strop-engine 0.25.0

//! Editable code collections (0044): picker results as one real buffer of
//! source excerpts. Edits to an excerpt write back to its source document
//! through the change-plan gateway at action boundaries; generated headers
//! are protected, and a source that moved on refuses by name.

#[cfg(test)]
mod tests;

use std::collections::HashMap;
use std::path::PathBuf;

use strop_core::id::{Arena, BufferRevision, DocumentId, DocumentKind};
use strop_core::{Buffer, Range};
use strop_workspace::ResourceLocation;

use super::changes::{ChangePlan, ChangeProducer, PlannedDocument};
use super::document::Document;
use super::Editor;

/// One excerpt: a whole-line span of a source document, remapped through
/// the source's change journal like any other saved anchor.
#[derive(Debug, Clone)]
pub(crate) struct Excerpt {
    pub source: DocumentId,
    /// Source byte span (whole lines), remapped on every source mutation.
    pub start: usize,
    pub end: usize,
    /// FNV-1a of the span's bytes at build/regeneration — the write-back
    /// staleness check.
    pub fingerprint: u64,
    /// Header line index in the shadow text (the title is line 0).
    pub view_line: usize,
    /// Source line count as rendered into the shadow.
    pub view_lines: usize,
    /// Body byte span in the view/shadow text (0049 §5 invalidation:
    /// source changes splice this span directly).
    pub view_start: usize,
    pub view_end: usize,
}

#[derive(Debug, Clone)]
pub(crate) struct Collection {
    pub title: String,
    pub excerpts: Vec<Excerpt>,
    /// Source saves in flight from a collection `:w`/`:wq`; the view
    /// closes only when every one confirms (0049 §5).
    pub pending_saves: usize,
    pub close_when_saved: bool,
    /// The canonical rendering as of the last sync. The sync diff is
    /// shadow vs current — no hidden state.
    pub shadow: String,
    /// The buffer revision at last sync — the cheap no-change check that
    /// keeps motions from materializing rope text on the input path.
    pub revision: BufferRevision,
}

/// An in-flight collection build: hits plus the count of background
/// source loads still outstanding (0044 v2 async source loading).
#[derive(Debug)]
pub(crate) struct CollectionBuild {
    pub title: String,
    pub hits: Vec<(std::path::PathBuf, usize)>,
    /// Remote hits resolve against open remote documents at build.
    pub remote_hits: Vec<(strop_workspace::RemoteEndpoint, std::path::PathBuf, usize)>,
    pub waiting: usize,
}

fn fingerprint(text: &str) -> u64 {
    let mut hash: u64 = 0xcbf29ce484222325;
    for byte in text.as_bytes() {
        hash = (hash ^ u64::from(*byte)).wrapping_mul(0x100000001b3);
    }
    hash
}

/// The canonical rendering: title, then per excerpt a header line and its
/// source text. Re-anchors each excerpt's view span as it is emitted. An
/// associated function over disjoint fields, so the map entry can be
/// re-anchored while the editor borrows `docs` and `cwd`.
fn render(
    docs: &Arena<DocumentKind, Document>,
    cwd: &std::path::Path,
    collection: &mut Collection,
) -> String {
    let mut text = format!(
        "collection: {} — {} excerpt(s) (edits write back at action boundaries; g<Space> opens source)\n",
        collection.title,
        collection.excerpts.len()
    );
    let mut line = 1;
    for excerpt in &mut collection.excerpts {
        let source = &docs.get(excerpt.source).unwrap().buf;
        let path = source
            .path
            .as_ref()
            .map(|path| path.strip_prefix(cwd).unwrap_or(path).display().to_string())
            .unwrap_or_else(|| "[scratch]".into());
        let first = source.line_of(excerpt.start) + 1;
        text.push_str(&format!("── {path}:{first} ──\n"));
        let body = source
            .text()
            .byte_slice(excerpt.start..excerpt.end)
            .to_string();
        #[cfg(test)]
        eprintln!(
            "render excerpt src={:?} span={}..{} body={body:?}",
            excerpt.source, excerpt.start, excerpt.end
        );
        excerpt.view_line = line;
        excerpt.view_start = text.len();
        excerpt.view_lines = body.lines().count().max(1);
        excerpt.fingerprint = fingerprint(&body);
        text.push_str(&body);
        if !body.ends_with('\n') {
            text.push('\n');
        }
        excerpt.view_end = text.len();
        line += 1 + excerpt.view_lines;
    }
    text
}

impl Editor {
    /// `ctrl-o` in a result picker: open the listed hits as an editable
    /// collection. Hits whose files are not open local documents are
    /// counted and skipped with a message; remote hits carry no local
    /// payload, so they are skipped the same way.
    pub(crate) fn open_collection_from_picker(&mut self) {
        let Some(glue) = &self.picker else {
            return;
        };
        let kind = glue.picker.kind;
        if !matches!(
            kind,
            strop_picker::Kind::Locations
                | strop_picker::Kind::Diagnostics
                | strop_picker::Kind::Grep
        ) {
            self.message = "collections come from a results list".into();
            return;
        }
        // Local hits and remote hits alike; remote ones resolve against
        // open remote documents (0040 permits gate their write-back).
        let mut hits: Vec<(std::path::PathBuf, usize)> = Vec::new();
        let mut remote_hits: Vec<(strop_workspace::RemoteEndpoint, std::path::PathBuf, usize)> =
            Vec::new();
        for item in glue.picker.items.iter() {
            match &item.payload {
                strop_picker::Payload::Grep { path, line, .. } => {
                    hits.push((path.clone(), line.saturating_sub(1)));
                }
                strop_picker::Payload::Remote {
                    endpoint,
                    path,
                    line,
                    ..
                } => remote_hits.push((endpoint.clone(), path.clone(), line.saturating_sub(1))),
                _ => {}
            }
        }
        let title = kind.title().trim().to_string();
        self.close_picker();
        // Unopened sources load in the background (never switching focus);
        // the build assembles when the last one lands.
        let mut to_load: Vec<std::path::PathBuf> = Vec::new();
        for (path, _) in &hits {
            let absolute = if path.is_absolute() {
                path.clone()
            } else {
                self.cwd.join(path)
            };
            let open = self.docs.iter().any(|(_, doc)| {
                doc.matches_target(&crate::files::FileTarget::Local(absolute.clone()))
            });
            if !open && !to_load.contains(&absolute) {
                to_load.push(absolute);
            }
        }
        let waiting = to_load.len();
        let build = CollectionBuild {
            title,
            hits,
            remote_hits,
            waiting,
        };
        if to_load.is_empty() {
            self.build_collection(build);
            return;
        }
        self.collection_build = Some(build);
        self.message = format!("collection: loading {waiting} source(s)…");
        for path in to_load {
            self.request_open(path, crate::editor::io::OpenIntent::Background);
        }
    }

    /// A background source load landed (or failed): the pending build
    /// counts down and assembles when its sources are all in.
    pub(crate) fn collection_source_ready(&mut self, _document: DocumentId) {
        let Some(build) = &mut self.collection_build else {
            strop_trace::record_with(
                strop_trace::EventKind::JobFinished,
                || serde_json::json!({"service":"collection","result":"ready-without-build"}),
            );
            return;
        };
        build.waiting = build.waiting.saturating_sub(1);
        strop_trace::record_with(
            strop_trace::EventKind::JobFinished,
            || serde_json::json!({"service":"collection","result":"source-ready","waiting":build.waiting}),
        );
        if build.waiting == 0 {
            let build = self.collection_build.take().unwrap();
            self.build_collection(build);
        }
    }

    fn build_collection(&mut self, build: CollectionBuild) {
        let CollectionBuild {
            title,
            hits,
            remote_hits,
            ..
        } = build;
        let mut by_doc: HashMap<DocumentId, Vec<usize>> = HashMap::new();
        let mut skipped = 0;
        for (path, line) in hits {
            let absolute = if path.is_absolute() {
                path
            } else {
                self.cwd.join(path)
            };
            let Some(document) = self.docs.iter().find_map(|(id, doc)| {
                doc.matches_target(&crate::files::FileTarget::Local(absolute.clone()))
                    .then_some(id)
            }) else {
                skipped += 1;
                continue;
            };
            by_doc.entry(document).or_default().push(line);
        }
        for (endpoint, path, line) in remote_hits {
            let document = self.docs.iter().find_map(|(id, doc)| {
                doc.remote_metadata().and_then(|source| {
                    (source.file.endpoint() == &endpoint && source.file.path() == path.as_path())
                        .then_some(id)
                })
            });
            match document {
                Some(id) => by_doc.entry(id).or_default().push(line),
                None => skipped += 1,
            }
        }
        if by_doc.is_empty() {
            self.message = "no open buffers among the results — open them first".into();
            return;
        }
        let mut excerpts = Vec::new();
        for (source, mut lines) in by_doc {
            lines.sort_unstable();
            lines.dedup();
            let buf = &self.docs.get(source).unwrap().buf;
            // Merge adjacent lines into one excerpt so an edit never
            // applies twice to overlapping spans.
            let mut spans: Vec<(usize, usize)> = Vec::new();
            for line in lines {
                if line >= buf.len_lines() {
                    continue;
                }
                match spans.last_mut() {
                    Some((_, end)) if line <= *end => *end = line + 1,
                    _ => spans.push((line, line + 1)),
                }
            }
            for (start_line, end_line) in spans {
                let start = buf.line_start(start_line);
                let end = if end_line >= buf.len_lines() {
                    buf.len_bytes()
                } else {
                    buf.line_start(end_line)
                };
                let text = buf.text().byte_slice(start..end).to_string();
                excerpts.push(Excerpt {
                    source,
                    start,
                    end,
                    fingerprint: fingerprint(&text),
                    view_line: 0,
                    view_lines: 0,
                    view_start: 0,
                    view_end: 0,
                });
            }
        }
        excerpts.sort_by_key(|excerpt| (excerpt.source, excerpt.start));
        let excerpt_count = excerpts.len();
        let title_for_trace = title.clone();
        let id = self.docs.insert(Document::output(Buffer::from_text("")));
        // The modeline names the collection, never [scratch] (0049 §6).
        self.docs.get_mut(id).unwrap().buf.name = Some(format!("collection: {title}"));
        let mut collection = Collection {
            title,
            excerpts,
            pending_saves: 0,
            close_when_saved: false,
            shadow: String::new(),
            revision: BufferRevision::new(0),
        };
        let text = render(&self.docs, &self.cwd, &mut collection);
        collection.shadow = text.clone();
        self.collections.insert(id, collection);
        let _ = self.doc_mut(id).buf.system_edit().replace_all(&text);
        self.docs.get_mut(id).unwrap().buf.readonly = false;
        let revision = self.docs.get(id).unwrap().buf.revision();
        self.collections.get_mut(&id).unwrap().revision = revision;
        strop_trace::record_with(strop_trace::EventKind::JobFinished, || {
            serde_json::json!({
                "service":"collection","result":"built","excerpts":excerpt_count,
                "skipped":skipped,"title":title_for_trace,
            })
        });
        self.drop_stale_scratch(id);
        self.switch_to(id);
        self.set_head(0);
        self.message = match skipped {
            0 => format!("collection: {excerpt_count} excerpt(s)"),
            _ => format!("collection built; {skipped} hit(s) skipped (not open local buffers)"),
        };
    }

    /// Every normal-mode action boundary in a collection buffer is a
    /// write-back attempt — gated on the buffer revision so motions and
    /// in-progress insert typing never materialize rope text.
    pub(crate) fn maybe_sync_collection(&mut self) {
        if self.docs.is_empty() {
            return;
        }
        let id = self.current();
        let revision = self.buf().revision();
        let Some(stored) = self.collections.get(&id).map(|c| c.revision) else {
            return;
        };
        if revision == stored {
            return;
        }
        let current = self.buf().text().to_string();
        if current == self.collections[&id].shadow {
            self.collections.get_mut(&id).unwrap().revision = revision;
            return;
        }
        // Write-back against a working copy; the entry stays in the map
        // so the change-journal remap still tracks its anchors mid-apply.
        let working = self.collections[&id].clone();
        if let Err(reason) = self.collection_write_back(&working, &current) {
            self.message = reason;
        }
        let open = working
            .excerpts
            .iter()
            .all(|excerpt| self.docs.get(excerpt.source).is_some());
        if !open {
            self.message = "collection: a source buffer was closed — view dropped".into();
            self.collections.remove(&id);
            return;
        }
        // The source is authoritative: regenerate the view and reset the
        // shadow whether or not the write-back landed.
        self.collection_render_view(id);
    }

    /// Re-render the collection view from its sources and reset shadow +
    /// revision together (0049 §5: no stale text may be presented).
    pub(crate) fn collection_render_view(&mut self, id: DocumentId) {
        // Preserve the logical caret across the regeneration (0049 §5):
        // same row/column clamped into the new text.
        let caret = if self.current() == id {
            Some((
                self.buf().line_of(self.head()),
                self.buf().col_of(self.head()),
            ))
        } else {
            None
        };
        let text = {
            let entry = self.collections.get_mut(&id).unwrap();
            render(&self.docs, &self.cwd, entry)
        };
        {
            let entry = self.collections.get_mut(&id).unwrap();
            entry.shadow = text.clone();
        }
        let _ = self.doc_mut(id).buf.system_edit().replace_all(&text);
        if let Some((line, col)) = caret {
            let line = line.min(self.docs.get(id).unwrap().buf.len_lines().saturating_sub(1));
            let head = self.docs.get(id).unwrap().buf.clamp_boundary(
                self.docs
                    .get(id)
                    .unwrap()
                    .buf
                    .line_start(line)
                    .saturating_add(col),
            );
            if self.current() == id {
                self.set_head(head);
                self.clamp_cursor();
            }
        }
        let revision = self.docs.get(id).unwrap().buf.revision();
        self.collections.get_mut(&id).unwrap().revision = revision;
        // The view is a presentation: its dirty bit is never the story
        // (0049 §5 — the sources own unsaved state).
        self.docs.get_mut(id).unwrap().buf.dirty = false;
    }

    /// A source change strictly inside one excerpt (0049 §5): splice the
    /// excerpt's view span with the new source body instead of
    /// re-rendering the whole view. The caller gates on a clean view
    /// (no unsynced user edit) — the spans assume shadow == view.
    pub(crate) fn collection_splice_excerpt(&mut self, id: DocumentId, index: usize) {
        let (source, view_start, view_end, view_lines) = {
            let entry = &self.collections[&id];
            let excerpt = &entry.excerpts[index];
            (
                excerpt.source,
                excerpt.view_start,
                excerpt.view_end,
                excerpt.view_lines,
            )
        };
        let Some(source_doc) = self.docs.get(source) else {
            return;
        };
        let excerpt_span = {
            let entry = &self.collections[&id];
            let excerpt = &entry.excerpts[index];
            (excerpt.start, excerpt.end)
        };
        let mut body = source_doc
            .buf
            .text()
            .byte_slice(excerpt_span.0..excerpt_span.1)
            .to_string();
        #[cfg(test)]
        eprintln!("splice coll={id:?} ex={index} span={excerpt_span:?} view={view_start}..{view_end} body={body:?}");
        if !body.ends_with('\n') {
            body.push('\n');
        }
        let new_lines = body.lines().count().max(1);
        // Splice the collection buffer at the excerpt's view span; the
        // view is clean, so the spans index it directly.
        {
            let doc = self.docs.get_mut(id).unwrap();
            let _ = doc
                .buf
                .system_edit()
                .replace(Range::charwise(view_start, view_end), &body);
        }
        // The splice's own journal entry feeds the view analysis and is
        // then consumed: the write-back diff must never see it.
        {
            let doc = self.docs.get_mut(id).unwrap();
            let changes: Vec<_> = doc.buf.changes().to_vec();
            self.analysis.edits(id, &changes);
            doc.buf.clear_changes();
        }
        let byte_delta = body.len() as isize - (view_end - view_start) as isize;
        let line_delta = new_lines as isize - view_lines as isize;
        let entry = self.collections.get_mut(&id).unwrap();
        // Shadow moves with the view, byte-identical region.
        entry.shadow.replace_range(view_start..view_end, &body);
        let mut seen = false;
        for excerpt in &mut entry.excerpts {
            if seen {
                excerpt.view_start = (excerpt.view_start as isize + byte_delta) as usize;
                excerpt.view_end = (excerpt.view_end as isize + byte_delta) as usize;
                excerpt.view_line = (excerpt.view_line as isize + line_delta) as usize;
            } else if excerpt.view_start == view_start {
                seen = true;
                excerpt.view_lines = new_lines;
                excerpt.view_end = view_start + body.len();
                excerpt.fingerprint = fingerprint(&body);
            }
        }
        let revision = self.docs.get(id).unwrap().buf.revision();
        self.collections.get_mut(&id).unwrap().revision = revision;
    }
    /// Line-level diff: common prefix/suffix lines trim first (0049 §5 —
    /// the 2,000-excerpt audit stall was the full-view O(n²) LCS on a
    /// one-line edit); the dynamic table only ever sees the changed
    /// middle. Disjoint edit regions in one batch fall back to the LCS
    /// over that middle only.
    fn diff_lines(
        shadow: &[&str],
        current: &[&str],
    ) -> Vec<(std::ops::Range<usize>, std::ops::Range<usize>)> {
        let prefix = shadow
            .iter()
            .zip(current.iter())
            .take_while(|(a, b)| a == b)
            .count();
        let suffix = shadow[prefix..]
            .iter()
            .rev()
            .zip(current[prefix.min(current.len())..].iter().rev())
            .take_while(|(a, b)| a == b)
            .count();
        let smid = &shadow[prefix..shadow.len() - suffix.min(shadow.len() - prefix)];
        let cmid = &current[prefix..current.len() - suffix.min(current.len() - prefix)];
        if smid.is_empty() && cmid.is_empty() {
            return Vec::new();
        }
        Self::diff_lines_middle(
            &shadow[prefix..prefix + smid.len()],
            &current[prefix..prefix + cmid.len()],
        )
        .into_iter()
        .map(|(old, new)| {
            (
                old.start + prefix..old.end + prefix,
                new.start + prefix..new.end + prefix,
            )
        })
        .collect()
    }

    /// The LCS table over the changed middle only.
    fn diff_lines_middle(
        shadow: &[&str],
        current: &[&str],
    ) -> Vec<(std::ops::Range<usize>, std::ops::Range<usize>)> {
        let (n, m) = (shadow.len(), current.len());
        // lcs[i][j] = LCS length of shadow[i..] vs current[j..]
        let mut lcs = vec![vec![0usize; m + 1]; n + 1];
        for i in (0..n).rev() {
            for j in (0..m).rev() {
                lcs[i][j] = if shadow[i] == current[j] {
                    lcs[i + 1][j + 1] + 1
                } else {
                    lcs[i + 1][j].max(lcs[i][j + 1])
                };
            }
        }
        let mut hunks = Vec::new();
        let (mut i, mut j) = (0, 0);
        while i < n || j < m {
            if i < n && j < m && shadow[i] == current[j] {
                i += 1;
                j += 1;
                continue;
            }
            let (si, sj) = (i, j);
            while i < n || j < m {
                if i < n && j < m && shadow[i] == current[j] {
                    break;
                }
                if i < n && (j == m || lcs[i + 1][j] >= lcs[i][j + 1]) {
                    i += 1;
                } else {
                    j += 1;
                }
            }
            hunks.push((si..i, sj..j));
        }
        hunks
    }

    /// A shadow line's position in the current text, given the hunks.
    /// An insertion exactly AT the line attaches forward: span starts map
    /// without it (the inserted text joins the span), span ends with it.
    fn map_line(
        hunks: &[(std::ops::Range<usize>, std::ops::Range<usize>)],
        line: usize,
        count_at_boundary: bool,
    ) -> usize {
        let mut current = line;
        for (old, new) in hunks {
            let counts =
                old.end < line || (old.end == line && (!old.is_empty() || count_at_boundary));
            if counts {
                current += new.len() - old.len();
            } else {
                break;
            }
        }
        current
    }

    /// Diff shadow vs current and write back every touched excerpt as one
    /// change plan (0044 v2: multiple regions across excerpts, one batch
    /// per source document). Structure lines (title, headers) are never
    /// editable; a hunk touching one refuses the whole sync.
    fn collection_write_back(
        &mut self,
        collection: &Collection,
        current: &str,
    ) -> Result<(), String> {
        let shadow_lines: Vec<&str> = collection.shadow.split_inclusive('\n').collect();
        let current_lines: Vec<&str> = current.split_inclusive('\n').collect();
        let hunks = Self::diff_lines(&shadow_lines, &current_lines);
        if hunks.is_empty() {
            return Ok(());
        }
        // Every hunk must sit fully inside one excerpt's body span.
        let mut touched: Vec<usize> = Vec::new();
        for (old, _) in &hunks {
            let mut owner = None;
            for (index, excerpt) in collection.excerpts.iter().enumerate() {
                let lo = excerpt.view_line + 1;
                let hi = excerpt.view_line + excerpt.view_lines + 1;
                let inside = if old.is_empty() {
                    // an insertion belongs to a body only inside it
                    old.start >= lo && old.start < hi
                } else {
                    old.start >= lo && old.end <= hi
                };
                if inside {
                    owner = Some(index);
                    break;
                }
                // Overlap without containment crosses a boundary.
                if !old.is_empty() && old.start < hi && old.end > lo {
                    return Err(
                        "edit touches a header or spans excerpts — refused; view refreshed".into(),
                    );
                }
            }
            let Some(index) = owner else {
                return Err(
                    "edit touches the title, a header, or the collection's structure — refused; view refreshed"
                        .into(),
                );
            };
            if !touched.contains(&index) {
                touched.push(index);
            }
        }
        // One replacement per touched excerpt: its whole body span as it
        // currently reads — partial hunks carry their unchanged context.
        let mut by_source: Vec<(DocumentId, Vec<strop_core::Replacement>, ResourceLocation)> =
            Vec::new();
        for index in touched {
            let excerpt = &collection.excerpts[index];
            let source = self
                .docs
                .get(excerpt.source)
                .ok_or_else(|| "collection: a source buffer was closed".to_string())?;
            let present = source
                .buf
                .text()
                .byte_slice(excerpt.start..excerpt.end)
                .to_string();
            if fingerprint(&present) != excerpt.fingerprint {
                return Err(
                    "collection: a source changed elsewhere — refused; view refreshed".into(),
                );
            }
            if source.buf.readonly {
                return Err(
                    "collection: a source is read-only (remote sources need :remote edit first) — refused; view refreshed"
                        .into(),
                );
            }
            let lo = excerpt.view_line + 1;
            let hi = excerpt.view_line + excerpt.view_lines + 1;
            let cur_lo = Self::map_line(&hunks, lo, false);
            let cur_hi = Self::map_line(&hunks, hi, true);
            let mut replacement: String = current_lines[cur_lo..cur_hi].concat();
            if !replacement.is_empty() && !replacement.ends_with('\n') {
                replacement.push('\n');
            }
            let edit = strop_core::Replacement::new(
                Range::charwise(excerpt.start, excerpt.end),
                replacement,
            );
            let location = match &source.source {
                super::document::DocumentSource::Remote(remote) => ResourceLocation::remote(
                    remote.file.endpoint().clone(),
                    remote.file.path().to_path_buf(),
                ),
                _ => ResourceLocation::local(source.buf.path.clone().unwrap_or_default()),
            };
            match by_source
                .iter_mut()
                .find(|(id, _, _)| *id == excerpt.source)
            {
                Some((_, edits, _)) => edits.push(edit),
                None => by_source.push((excerpt.source, vec![edit], location)),
            }
        }
        let documents = by_source
            .into_iter()
            .map(|(document, edits, location)| PlannedDocument {
                location,
                document,
                base: self.docs.get(document).unwrap().buf.revision(),
                edits,
            })
            .collect();
        let plan = ChangePlan {
            producer: ChangeProducer::CollectionEdit,
            documents,
            refused: Vec::new(),
        };
        self.apply_change_plan(plan);
        Ok(())
    }
}

impl Editor {
    /// `u` in a collection (0049 §5): undo the newest edit group that
    /// came FROM this collection, across its actual sources. Preflight
    /// every member — a source edited since refuses the whole group by
    /// name, and the receipt is never consumed on refusal.
    pub(crate) fn collection_undo(&mut self) {
        let id = self.current();
        let Some(sources) = self
            .collections
            .get(&id)
            .map(|c| c.excerpts.iter().map(|e| e.source).collect::<Vec<_>>())
        else {
            return;
        };
        let Some((index, mut receipt)) = self.changes.take_newest_matching(|receipt| {
            receipt.producer == "collection edit"
                && receipt
                    .applied
                    .iter()
                    .any(|(document, ..)| sources.contains(document))
        }) else {
            self.message = "already at oldest change".into();
            return;
        };
        let mut moved = 0;
        for (document, _before, after) in &receipt.applied {
            match self.docs.get(*document) {
                Some(doc) if doc.buf.revision() == *after => {}
                Some(_) => {
                    let name = self
                        .docs
                        .get(*document)
                        .and_then(|d| d.buf.path.clone())
                        .map(|p| p.display().to_string())
                        .unwrap_or_else(|| "a source".into());
                    self.changes.restore(index, receipt);
                    self.message =
                        format!("collection undo refused: {name} changed since — resolve it first");
                    return;
                }
                None => {
                    self.changes.restore(index, receipt);
                    self.message = "collection undo refused: a source buffer was closed".into();
                    return;
                }
            }
        }
        let mut depths = Vec::with_capacity(receipt.applied.len());
        for (document, ..) in &receipt.applied {
            let undone_ok = matches!(self.doc_mut(*document).buf.undo(), Ok(Some(_)));
            if undone_ok {
                moved += 1;
            }
            depths.push(
                self.docs
                    .get(*document)
                    .map(|doc| doc.buf.history().depth())
                    .unwrap_or(0),
            );
        }
        receipt.redo_depths = Some(depths);
        // The undo's own journal refreshes the dependent views (0049 §5
        // invalidation) — no explicit render here.
        self.changes.push_undone(receipt);
        self.message = format!("undid collection edit across {moved} buffer(s)");
    }

    /// `ctrl-r` in a collection: redo the newest undone group of this
    /// collection, same preflight rules as undo.
    pub(crate) fn collection_redo(&mut self) {
        let id = self.current();
        let Some(sources) = self
            .collections
            .get(&id)
            .map(|c| c.excerpts.iter().map(|e| e.source).collect::<Vec<_>>())
        else {
            return;
        };
        let Some(receipt) = self.changes.take_undone_matching(|receipt| {
            receipt
                .applied
                .iter()
                .any(|(document, ..)| sources.contains(document))
        }) else {
            self.message = "nothing to redo".into();
            return;
        };
        // Revisions are monotonic — an undo never returns to one — so
        // preflight the undone position by history depth (0049 §5).
        let depths = receipt.redo_depths.clone();
        for (member, (document, ..)) in receipt.applied.iter().enumerate() {
            let at = self
                .docs
                .get(*document)
                .map(|doc| doc.buf.history().depth());
            if at != depths.as_ref().map(|d| d[member]) {
                self.changes.push_undone(receipt);
                self.message = "collection redo refused: a source changed since the undo".into();
                return;
            }
        }
        let mut moved = 0;
        for (document, ..) in &receipt.applied {
            if matches!(self.doc_mut(*document).buf.redo(), Ok(Some(_))) {
                moved += 1;
            }
        }
        self.changes.push_receipt_back(receipt);
        self.message = format!("redid collection edit across {moved} buffer(s)");
    }
}

impl Editor {
    /// `:w` in a collection (0049 §5): save the dirty SOURCES through
    /// their own save paths — never the presentation. `:w PATH` refuses:
    /// the view is not a file and exporting it is not this operation.
    pub(crate) fn collection_save(&mut self, target: Option<PathBuf>, force: bool, close: bool) {
        let id = self.current();
        if target.is_some() {
            self.message = "a collection has no file of its own — :w saves its sources;                             exporting the view is unsupported"
                .into();
            return;
        }
        let Some(sources) = self.collections.get(&id).map(|c| {
            let mut seen: Vec<DocumentId> = c.excerpts.iter().map(|e| e.source).collect();
            seen.dedup();
            seen
        }) else {
            return;
        };
        let mut queued = 0;
        let mut refused: Vec<String> = Vec::new();
        for source in sources {
            let Some(doc) = self.docs.get(source) else {
                continue;
            };
            if !doc.buf.dirty {
                continue;
            }
            let name = doc
                .buf
                .path
                .as_ref()
                .map(|p| p.display().to_string())
                .unwrap_or_else(|| "[scratch]".into());
            if doc.buf.readonly {
                refused.push(name);
                continue;
            }
            // Readonly/remote-permit refusals stay authoritative inside
            // the save path itself (0040); :w! grants no new capability.
            self.request_save_document(source, None, force, false);
            queued += 1;
        }
        if let Some(collection) = self.collections.get_mut(&id) {
            collection.pending_saves = queued;
            collection.close_when_saved = close && refused.is_empty() && queued > 0;
        }
        if queued == 0 && refused.is_empty() {
            if close {
                self.close_pane_or_buffer(false);
            } else {
                self.message = "collection: all sources are saved".into();
            }
            return;
        }
        if !refused.is_empty() {
            self.message = format!(
                "collection: saving {queued} source(s); read-only skipped: {}",
                refused.join(", ")
            );
        } else {
            self.message = format!("collection: saving {queued} source(s)");
        }
    }

    /// A source save completed (0049 §5): count down; the `:wq` view
    /// closes only when every save confirmed. A failure cancels the
    /// close and stays visible.
    pub(crate) fn collection_save_progress(&mut self, document: DocumentId, saved: bool) {
        let mut close: Option<DocumentId> = None;
        for (id, collection) in self.collections.iter_mut() {
            if collection.pending_saves == 0
                || !collection.excerpts.iter().any(|e| e.source == document)
            {
                continue;
            }
            if !saved {
                collection.pending_saves = 0;
                collection.close_when_saved = false;
                continue;
            }
            collection.pending_saves = collection.pending_saves.saturating_sub(1);
            if collection.pending_saves == 0 && collection.close_when_saved {
                close = Some(*id);
            }
        }
        if let Some(id) = close {
            if self.current() == id {
                self.close_pane_or_buffer(false);
            } else if let Some(collection) = self.collections.get_mut(&id) {
                collection.close_when_saved = false;
                self.message = "collection: sources saved".into();
            }
        }
    }
}

impl Editor {
    /// `g<Space>` in a collection, Enter on a header row, and
    /// `:collection source` (0049 §5): open the full source under the
    /// caret — the live document with its unsaved edits, never a disk
    /// reload. A body row maps to the exact source position; a header
    /// row opens the file at that excerpt's first line. The jump is
    /// recorded so Ctrl-O returns to the collection working context.
    pub fn collection_open_source_pub(&mut self) {
        self.collection_open_source();
    }

    pub(crate) fn collection_open_source(&mut self) {
        let id = self.current();
        let cursor_line = self.buf().line_of(self.head());
        let cursor_col = self.buf().col_of(self.head());
        let Some(collection) = self.collections.get(&id) else {
            return;
        };
        let mut target: Option<(DocumentId, usize)> = None;
        for excerpt in &collection.excerpts {
            if cursor_line == excerpt.view_line {
                // header row: the file, at this excerpt's first line
                target = Some((excerpt.source, excerpt.start));
                break;
            }
            if cursor_line > excerpt.view_line
                && cursor_line <= excerpt.view_line + excerpt.view_lines
            {
                // body row: same line-in-excerpt, same column
                let Some(source) = self.docs.get(excerpt.source) else {
                    break;
                };
                let source_line =
                    source.buf.line_of(excerpt.start) + (cursor_line - excerpt.view_line - 1);
                let line = source_line.min(source.buf.len_lines().saturating_sub(1));
                target = Some((
                    excerpt.source,
                    source
                        .buf
                        .clamp_boundary(source.buf.line_start(line).saturating_add(cursor_col)),
                ));
                break;
            }
        }
        let Some((document, head)) = target else {
            self.message = "not on an excerpt".into();
            return;
        };
        if self.docs.get(document).is_none() {
            self.message = "collection: that source was closed".into();
            return;
        }
        self.push_jump();
        self.switch_to(document);
        self.set_head(head);
        self.clamp_cursor();
        self.scroll_to_cursor(self.view_rows());
    }
}

impl Editor {
    /// The SOURCE line number for a collection view row (0049 §6):
    /// Some(Some(n)) for body rows, Some(None) for chrome (title,
    /// headers — the gutter stays blank there), None for ordinary
    /// buffers.
    pub fn collection_source_lineno(
        &self,
        doc: strop_core::id::DocumentId,
        line: usize,
    ) -> Option<Option<usize>> {
        let collection = self.collections.get(&doc)?;
        for excerpt in &collection.excerpts {
            if line == excerpt.view_line {
                return Some(None); // header row
            }
            if line > excerpt.view_line && line <= excerpt.view_line + excerpt.view_lines {
                let source = self.docs.get(excerpt.source)?;
                let first = source.buf.line_of(excerpt.start);
                return Some(Some(first + (line - excerpt.view_line - 1) + 1));
            }
        }
        Some(None) // title row
    }
}