fn mark_node_covering_span(
        &mut self,
        node_id: IrNodeIdV0,
        canonical_text: String,
        deleted: bool,
        source_span_start: usize,
        source_span_end: usize,
    ) -> Result<(), IrTransactionErrorV0> {
        let Some(node) = self.working.nodes.get(node_id.index()) else {
            return Err(IrTransactionErrorV0::UnknownNode {
                node_index: node_id.index(),
            });
        };
        if source_span_start > node.source_span_start
            || source_span_end < node.source_span_end
            || source_span_start > source_span_end
            || source_span_end > self.working.source_text.len()
            || !self.working.source_text.is_char_boundary(source_span_start)
            || !self.working.source_text.is_char_boundary(source_span_end)
        {
            return Err(IrTransactionErrorV0::InvalidSourceSpan {
                node_index: node_id.index(),
                source_span_start,
                source_span_end,
            });
        }
        self.mark_node_synthesized(node_id, canonical_text, deleted)?;
        let node = &mut self.working.nodes[node_id.index()];
        node.source_span_start = source_span_start;
        node.source_span_end = source_span_end;
        refresh_transform_ir_metadata(&mut self.working);
        Ok(())
    }

    fn push_synthesized_origin(
        &mut self,
        parent_node_ids: impl IntoIterator<Item = IrNodeIdV0>,
    ) -> usize {
        let origin_index = self.working.origins.len();
        self.working.origins.push(NodeTextOriginV0::Synthesized {
            pass_id: self.pass_id.clone(),
            parent_node_ids: parent_node_ids.into_iter().collect(),
        });
        origin_index
    }

    fn copy_ir_subtree_before_anchor(
        &mut self,
        copy_state: &mut IrSubtreeCopyStateV0<'_, '_, '_>,
        source_node_id: IrNodeIdV0,
        parent: Option<IrNodeIdV0>,
    ) -> Result<IrNodeIdV0, IrTransactionErrorV0> {
        if let Some(copied_node_id) = copy_state.node_mapping[source_node_id.index()] {
            return Ok(copied_node_id);
        }
        let source_node = &copy_state.inserted_ir.nodes[source_node_id.index()];
        let canonical_text =
            canonical_text_override_for_node(copy_state.canonical_text_overrides, source_node_id)
                .map(str::to_string)
                .map(Ok)
                .unwrap_or_else(|| {
                    source_slice(
                        copy_state.inserted_ir,
                        source_node.node_id.index(),
                        source_node.source_span_start,
                        source_node.source_span_end,
                    )
                    .map(str::to_string)
                    .map_err(|_| IrTransactionErrorV0::InvalidSourceSpan {
                        node_index: source_node.node_id.index(),
                        source_span_start: source_node.source_span_start,
                        source_span_end: source_node.source_span_end,
                    })
                })?;
        let anchor_source_span_start =
            self.working.nodes[copy_state.anchor_id.index()].source_span_start;
        let node_id = IrNodeIdV0(self.working.nodes.len());
        let origin_index = self.push_synthesized_origin([copy_state.anchor_id]);
        let global_order = *copy_state.next_global_order;
        *copy_state.next_global_order += 1;
        self.working.nodes.push(IrNodeV0 {
            node_id,
            kind: source_node.kind,
            parent,
            children: Vec::new(),
            source_span_start: anchor_source_span_start,
            source_span_end: anchor_source_span_start,
            origin_index,
            global_order,
            dirty: true,
            deleted: false,
            canonical_text: Some(canonical_text),
            block_span: None,
            owner_block_span: None,
        });
        copy_state.node_mapping[source_node_id.index()] = Some(node_id);
        copy_state.copied_nodes.push(node_id);

        let copied_children = sorted_child_nodes(copy_state.inserted_ir, source_node)
            .into_iter()
            .filter(|child_id| !copy_state.inserted_ir.nodes[child_id.index()].deleted)
            .map(|child_id| self.copy_ir_subtree_before_anchor(copy_state, child_id, Some(node_id)))
            .collect::<Result<Vec<_>, _>>()?;
        self.working.nodes[node_id.index()].children = copied_children;
        Ok(node_id)
    }

    fn insert_node_in_parent(&mut self, anchor_id: IrNodeIdV0, node_id: IrNodeIdV0) {
        let parent = self.working.nodes[node_id.index()].parent;
        match parent {
            Some(parent_id) => insert_before_in_list(
                &mut self.working.nodes[parent_id.index()].children,
                anchor_id,
                node_id,
            ),
            None => insert_before_in_list(&mut self.working.root_nodes, anchor_id, node_id),
        }
    }

    fn promote_nodes_after_anchor(&mut self, anchor_id: IrNodeIdV0, node_ids: &[IrNodeIdV0]) {
        let parent = self.working.nodes[anchor_id.index()].parent;
        let list = match parent {
            Some(parent_id) => &mut self.working.nodes[parent_id.index()].children,
            None => &mut self.working.root_nodes,
        };
        let mut insert_index = list
            .iter()
            .position(|candidate| *candidate == anchor_id)
            .map_or(list.len(), |index| index + 1);
        for node_id in node_ids {
            if list.contains(node_id) {
                continue;
            }
            list.insert(insert_index, *node_id);
            insert_index += 1;
        }
    }

    fn node_should_be_promoted_by_unwrap(
        &self,
        wrapper_kind: IrNodeKindV0,
        child_id: IrNodeIdV0,
    ) -> bool {
        wrapper_kind != IrNodeKindV0::StyleRule
            || self.working.nodes[child_id.index()].kind != IrNodeKindV0::Selector
    }
}

pub fn summarize_transform_ir_identity_round_trip(
    source: &str,
    dialect: StyleDialect,
    source_id: impl Into<String>,
) -> Result<TransformIrIdentityRoundTripV0, TransformIrPrintErrorV0> {
    let source_id = source_id.into();
    let ir = lower_transform_ir_from_source(source, dialect, source_id.clone());
    let printed_css = print_transform_ir_css(&ir)?;
    Ok(TransformIrIdentityRoundTripV0 {
        schema_version: "0",
        product: "omena-transform-cst.transform-ir-identity-round-trip",
        source_id,
        dialect: dialect_label(dialect),
        source_byte_len: source.len(),
        printed_byte_len: printed_css.len(),
        node_count: ir.nodes.len(),
        original_node_count: ir.original_node_count,
        synthesized_node_count: ir.synthesized_node_count,
        parser_error_count: ir.parser_error_count,
        all_nodes_original: ir.all_nodes_original(),
        byte_identical: printed_css == source,
        printed_css,
    })
}

fn candidate_from_typed_node<T: TypedCstNode>(kind: IrNodeKindV0, node: T) -> CandidateNodeV0 {
    let range = node.text_range();
    CandidateNodeV0 {
        kind,
        source_span_start: range.start().into(),
        source_span_end: range.end().into(),
        block_span: None,
        owner_block_span: None,
    }
}

fn collect_structural_block_spans(root: &SyntaxNode) -> Vec<IrBlockSpanV0> {
    let mut spans = root
        .descendants()
        .filter(|node| syntax_kind_can_own_block(node.kind()))
        .filter_map(structural_block_span)
        .collect::<Vec<_>>();
    spans.sort_unstable();
    spans.dedup();
    spans
}

fn structural_block_span(node: &SyntaxNode) -> Option<IrBlockSpanV0> {
    let open = node
        .descendants_with_tokens()
        .filter_map(|element| element.into_token())
        .find(|token| token.kind() == SyntaxKind::LeftBrace)?
        .text_range();
    let close = node
        .descendants_with_tokens()
        .filter_map(|element| element.into_token())
        .filter(|token| token.kind() == SyntaxKind::RightBrace)
        .last()?
        .text_range();
    let prelude_start = node.text_range().start().into();
    let open_brace_start = open.start().into();
    let body_start = open.end().into();
    let body_end = close.start().into();
    let rule_end = close.end().into();
    (prelude_start <= open_brace_start && body_start <= body_end).then_some(IrBlockSpanV0 {
        prelude_start,
        open_brace_start,
        body_start,
        body_end,
        rule_end,
    })
}

fn syntax_kind_can_own_block(kind: SyntaxKind) -> bool {
    omena_parser::is_at_rule_node_kind(kind)
        || matches!(
            kind,
            SyntaxKind::Rule
                | SyntaxKind::KeyframeBlock
                | SyntaxKind::CssModuleExportBlock
                | SyntaxKind::CssModuleImportBlock
                | SyntaxKind::ScssControlIf
                | SyntaxKind::ScssControlElse
                | SyntaxKind::ScssControlEach
                | SyntaxKind::ScssControlFor
                | SyntaxKind::ScssControlWhile
                | SyntaxKind::LessMixinDeclaration
                | SyntaxKind::LessDetachedRulesetNode
        )
}

fn assign_candidate_block_spans(candidate: &mut CandidateNodeV0, spans: &[IrBlockSpanV0]) {
    if candidate.source_span_start == candidate.source_span_end {
        return;
    }
    candidate.block_span = block_span_for_range(
        candidate.source_span_start,
        candidate.source_span_end,
        spans,
    );
    candidate.owner_block_span = owner_block_span_for_range(
        candidate.source_span_start,
        candidate.source_span_end,
        spans,
    );
}

fn block_span_for_range(
    source_span_start: usize,
    source_span_end: usize,
    spans: &[IrBlockSpanV0],
) -> Option<IrBlockSpanV0> {
    spans
        .iter()
        .copied()
        .find(|span| span.prelude_start == source_span_start && span.rule_end == source_span_end)
        .or_else(|| {
            spans
                .iter()
                .copied()
                .filter(|span| {
                    source_span_start <= span.prelude_start && span.rule_end <= source_span_end
                })
                .min_by_key(|span| span.rule_end.saturating_sub(span.prelude_start))
        })
}

fn owner_block_span_for_range(
    source_span_start: usize,
    source_span_end: usize,
    spans: &[IrBlockSpanV0],
) -> Option<IrBlockSpanV0> {
    spans
        .iter()
        .copied()
        .filter(|span| span.body_start <= source_span_start && source_span_end <= span.body_end)
        .min_by_key(|span| span.body_end.saturating_sub(span.body_start))
}

pub fn structural_block_spans_for_source(
    source: &str,
    dialect: StyleDialect,
) -> Vec<IrBlockSpanV0> {
    let parsed = parse_only(source, dialect);
    collect_structural_block_spans(parsed.cst().root())
}

fn refresh_ir_block_spans(ir: &mut TransformIrV0) {
    let Some(dialect) = dialect_from_label(ir.dialect) else {
        return;
    };
    let spans = structural_block_spans_for_source(ir.source_text.as_str(), dialect);
    for node in &mut ir.nodes {
        if node.deleted || node.source_span_start == node.source_span_end {
            node.block_span = None;
            node.owner_block_span = None;
            continue;
        }
        node.block_span = block_span_for_range(
            node.source_span_start,
            node.source_span_end,
            spans.as_slice(),
        );
        node.owner_block_span = owner_block_span_for_range(
            node.source_span_start,
            node.source_span_end,
            spans.as_slice(),
        );
    }
    ir.structural_block_spans = spans;
}

fn dialect_from_label(label: &str) -> Option<StyleDialect> {
    match label {
        "css" => Some(StyleDialect::Css),
        "scss" => Some(StyleDialect::Scss),
        "sass" => Some(StyleDialect::Sass),
        "less" => Some(StyleDialect::Less),
        _ => None,
    }
}

fn block_spans_for_ir_text(ir: &TransformIrV0, source: &str) -> Vec<IrBlockSpanV0> {
    dialect_from_label(ir.dialect)
        .map(|dialect| structural_block_spans_for_source(source, dialect))
        .unwrap_or_default()
}

fn trimmed_prelude_span(source: &str, span: IrBlockSpanV0) -> Option<(usize, usize)> {
    let prelude = source.get(span.prelude_start..span.open_brace_start)?;
    let start = span.prelude_start + prelude.len().saturating_sub(prelude.trim_start().len());
    let end = span
        .open_brace_start
        .saturating_sub(prelude.len().saturating_sub(prelude.trim_end().len()));
    (start < end).then_some((start, end))
}

fn block_span_for_rendered_start(
    source: &str,
    spans: &[IrBlockSpanV0],
    start: usize,
) -> Option<IrBlockSpanV0> {
    spans.iter().copied().find(|span| {
        trimmed_prelude_span(source, *span).is_some_and(|(prelude_start, _)| prelude_start == start)
    })
}

const fn dialect_label(dialect: StyleDialect) -> &'static str {
    match dialect {
        StyleDialect::Css => "css",
        StyleDialect::Scss => "scss",
        StyleDialect::Sass => "sass",
        StyleDialect::Less => "less",
    }
}

fn assign_parent_links(nodes: &mut [IrNodeV0]) {
    for index in 0..nodes.len() {
        let parent = nearest_parent_index(index, nodes);
        nodes[index].parent = parent.map(IrNodeIdV0);
    }
    for index in 0..nodes.len() {
        if let Some(parent) = nodes[index].parent {
            nodes[parent.index()].children.push(IrNodeIdV0(index));
        }
    }
}

fn refresh_transform_ir_metadata(ir: &mut TransformIrV0) {
    ir.indexes = build_indexes(&ir.nodes);
    ir.original_node_count = ir
        .nodes
        .iter()
        .filter(|node| {
            !node.deleted
                && ir
                    .origins
                    .get(node.origin_index)
                    .is_some_and(NodeTextOriginV0::is_original)
        })
        .count();
    ir.synthesized_node_count = ir
        .nodes
        .iter()
        .filter(|node| {
            !node.deleted
                && ir
                    .origins
                    .get(node.origin_index)
                    .is_some_and(|origin| !origin.is_original())
        })
        .count();
}

fn validate_transaction_commit(
    ir: &TransformIrV0,
    changed_node_ids: &[IrNodeIdV0],
    declared_region: IrEditRegionV0,
) -> Result<(), IrTransactionValidationErrorV0> {
    validate_no_dangling_nodes(ir)?;
    validate_parent_child_links(ir)?;
    validate_declaration_ownership(ir)?;
    validate_global_order_slots(ir)?;
    validate_provenance(ir)?;
    validate_changed_nodes_inside_region(ir, changed_node_ids, declared_region)?;
    validate_changed_nodes_outside_parse_errors(ir, changed_node_ids)?;
    Ok(())
}

fn validate_no_dangling_nodes(ir: &TransformIrV0) -> Result<(), IrTransactionValidationErrorV0> {
    for node in &ir.nodes {
        if let Some(parent) = node.parent
            && parent.index() >= ir.nodes.len()
        {
            return Err(IrTransactionValidationErrorV0::DanglingNode {
                node_index: node.node_id.index(),
                dangling_node_index: parent.index(),
            });
        }
        for child in &node.children {
            if child.index() >= ir.nodes.len() {
                return Err(IrTransactionValidationErrorV0::DanglingNode {
                    node_index: node.node_id.index(),
                    dangling_node_index: child.index(),
                });
            }
        }
    }
    Ok(())
}

fn validate_parent_child_links(ir: &TransformIrV0) -> Result<(), IrTransactionValidationErrorV0> {
    for node in &ir.nodes {
        if let Some(parent) = node.parent {
            let parent_node = &ir.nodes[parent.index()];
            if parent == node.node_id || !parent_node.children.contains(&node.node_id) {
                return Err(IrTransactionValidationErrorV0::ParentChildLinkMismatch {
                    node_index: node.node_id.index(),
                    parent_index: parent.index(),
                });
            }
        }
        for child in &node.children {
            if ir.nodes[child.index()].parent != Some(node.node_id) {
                return Err(IrTransactionValidationErrorV0::ParentChildLinkMismatch {
                    node_index: child.index(),
                    parent_index: node.node_id.index(),
                });
            }
        }
    }
    Ok(())
}

fn validate_declaration_ownership(
    ir: &TransformIrV0,
) -> Result<(), IrTransactionValidationErrorV0> {
    for node in &ir.nodes {
        if node.deleted || node.kind != IrNodeKindV0::Declaration {
            continue;
        }
        if !has_rule_owner(ir, node)
            && !has_icss_root_declaration_owner(ir, node)
            && !has_less_mixin_declaration_owner(ir, node)
        {
            return Err(
                IrTransactionValidationErrorV0::DeclarationWithoutRuleOwner {
                    node_index: node.node_id.index(),
                },
            );
        }
    }
    Ok(())
}

fn validate_global_order_slots(ir: &TransformIrV0) -> Result<(), IrTransactionValidationErrorV0> {
    let mut seen = BTreeSet::new();
    for node in ir.nodes.iter().filter(|node| !node.deleted) {
        if !seen.insert(node.global_order) {
            return Err(IrTransactionValidationErrorV0::DuplicateGlobalOrder {
                global_order: node.global_order,
            });
        }
    }
    Ok(())
}

fn validate_provenance(ir: &TransformIrV0) -> Result<(), IrTransactionValidationErrorV0> {
    for node in ir.nodes.iter().filter(|node| !node.deleted) {
        let Some(origin) = ir.origins.get(node.origin_index) else {
            return Err(IrTransactionValidationErrorV0::MissingProvenance {
                node_index: node.node_id.index(),
                origin_index: node.origin_index,
            });
        };
        match origin {
            NodeTextOriginV0::Original {
                source_span_start,
                source_span_end,
                ..
            } => {
                if source_slice(
                    ir,
                    node.node_id.index(),
                    *source_span_start,
                    *source_span_end,
                )
                .is_err()
                {
                    return Err(IrTransactionValidationErrorV0::MissingProvenance {
                        node_index: node.node_id.index(),
                        origin_index: node.origin_index,
                    });
                }
            }
            NodeTextOriginV0::Synthesized { .. } => {
                if node.canonical_text.is_none() {
                    return Err(IrTransactionValidationErrorV0::MissingProvenance {
                        node_index: node.node_id.index(),
                        origin_index: node.origin_index,
                    });
                }
            }
        }
    }
    Ok(())
}

fn validate_changed_nodes_inside_region(
    ir: &TransformIrV0,
    changed_node_ids: &[IrNodeIdV0],
    declared_region: IrEditRegionV0,
) -> Result<(), IrTransactionValidationErrorV0> {
    for node_id in changed_node_ids {
        let node = &ir.nodes[node_id.index()];
        if !declared_region.contains_span(node.source_span_start, node.source_span_end) {
            return Err(IrTransactionValidationErrorV0::EditOutsideDeclaredRegion {
                node_index: node.node_id.index(),
                region: declared_region,
            });
        }
    }
    Ok(())
}

fn validate_changed_nodes_outside_parse_errors(
    ir: &TransformIrV0,
    changed_node_ids: &[IrNodeIdV0],
) -> Result<(), IrTransactionValidationErrorV0> {
    for node_id in changed_node_ids {
        let node = &ir.nodes[node_id.index()];
        if let Some(parse_error_span) = ir.parse_error_spans.iter().copied().find(|span| {
            spans_overlap(
                node.source_span_start,
                node.source_span_end,
                span.source_span_start,
                span.source_span_end,
            ) && !changed_node_preserves_parse_error_source(ir, node, *span)
        }) {
            return Err(IrTransactionValidationErrorV0::EditInsideParseErrorRegion {
                node_index: node.node_id.index(),
                parse_error_span,
            });
        }
    }
    Ok(())
}

fn changed_node_preserves_parse_error_source(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    parse_error_span: TransformIrParseErrorSpanV0,
) -> bool {
    if changed_node_deletes_structural_parse_error_region(node, parse_error_span) {
        return true;
    }
    if node.deleted
        || parse_error_span.source_span_start < node.source_span_start
        || parse_error_span.source_span_end > node.source_span_end
    {
        return false;
    }

    let Some(canonical_text) = node.canonical_text.as_deref() else {
        return false;
    };
    let Some((context_start, context_end)) = parse_error_context_span(ir, node, parse_error_span)
    else {
        return false;
    };
    let Ok(parse_error_source) = source_slice(ir, node.node_id.index(), context_start, context_end)
    else {
        return false;
    };

    !parse_error_source.is_empty() && canonical_text.contains(parse_error_source)
}

fn changed_node_deletes_structural_parse_error_region(
    node: &IrNodeV0,
    parse_error_span: TransformIrParseErrorSpanV0,
) -> bool {
    node.deleted
        && node.canonical_text.as_deref().is_some_and(str::is_empty)
        && matches!(
            node.kind,
            IrNodeKindV0::StyleRule | IrNodeKindV0::AtRule | IrNodeKindV0::Declaration
        )
        && node.source_span_start <= parse_error_span.source_span_start
        && parse_error_span.source_span_end <= node.source_span_end
}

fn parse_error_context_span(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    parse_error_span: TransformIrParseErrorSpanV0,
) -> Option<(usize, usize)> {
    if parse_error_span.source_span_start > parse_error_span.source_span_end
        || parse_error_span.source_span_end > ir.source_text.len()
    {
        return None;
    }
    let bytes = ir.source_text.as_bytes();
    let mut start = parse_error_span.source_span_start;
    let mut end = parse_error_span.source_span_end;

    while start > node.source_span_start && is_parse_error_context_byte(bytes[start - 1]) {
        start -= 1;
    }
    while end < node.source_span_end && is_parse_error_context_byte(bytes[end]) {
        end += 1;
    }

    (start < end).then_some((start, end))
}

const fn is_parse_error_context_byte(byte: u8) -> bool {
    byte.is_ascii_alphanumeric()
        || matches!(
            byte,
            b'-' | b'_' | b'.' | b'$' | b'#' | b'%' | b'@' | b'/' | b'\\'
        )
}

fn has_rule_owner(ir: &TransformIrV0, node: &IrNodeV0) -> bool {
    let mut parent = node.parent;
    while let Some(parent_id) = parent {
        let parent_node = &ir.nodes[parent_id.index()];
        if matches!(
            parent_node.kind,
            IrNodeKindV0::StyleRule | IrNodeKindV0::AtRule | IrNodeKindV0::Selector
        ) {
            return true;
        }
        parent = parent_node.parent;
    }
    false
}

fn has_icss_root_declaration_owner(ir: &TransformIrV0, node: &IrNodeV0) -> bool {
    if node.parent.is_some() {
        return false;
    }
    root_declaration_owner_prelude(ir, node)
        .is_some_and(|prelude| prelude == ":export" || prelude.starts_with(":import("))
}

fn has_less_mixin_declaration_owner(ir: &TransformIrV0, node: &IrNodeV0) -> bool {
    ir.dialect == "less"
        && node.parent.is_none()
        && root_declaration_owner_prelude(ir, node).is_some_and(less_prelude_is_callable_mixin)
}

fn root_declaration_owner_prelude<'source>(
    ir: &'source TransformIrV0,
    node: &IrNodeV0,
) -> Option<&'source str> {
    let span = node.owner_block_span?;
    ir.source_text
        .get(span.prelude_start..span.open_brace_start)
        .map(str::trim)
}

fn less_prelude_is_callable_mixin(prelude: &str) -> bool {
    let bytes = prelude.as_bytes();
    let mut index = 0;
    while index < bytes.len() && bytes[index].is_ascii_whitespace() {
        index += 1;
    }
    if index >= bytes.len() || !matches!(bytes[index], b'.' | b'#') {
        return false;
    }
    index += 1;
    if index >= bytes.len() {
        return false;
    }
    while index < bytes.len() {
        match bytes[index] {
            byte if byte.is_ascii_alphanumeric() || matches!(byte, b'_' | b'-') => {
                index += 1;
            }
            b'\\' => {
                index = index.saturating_add(2);
            }
            _ => break,
        }
    }
    while index < bytes.len() && bytes[index].is_ascii_whitespace() {
        index += 1;
    }
    bytes.get(index) == Some(&b'(')
}

fn sorted_root_nodes(ir: &TransformIrV0) -> Vec<IrNodeIdV0> {
    let mut root_nodes = ir.root_nodes.clone();
    root_nodes.sort_by_key(|node_id| {
        let node = &ir.nodes[node_id.index()];
        (node.source_span_start, node.global_order)
    });
    root_nodes
}

fn active_subtree_node_count(ir: &TransformIrV0, node_id: IrNodeIdV0) -> usize {
    let node = &ir.nodes[node_id.index()];
    if node.deleted {
        return 0;
    }
    1 + node
        .children
        .iter()
        .map(|child_id| active_subtree_node_count(ir, *child_id))
        .sum::<usize>()
}

fn root_canonical_text_overrides(
    ir: &TransformIrV0,
    root_ids: &[IrNodeIdV0],
) -> Result<Vec<(IrNodeIdV0, String)>, IrTransactionErrorV0> {
    let mut overrides = Vec::with_capacity(root_ids.len());
    let mut cursor = 0usize;
    for (index, root_id) in root_ids.iter().copied().enumerate() {
        let node = &ir.nodes[root_id.index()];
        let end = root_ids
            .get(index + 1)
            .map(|next_root_id| ir.nodes[next_root_id.index()].source_span_start)
            .unwrap_or(ir.source_text.len());
        let start = cursor.min(node.source_span_start);
        let text = source_slice(ir, node.node_id.index(), start, end).map_err(|_| {
            IrTransactionErrorV0::InvalidSourceSpan {
                node_index: node.node_id.index(),
                source_span_start: start,
                source_span_end: end,
            }
        })?;
        overrides.push((root_id, text.to_string()));
        cursor = end;
    }
    Ok(overrides)
}

fn canonical_text_override_for_node(
    overrides: &[(IrNodeIdV0, String)],
    node_id: IrNodeIdV0,
) -> Option<&str> {
    overrides
        .iter()
        .find_map(|(candidate_id, text)| (*candidate_id == node_id).then_some(text.as_str()))
}

fn render_node_css(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
) -> Result<String, TransformIrPrintErrorV0> {
    let node = &ir.nodes[node_id.index()];
    if node.deleted {
        return Ok(String::new());
    }
    if node.dirty {
        let Some(canonical_text) = &node.canonical_text else {
            return Err(TransformIrPrintErrorV0::MissingSynthesizedText {
                node_index: node.node_id.index(),
            });
        };
        return render_dirty_node_with_children(ir, node, canonical_text);
    }

    render_original_node_with_children(ir, node)
}

fn render_node_css_with_spans(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    output: &mut String,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    let node = &ir.nodes[node_id.index()];
    let rendered_start = output.len();
    if node.deleted {
        assign_deleted_subtree_spans(ir, node_id, rendered_start, node_spans);
        return Ok(());
    }

    if node.dirty {
        let Some(canonical_text) = &node.canonical_text else {
            return Err(TransformIrPrintErrorV0::MissingSynthesizedText {
                node_index: node.node_id.index(),
            });
        };
        render_dirty_node_with_children_and_spans(ir, node, canonical_text, output, node_spans)?;
    } else {
        render_original_node_with_children_and_spans(ir, node, output, node_spans)?;
    }

    node_spans[node_id.index()] = Some((rendered_start, output.len()));
    Ok(())
}

fn assign_deleted_subtree_spans(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    rendered_start: usize,
    node_spans: &mut [Option<(usize, usize)>],
) {
    node_spans[node_id.index()] = Some((rendered_start, rendered_start));
    for child_id in sorted_child_nodes(ir, &ir.nodes[node_id.index()]) {
        assign_deleted_subtree_spans(ir, child_id, rendered_start, node_spans);
    }
}

fn deleted_subtree_flags(ir: &TransformIrV0) -> Vec<bool> {
    ir.nodes
        .iter()
        .map(|node| node.deleted || has_deleted_ancestor(ir, node))
        .collect()
}

fn has_deleted_ancestor(ir: &TransformIrV0, node: &IrNodeV0) -> bool {
    let mut parent = node.parent;
    while let Some(parent_id) = parent {
        let parent_node = &ir.nodes[parent_id.index()];
        if parent_node.deleted {
            return true;
        }
        parent = parent_node.parent;
    }
    false
}

fn remap_parse_error_spans_after_materialization(
    ir: &TransformIrV0,
    printed_css: &str,
    materialized_spans: &[(usize, usize)],
    deleted_subtree_nodes: &[bool],
) -> Result<Vec<TransformIrParseErrorSpanV0>, TransformIrPrintErrorV0> {
    let mut remapped_spans = Vec::with_capacity(ir.parse_error_spans.len());
    for parse_error_span in ir.parse_error_spans.iter().copied() {
        if parse_error_span.source_span_start > parse_error_span.source_span_end
            || parse_error_span.source_span_end > ir.source_text.len()
            || !ir
                .source_text
                .is_char_boundary(parse_error_span.source_span_start)
            || !ir
                .source_text
                .is_char_boundary(parse_error_span.source_span_end)
        {
            return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
                parser_error_count: ir.parser_error_count.max(ir.parse_error_spans.len()),
            });
        }
        let Some(container) = parse_error_container_node(ir, parse_error_span) else {
            return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
                parser_error_count: ir.parser_error_count.max(ir.parse_error_spans.len()),
            });
        };
        if deleted_subtree_nodes[container.node_id.index()] {
            continue;
        }
        let Some((rendered_start, _)) = materialized_spans.get(container.node_id.index()).copied()
        else {
            return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
                parser_error_count: ir.parser_error_count.max(ir.parse_error_spans.len()),
            });
        };
        let Some(remapped_span) =
            remap_parse_error_span_with_container(ir, container, parse_error_span, rendered_start)
        else {
            return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
                parser_error_count: ir.parser_error_count.max(ir.parse_error_spans.len()),
            });
        };
        if remapped_span.source_span_start > remapped_span.source_span_end
            || remapped_span.source_span_end > printed_css.len()
            || !printed_css.is_char_boundary(remapped_span.source_span_start)
            || !printed_css.is_char_boundary(remapped_span.source_span_end)
        {
            if container.dirty {
                continue;
            }
            return Err(TransformIrPrintErrorV0::CannotMaterializeParseErrorSpans {
                parser_error_count: ir.parser_error_count.max(ir.parse_error_spans.len()),
            });
        }
        remapped_spans.push(remapped_span);
    }
    Ok(remapped_spans)
}

fn parse_error_container_node(
    ir: &TransformIrV0,
    parse_error_span: TransformIrParseErrorSpanV0,
) -> Option<&IrNodeV0> {
    ir.nodes
        .iter()
        .filter(|node| {
            node.source_span_start <= parse_error_span.source_span_start
                && parse_error_span.source_span_end <= node.source_span_end
        })
        .min_by_key(|node| {
            (
                if node.dirty || node.deleted { 0 } else { 1 },
                node.source_span_len(),
            )
        })
}

fn remap_parse_error_span_with_container(
    ir: &TransformIrV0,
    container: &IrNodeV0,
    parse_error_span: TransformIrParseErrorSpanV0,
    rendered_start: usize,
) -> Option<TransformIrParseErrorSpanV0> {
    let (relative_start, relative_end) = if container.dirty {
        remap_parse_error_relative_span_inside_dirty_node(ir, container, parse_error_span)?
    } else {
        (
            parse_error_span
                .source_span_start
                .checked_sub(container.source_span_start)?,
            parse_error_span
                .source_span_end
                .checked_sub(container.source_span_start)?,
        )
    };
    Some(TransformIrParseErrorSpanV0 {
        source_span_start: rendered_start.checked_add(relative_start)?,
        source_span_end: rendered_start.checked_add(relative_end)?,
    })
}

fn remap_parse_error_relative_span_inside_dirty_node(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    parse_error_span: TransformIrParseErrorSpanV0,
) -> Option<(usize, usize)> {
    if node.deleted
        || parse_error_span.source_span_start < node.source_span_start
        || parse_error_span.source_span_end > node.source_span_end
    {
        return None;
    }
    let canonical_text = node.canonical_text.as_deref()?;
    let projection = dirty_node_text_projection(ir, node, canonical_text).ok()?;
    let original_start = parse_error_span
        .source_span_start
        .checked_sub(node.source_span_start)?;
    let original_end = parse_error_span
        .source_span_end
        .checked_sub(node.source_span_start)?;
    if let (Some(projected_start), Some(projected_end)) = (
        project_dirty_node_original_offset(&projection, original_start),
        project_dirty_node_original_offset(&projection, original_end),
    ) {
        return Some((projected_start, projected_end));
    }
    let (context_start, context_end) = parse_error_context_span(ir, node, parse_error_span)?;
    let context_text = source_slice(ir, node.node_id.index(), context_start, context_end).ok()?;
    if context_text.is_empty() {
        return None;
    }
    let context_offset = canonical_text.find(context_text)?;
    let relative_start_in_context = parse_error_span
        .source_span_start
        .checked_sub(context_start)?;
    let relative_end_in_context = parse_error_span
        .source_span_end
        .checked_sub(context_start)?;
    Some((
        context_offset.checked_add(relative_start_in_context)?,
        context_offset.checked_add(relative_end_in_context)?,
    ))
}

struct DirtyNodeTextProjectionV0 {
    original_replacement_start: usize,
    original_replacement_end: usize,
    rendered_replacement_end: usize,
}

fn render_dirty_node_with_children(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    canonical_text: &str,
) -> Result<String, TransformIrPrintErrorV0> {
    if node_has_zero_width_synthesized_span(ir, node) {
        return Ok(canonical_text.to_string());
    }
    let projection = dirty_node_text_projection(ir, node, canonical_text)?;
    let mut output = String::new();
    let mut cursor = 0;
    let mut child_was_composed = false;

    for child_id in sorted_child_nodes(ir, node) {
        if child_id == node.node_id {
            continue;
        }
        if !node_subtree_has_mutation(ir, child_id) {
            continue;
        }
        let child = &ir.nodes[child_id.index()];
        let Some(child_start) = child
            .source_span_start
            .checked_sub(node.source_span_start)
            .and_then(|offset| project_dirty_node_original_offset(&projection, offset))
        else {
            return Ok(canonical_text.to_string());
        };
        let Some(child_end) = child
            .source_span_end
            .checked_sub(node.source_span_start)
            .and_then(|offset| project_dirty_node_original_offset(&projection, offset))
        else {
            return Ok(canonical_text.to_string());
        };
        if child_start < cursor
            || child_end < child_start
            || child_end > canonical_text.len()
            || !canonical_text.is_char_boundary(child_start)
            || !canonical_text.is_char_boundary(child_end)
        {
            return Ok(canonical_text.to_string());
        }
        output.push_str(&canonical_text[cursor..child_start]);
        output.push_str(render_node_css(ir, child_id)?.as_str());
        cursor = child_end;
        child_was_composed = true;
    }

    if !child_was_composed {
        return Ok(canonical_text.to_string());
    }
    output.push_str(&canonical_text[cursor..]);
    Ok(output)
}

fn render_dirty_node_with_children_and_spans(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    canonical_text: &str,
    output: &mut String,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    if node_has_zero_width_synthesized_span(ir, node) {
        let rendered_start = output.len();
        output.push_str(canonical_text);
        assign_rendered_subtree_spans(
            ir,
            node.node_id,
            rendered_start,
            rendered_start + canonical_text.len(),
            output,
            node_spans,
        )?;
        return Ok(());
    }
    let projection = dirty_node_text_projection(ir, node, canonical_text)?;
    let rendered_start = output.len();
    let mut cursor = 0;
    let mut child_was_composed = false;

    for child_id in sorted_child_nodes(ir, node) {
        if child_id == node.node_id {
            continue;
        }
        let child = &ir.nodes[child_id.index()];
        let projected_child_start = child
            .source_span_start
            .checked_sub(node.source_span_start)
            .and_then(|offset| project_dirty_node_original_offset(&projection, offset));
        let projected_child_end = child
            .source_span_end
            .checked_sub(node.source_span_start)
            .and_then(|offset| project_dirty_node_original_offset(&projection, offset));
        let projected_offsets = projected_child_start.zip(projected_child_end);
        let direct_offsets = direct_child_replacement_offsets(ir, node, child, canonical_text);
        let rendered_offsets =
            rendered_child_offsets_in_dirty_node(ir, node, child, canonical_text, cursor)?;
        let prefer_rendered_offsets = rendered_offsets.is_some()
            && matches!(
                (node.kind, child.kind),
                (_, IrNodeKindV0::StyleRule)
                    | (_, IrNodeKindV0::Selector)
                    | (_, IrNodeKindV0::Declaration)
                    | (IrNodeKindV0::Declaration, IrNodeKindV0::Value)
            );
        let selected_offsets = if prefer_rendered_offsets {
            rendered_offsets
        } else {
            projected_offsets.or(direct_offsets).or(rendered_offsets)
        };
        let used_direct_offsets =
            !prefer_rendered_offsets && projected_offsets.is_none() && direct_offsets.is_some();
        let used_rendered_offsets =
            selected_offsets == rendered_offsets && rendered_offsets.is_some();
        let Some((child_start, child_end)) = selected_offsets else {
            return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
                node_index: node.node_id.index(),
                child_index: child.node_id.index(),
            });
        };
        if child_start < cursor
            || child_end < child_start
            || child_end > canonical_text.len()
            || !canonical_text.is_char_boundary(child_start)
            || !canonical_text.is_char_boundary(child_end)
        {
            return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
                node_index: node.node_id.index(),
                child_index: child.node_id.index(),
            });
        }
        output.push_str(&canonical_text[cursor..child_start]);
        if node_subtree_has_mutation(ir, child_id) {
            render_node_css_with_spans(ir, child_id, output, node_spans)?;
        } else {
            output.push_str(&canonical_text[child_start..child_end]);
            if used_direct_offsets {
                assign_direct_original_subtree_spans(
                    ir,
                    child_id,
                    rendered_start + child_start,
                    child.source_span_start,
                    node_spans,
                )?;
            } else if used_rendered_offsets {
                assign_rendered_subtree_spans(
                    ir,
                    child_id,
                    rendered_start + child_start,
                    rendered_start + child_end,
                    output,
                    node_spans,
                )?;
            } else {
                assign_projected_original_subtree_spans(
                    ir,
                    child_id,
                    rendered_start,
                    &projection,
                    node.source_span_start,
                    canonical_text,
                    node_spans,
                )?;
            }
        }
        cursor = child_end;
        child_was_composed = true;
    }

    if !child_was_composed {
        output.push_str(canonical_text);
        return Ok(());
    }
    output.push_str(&canonical_text[cursor..]);
    Ok(())
}

fn rendered_child_offsets_in_dirty_node(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Result<Option<(usize, usize)>, TransformIrPrintErrorV0> {
    if node.kind == IrNodeKindV0::StyleRule && child.kind == IrNodeKindV0::Selector {
        return Ok(style_rule_selector_offsets_for_child(
            ir,
            child,
            canonical_text,
            cursor,
        ));
    }

    let rendered_child = render_node_css(ir, child.node_id)?;
    if rendered_child.is_empty() {
        return Ok(Some((cursor, cursor)));
    }
    Ok(
        find_rendered_child_after(canonical_text, rendered_child.as_str(), cursor)
            .or_else(|| {
                (child.kind == IrNodeKindV0::StyleRule)
                    .then(|| {
                        style_rule_offsets_by_nested_selector_chunk(
                            ir,
                            node,
                            child,
                            canonical_text,
                            cursor,
                        )
                    })
                    .flatten()
            })
            .or_else(|| {
                (child.kind == IrNodeKindV0::StyleRule)
                    .then(|| style_rule_offsets_by_block(ir, child, canonical_text, cursor))
                    .flatten()
            })
            .or_else(|| {
                (child.kind == IrNodeKindV0::AtRule)
                    .then(|| at_rule_offsets_in_dirty_node(ir, node, child, canonical_text, cursor))
                    .flatten()
            })
            .or_else(|| {
                (child.kind == IrNodeKindV0::StyleRule)
                    .then(|| style_rule_offsets_by_selector(ir, child, canonical_text, cursor))
                    .flatten()
            })
            .or_else(|| {
                (child.kind == IrNodeKindV0::Declaration)
                    .then(|| declaration_offsets_by_property(ir, child, canonical_text, cursor))
                    .flatten()
            }),
    )
}

fn selector_is_css_module_scope_wrapper(ir: &TransformIrV0, child: &IrNodeV0) -> bool {
    let Some(selector_source) = ir
        .source_text
        .get(child.source_span_start..child.source_span_end)
    else {
        return false;
    };
    let selector = selector_source.trim();
    selector == ":local" || selector == ":global"
}

fn style_rule_selector_offsets_for_child(
    ir: &TransformIrV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    if selector_is_css_module_scope_wrapper(ir, child) {
        return Some((cursor, cursor));
    }
    let (selector_start, selector_end) = style_rule_selector_offsets(ir, canonical_text)?;
    if selector_end < cursor {
        return None;
    }
    let parent = child
        .parent
        .and_then(|parent_id| ir.nodes.get(parent_id.index()))?;
    let expected_selector = expanded_style_rule_selector(ir, parent)
        .or_else(|| style_rule_source_selector(ir, parent).map(str::to_string));
    let rendered_selector = canonical_text.get(selector_start..selector_end)?.trim();
    if let Some(expected_selector) = expected_selector {
        if rendered_selector == expected_selector {
            Some((selector_start, selector_end))
        } else if parent_has_style_rule_children(ir, parent) || cursor > selector_start {
            Some((cursor, cursor))
        } else {
            Some((selector_start, selector_end))
        }
    } else if render_node_css(ir, child.node_id)
        .ok()
        .is_some_and(|selector| selector.trim() == rendered_selector)
    {
        Some((selector_start, selector_end))
    } else {
        None
    }
}

fn parent_has_style_rule_children(ir: &TransformIrV0, parent: &IrNodeV0) -> bool {
    parent.children.iter().any(|child_id| {
        ir.nodes
            .get(child_id.index())
            .is_some_and(|child| !child.deleted && child.kind == IrNodeKindV0::StyleRule)
    })
}

fn style_rule_selector_offsets(ir: &TransformIrV0, canonical_text: &str) -> Option<(usize, usize)> {
    let brace = block_spans_for_ir_text(ir, canonical_text)
        .into_iter()
        .map(|span| span.open_brace_start)
        .min()?;
    if brace > 0 && canonical_text.is_char_boundary(brace) {
        Some((0, brace))
    } else {
        None
    }
}

fn find_rendered_child_after(
    canonical_text: &str,
    rendered_child: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let haystack = canonical_text.get(cursor..)?;
    let offset = haystack.find(rendered_child)?;
    let start = cursor.checked_add(offset)?;
    let end = start.checked_add(rendered_child.len())?;
    Some((start, end))
}

fn style_rule_offsets_by_block(
    ir: &TransformIrV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let child_block = child.block_span?;
    let block = ir
        .source_text
        .get(child_block.open_brace_start..child_block.rule_end)?;
    let (block_rendered_start, block_rendered_end) =
        find_rendered_child_after(canonical_text, block, cursor)?;
    let rendered_blocks = block_spans_for_ir_text(ir, canonical_text);
    let rendered_block = rendered_blocks
        .iter()
        .copied()
        .find(|span| span.open_brace_start == block_rendered_start)?;
    let rule_start = rendered_block.prelude_start;
    let leading_trim = canonical_text.get(rule_start..block_rendered_start)?.len()
        - canonical_text
            .get(rule_start..block_rendered_start)?
            .trim_start()
            .len();
    Some((rule_start + leading_trim, block_rendered_end))
}

fn style_rule_offsets_by_selector(
    ir: &TransformIrV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let child_block = child.block_span?;
    let selector = ir
        .source_text
        .get(child_block.prelude_start..child_block.open_brace_start)?
        .trim();
    if selector.is_empty() {
        return None;
    }
    let haystack = canonical_text.get(cursor..)?;
    let selector_offset = haystack.find(selector)?;
    let start = cursor.checked_add(selector_offset)?;
    let rendered_blocks = block_spans_for_ir_text(ir, canonical_text);
    let rendered_block = block_span_for_rendered_start(canonical_text, &rendered_blocks, start)?;
    Some((start, rendered_block.rule_end))
}

fn style_rule_offsets_by_nested_selector_chunk(
    ir: &TransformIrV0,
    parent: &IrNodeV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let selector = expanded_style_rule_selector(ir, child)?;
    let start = find_rendered_child_after(canonical_text, selector.as_str(), cursor)?.0;
    let next_sibling_start = sorted_child_nodes(ir, parent)
        .into_iter()
        .map(|sibling_id| &ir.nodes[sibling_id.index()])
        .filter(|sibling| {
            sibling.kind == IrNodeKindV0::StyleRule
                && sibling.parent == child.parent
                && sibling.global_order > child.global_order
        })
        .filter_map(|sibling| {
            let sibling_selector = expanded_style_rule_selector(ir, sibling)?;
            find_rendered_child_after(
                canonical_text,
                sibling_selector.as_str(),
                start + selector.len(),
            )
            .map(|(sibling_start, _)| sibling_start)
        })
        .min();
    let raw_end = next_sibling_start.unwrap_or(canonical_text.len());
    let slice = canonical_text.get(start..raw_end)?;
    let end = raw_end.saturating_sub(slice.len().saturating_sub(slice.trim_end().len()));
    (start < end).then_some((start, end))
}

fn expanded_style_rule_selector(ir: &TransformIrV0, node: &IrNodeV0) -> Option<String> {
    if node.kind != IrNodeKindV0::StyleRule {
        return None;
    }
    let selector = style_rule_source_selector(ir, node)?;
    let Some(parent_id) = node.parent else {
        return Some(selector.to_string());
    };
    let parent = &ir.nodes[parent_id.index()];
    let parent_selector = match parent.kind {
        IrNodeKindV0::StyleRule => expanded_style_rule_selector(ir, parent)?,
        IrNodeKindV0::AtRule => expanded_nest_at_rule_selector(ir, parent)
            .or_else(|| nearest_ancestor_style_rule_selector(ir, parent))?,
        _ => return Some(selector.to_string()),
    };
    if selector.contains('&') {
        Some(selector.replace('&', parent_selector.as_str()))
    } else {
        Some(format!("{parent_selector} {selector}"))
    }
}

fn at_rule_offsets_in_dirty_node(
    ir: &TransformIrV0,
    parent: &IrNodeV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let child_block = child.block_span?;
    let prelude = ir
        .source_text
        .get(child_block.prelude_start..child_block.open_brace_start)?
        .trim();
    if prelude.is_empty() {
        return None;
    }
    if prelude.starts_with("@nest") {
        let selector = expanded_nest_at_rule_selector(ir, child)?;
        let start = find_rendered_child_after(canonical_text, selector.as_str(), cursor)?.0;
        let end = next_rendered_sibling_start(ir, parent, child, canonical_text, start)
            .unwrap_or(canonical_text.len());
        return trim_rendered_range_end(canonical_text, start, end);
    }
    let start = find_rendered_child_after(canonical_text, prelude, cursor)?.0;
    let rendered_blocks = block_spans_for_ir_text(ir, canonical_text);
    let rendered_block = block_span_for_rendered_start(canonical_text, &rendered_blocks, start)?;
    Some((start, rendered_block.rule_end))
}

fn next_rendered_sibling_start(
    ir: &TransformIrV0,
    parent: &IrNodeV0,
    child: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<usize> {
    sorted_child_nodes(ir, parent)
        .into_iter()
        .map(|sibling_id| &ir.nodes[sibling_id.index()])
        .filter(|sibling| {
            sibling.parent == child.parent
                && sibling.global_order > child.global_order
                && !sibling.deleted
        })
        .filter_map(|sibling| rendered_node_start_hint(ir, sibling, canonical_text, cursor))
        .min()
}

fn rendered_node_start_hint(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    canonical_text: &str,
    cursor: usize,
) -> Option<usize> {
    match node.kind {
        IrNodeKindV0::StyleRule => {
            let selector = expanded_style_rule_selector(ir, node)
                .or_else(|| style_rule_source_selector(ir, node).map(str::to_string))?;
            find_rendered_child_after(canonical_text, selector.as_str(), cursor)
                .map(|(start, _)| start)
        }
        IrNodeKindV0::AtRule => {
            if let Some(selector) = expanded_nest_at_rule_selector(ir, node) {
                return find_rendered_child_after(canonical_text, selector.as_str(), cursor)
                    .map(|(start, _)| start);
            }
            let block = node.block_span?;
            let prelude = ir
                .source_text
                .get(block.prelude_start..block.open_brace_start)?
                .trim();
            find_rendered_child_after(canonical_text, prelude, cursor).map(|(start, _)| start)
        }
        _ => None,
    }
}

fn trim_rendered_range_end(
    canonical_text: &str,
    start: usize,
    end: usize,
) -> Option<(usize, usize)> {
    let slice = canonical_text.get(start..end)?;
    let trimmed_end = end.saturating_sub(slice.len().saturating_sub(slice.trim_end().len()));
    (start < trimmed_end).then_some((start, trimmed_end))
}

fn expanded_nest_at_rule_selector(ir: &TransformIrV0, node: &IrNodeV0) -> Option<String> {
    if node.kind != IrNodeKindV0::AtRule {
        return None;
    }
    let block = node.block_span?;
    let prelude = ir
        .source_text
        .get(block.prelude_start..block.open_brace_start)?
        .trim();
    let nest_selector = prelude.strip_prefix("@nest")?.trim();
    if nest_selector.is_empty() {
        return None;
    }
    let ancestor_selector = nearest_ancestor_style_rule_selector(ir, node)?;
    if nest_selector.contains('&') {
        Some(nest_selector.replace('&', ancestor_selector.as_str()))
    } else {
        Some(format!("{ancestor_selector} {nest_selector}"))
    }
}

fn nearest_ancestor_style_rule_selector(ir: &TransformIrV0, node: &IrNodeV0) -> Option<String> {
    let mut parent = node
        .parent
        .and_then(|parent_id| ir.nodes.get(parent_id.index()));
    while let Some(parent_node) = parent {
        if parent_node.kind == IrNodeKindV0::StyleRule {
            return expanded_style_rule_selector(ir, parent_node);
        }
        parent = parent_node
            .parent
            .and_then(|parent_id| ir.nodes.get(parent_id.index()));
    }
    None
}

fn style_rule_source_selector<'source>(
    ir: &'source TransformIrV0,
    node: &IrNodeV0,
) -> Option<&'source str> {
    let block = node.block_span?;
    let selector = ir
        .source_text
        .get(block.prelude_start..block.open_brace_start)?
        .trim();
    (!selector.is_empty()).then_some(selector)
}

fn dirty_node_text_projection(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    canonical_text: &str,
) -> Result<DirtyNodeTextProjectionV0, TransformIrPrintErrorV0> {
    let original_text = source_slice(
        ir,
        node.node_id.index(),
        node.source_span_start,
        node.source_span_end,
    )?;
    let common_prefix_len = common_prefix_byte_len(original_text, canonical_text);
    let common_suffix_len =
        common_suffix_byte_len_after_prefix(original_text, canonical_text, common_prefix_len);

    Ok(DirtyNodeTextProjectionV0 {
        original_replacement_start: common_prefix_len,
        original_replacement_end: original_text.len().saturating_sub(common_suffix_len),
        rendered_replacement_end: canonical_text.len().saturating_sub(common_suffix_len),
    })
}

fn project_dirty_node_original_offset(
    projection: &DirtyNodeTextProjectionV0,
    original_offset: usize,
) -> Option<usize> {
    if original_offset <= projection.original_replacement_start {
        return Some(original_offset);
    }
    if original_offset >= projection.original_replacement_end {
        let delta = projection.rendered_replacement_end as isize
            - projection.original_replacement_end as isize;
        return apply_offset_delta(original_offset, delta);
    }
    None
}

fn common_prefix_byte_len(left: &str, right: &str) -> usize {
    let mut byte_len = 0;
    for (left_char, right_char) in left.chars().zip(right.chars()) {
        if left_char != right_char {
            break;
        }
        byte_len += left_char.len_utf8();
    }
    byte_len
}

fn common_suffix_byte_len_after_prefix(left: &str, right: &str, prefix_len: usize) -> usize {
    let mut byte_len = 0;
    for (left_char, right_char) in left[prefix_len..]
        .chars()
        .rev()
        .zip(right[prefix_len..].chars().rev())
    {
        if left_char != right_char {
            break;
        }
        byte_len += left_char.len_utf8();
    }
    byte_len
}

fn apply_offset_delta(offset: usize, delta: isize) -> Option<usize> {
    if delta >= 0 {
        offset.checked_add(delta as usize)
    } else {
        offset.checked_sub((-delta) as usize)
    }
}

fn node_subtree_has_mutation(ir: &TransformIrV0, node_id: IrNodeIdV0) -> bool {
    let node = &ir.nodes[node_id.index()];
    node.deleted
        || node.dirty
        || node
            .children
            .iter()
            .any(|child_id| node_subtree_has_mutation(ir, *child_id))
}

fn direct_child_replacement_offsets(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    child: &IrNodeV0,
    canonical_text: &str,
) -> Option<(usize, usize)> {
    let children = sorted_child_nodes(ir, node)
        .into_iter()
        .map(|child_id| &ir.nodes[child_id.index()])
        .filter(|candidate| !candidate.deleted)
        .collect::<Vec<_>>();
    let first_child = children.first()?;
    let last_child = children.last()?;
    let direct_source = ir
        .source_text
        .get(first_child.source_span_start..last_child.source_span_end)?;
    if direct_source.trim() != canonical_text.trim()
        || child.source_span_start < first_child.source_span_start
        || child.source_span_end > last_child.source_span_end
    {
        return None;
    }
    let direct_leading_trim = direct_source.len() - direct_source.trim_start().len();
    let canonical_leading_trim = canonical_text.len() - canonical_text.trim_start().len();
    let child_start_offset = child
        .source_span_start
        .checked_sub(first_child.source_span_start)?
        .checked_sub(direct_leading_trim)?;
    let child_end_offset = child
        .source_span_end
        .checked_sub(first_child.source_span_start)?
        .checked_sub(direct_leading_trim)?;
    let child_start = canonical_leading_trim.checked_add(child_start_offset)?;
    let child_end = canonical_leading_trim.checked_add(child_end_offset)?;
    if child_start <= child_end
        && child_end <= canonical_text.len()
        && canonical_text.is_char_boundary(child_start)
        && canonical_text.is_char_boundary(child_end)
    {
        Some((child_start, child_end))
    } else {
        None
    }
}

fn assign_direct_original_subtree_spans(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    rendered_node_start: usize,
    original_node_start: usize,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    let node = &ir.nodes[node_id.index()];
    let rendered_start = node
        .source_span_start
        .checked_sub(original_node_start)
        .and_then(|offset| rendered_node_start.checked_add(offset))
        .ok_or(TransformIrPrintErrorV0::UnprojectableDirtyChild {
            node_index: node_id.index(),
            child_index: node_id.index(),
        })?;
    let rendered_end = node
        .source_span_end
        .checked_sub(original_node_start)
        .and_then(|offset| rendered_node_start.checked_add(offset))
        .ok_or(TransformIrPrintErrorV0::UnprojectableDirtyChild {
            node_index: node_id.index(),
            child_index: node_id.index(),
        })?;
    if rendered_end < rendered_start {
        return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
            node_index: node_id.index(),
            child_index: node_id.index(),
        });
    }
    node_spans[node_id.index()] = Some((rendered_start, rendered_end));

    for child_id in sorted_child_nodes(ir, node) {
        assign_direct_original_subtree_spans(
            ir,
            child_id,
            rendered_node_start,
            original_node_start,
            node_spans,
        )?;
    }
    Ok(())
}

fn assign_rendered_subtree_spans(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    rendered_start: usize,
    rendered_end: usize,
    rendered_css: &str,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    if rendered_end < rendered_start || rendered_end > rendered_css.len() {
        return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
            node_index: node_id.index(),
            child_index: node_id.index(),
        });
    }
    node_spans[node_id.index()] = Some((rendered_start, rendered_end));

    let rendered_slice = &rendered_css[rendered_start..rendered_end];
    let mut cursor = 0;
    for child_id in sorted_child_nodes(ir, &ir.nodes[node_id.index()]) {
        let child = &ir.nodes[child_id.index()];
        let rendered_child = render_node_css(ir, child_id)?;
        let child_offsets =
            find_rendered_child_after(rendered_slice, rendered_child.as_str(), cursor)
                .or_else(|| {
                    (child.kind == IrNodeKindV0::AtRule
                        && !rendered_slice.contains(rendered_child.as_str()))
                    .then_some((cursor, cursor))
                })
                .or_else(|| {
                    (child.kind == IrNodeKindV0::StyleRule)
                        .then(|| {
                            style_rule_offsets_by_nested_selector_chunk(
                                ir,
                                &ir.nodes[node_id.index()],
                                child,
                                rendered_slice,
                                cursor,
                            )
                        })
                        .flatten()
                })
                .or_else(|| {
                    (ir.nodes[node_id.index()].kind == IrNodeKindV0::StyleRule
                        && child.kind == IrNodeKindV0::Selector)
                        .then(|| {
                            style_rule_selector_offsets_for_child(ir, child, rendered_slice, cursor)
                        })
                        .flatten()
                })
                .or_else(|| {
                    (child.kind == IrNodeKindV0::Declaration)
                        .then(|| declaration_offsets_by_property(ir, child, rendered_slice, cursor))
                        .flatten()
                })
                .or_else(|| {
                    (ir.nodes[node_id.index()].kind == IrNodeKindV0::Declaration
                        && child.kind == IrNodeKindV0::Value)
                        .then(|| declaration_value_offsets(rendered_slice))
                        .flatten()
                })
                .or_else(|| {
                    if ir.nodes[node_id.index()].kind == IrNodeKindV0::Selector
                        && child.kind == IrNodeKindV0::Selector
                    {
                        Some(if cursor == 0 {
                            (0, rendered_slice.len())
                        } else {
                            (cursor, cursor)
                        })
                    } else {
                        None
                    }
                });
        let Some((child_start, child_end)) = child_offsets else {
            return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
                node_index: node_id.index(),
                child_index: child_id.index(),
            });
        };
        assign_rendered_subtree_spans(
            ir,
            child_id,
            rendered_start + child_start,
            rendered_start + child_end,
            rendered_css,
            node_spans,
        )?;
        cursor = child_end;
    }
    Ok(())
}

fn declaration_offsets_by_property(
    ir: &TransformIrV0,
    child: &IrNodeV0,
    rendered_slice: &str,
    cursor: usize,
) -> Option<(usize, usize)> {
    let child_source = ir
        .source_text
        .get(child.source_span_start..child.source_span_end)?;
    let property_end = child_source.find(':')?;
    let property = child_source.get(..property_end)?.trim();
    if property.is_empty() {
        return None;
    }
    let haystack = rendered_slice.get(cursor..)?;
    let property_offset = haystack.find(property)?;
    let start = cursor.checked_add(property_offset)?;
    let declaration_tail = rendered_slice.get(start..)?;
    let semicolon_offset = declaration_tail.find(';')?;
    let end = start.checked_add(semicolon_offset + 1)?;
    Some((start, end))
}

fn declaration_value_offsets(rendered_slice: &str) -> Option<(usize, usize)> {
    let colon = rendered_slice.find(':')?;
    let semicolon = rendered_slice[colon..].find(';')?.checked_add(colon)?;
    let start = colon.checked_add(1)?;
    if start <= semicolon
        && rendered_slice.is_char_boundary(start)
        && rendered_slice.is_char_boundary(semicolon)
    {
        Some((start, semicolon))
    } else {
        None
    }
}

fn render_original_node_with_children(
    ir: &TransformIrV0,
    node: &IrNodeV0,
) -> Result<String, TransformIrPrintErrorV0> {
    let mut output = String::new();
    let mut cursor = node.source_span_start;
    for child_id in sorted_child_nodes(ir, node) {
        let child = &ir.nodes[child_id.index()];
        if child.source_span_start < node.source_span_start
            || child.source_span_end > node.source_span_end
            || child.source_span_start < cursor
        {
            continue;
        }
        output.push_str(source_slice(
            ir,
            node.node_id.index(),
            cursor,
            child.source_span_start,
        )?);
        output.push_str(render_node_css(ir, child_id)?.as_str());
        cursor = child.source_span_end;
    }
    output.push_str(source_slice(
        ir,
        node.node_id.index(),
        cursor,
        node.source_span_end,
    )?);
    Ok(output)
}

fn node_has_zero_width_synthesized_span(ir: &TransformIrV0, node: &IrNodeV0) -> bool {
    node.source_span_start == node.source_span_end
        && ir
            .origins
            .get(node.origin_index)
            .is_some_and(|origin| !origin.is_original())
}

fn render_original_node_with_children_and_spans(
    ir: &TransformIrV0,
    node: &IrNodeV0,
    output: &mut String,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    let mut cursor = node.source_span_start;
    for child_id in sorted_child_nodes(ir, node) {
        let child = &ir.nodes[child_id.index()];
        if child.source_span_start < node.source_span_start
            || child.source_span_end > node.source_span_end
            || child.source_span_start < cursor
        {
            continue;
        }
        output.push_str(source_slice(
            ir,
            node.node_id.index(),
            cursor,
            child.source_span_start,
        )?);
        render_node_css_with_spans(ir, child_id, output, node_spans)?;
        cursor = child.source_span_end;
    }
    output.push_str(source_slice(
        ir,
        node.node_id.index(),
        cursor,
        node.source_span_end,
    )?);
    Ok(())
}

fn assign_projected_original_subtree_spans(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    rendered_parent_start: usize,
    projection: &DirtyNodeTextProjectionV0,
    original_parent_start: usize,
    canonical_text: &str,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    let node = &ir.nodes[node_id.index()];
    let projected_start = node
        .source_span_start
        .checked_sub(original_parent_start)
        .and_then(|offset| project_dirty_node_original_offset(projection, offset))
        .and_then(|offset| rendered_parent_start.checked_add(offset));
    let projected_end = node
        .source_span_end
        .checked_sub(original_parent_start)
        .and_then(|offset| project_dirty_node_original_offset(projection, offset))
        .and_then(|offset| rendered_parent_start.checked_add(offset));
    let (rendered_start, rendered_end) = match (projected_start, projected_end) {
        (Some(rendered_start), Some(rendered_end)) => (rendered_start, rendered_end),
        _ => {
            let rendered_search_start = projection
                .original_replacement_start
                .min(projection.rendered_replacement_end)
                .min(canonical_text.len());
            if node.kind == IrNodeKindV0::Selector
                && let Some((selector_start, selector_end)) =
                    style_rule_selector_offsets(ir, canonical_text)
                && let (Some(rendered_start), Some(rendered_end)) = (
                    rendered_parent_start.checked_add(selector_start),
                    rendered_parent_start.checked_add(selector_end),
                )
            {
                node_spans[node_id.index()] = Some((rendered_start, rendered_end));
                return Ok(());
            }
            if let Some(rendered_node_start) = rendered_original_subtree_start_in_parent_text(
                ir,
                node_id,
                canonical_text,
                rendered_search_start,
            )
            .and_then(|offset| rendered_parent_start.checked_add(offset))
            {
                assign_direct_original_subtree_spans(
                    ir,
                    node_id,
                    rendered_node_start,
                    node.source_span_start,
                    node_spans,
                )?;
                return Ok(());
            }
            if let Some((rendered_node_start, rendered_node_end)) =
                rendered_expanded_style_rule_offsets_in_parent_text(
                    ir,
                    node_id,
                    canonical_text,
                    rendered_search_start,
                )
            {
                assign_rendered_subtree_spans_from_parent_text(
                    ir,
                    node_id,
                    rendered_parent_start,
                    rendered_node_start,
                    rendered_node_end,
                    canonical_text,
                    node_spans,
                )?;
                return Ok(());
            }
            return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
                node_index: node_id.index(),
                child_index: node_id.index(),
            });
        }
    };
    if rendered_end < rendered_start
        || rendered_end.saturating_sub(rendered_parent_start) > canonical_text.len()
    {
        return Err(TransformIrPrintErrorV0::UnprojectableDirtyChild {
            node_index: node_id.index(),
            child_index: node_id.index(),
        });
    }
    node_spans[node_id.index()] = Some((rendered_start, rendered_end));

    for child_id in sorted_child_nodes(ir, node) {
        assign_projected_original_subtree_spans(
            ir,
            child_id,
            rendered_parent_start,
            projection,
            original_parent_start,
            canonical_text,
            node_spans,
        )?;
    }
    Ok(())
}

fn rendered_original_subtree_start_in_parent_text(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    canonical_text: &str,
    search_start: usize,
) -> Option<usize> {
    let rendered_node = render_node_css(ir, node_id).ok()?;
    if rendered_node.is_empty() {
        return Some(search_start);
    }
    find_rendered_child_after(canonical_text, rendered_node.as_str(), search_start)
        .map(|(rendered_start, _)| rendered_start)
}

fn rendered_expanded_style_rule_offsets_in_parent_text(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    canonical_text: &str,
    search_start: usize,
) -> Option<(usize, usize)> {
    let node = &ir.nodes[node_id.index()];
    if node.kind != IrNodeKindV0::StyleRule {
        return None;
    }
    let selector = expanded_style_rule_selector(ir, node)?;
    let start = find_rendered_child_after(canonical_text, selector.as_str(), search_start)?.0;
    let rendered_blocks = block_spans_for_ir_text(ir, canonical_text);
    let rendered_block = block_span_for_rendered_start(canonical_text, &rendered_blocks, start)?;
    Some((start, rendered_block.rule_end))
}

fn assign_rendered_subtree_spans_from_parent_text(
    ir: &TransformIrV0,
    node_id: IrNodeIdV0,
    rendered_parent_start: usize,
    rendered_start: usize,
    rendered_end: usize,
    canonical_text: &str,
    node_spans: &mut [Option<(usize, usize)>],
) -> Result<(), TransformIrPrintErrorV0> {
    let mut local_spans = vec![None; node_spans.len()];
    assign_rendered_subtree_spans(
        ir,
        node_id,
        rendered_start,
        rendered_end,
        canonical_text,
        local_spans.as_mut_slice(),
    )?;
    for (index, span) in local_spans.into_iter().enumerate() {
        let Some((local_start, local_end)) = span else {
            continue;
        };
        node_spans[index] = Some((
            rendered_parent_start + local_start,
            rendered_parent_start + local_end,
        ));
    }
    Ok(())
}

fn sorted_child_nodes(ir: &TransformIrV0, node: &IrNodeV0) -> Vec<IrNodeIdV0> {
    let mut children = node.children.clone();
    children.sort_by_key(|child_id| {
        let child = &ir.nodes[child_id.index()];
        (child.source_span_start, child.global_order)
    });
    children
}

fn insert_before_in_list(list: &mut Vec<IrNodeIdV0>, anchor_id: IrNodeIdV0, node_id: IrNodeIdV0) {
    let insert_index = list
        .iter()
        .position(|candidate| *candidate == anchor_id)
        .unwrap_or(list.len());
    list.insert(insert_index, node_id);
}

const fn spans_overlap(
    left_start: usize,
    left_end: usize,
    right_start: usize,
    right_end: usize,
) -> bool {
    left_start < right_end && right_start < left_end
}

fn nearest_parent_index(index: usize, nodes: &[IrNodeV0]) -> Option<usize> {
    let node = &nodes[index];
    nodes
        .iter()
        .enumerate()
        .filter(|(candidate_index, candidate)| {
            *candidate_index != index
                && candidate.source_span_start <= node.source_span_start
                && candidate.source_span_end >= node.source_span_end
                && candidate.source_span_len() > node.source_span_len()
        })
        .min_by_key(|(_, candidate)| candidate.source_span_len())
        .map(|(candidate_index, _)| candidate_index)
}

fn build_indexes(nodes: &[IrNodeV0]) -> TransformIrIndexesV0 {
    let mut by_kind = Vec::new();
    for kind in [
        IrNodeKindV0::StyleRule,
        IrNodeKindV0::AtRule,
        IrNodeKindV0::Declaration,
        IrNodeKindV0::Selector,
        IrNodeKindV0::Value,
        IrNodeKindV0::UrlValue,
    ] {
        by_kind.push(TransformIrKindIndexV0 {
            kind,
            node_ids: nodes
                .iter()
                .filter(|node| node.kind == kind)
                .map(|node| node.node_id)
                .collect(),
        });
    }

    let mut parents = nodes.iter().map(|node| node.parent).collect::<Vec<_>>();
    parents.sort();
    parents.dedup();
    let by_parent = parents
        .into_iter()
        .map(|parent| TransformIrParentIndexV0 {
            parent,
            node_ids: nodes
                .iter()
                .filter(|node| node.parent == parent)
                .map(|node| node.node_id)
                .collect(),
        })
        .collect();

    TransformIrIndexesV0 { by_kind, by_parent }
}

fn validate_node_origins(ir: &TransformIrV0) -> Result<(), TransformIrPrintErrorV0> {
    for node in &ir.nodes {
        let Some(origin) = ir.origins.get(node.origin_index) else {
            return Err(TransformIrPrintErrorV0::MissingNodeOrigin {
                node_index: node.node_id.index(),
            });
        };
        if let NodeTextOriginV0::Original {
            source_span_start,
            source_span_end,
            ..
        } = origin
        {
            source_slice(
                ir,
                node.node_id.index(),
                *source_span_start,
                *source_span_end,
            )?;
        }
    }
    Ok(())
}

fn source_slice(
    ir: &TransformIrV0,
    node_index: usize,
    source_span_start: usize,
    source_span_end: usize,
) -> Result<&str, TransformIrPrintErrorV0> {
    if source_span_start > source_span_end
        || source_span_end > ir.source_text.len()
        || !ir.source_text.is_char_boundary(source_span_start)
        || !ir.source_text.is_char_boundary(source_span_end)
    {
        return Err(TransformIrPrintErrorV0::InvalidOriginalSpan {
            node_index,
            source_span_start,
            source_span_end,
            source_byte_len: ir.source_text.len(),
        });
    }
    Ok(&ir.source_text[source_span_start..source_span_end])
}

const fn kind_order(kind: IrNodeKindV0) -> u8 {
    match kind {
        IrNodeKindV0::StyleRule => 0,
        IrNodeKindV0::AtRule => 1,
        IrNodeKindV0::Selector => 2,
        IrNodeKindV0::Declaration => 3,
        IrNodeKindV0::Value => 4,
        IrNodeKindV0::UrlValue => 5,
    }
}

#[cfg(test)]
mod tests {
    use super::{
        IrEditRegionV0, IrNodeIdV0, IrNodeKindV0, IrTransactionErrorV0, IrTransactionV0,
        IrTransactionValidationErrorV0, NodeTextOriginV0, TransformIrParseErrorSpanV0,
        TransformIrPrintErrorV0, has_less_mixin_declaration_owner, lower_transform_ir_from_source,
        materialize_transform_ir_printed_source, print_transform_ir_css,
        summarize_transform_ir_identity_round_trip, validate_transaction_commit,
    };
    use omena_parser::StyleDialect;

    #[test]
    fn transform_ir_identity_round_trip_keeps_original_origins() -> Result<(), String> {
        let source = r#".card {
  color: red;
}
@media (min-width: 40rem) {
  .card { color: blue; }
}
"#;
        let summary =
            summarize_transform_ir_identity_round_trip(source, StyleDialect::Css, "fixture:card")
                .map_err(|err| format!("round trip should print: {err:?}"))?;

        assert_eq!(
            summary.product,
            "omena-transform-cst.transform-ir-identity-round-trip"
        );
        assert!(summary.byte_identical);
        assert!(summary.all_nodes_original);
        assert_eq!(summary.synthesized_node_count, 0);
        assert_eq!(summary.printed_css, source);
        assert!(summary.node_count >= 5);
        Ok(())
    }

    #[test]
    fn transform_ir_lowers_css_module_value_statements_as_at_rule_nodes() -> Result<(), String> {
        let source = r#"@value used: red; @value dead: blue; .button { color: used; }"#;
        let ir = lower_transform_ir_from_source(source, StyleDialect::Css, "css-module-values");
        let statement_start = source
            .find("@value dead")
            .ok_or_else(|| "fixture should contain dead @value".to_string())?;
        let statement_end = statement_start + "@value dead: blue;".len();

        assert!(ir.nodes.iter().any(|node| {
            node.kind == IrNodeKindV0::AtRule
                && node.source_span_start == statement_start
                && node.source_span_end == statement_end
        }));
        assert_eq!(
            print_transform_ir_css(&ir).map_err(|err| format!("print should succeed: {err:?}"))?,
            source
        );
        Ok(())
    }

    #[test]
    fn transform_ir_retains_non_node_structural_block_spans() {
        let source = "@keyframes fade { from { opacity: 0; } to { opacity: 1; } }";
        let ir = lower_transform_ir_from_source(source, StyleDialect::Css, "keyframe-block-spans");
        let preludes = ir
            .structural_block_spans()
            .iter()
            .filter_map(|span| source.get(span.prelude_start..span.open_brace_start))
            .map(str::trim)
            .collect::<Vec<_>>();

        assert_eq!(preludes, vec!["@keyframes fade", "from", "to"]);
    }

    #[test]
    fn css_module_value_statement_span_ignores_semicolons_inside_values() {
        let statement = r#"@value marker: "a;b";"#;
        let source = format!("{statement} .button {{ content: marker; }}");
        let ir = lower_transform_ir_from_source(
            source.as_str(),
            StyleDialect::Css,
            "css-module-value-span",
        );
        let statements = ir
            .nodes
            .iter()
            .filter(|node| node.kind == IrNodeKindV0::AtRule)
            .map(|node| &source[node.source_span_start..node.source_span_end])
            .collect::<Vec<_>>();

        assert_eq!(statements, vec![statement]);
    }

    #[test]
    fn transform_ir_lowers_url_values_as_typed_nodes() -> Result<(), String> {
        let source = r#".card { background-image: url("../img/icon.svg"); }"#;
        let ir = lower_transform_ir_from_source(source, StyleDialect::Css, "url-values");
        let url_start = source
            .find("url(")
            .ok_or_else(|| "fixture should contain url(...)".to_string())?;
        let url_end = url_start + r#"url("../img/icon.svg")"#.len();
        let url_node = ir
            .nodes
            .iter()
            .find(|node| {
                node.kind == IrNodeKindV0::UrlValue
                    && node.source_span_start == url_start
                    && node.source_span_end == url_end
            })
            .ok_or_else(|| "URL value should lower to a typed IR node".to_string())?;

        assert!(ir.indexes.by_kind.iter().any(|index| {
            index.kind == IrNodeKindV0::UrlValue && index.node_ids.contains(&url_node.node_id)
        }));
        assert_eq!(
            print_transform_ir_css(&ir).map_err(|err| format!("print should succeed: {err:?}"))?,
            source
        );
        Ok(())
    }

    #[test]
    fn transform_ir_indexes_structural_node_kinds() {
        let ir = lower_transform_ir_from_source(
            ".card { color: red; }\n@supports (display: grid) { .grid { display: grid; } }",
            StyleDialect::Css,
            "fixture:index",
        );

        assert_eq!(ir.product, "omena-transform-cst.transform-ir");
        assert!(ir.all_nodes_original());
        assert_eq!(ir.original_node_count, ir.nodes.len());
        assert!(ir.root_nodes.iter().all(|node_id| {
            ir.nodes[node_id.index()].kind == IrNodeKindV0::StyleRule
                || ir.nodes[node_id.index()].kind == IrNodeKindV0::AtRule
        }));
        assert!(ir.indexes.by_kind.iter().any(|index| {
            index.kind == IrNodeKindV0::Declaration && !index.node_ids.is_empty()
        }));
        assert!(ir.origins.iter().all(NodeTextOriginV0::is_original));
    }

    #[test]
    fn ir_transaction_commits_value_rewrite_through_printer() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "rewrite");
        assert_eq!(ir.ir_epoch(), 0);
        let value_id = first_node_id(&ir, IrNodeKindV0::Value)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "rewrite-value", region);
        transaction
            .rewrite_value(value_id, " blue")
            .map_err(|err| format!("rewrite value should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert!(!ir.all_nodes_original());
        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("mutated IR should print: {err:?}"))?,
            ".card { color: blue; }"
        );
        assert_eq!(ir.ir_epoch(), 1);
        Ok(())
    }

    #[test]
    fn ir_epoch_advances_once_for_each_committed_transaction() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".card { color: red; background: white; }",
            StyleDialect::Css,
            "epoch-currency",
        );
        assert_eq!(ir.ir_epoch(), 0);

        let values = ir
            .nodes
            .iter()
            .filter(|node| node.kind == IrNodeKindV0::Value)
            .map(|node| node.node_id)
            .collect::<Vec<_>>();
        let first_value = *values
            .first()
            .ok_or_else(|| "fixture should contain a first value".to_string())?;
        let second_value = *values
            .get(1)
            .ok_or_else(|| "fixture should contain a second value".to_string())?;

        let source_byte_len = ir.source_byte_len;
        let mut transaction = IrTransactionV0::new(
            &mut ir,
            "rewrite-values",
            IrEditRegionV0::full(source_byte_len),
        );
        transaction
            .rewrite_value(first_value, " blue")
            .map_err(|err| format!("first value rewrite should be accepted: {err:?}"))?;
        transaction
            .rewrite_value(second_value, " black")
            .map_err(|err| format!("second value rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(ir.ir_epoch(), 1);
        let serialized = serde_json::to_string(&ir)
            .map_err(|err| format!("IR serialization should succeed: {err:?}"))?;
        assert!(!serialized.contains("irEpoch"));
        assert!(!serialized.contains("ir_epoch"));
        assert!(!serialized.contains("blockSpan"));
        assert!(!serialized.contains("ownerBlockSpan"));
        assert!(!serialized.contains("structuralBlockSpans"));

        let source_byte_len = ir.source_byte_len;
        let mut followup = IrTransactionV0::new(
            &mut ir,
            "rewrite-again",
            IrEditRegionV0::full(source_byte_len),
        );
        followup
            .rewrite_value(first_value, " green")
            .map_err(|err| format!("follow-up value rewrite should be accepted: {err:?}"))?;
        followup
            .commit()
            .map_err(|err| format!("follow-up transaction should commit: {err:?}"))?;

        assert_eq!(ir.ir_epoch(), 2);
        Ok(())
    }

    #[test]
    fn transform_ir_reconstruction_round_trip_exercises_dirty_node_spans() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".card { color: red; background: white; }",
            StyleDialect::Css,
            "rewrite-spans",
        );
        let value_id = first_node_id(&ir, IrNodeKindV0::Value)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "rewrite-value", region);
        transaction
            .rewrite_value(value_id, " blue")
            .map_err(|err| format!("rewrite value should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert!(!ir.all_nodes_original());
        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("dirty-node materialization should succeed: {err:?}"))?;
        assert_eq!(printed, ".card { color: blue; background: white; }");
        assert!(ir.all_nodes_original());
        assert_eq!(ir.source_text(), printed);
        Ok(())
    }

    #[test]
    fn materialized_transaction_rebases_source_spans_for_next_transaction() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "material");
        let value_id = first_node_id(&ir, IrNodeKindV0::Value)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "rewrite-value", region);
        transaction
            .rewrite_value(value_id, " blue")
            .map_err(|err| format!("first rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("first transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("materialization should succeed: {err:?}"))?;
        assert_eq!(printed, ".card { color: blue; }");
        assert_eq!(ir.source_text(), ".card { color: blue; }");
        assert!(ir.all_nodes_original());
        assert_eq!(ir.synthesized_node_count, 0);
        let value = &ir.nodes[value_id.index()];
        assert_eq!(
            &ir.source_text()[value.source_span_start..value.source_span_end],
            " blue"
        );

        let mut transaction =
            IrTransactionV0::new(&mut ir, "rewrite-value-again", IrEditRegionV0::full(22));
        transaction
            .rewrite_value(value_id, " green")
            .map_err(|err| format!("second rewrite should use materialized spans: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("second transaction should commit: {err:?}"))?;

        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("second mutation should print: {err:?}"))?,
            ".card { color: green; }"
        );
        Ok(())
    }

    #[test]
    fn materialization_rejects_shifted_typed_block_span() -> Result<(), String> {
        let source = "@scope (.card) { .title{color:red;} }";
        let canonical = "@scope (._card_x) { .title { color:red;} }";
        let base = lower_transform_ir_from_source(source, StyleDialect::Css, "typed-span-guard");
        let at_rule = first_node_id(&base, IrNodeKindV0::AtRule)?;
        let nested_rule = base
            .nodes
            .iter()
            .find(|node| node.kind == IrNodeKindV0::StyleRule && node.parent == Some(at_rule))
            .map(|node| node.node_id)
            .ok_or_else(|| "fixture should expose a nested style rule".to_string())?;

        let mut control = base.clone();
        let mut control_transaction = IrTransactionV0::new(
            &mut control,
            "typed-span-control",
            IrEditRegionV0::full(source.len()),
        );
        control_transaction
            .replace_node(at_rule, canonical)
            .map_err(|error| format!("control rewrite should be accepted: {error:?}"))?;
        control_transaction
            .commit()
            .map_err(|error| format!("control transaction should commit: {error:?}"))?;
        assert_eq!(
            materialize_transform_ir_printed_source(&mut control)
                .map_err(|error| format!("control materialization should succeed: {error:?}"))?,
            canonical
        );

        let mut shifted = base;
        let block = shifted.nodes[nested_rule.index()]
            .block_span
            .as_mut()
            .ok_or_else(|| "fixture should expose a typed block span".to_string())?;
        block.open_brace_start = block.open_brace_start.saturating_add(1);

        let mut transaction = IrTransactionV0::new(
            &mut shifted,
            "typed-span-guard",
            IrEditRegionV0::full(source.len()),
        );
        transaction
            .replace_node(at_rule, canonical)
            .map_err(|error| format!("rule rewrite should be accepted: {error:?}"))?;
        transaction
            .commit()
            .map_err(|error| format!("transaction should commit: {error:?}"))?;

        let materialized = materialize_transform_ir_printed_source(&mut shifted);
        assert!(matches!(
            materialized,
            Err(TransformIrPrintErrorV0::UnprojectableDirtyChild { .. })
        ));
        Ok(())
    }

    #[test]
    fn materialized_deletion_rebases_deleted_subtree_spans() -> Result<(), String> {
        let source = ".dead { color: red; } .used { color: blue; }";
        let mut ir = lower_transform_ir_from_source(source, StyleDialect::Css, "delete-material");
        let deleted_rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let deleted_descendants = ir.nodes[deleted_rule.index()].children.clone();
        let region = IrEditRegionV0::full(source.len());
        let mut transaction = IrTransactionV0::new(&mut ir, "delete-rule", region);
        transaction
            .delete_node(deleted_rule)
            .map_err(|err| format!("rule delete should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("deletion materialization should succeed: {err:?}"))?;

        assert_eq!(printed, " .used { color: blue; }");
        assert_eq!(ir.source_text(), " .used { color: blue; }");
        assert!(ir.nodes[deleted_rule.index()].deleted);
        assert!(
            deleted_descendants
                .iter()
                .all(|node_id| ir.nodes[node_id.index()].deleted)
        );
        assert!(deleted_descendants.iter().all(|node_id| {
            ir.nodes[node_id.index()].source_span_start == ir.nodes[node_id.index()].source_span_end
        }));
        Ok(())
    }

    #[test]
    fn ir_transaction_unwraps_wrapper_node_by_promoting_children() -> Result<(), String> {
        let source = "@media all { .used { color: blue; } }";
        let mut ir = lower_transform_ir_from_source(source, StyleDialect::Css, "unwrap-node");
        let wrapper = first_node_id(&ir, IrNodeKindV0::AtRule)?;
        let child = ir.nodes[wrapper.index()]
            .children
            .first()
            .copied()
            .ok_or_else(|| "wrapper should expose a child rule".to_string())?;
        let region = IrEditRegionV0::full(source.len());
        let mut transaction = IrTransactionV0::new(&mut ir, "unwrap-node", region);
        transaction
            .unwrap_node(wrapper)
            .map_err(|err| format!("wrapper unwrap should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(ir.nodes[child.index()].parent, None);
        assert!(ir.root_nodes.contains(&child));
        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("unwrapped IR should print: {err:?}"))?,
            ".used { color: blue; }"
        );
        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("unwrap materialization should succeed: {err:?}"))?;
        assert_eq!(printed, ".used { color: blue; }");
        Ok(())
    }

    #[test]
    fn lower_transform_ir_exposes_css_module_composes_declaration() {
        let source = ".button { composes: base utility from \"./base.css\"; color: red; }";
        let ir = lower_transform_ir_from_source(source, StyleDialect::Css, "composes-declaration");

        assert!(ir.nodes.iter().any(|node| {
            node.kind == IrNodeKindV0::Declaration
                && &source[node.source_span_start..node.source_span_end]
                    == "composes: base utility from \"./base.css\";"
        }));
    }

    #[test]
    fn css_module_fact_spans_follow_syntax_across_delimiter_strings() {
        let composes = r#"composes: base from "./tokens;a.css";"#;
        let source = format!(".button {{ {composes} color: red; }}");
        let ir = lower_transform_ir_from_source(
            source.as_str(),
            StyleDialect::Css,
            "css-module-composes-span",
        );
        let composes_nodes = ir
            .nodes
            .iter()
            .filter(|node| {
                node.kind == IrNodeKindV0::Declaration
                    && source[node.source_span_start..node.source_span_end].starts_with("composes")
            })
            .map(|node| &source[node.source_span_start..node.source_span_end])
            .collect::<Vec<_>>();
        assert_eq!(composes_nodes, vec![composes]);

        let icss = r#":export { marker: "}"; next: blue; }"#;
        let ir = lower_transform_ir_from_source(icss, StyleDialect::Css, "icss-block-span");
        let icss_blocks = ir
            .nodes
            .iter()
            .filter(|node| node.kind == IrNodeKindV0::StyleRule)
            .map(|node| &icss[node.source_span_start..node.source_span_end])
            .collect::<Vec<_>>();
        assert_eq!(icss_blocks, vec![icss]);
    }

    #[test]
    fn ir_transaction_exposes_replace_delete_and_insert_mutators() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".card { color: red; }\n.tile { color: blue; }",
            StyleDialect::Css,
            "mutators",
        );
        let selector_id = first_node_id(&ir, IrNodeKindV0::Selector)?;
        let rule_id = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "mutator-smoke", region);
        transaction
            .replace_node(selector_id, ".panel")
            .map_err(|err| format!("replace node should be accepted: {err:?}"))?;
        transaction
            .insert_before(
                rule_id,
                IrNodeKindV0::StyleRule,
                ".inserted { color: green; }\n",
            )
            .map_err(|err| format!("insert before should be accepted: {err:?}"))?;
        transaction
            .delete_node(rule_id)
            .map_err(|err| format!("delete node should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(ir.synthesized_node_count, 2);
        assert!(ir.nodes.iter().any(|node| node.deleted));
        Ok(())
    }

    #[test]
    fn ir_transaction_inserts_ir_root_subtrees_before_anchor() -> Result<(), String> {
        let source = r#"@import "./tokens.css"; .button { color: var(--alias); }"#;
        let mut ir = lower_transform_ir_from_source(source, StyleDialect::Css, "import-graft");
        let replacement_ir = lower_transform_ir_from_source(
            ":root { --alias: var(--brand); --brand: red; }",
            StyleDialect::Css,
            "import-graft.inserted",
        );
        let anchor = first_node_id(&ir, IrNodeKindV0::AtRule)?;
        let mut transaction =
            IrTransactionV0::new(&mut ir, "import-inline", IrEditRegionV0::full(source.len()));
        let roots = transaction
            .insert_ir_roots_before(anchor, &replacement_ir)
            .map_err(|err| format!("subtree graft should be accepted: {err:?}"))?;
        transaction
            .delete_node(anchor)
            .map_err(|err| format!("anchor delete should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(roots.len(), 1);
        assert!(ir.nodes.iter().any(|node| {
            !node.deleted
                && node.kind == IrNodeKindV0::Declaration
                && node
                    .canonical_text
                    .as_deref()
                    .is_some_and(|text| text.contains("--alias"))
        }));

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("grafted IR should materialize: {err:?}"))?;
        assert_eq!(
            printed,
            ":root { --alias: var(--brand); --brand: red; } .button { color: var(--alias); }"
        );
        let alias_value = ir
            .nodes
            .iter()
            .find(|node| {
                !node.deleted
                    && node.kind == IrNodeKindV0::Value
                    && ir.source_text()[node.source_span_start..node.source_span_end].trim()
                        == "var(--brand)"
            })
            .map(|node| node.node_id)
            .ok_or_else(|| "materialized graft should expose inserted value node".to_string())?;
        let mut followup = IrTransactionV0::new(
            &mut ir,
            "design-token-routing",
            IrEditRegionV0::full(printed.len()),
        );
        followup
            .rewrite_value(alias_value, " red")
            .map_err(|err| format!("inserted value rewrite should be accepted: {err:?}"))?;
        followup
            .commit()
            .map_err(|err| format!("follow-up transaction should commit: {err:?}"))?;

        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("follow-up IR should print: {err:?}"))?,
            ":root { --alias: red; --brand: red; } .button { color: var(--alias); }"
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_preserves_inter_root_spacing_for_inserted_ir() -> Result<(), String> {
        let source = r#"@import "./components.css"; .app { color: green; }"#;
        let mut ir = lower_transform_ir_from_source(source, StyleDialect::Css, "multi-root-graft");
        let replacement_ir = lower_transform_ir_from_source(
            ".base { color: red; } .token { color: blue; }",
            StyleDialect::Css,
            "multi-root-graft.inserted",
        );
        let anchor = first_node_id(&ir, IrNodeKindV0::AtRule)?;
        let mut transaction =
            IrTransactionV0::new(&mut ir, "import-inline", IrEditRegionV0::full(source.len()));
        transaction
            .insert_ir_roots_before(anchor, &replacement_ir)
            .map_err(|err| format!("multi-root graft should be accepted: {err:?}"))?;
        transaction
            .delete_node(anchor)
            .map_err(|err| format!("anchor delete should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("multi-root graft should materialize: {err:?}"))?;
        assert_eq!(
            printed,
            ".base { color: red; } .token { color: blue; } .app { color: green; }"
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_replaces_node_across_consumed_sibling_span() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".a { color: red; } .a { background: blue; }",
            StyleDialect::Css,
            "covering-span",
        );
        let rule_ids = ir
            .nodes
            .iter()
            .filter(|node| node.kind == IrNodeKindV0::StyleRule)
            .map(|node| node.node_id)
            .collect::<Vec<_>>();
        let first_rule = *rule_ids
            .first()
            .ok_or_else(|| "fixture should produce the first rule".to_string())?;
        let second_rule = *rule_ids
            .get(1)
            .ok_or_else(|| "fixture should produce the second rule".to_string())?;
        let span_start = ir.nodes[first_rule.index()].source_span_start;
        let span_end = ir.nodes[second_rule.index()].source_span_end;
        let region = IrEditRegionV0 {
            source_span_start: span_start,
            source_span_end: span_end,
        };
        let mut transaction = IrTransactionV0::new(&mut ir, "rule-merge", region);
        transaction
            .replace_node_covering_span(
                first_rule,
                ".a { color: red; background: blue; }",
                span_start,
                span_end,
            )
            .map_err(|err| format!("covering replacement should be accepted: {err:?}"))?;
        transaction
            .delete_node(second_rule)
            .map_err(|err| format!("covered sibling should be deletable: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("mutated IR should print: {err:?}"))?,
            ".a { color: red; background: blue; }"
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_prints_dirty_child_inside_dirty_parent_when_spans_project()
    -> Result<(), String> {
        let source = "@scope (.card) { .title { color: red; } }";
        let mut ir = lower_transform_ir_from_source(source, StyleDialect::Css, "nested-dirty");
        let at_rule = first_node_id(&ir, IrNodeKindV0::AtRule)?;
        let nested_rule = ir
            .nodes
            .iter()
            .find(|node| node.kind == IrNodeKindV0::StyleRule && node.parent == Some(at_rule))
            .map(|node| node.node_id)
            .ok_or_else(|| "fixture should expose a nested style rule".to_string())?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "nested-dirty", region);
        transaction
            .replace_node(at_rule, "@scope (._card_x) { .title { color: red; } }")
            .map_err(|err| format!("at-rule rewrite should be accepted: {err:?}"))?;
        transaction
            .replace_node(nested_rule, "._title_z{ color: red; }")
            .map_err(|err| format!("nested rule rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        assert_eq!(
            print_transform_ir_css(&ir)
                .map_err(|err| format!("mutated IR should print: {err:?}"))?,
            "@scope (._card_x) { ._title_z{ color: red; } }"
        );
        Ok(())
    }

    #[test]
    fn materialized_nested_dirty_transaction_rebases_projected_child_span() -> Result<(), String> {
        let source = "@scope (.card) { .title { color: red; } }";
        let mut ir =
            lower_transform_ir_from_source(source, StyleDialect::Css, "nested-materialized");
        let at_rule = first_node_id(&ir, IrNodeKindV0::AtRule)?;
        let nested_rule = ir
            .nodes
            .iter()
            .find(|node| node.kind == IrNodeKindV0::StyleRule && node.parent == Some(at_rule))
            .map(|node| node.node_id)
            .ok_or_else(|| "fixture should expose a nested style rule".to_string())?;
        let mut transaction = IrTransactionV0::new(
            &mut ir,
            "nested-materialized",
            IrEditRegionV0::full(source.len()),
        );
        transaction
            .replace_node(at_rule, "@scope (._card_x) { .title { color: red; } }")
            .map_err(|err| format!("at-rule rewrite should be accepted: {err:?}"))?;
        transaction
            .replace_node(nested_rule, "._title_z{ color: red; }")
            .map_err(|err| format!("nested rule rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("nested materialization should succeed: {err:?}"))?;
        assert_eq!(printed, "@scope (._card_x) { ._title_z{ color: red; } }");
        assert!(ir.all_nodes_original());
        let nested = &ir.nodes[nested_rule.index()];
        assert_eq!(
            &ir.source_text()[nested.source_span_start..nested.source_span_end],
            "._title_z{ color: red; }"
        );
        Ok(())
    }

    #[test]
    fn materialized_nested_bem_transaction_rebases_expanded_selector_chunks() -> Result<(), String>
    {
        let source = r#".dashboard {
  &__card0 {
    color: red;

    &--active {
      border-color: blue;
    }
  }

  &__card1 {
    color: green;
  }
}"#;
        let mut ir =
            lower_transform_ir_from_source(source, StyleDialect::Scss, "nested-bem-materialized");
        let root = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let canonical_text = ".dashboard__card0 { color: red; } .dashboard__card0--active { border-color: blue; } .dashboard__card1 { color: green; }";
        let mut transaction = IrTransactionV0::new(
            &mut ir,
            "nesting-unwrap",
            IrEditRegionV0::full(source.len()),
        );
        transaction
            .replace_node(root, canonical_text)
            .map_err(|err| format!("BEM nesting rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("BEM nesting transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("BEM nesting materialization should succeed: {err:?}"))?;

        assert_eq!(printed, canonical_text);
        assert!(ir.all_nodes_original());
        assert!(ir.source_text().contains(".dashboard__card0--active"));
        Ok(())
    }

    #[test]
    fn materialized_nested_descendant_transaction_rebases_expanded_selector_chunks()
    -> Result<(), String> {
        let source = r#".component {
  &--tone-0 {
    @include elevation(1px);

    .component__label0 {
      color: var(--tone-0);
    }
  }
}"#;
        let mut ir = lower_transform_ir_from_source(
            source,
            StyleDialect::Scss,
            "nested-descendant-materialized",
        );
        let root = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let canonical_text = ".component--tone-0 .component__label0 { color: var(--tone-0); }";
        let mut transaction = IrTransactionV0::new(
            &mut ir,
            "nesting-unwrap",
            IrEditRegionV0::full(source.len()),
        );
        transaction
            .replace_node(root, canonical_text)
            .map_err(|err| format!("descendant nesting rewrite should be accepted: {err:?}"))?;
        transaction
            .commit()
            .map_err(|err| format!("descendant nesting transaction should commit: {err:?}"))?;

        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|err| format!("descendant nesting materialization should succeed: {err:?}"))?;

        assert_eq!(printed, canonical_text);
        assert!(ir.all_nodes_original());
        assert!(
            ir.source_text()
                .contains(".component--tone-0 .component__label0")
        );
        Ok(())
    }

    #[test]
    fn lower_transform_ir_preserves_less_rule_after_mixin_declaration() -> Result<(), String> {
        let source = ".space() when (isnumber($margin)) { padding: $margin; } .button { .space(); margin: 2px; }";
        let ir = lower_transform_ir_from_source(source, StyleDialect::Less, "less-mixin-rule");
        let button_rule = ir.nodes.iter().find(|node| {
            node.kind == IrNodeKindV0::StyleRule
                && source[node.source_span_start..node.source_span_end].starts_with(".button")
        });

        assert!(
            button_rule.is_some(),
            "ordinary Less rule after mixin declaration should lower as a style-rule node"
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_dangling_nodes() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "dangling");
        ir.nodes[0].children.push(IrNodeIdV0(usize::MAX));

        let err = validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .err()
            .ok_or_else(|| "dangling child must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::DanglingNode {
                node_index: 0,
                dangling_node_index: usize::MAX,
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_parent_child_mismatch() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "links");
        let child = first_node_id(&ir, IrNodeKindV0::Declaration)?;
        let parent = ir.nodes[child.index()]
            .parent
            .ok_or_else(|| "declaration should have a parent".to_string())?;
        ir.nodes[parent.index()]
            .children
            .retain(|candidate| *candidate != child);

        let err = validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .err()
            .ok_or_else(|| "parent/child mismatch must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::ParentChildLinkMismatch {
                node_index: child.index(),
                parent_index: parent.index(),
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_declaration_without_rule_owner() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "owner");
        let declaration = first_node_id(&ir, IrNodeKindV0::Declaration)?;
        if let Some(parent) = ir.nodes[declaration.index()].parent {
            ir.nodes[parent.index()]
                .children
                .retain(|candidate| *candidate != declaration);
        }
        ir.nodes[declaration.index()].parent = None;

        let err = validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .err()
            .ok_or_else(|| "orphan declaration must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::DeclarationWithoutRuleOwner {
                node_index: declaration.index(),
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_accepts_less_mixin_declaration_owned_root_declarations() -> Result<(), String>
    {
        let source = ".space() when (isnumber($margin)) { padding: $margin; }";
        let ir = lower_transform_ir_from_source(source, StyleDialect::Less, "less-mixin-owner");

        validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .map_err(|err| format!("Less mixin declaration contents should be owned: {err:?}"))?;
        Ok(())
    }

    #[test]
    fn typed_block_ownership_accepts_supported_root_declarations() -> Result<(), String> {
        for (source, dialect) in [
            (":export { token: red; }", StyleDialect::Css),
            (
                ":import(\"./tokens.css\") { token: remote; }",
                StyleDialect::Css,
            ),
            (
                ".space() when (isnumber($margin)) { padding: $margin; }",
                StyleDialect::Less,
            ),
            (".card { color: red; }", StyleDialect::Css),
        ] {
            let ir = lower_transform_ir_from_source(source, dialect, "block-owner-oracle");
            validate_transaction_commit(&ir, &[], IrEditRegionV0::full(source.len()))
                .map_err(|error| format!("typed ownership rejected {source:?}: {error:?}"))?;
        }
        Ok(())
    }

    #[test]
    fn typed_block_ownership_ignores_braces_inside_less_values() -> Result<(), String> {
        let source = ".space() { color: red; content: \"{\"; padding: 1px; }";
        let ir = lower_transform_ir_from_source(source, StyleDialect::Less, "typed-block-owner");
        let padding = ir
            .nodes
            .iter()
            .find(|node| {
                node.kind == IrNodeKindV0::Declaration
                    && ir
                        .source_text()
                        .get(node.source_span_start..node.source_span_end)
                        .is_some_and(|text| text.starts_with("padding"))
            })
            .ok_or_else(|| "fixture should expose the padding declaration".to_string())?;

        assert!(has_less_mixin_declaration_owner(&ir, padding));
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_duplicate_global_order() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "order");
        let duplicate_order = ir.nodes[0].global_order;
        ir.nodes[1].global_order = duplicate_order;

        let err = validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .err()
            .ok_or_else(|| "duplicate global order must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::DuplicateGlobalOrder {
                global_order: duplicate_order,
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_missing_provenance() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".card { color: red; }",
            StyleDialect::Css,
            "provenance",
        );
        ir.nodes[0].origin_index = usize::MAX;

        let err = validate_transaction_commit(&ir, &[], IrEditRegionV0::full(ir.source_byte_len))
            .err()
            .ok_or_else(|| "missing provenance must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::MissingProvenance {
                node_index: 0,
                origin_index: usize::MAX,
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_edits_outside_declared_region() -> Result<(), String> {
        let ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "region");
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0 {
            source_span_start: ir.source_byte_len,
            source_span_end: ir.source_byte_len,
        };

        let err = validate_transaction_commit(&ir, &[rule], region)
            .err()
            .ok_or_else(|| "outside-region edit must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::EditOutsideDeclaredRegion {
                node_index: rule.index(),
                region,
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_edits_inside_parse_error_region() -> Result<(), String> {
        let mut ir = lower_transform_ir_from_source(
            ".card { color: red; }",
            StyleDialect::Css,
            "parse-error",
        );
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let parse_error_span = TransformIrParseErrorSpanV0 {
            source_span_start: ir.nodes[rule.index()].source_span_start,
            source_span_end: ir.nodes[rule.index()].source_span_end,
        };
        ir.parse_error_spans.push(parse_error_span);

        let err =
            validate_transaction_commit(&ir, &[rule], IrEditRegionV0::full(ir.source_byte_len))
                .err()
                .ok_or_else(|| "parse-error edit must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionValidationErrorV0::EditInsideParseErrorRegion {
                node_index: rule.index(),
                parse_error_span,
            }
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_allows_parent_rewrite_when_parse_error_source_is_preserved()
    -> Result<(), String> {
        let source = ".card { color: tokens.$accent; }";
        let mut ir =
            lower_transform_ir_from_source(source, StyleDialect::Scss, "preserved-parse-error");
        if ir.parser_error_count == 0 {
            return Err("fixture must expose a SCSS parse-error token".to_string());
        }
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let canonical_text = ".card { color: tokens.$accent; background: red; }";

        let mut transaction = IrTransactionV0::new(&mut ir, "preserve-parse-error", region);
        transaction
            .replace_node(rule, canonical_text)
            .map_err(|error| format!("{error:?}"))?;
        transaction.commit().map_err(|error| format!("{error:?}"))?;

        assert_eq!(
            print_transform_ir_css(&ir).map_err(|error| format!("{error:?}"))?,
            canonical_text
        );
        let printed = materialize_transform_ir_printed_source(&mut ir).map_err(|error| {
            format!("materialization should preserve parse-error spans: {error:?}")
        })?;
        assert_eq!(printed, canonical_text);
        assert!(ir.parser_error_count > 0);
        assert!(!ir.parse_error_spans.is_empty());
        assert!(ir.parse_error_spans.iter().all(|span| {
            span.source_span_start <= span.source_span_end
                && span.source_span_end <= ir.source_text().len()
                && ir.source_text().is_char_boundary(span.source_span_start)
                && ir.source_text().is_char_boundary(span.source_span_end)
        }));
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_parent_rewrite_when_parse_error_source_is_removed()
    -> Result<(), String> {
        let source = ".card { color: tokens.$accent; }";
        let mut ir =
            lower_transform_ir_from_source(source, StyleDialect::Scss, "removed-parse-error");
        let parse_error_span = ir
            .parse_error_spans
            .first()
            .copied()
            .ok_or_else(|| "fixture must expose a SCSS parse-error token".to_string())?;
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "remove-parse-error", region);
        transaction
            .replace_node(rule, ".card { color: blue; }")
            .map_err(|error| format!("{error:?}"))?;

        let err = transaction
            .commit()
            .err()
            .ok_or_else(|| "parse-error removal must fail validation".to_string())?;

        assert_eq!(
            err,
            IrTransactionErrorV0::Validation(
                IrTransactionValidationErrorV0::EditInsideParseErrorRegion {
                    node_index: rule.index(),
                    parse_error_span,
                }
            )
        );
        Ok(())
    }

    #[test]
    fn ir_transaction_allows_structural_rule_deletion_with_parse_error_region() -> Result<(), String>
    {
        let source = ".dead { color: tokens.$accent; }\n.used { color: blue; }";
        let mut ir =
            lower_transform_ir_from_source(source, StyleDialect::Scss, "delete-parse-error");
        let parse_error_span = ir
            .parse_error_spans
            .first()
            .copied()
            .ok_or_else(|| "fixture must expose a SCSS parse-error token".to_string())?;
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "delete-parse-error-rule", region);
        transaction
            .delete_node(rule)
            .map_err(|error| format!("{error:?}"))?;

        transaction.commit().map_err(|error| format!("{error:?}"))?;

        assert!(
            print_transform_ir_css(&ir)
                .map_err(|error| format!("{error:?}"))?
                .contains(".used { color: blue; }")
        );
        assert!(
            parse_error_span.source_span_start >= ir.nodes[rule.index()].source_span_start
                && parse_error_span.source_span_end <= ir.nodes[rule.index()].source_span_end
        );
        let printed = materialize_transform_ir_printed_source(&mut ir)
            .map_err(|error| format!("deleted parse-error region should materialize: {error:?}"))?;
        assert_eq!(printed, "\n.used { color: blue; }");
        assert_eq!(ir.parser_error_count, 0);
        assert!(ir.parse_error_spans.is_empty());
        Ok(())
    }

    #[test]
    fn ir_transaction_rejects_non_value_rewrite_value() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "kind");
        let rule = first_node_id(&ir, IrNodeKindV0::StyleRule)?;
        let region = IrEditRegionV0::full(ir.source_byte_len);
        let mut transaction = IrTransactionV0::new(&mut ir, "rewrite-value", region);
        let err = transaction
            .rewrite_value(rule, "blue")
            .err()
            .ok_or_else(|| "non-value rewrite must fail".to_string())?;

        assert_eq!(
            err,
            IrTransactionErrorV0::NodeKindMismatch {
                node_index: rule.index(),
                expected: IrNodeKindV0::Value,
                actual: IrNodeKindV0::StyleRule,
            }
        );
        Ok(())
    }

    #[test]
    fn transform_ir_printer_rejects_invalid_original_span() -> Result<(), String> {
        let mut ir =
            lower_transform_ir_from_source(".card { color: red; }", StyleDialect::Css, "bad-span");
        let first_node = ir
            .nodes
            .first()
            .ok_or_else(|| "fixture should produce an IR node".to_string())?;
        let origin_index = first_node.origin_index;
        ir.origins[origin_index] = NodeTextOriginV0::Original {
            source_id: "bad-span".to_string(),
            source_span_start: 0,
            source_span_end: usize::MAX,
        };

        let err = match print_transform_ir_css(&ir) {
            Ok(_) => return Err("invalid original span must fail printing".to_string()),
            Err(err) => err,
        };

        assert_eq!(
            err,
            TransformIrPrintErrorV0::InvalidOriginalSpan {
                node_index: first_node.node_id.index(),
                source_span_start: 0,
                source_span_end: usize::MAX,
                source_byte_len: 21,
            }
        );
        Ok(())
    }

    fn first_node_id(ir: &super::TransformIrV0, kind: IrNodeKindV0) -> Result<IrNodeIdV0, String> {
        ir.nodes
            .iter()
            .find(|node| node.kind == kind)
            .map(|node| node.node_id)
            .ok_or_else(|| format!("missing node kind {kind:?}"))
    }
}