alef 0.115.6

//! Finds the segments of a fixture path that step through a data-carrying enum, from the IR's
//! own type graph.
//!
//! A path such as `choices[0].message.content.parts[0].text` names two enum hops. `content` is
//! an enum with a `Parts(Vec<Piece>)` variant, and `text` is a field of the `Piece::Text`
//! variant. Neither hop is a struct field in the bindings, so a renderer that spells each
//! segment as `.name` cannot work: Rust needs a `match` on the variant (E0609 otherwise), and
//! Python reads the value below a dict-shaped variant getter as `json.loads` output, so every
//! segment after the getter is a dict lookup.
//!
//! The walk is type-driven, never name-driven. It starts at the call's result type, follows
//! struct fields through the IR's field graph, and at an enum asks which variant the segment
//! names (by the variant's own name) or declares (by a field of a struct variant). A segment
//! that names no single variant is left alone, and the renderer keeps its previous output.
use std::collections::{HashMap, HashSet};

use crate::codegen::naming::{internal_rust_identifier, pascal_to_snake};

use super::optional_renderers::{push_key_field_name, push_key_index_suffix};
use super::parse::segment_name;
use super::types::{FieldResolver, PathSegment, VariantShape};

/// What a variant segment binds in a `match`.
enum VariantBind {
    /// `Enum::Variant(v)`: the single field of a tuple variant.
    Tuple,
    /// `Enum::Variant { field: v, .. }`: one named field of a struct variant.
    Field(String),
}

/// One path segment that steps through an enum.
pub(super) struct VariantCrossing {
    /// The tracked path key at this segment, built the way every renderer builds it.
    pub(super) key: String,
    enum_name: String,
    variant: String,
    bind: VariantBind,
    only_variant: bool,
    /// The segment names a variant that the pyo3 binding exposes through its dict-shaped getter.
    pub(super) python_json: bool,
    /// Index of the segment in the path.
    segment_index: usize,
    /// The segment names a newtype variant of an untagged enum, whose napi and wasm value is the
    /// enum value itself.
    bare_value: bool,
    python_getter: String,
    python_wire_prefix: Vec<String>,
    python_wire_fields: HashMap<String, String>,
    pub(super) output_type: Option<String>,
    kind: super::types::WireValueKind,
}

impl VariantCrossing {
    pub(super) fn python_step(&self) -> super::python_renderer::PythonAccessStep {
        let field_key = match &self.bind {
            VariantBind::Tuple => None,
            VariantBind::Field(field) => self.python_wire_fields.get(field).map(String::as_str),
        };
        let native_keys = super::python_access_steps::json_keys(field_key);
        let json_keys = self
            .python_wire_prefix
            .iter()
            .map(String::as_str)
            .chain(field_key)
            .map(str::to_string)
            .collect();
        super::python_renderer::PythonAccessStep {
            native_suffix: Some(format!(".{}{native_keys}", self.python_getter)),
            json_keys,
            kind: self.kind,
            starts_json: self.python_json,
        }
    }

    /// The arms of the `match` that reads this segment, without the surrounding braces.
    fn rust_arms(&self, module: Option<&str>) -> String {
        let variant = &self.variant;
        let type_name = internal_rust_identifier(&self.enum_name);
        let enum_name = match module {
            Some(module) => format!("{module}::{type_name}"),
            None => type_name,
        };
        let field = match &self.bind {
            VariantBind::Tuple => None,
            VariantBind::Field(field) => Some(internal_rust_identifier(field)),
        };
        crate::e2e::template_env::render(
            "rust/variant_match_arms.rs.jinja",
            minijinja::context! {
                enum_name, variant => internal_rust_identifier(variant), field,
                fallback => !self.only_variant,
            },
        )
        .trim_end()
        .to_string()
    }
}

/// A variant that a segment reads, how to bind it, and the declared type of what it binds.
struct FoundVariant<'a> {
    shape: &'a VariantShape,
    bind: VariantBind,
    next: Option<String>,
    /// The segment names the variant itself, as opposed to a field the variant declares.
    by_name: bool,
}

impl FoundVariant<'_> {
    fn into_crossing(self, owner: &str, key: &str, segment_index: usize, only_variant: bool) -> VariantCrossing {
        let field = match &self.bind {
            VariantBind::Tuple => self.shape.fields.first().map(|(name, _)| name),
            VariantBind::Field(name) => Some(name),
        };
        let kind = field
            .and_then(|name| self.shape.wire_kinds.get(name))
            .copied()
            .unwrap_or_default();
        VariantCrossing {
            kind,
            key: key.to_string(),
            enum_name: owner.to_string(),
            variant: self.shape.name.clone(),
            bind: self.bind,
            only_variant,
            python_json: self.shape.python_json_getter,
            segment_index,
            bare_value: self.by_name && self.shape.untagged_newtype,
            python_getter: self.shape.python_getter.clone(),
            python_wire_prefix: self.shape.python_wire_prefix.clone(),
            python_wire_fields: self.shape.python_wire_fields.clone(),
            output_type: self.next,
        }
    }
}

/// The variant of `shapes` that `name` reads, with how to bind it and the declared type of what
/// it binds. A variant named like the segment wins; otherwise the one struct variant that
/// declares a field of that name. Two variants declaring the same field name is ambiguous and
/// answers `None`, because one `match` arm cannot read both.
fn find_variant<'a>(shapes: &'a [VariantShape], name: &str) -> Option<FoundVariant<'a>> {
    if let Some(shape) = shapes
        .iter()
        .find(|shape| shape.name == name || pascal_to_snake(&shape.name) == name)
        && let [(field, next)] = shape.fields.as_slice()
    {
        let bind = if shape.is_tuple {
            VariantBind::Tuple
        } else {
            VariantBind::Field(field.clone())
        };
        return Some(FoundVariant {
            shape,
            bind,
            next: next.clone(),
            by_name: true,
        });
    }
    let snake = pascal_to_snake(name);
    let declares = |shape: &&VariantShape| {
        !shape.is_tuple && shape.fields.iter().any(|(field, _)| pascal_to_snake(field) == snake)
    };
    let mut declaring = shapes.iter().filter(declares);
    let shape = declaring.next()?;
    if declaring.next().is_some() {
        return None;
    }
    let (field, next) = shape.fields.iter().find(|(field, _)| pascal_to_snake(field) == snake)?;
    Some(FoundVariant {
        shape,
        bind: VariantBind::Field(field.clone()),
        next: next.clone(),
        by_name: false,
    })
}

impl FieldResolver {
    /// Every segment of `segments` that steps through an enum, in path order.
    pub(super) fn variant_crossings(&self, segments: &[PathSegment]) -> Vec<VariantCrossing> {
        let map = &self.ir_enum_map;
        let mut crossings = Vec::new();
        let mut cursor = map.root_type.clone();
        let mut key = String::new();
        for (segment_index, segment) in segments.iter().enumerate() {
            let Some(name) = segment_name(segment) else {
                continue;
            };
            push_key_field_name(&mut key, segment);
            let Some(owner) = cursor.take() else {
                break;
            };
            cursor = if let Some(shapes) = map.variant_shapes.get(&owner) {
                let Some(found) = find_variant(shapes, name) else { break };
                let next = found.next.clone();
                crossings.push(found.into_crossing(&owner, &key, segment_index, shapes.len() == 1));
                next
            } else {
                map.enum_field_types
                    .get(&owner)
                    .and_then(|fields| fields.get(name))
                    .or_else(|| map.field_types.get(&owner).and_then(|fields| fields.get(name)))
                    .cloned()
            };
            push_key_index_suffix(&mut key, segment);
        }
        crossings
    }

    /// The `match` arms that read each enum segment of `segments` in Rust, keyed by the tracked path
    /// key. A segment the renderer would emit as a method call (`parts()`) is left out: the
    /// consumer's binding has a real method there.
    pub(super) fn rust_variant_matches(&self, segments: &[PathSegment]) -> HashMap<String, String> {
        self.variant_crossings(segments)
            .into_iter()
            .filter(|crossing| {
                !(self.method_calls.contains(&crossing.key) && !self.result_fields.contains(&crossing.key))
            })
            .map(|crossing| {
                let arms = crossing.rust_arms(self.rust_enum_module.as_deref());
                (crossing.key, arms)
            })
            .collect()
    }

    /// The tracked path keys of the segments below which Python reads `json.loads` output.
    pub(super) fn python_json_crossings(&self, segments: &[PathSegment]) -> HashSet<String> {
        self.variant_crossings(segments)
            .into_iter()
            .filter(|crossing| crossing.python_json)
            .map(|crossing| crossing.key)
            .collect()
    }

    pub(super) fn first_bare_variant(&self, segments: &[PathSegment]) -> Option<usize> {
        self.variant_crossings(segments)
            .into_iter()
            .find(|crossing| crossing.bare_value)
            .map(|crossing| crossing.segment_index)
    }
}