//! Current-working-copy conflict inputs and guarded saves. Browsing never snapshots jj.
use crate::repository::{jj_command, safe_path, store_for_jj};
use std::{
    collections::BTreeMap,
    ffi::OsString,
    fs::{self, File, OpenOptions},
    io::Write,
    ops::Range,
    path::{Path, PathBuf},
    process::Command,
    sync::atomic::{AtomicU64, Ordering},
};

const LIMIT: usize = 16 * 1024 * 1024;
static NEXT: AtomicU64 = AtomicU64::new(0);

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Checkout {
    commit: String,
    change: String,
    operation: String,
    state: Vec<u8>,
}
#[derive(Clone, Debug)]
pub struct Workspace {
    pub root: PathBuf,
    pub checkout: Checkout,
    pub files: Vec<ConflictFile>,
}
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FileKind {
    Text,
    Binary,
    Symlink,
    Deleted,
    Submodule,
    Directory,
}
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum Status {
    Unresolved,
    Resolved,
    Unconfirmed,
}
#[derive(Clone, Debug)]
pub struct Source {
    pub label: String,
    pub base: bool,
    pub kind: FileKind,
    pub bytes: Vec<u8>,
    pub tree_id: String,
    term: usize,
    sides: usize,
    bases: usize,
    node: Node,
}
impl Source {
    pub fn text(&self) -> Option<&str> {
        (self.kind == FileKind::Text)
            .then(|| std::str::from_utf8(&self.bytes).ok())
            .flatten()
    }
}
#[derive(Clone, Debug)]
pub struct ConflictFile {
    pub path: PathBuf,
    pub sources: Vec<Source>,
    pub result: Option<String>,
    pub notice: Option<String>,
    pub status: Status,
    baseline: Node,
}
#[derive(Clone, Debug)]
pub enum Resolution {
    Text(String),
    Source(usize),
}
#[derive(Clone, Debug)]
pub struct SaveOutcome {
    pub checkout: Checkout,
    pub file: ConflictFile,
    /// A write succeeded but jj confirmation failed. Never interpret this as resolved.
    pub confirmation: Option<String>,
}
#[derive(Clone, Debug, Eq, PartialEq)]
enum Node {
    Absent,
    File(Vec<u8>, u32),
    Symlink(Vec<u8>),
    Directory(Vec<(OsString, Node)>),
    Submodule(String),
}
impl Node {
    fn kind(&self) -> FileKind {
        match self {
            Self::Absent => FileKind::Deleted,
            Self::File(bytes, _)
                if std::str::from_utf8(bytes).is_ok_and(|s| {
                    s.chars()
                        .all(|ch| !ch.is_control() || matches!(ch, '\n' | '\r' | '\t'))
                }) =>
            {
                FileKind::Text
            }
            Self::File(..) => FileKind::Binary,
            Self::Symlink(_) => FileKind::Symlink,
            Self::Directory(_) => FileKind::Directory,
            Self::Submodule(_) => FileKind::Submodule,
        }
    }
    fn bytes(&self) -> &[u8] {
        match self {
            Self::File(bytes, _) | Self::Symlink(bytes) => bytes,
            _ => &[],
        }
    }
}
fn check(cancelled: &dyn Fn() -> bool) -> Result<(), String> {
    if cancelled() {
        Err("Conflict operation cancelled".into())
    } else {
        Ok(())
    }
}
fn run(command: Command, cancelled: &dyn Fn() -> bool) -> Result<Vec<u8>, String> {
    let description = format!("{command:?}");
    crate::blame::run(command, &[], cancelled)?
        .ok_or_else(|| format!("Jujutsu conflict command failed: {description}"))
}
fn text(bytes: Vec<u8>) -> Result<String, String> {
    String::from_utf8(bytes).map_err(|_| "Jujutsu returned non-UTF-8 metadata".into())
}
fn git(store: &Path) -> Command {
    let mut command = Command::new("git");
    command.arg("--no-pager").arg("--git-dir").arg(store).args([
        "-c",
        "core.hooksPath=/dev/null",
        "-c",
        "core.fsmonitor=false",
    ]);
    command
}
fn identity(root: &Path, cancelled: &dyn Fn() -> bool) -> Result<Checkout, String> {
    check(cancelled)?;
    let state_path = root.join(".jj/working_copy/checkout");
    let state = fs::read(&state_path).map_err(|e| format!("Cannot read local jj checkout: {e}"))?;
    let mut command = jj_command(root);
    command.args([
        "log",
        "--no-graph",
        "-r",
        "@",
        "-T",
        "\"[\" ++ json(commit_id) ++ \",\" ++ json(change_id) ++ \"]\"",
    ]);
    let (commit, change): (String, String) = serde_json::from_slice(&run(command, cancelled)?)
        .map_err(|e| format!("Invalid jj checkout identity: {e}"))?;
    let mut command = jj_command(root);
    command.args(["op", "log", "--no-graph", "-n", "1", "-T", "id"]);
    let operation = text(run(command, cancelled)?)?;
    if fs::read(state_path).map_err(|e| e.to_string())? != state {
        return Err("Jujutsu checkout changed while reading; reopen :resolve".into());
    }
    Ok(Checkout {
        commit,
        change,
        operation,
        state,
    })
}
fn entries(
    root: &Path,
    revision: &str,
    cancelled: &dyn Fn() -> bool,
) -> Result<Vec<PathBuf>, String> {
    let revision = format!("commit_id({})", serde_json::to_string(revision).unwrap());
    let mut command = jj_command(root);
    command.args([
        "file",
        "list",
        "-r",
        &revision,
        "-T",
        "if(conflict, json(path) ++ \"\\n\")",
    ]);
    let mut paths = Vec::new();
    for line in run(command, cancelled)?
        .split(|b| *b == b'\n')
        .filter(|line| !line.is_empty())
    {
        let path: String =
            serde_json::from_slice(line).map_err(|e| format!("Invalid jj conflict path: {e}"))?;
        let path = PathBuf::from(path);
        safe_path(&path)?;
        paths.push(path);
        if paths.len() > 100_000 {
            return Err("More than 100000 conflicted files".into());
        }
    }
    Ok(paths)
}
fn oid(value: &str) -> Result<&str, String> {
    if matches!(value.len(), 40 | 64) && value.bytes().all(|b| b.is_ascii_hexdigit()) {
        Ok(value)
    } else {
        Err("Invalid Git object ID in jj conflict inputs".into())
    }
}
fn trees(store: &Path, commit: &str, cancelled: &dyn Fn() -> bool) -> Result<Vec<String>, String> {
    let mut command = git(store);
    command.args(["cat-file", "commit", oid(commit)?]);
    let bytes = run(command, cancelled)?;
    // jj's Git format is an alternating add/remove/add merge, not a 3-way assumption.
    // https://github.com/jj-vcs/jj/blob/v0.46.0/lib/src/git_backend.rs
    let headers = bytes
        .split(|b| *b == b'\n')
        .take_while(|line| !line.is_empty());
    for line in headers {
        if let Some(value) = line.strip_prefix(b"jj:trees ") {
            let value = std::str::from_utf8(value).map_err(|_| "Invalid jj:trees header")?;
            let trees = value
                .split(' ')
                .map(|id| oid(id).map(str::to_owned))
                .collect::<Result<Vec<_>, _>>()?;
            if trees.len() < 3 || trees.len() % 2 == 0 {
                return Err("Invalid jj merge-tree shape".into());
            }
            return Ok(trees);
        }
    }
    Err("Conflicted jj commit has no supported jj:trees header; legacy conflict storage is unsupported".into())
}
fn provenance(
    root: &Path,
    store: &Path,
    commit: &str,
    cancelled: &dyn Fn() -> bool,
) -> Result<BTreeMap<String, String>, String> {
    let mut command = jj_command(root);
    let revision = format!(
        "ancestors(commit_id({}))",
        serde_json::to_string(commit).unwrap()
    );
    // ponytail: inspect the nearest 256 ancestors once; deeper inputs show their
    // exact tree ID. Expand the bounded batch only if provenance needs it.
    command.args(["log", "--no-graph", "-r", &revision, "-n", "256", "-T",
        "\"[\" ++ json(commit_id) ++ \",\" ++ json(change_id) ++ \",\" ++ json(local_bookmarks.map(|b| b.name())) ++ \"]\\n\""]);
    let mut commits = BTreeMap::new();
    let mut input = Vec::new();
    for line in run(command, cancelled)?
        .split(|b| *b == b'\n')
        .filter(|line| !line.is_empty())
    {
        let (id, change, bookmarks): (String, String, Vec<String>) =
            serde_json::from_slice(line).map_err(|e| format!("Invalid source provenance: {e}"))?;
        if id.bytes().all(|b| b == b'0') {
            continue;
        }
        oid(&id)?;
        let label = format!(
            "{}{}",
            &change[..change.len().min(12)],
            if bookmarks.is_empty() {
                String::new()
            } else {
                format!(" [{}]", bookmarks.join(", "))
            }
        );
        input.extend_from_slice(id.as_bytes());
        input.push(b'\n');
        commits.insert(id, (!bookmarks.is_empty(), label));
    }
    if input.is_empty() {
        return Ok(BTreeMap::new());
    }
    let mut command = git(store);
    command.args([
        "log",
        "--no-walk=unsorted",
        "--no-decorate",
        "--no-show-signature",
        "--format=%H %T",
        "--stdin",
    ]);
    let output = crate::blame::run(command, &input, cancelled)?
        .ok_or("Cannot read source provenance trees")?;
    let mut labels: BTreeMap<String, (bool, String)> = BTreeMap::new();
    for line in text(output)?.lines() {
        let (id, tree) = line
            .split_once(' ')
            .ok_or("Invalid source provenance tree record")?;
        oid(tree)?;
        let label = commits.get(id).ok_or("Unknown source provenance commit")?;
        if labels.get(tree).is_none_or(|old| !old.0 && label.0) {
            labels.insert(tree.to_owned(), label.clone());
        }
    }
    Ok(labels
        .into_iter()
        .map(|(tree, (_, label))| (tree, label))
        .collect())
}
fn os(bytes: Vec<u8>) -> Result<OsString, String> {
    #[cfg(unix)]
    {
        use std::os::unix::ffi::OsStringExt;
        Ok(OsString::from_vec(bytes))
    }
    #[cfg(not(unix))]
    {
        String::from_utf8(bytes)
            .map(OsString::from)
            .map_err(|_| "Non-UTF-8 path".into())
    }
}
fn os_bytes(value: OsString) -> Vec<u8> {
    #[cfg(unix)]
    {
        use std::os::unix::ffi::OsStringExt;
        value.into_vec()
    }
    #[cfg(not(unix))]
    {
        value.to_string_lossy().as_bytes().to_vec()
    }
}
fn blob(
    store: &Path,
    id: &str,
    budget: &mut usize,
    cancelled: &dyn Fn() -> bool,
) -> Result<Vec<u8>, String> {
    let mut command = git(store);
    command.args(["cat-file", "blob", oid(id)?]);
    let bytes = run(command, cancelled)?;
    if bytes.len() > LIMIT {
        return Err("Conflict input exceeds 16 MiB".into());
    }
    *budget = budget
        .checked_sub(bytes.len())
        .ok_or("Conflict source and disk inputs exceed 64 MiB total")?;
    Ok(bytes)
}
fn tree_entries(
    store: &Path,
    tree: &str,
    path: Option<&Path>,
    budget: &mut usize,
    cancelled: &dyn Fn() -> bool,
) -> Result<Vec<(OsString, Node)>, String> {
    let mut command = git(store);
    command.args(["--literal-pathspecs", "ls-tree", "-z", oid(tree)?]);
    if let Some(path) = path {
        command.arg("--").arg(path);
    }
    let mut result = Vec::new();
    for record in run(command, cancelled)?
        .split(|b| *b == 0)
        .filter(|r| !r.is_empty())
    {
        check(cancelled)?;
        let (header, name) = record.split_at(
            record
                .iter()
                .position(|b| *b == b'\t')
                .ok_or("Invalid Git tree record")?,
        );
        let fields = std::str::from_utf8(header)
            .map_err(|_| "Invalid Git tree header")?
            .split(' ')
            .collect::<Vec<_>>();
        if fields.len() != 3 {
            return Err("Invalid Git tree fields".into());
        }
        let mode = u32::from_str_radix(fields[0], 8).map_err(|_| "Invalid Git mode")?;
        let id = oid(fields[2])?;
        let node = match mode {
            0o100644 | 0o100755 => Node::File(blob(store, id, budget, cancelled)?, mode & 0o777),
            0o120000 => Node::Symlink(blob(store, id, budget, cancelled)?),
            0o040000 => Node::Directory(tree_entries(store, id, None, budget, cancelled)?),
            0o160000 => Node::Submodule(id.to_owned()),
            _ => return Err(format!("Unsupported Git conflict mode {mode:o}")),
        };
        result.push((os(name[1..].to_vec())?, node));
    }
    result.sort_by(|a, b| a.0.cmp(&b.0));
    Ok(result)
}
fn safe_ancestors(root: &Path, path: &Path) -> Result<(), String> {
    safe_path(path)?;
    let mut full = root.to_path_buf();
    for part in path.parent().into_iter().flat_map(Path::components) {
        full.push(part);
        let metadata = fs::symlink_metadata(&full)
            .map_err(|e| format!("Unsafe conflict parent {}: {e}", full.display()))?;
        if !metadata.is_dir() || metadata.file_type().is_symlink() {
            return Err(format!(
                "Conflict parent is not a real directory: {}",
                full.display()
            ));
        }
    }
    Ok(())
}
fn disk(path: &Path, budget: &mut usize, cancelled: &dyn Fn() -> bool) -> Result<Node, String> {
    check(cancelled)?;
    let metadata = match fs::symlink_metadata(path) {
        Ok(metadata) => metadata,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(Node::Absent),
        Err(e) => return Err(format!("{}: {e}", path.display())),
    };
    if metadata.file_type().is_symlink() {
        return Ok(Node::Symlink(os_bytes(
            fs::read_link(path)
                .map_err(|e| e.to_string())?
                .into_os_string(),
        )));
    }
    if metadata.is_dir() {
        let mut entries = Vec::new();
        for entry in fs::read_dir(path).map_err(|e| e.to_string())? {
            let entry = entry.map_err(|e| e.to_string())?;
            safe_path(Path::new(&entry.file_name()))?;
            entries.push((entry.file_name(), disk(&entry.path(), budget, cancelled)?));
        }
        entries.sort_by(|a, b| a.0.cmp(&b.0));
        return Ok(Node::Directory(entries));
    }
    if !metadata.is_file() {
        return Err(format!("Unsupported filesystem object: {}", path.display()));
    }
    if metadata.len() > LIMIT as u64 || metadata.len() > *budget as u64 {
        return Err("Conflict disk contents exceed 16 MiB per file or 64 MiB total".into());
    }
    let bytes = fs::read(path).map_err(|e| e.to_string())?;
    *budget = budget
        .checked_sub(bytes.len())
        .ok_or("Conflict disk contents exceed 64 MiB")?;
    #[cfg(unix)]
    let mode = {
        use std::os::unix::fs::PermissionsExt;
        metadata.permissions().mode() & 0o777
    };
    #[cfg(not(unix))]
    let mode = 0o644;
    Ok(Node::File(bytes, mode))
}
fn disk_result(node: &Node) -> Option<String> {
    (node.kind() == FileKind::Text)
        .then(|| String::from_utf8(node.bytes().to_vec()).ok())
        .flatten()
}

pub fn load(root: &Path, cancelled: &dyn Fn() -> bool) -> Result<Workspace, String> {
    let root = fs::canonicalize(root).map_err(|e| e.to_string())?;
    let root = root
        .ancestors()
        .find(|p| p.join(".jj").is_dir())
        .ok_or("Resolve requires a current Jujutsu working copy")?
        .to_path_buf();
    let checkout = identity(&root, cancelled)?;
    let paths = entries(&root, &checkout.commit, cancelled)?;
    let store = store_for_jj(&root)?;
    let trees = if paths.is_empty() {
        Vec::new()
    } else {
        trees(&store, &checkout.commit, cancelled)?
    };
    let (labels, provenance_notice) = if paths.is_empty() {
        (BTreeMap::new(), None)
    } else {
        match provenance(&root, &store, &checkout.commit, cancelled) {
            Ok(labels) => (labels, None),
            Err(error) => {
                check(cancelled)?;
                (
                    BTreeMap::new(),
                    Some(format!(
                        "Source provenance unavailable; showing exact tree IDs: {error}"
                    )),
                )
            }
        }
    };
    let mut files = Vec::new();
    let mut budget = 64 * 1024 * 1024;
    for path in paths {
        check(cancelled)?;
        safe_ancestors(&root, &path)?;
        let mut terms = Vec::new();
        for tree in &trees {
            let mut values = tree_entries(&store, tree, Some(&path), &mut budget, cancelled)?;
            if values.len() > 1 {
                return Err("Ambiguous Git tree conflict path".into());
            }
            terms.push(values.pop().map_or(Node::Absent, |(_, value)| value));
        }
        // Cancel equal add/remove terms exactly as jj simplifies a path's merge.
        let mut keep = vec![true; terms.len()];
        for base in (1..terms.len()).step_by(2) {
            if let Some(side) = (0..terms.len())
                .step_by(2)
                .find(|side| keep[*side] && terms[*side] == terms[base])
            {
                keep[base] = false;
                keep[side] = false;
            }
        }
        let mut sides = 0;
        let mut bases = 0;
        let mut sources = Vec::new();
        let num_sides = keep
            .iter()
            .enumerate()
            .filter(|(i, kept)| **kept && i % 2 == 0)
            .count();
        let num_bases = keep
            .iter()
            .enumerate()
            .filter(|(i, kept)| **kept && i % 2 == 1)
            .count();
        for (index, node) in terms.into_iter().enumerate().filter(|(i, _)| keep[*i]) {
            let base = index % 2 == 1;
            let term = if base {
                let n = bases;
                bases += 1;
                n
            } else {
                let n = sides;
                sides += 1;
                n
            };
            let tree_id = trees[index].clone();
            let provenance = labels
                .get(&tree_id)
                .cloned()
                .unwrap_or_else(|| format!("tree {}", &tree_id[..12]));
            sources.push(Source {
                label: format!(
                    "{} #{} - {} ({:?}{})",
                    if base { "Base" } else { "Side" },
                    term + 1,
                    provenance,
                    node.kind(),
                    if matches!(&node, Node::File(_, mode) if mode & 0o111 != 0) {
                        ", executable"
                    } else {
                        ""
                    }
                ),
                base,
                kind: node.kind(),
                bytes: node.bytes().to_vec(),
                tree_id,
                term,
                sides: num_sides,
                bases: num_bases,
                node,
            });
        }
        let baseline = disk(&root.join(&path), &mut budget, cancelled)?;
        let nontext = sources
            .iter()
            .any(|s| s.kind != FileKind::Text && !(s.base && s.kind == FileKind::Deleted));
        let result = if nontext {
            None
        } else {
            disk_result(&baseline)
        };
        let notice = match (nontext, &provenance_notice) {
            (true, Some(error)) => Some(format!("Non-text/type conflict: choose an explicit whole-file source; byte content and file type are preserved. {error}")),
            (true, None) => Some("Non-text/type conflict: choose an explicit whole-file source; byte content and file type are preserved".into()),
            (false, notice) => notice.clone(),
        };
        files.push(ConflictFile {
            path,
            sources,
            result,
            notice,
            status: Status::Unresolved,
            baseline,
        });
    }
    if identity(&root, cancelled)? != checkout {
        return Err("Jujutsu checkout changed while loading; reopen :resolve".into());
    }
    Ok(Workspace {
        root,
        checkout,
        files,
    })
}

// jj uses flock on this exact path, unlinks it before unlocking, and retries
// unlinked descriptors. Use the same protocol so checkout changes cannot race writes.
struct WorkingCopyLock {
    path: PathBuf,
    _file: File,
}
impl WorkingCopyLock {
    fn acquire(root: &Path) -> Result<Self, String> {
        let path = root.join(".jj/working_copy/working_copy.lock");
        loop {
            let file = OpenOptions::new()
                .create(true)
                .write(true)
                .truncate(false)
                .open(&path)
                .map_err(|e| e.to_string())?;
            file.try_lock()
                .map_err(|e| format!("Jujutsu working copy is busy: {e}"))?;
            #[cfg(unix)]
            {
                use std::os::unix::fs::MetadataExt;
                if file.metadata().map_err(|e| e.to_string())?.nlink() == 0 {
                    continue;
                }
            }
            return Ok(Self { path, _file: file });
        }
    }
}
impl Drop for WorkingCopyLock {
    fn drop(&mut self) {
        let _ = fs::remove_file(&self.path);
    }
}
struct Staged(PathBuf);
impl Drop for Staged {
    fn drop(&mut self) {
        let _ = remove(&self.0);
    }
}
impl Staged {
    fn new(parent: &Path) -> Result<Self, String> {
        for _ in 0..100 {
            let path = parent.join(format!(
                ".vamp-resolve-{}-{}",
                std::process::id(),
                NEXT.fetch_add(1, Ordering::Relaxed)
            ));
            let mut builder = fs::DirBuilder::new();
            #[cfg(unix)]
            {
                use std::os::unix::fs::DirBuilderExt;
                builder.mode(0o700);
            }
            match builder.create(&path) {
                Ok(()) => return Ok(Self(path)),
                Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => continue,
                Err(e) => return Err(e.to_string()),
            }
        }
        Err("Cannot create a private conflict save directory".into())
    }
}
fn remove(path: &Path) -> Result<(), String> {
    match fs::symlink_metadata(path) {
        Ok(metadata) if metadata.is_dir() => fs::remove_dir_all(path),
        Ok(_) => fs::remove_file(path),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
        Err(e) => return Err(e.to_string()),
    }
    .map_err(|e| e.to_string())
}
fn materialize(path: &Path, node: &Node, cancelled: &dyn Fn() -> bool) -> Result<(), String> {
    check(cancelled)?;
    match node {
        Node::Absent => Ok(()),
        Node::File(bytes, mode) => {
            let mut file = OpenOptions::new().write(true).create_new(true).open(path).map_err(|e| e.to_string())?;
            file.write_all(bytes).and_then(|_| file.sync_all()).map_err(|e| e.to_string())?;
            #[cfg(unix)] { use std::os::unix::fs::PermissionsExt; fs::set_permissions(path, fs::Permissions::from_mode(*mode)).map_err(|e| e.to_string())?; }
            Ok(())
        }
        Node::Symlink(bytes) => {
            let target = PathBuf::from(os(bytes.clone())?);
            #[cfg(unix)] { std::os::unix::fs::symlink(target, path).map_err(|e| e.to_string()) }
            #[cfg(not(unix))] { let _ = target; Err("Symlink resolution requires Unix symlink support".into()) }
        }
        Node::Directory(entries) => {
            fs::create_dir(path).map_err(|e| e.to_string())?;
            for (name, value) in entries { safe_path(Path::new(name))?; materialize(&path.join(name), value, cancelled)?; }
            Ok(())
        }
        Node::Submodule(_) => Err("Jujutsu does not materialize Git submodules; resolve this source with jj outside the editor".into()),
    }
}

pub fn save(
    workspace: &Workspace,
    file_index: usize,
    resolution: Resolution,
    cancelled: &dyn Fn() -> bool,
) -> Result<SaveOutcome, String> {
    check(cancelled)?;
    let file = workspace
        .files
        .get(file_index)
        .ok_or("Unknown resolver file")?;
    let desired = match resolution {
        Resolution::Text(text) => {
            if file.result.is_none()
                || (file.status != Status::Resolved
                    && file.sources.iter().any(|source| {
                        source.kind != FileKind::Text
                            && !(source.base && source.kind == FileKind::Deleted)
                    }))
            {
                return Err(
                    "Choose an explicit whole-file source for this non-text/type conflict".into(),
                );
            }
            if text.len() > LIMIT {
                return Err("Resolution exceeds 16 MiB".into());
            }
            let mode = match &file.baseline {
                Node::File(_, mode) => *mode,
                _ => 0o644,
            };
            Node::File(text.into_bytes(), mode)
        }
        Resolution::Source(index) => file
            .sources
            .get(index)
            .ok_or("Unknown conflict source")?
            .node
            .clone(),
    };
    if fs::canonicalize(&workspace.root).map_err(|e| e.to_string())? != workspace.root {
        return Err("Jujutsu workspace path changed; no file written. Reopen :resolve".into());
    }
    let lock = WorkingCopyLock::acquire(&workspace.root)?;
    if identity(&workspace.root, cancelled)? != workspace.checkout {
        return Err("Jujutsu checkout changed; no file written. Reopen :resolve".into());
    }
    safe_ancestors(&workspace.root, &file.path)?;
    let path = workspace.root.join(&file.path);
    if disk(&path, &mut (64 * 1024 * 1024), cancelled)? != file.baseline {
        return Err("Conflict file changed externally; no file written. Reopen :resolve".into());
    }
    if matches!(file.baseline, Node::Directory(_))
        && !file
            .sources
            .iter()
            .any(|source| source.node == file.baseline)
    {
        return Err("Directory contains untracked or modified children; no files written. Preserve those files before choosing a whole-file resolution".into());
    }
    let staged = Staged::new(path.parent().ok_or("Missing conflict parent")?)?;
    let replacement = staged.0.join("result");
    materialize(&replacement, &desired, cancelled)?;
    check(cancelled)?;
    // Recheck immediately before replacing, including filesystem ancestors.
    safe_ancestors(&workspace.root, &file.path)?;
    if identity(&workspace.root, cancelled)? != workspace.checkout
        || disk(&path, &mut (64 * 1024 * 1024), cancelled)? != file.baseline
    {
        return Err("Checkout or conflict file changed; no file written. Reopen :resolve".into());
    }
    if matches!(desired, Node::Absent | Node::Directory(_))
        || matches!(file.baseline, Node::Directory(_))
    {
        let backup = staged.0.join("original");
        if !matches!(file.baseline, Node::Absent) {
            fs::rename(&path, &backup).map_err(|e| e.to_string())?;
        }
        if !matches!(desired, Node::Absent)
            && let Err(error) = fs::rename(&replacement, &path)
        {
            if !matches!(file.baseline, Node::Absent)
                && let Err(restore) = fs::rename(&backup, &path)
            {
                let location = backup.display().to_string();
                std::mem::forget(staged);
                return Err(format!(
                    "Cannot install resolution: {error}; cannot restore original: {restore}; original retained at {location}"
                ));
            }
            return Err(error.to_string());
        }
    } else {
        fs::rename(&replacement, &path).map_err(|e| e.to_string())?;
    }
    let cleanup_error = remove(&staged.0).err().map(|error| format!("Saved; private backup cleanup failed at {}: {error}; jj confirmation was not attempted", staged.0.display()));
    drop(staged);
    drop(lock);
    let mut saved = file.clone();
    saved.baseline = desired;
    saved.result = disk_result(&saved.baseline);
    saved.status = Status::Unconfirmed;
    if let Some(error) = cleanup_error {
        return Ok(SaveOutcome {
            checkout: workspace.checkout.clone(),
            file: saved,
            confirmation: Some(error),
        });
    }
    // A cancellation after the write must still produce a saved/unconfirmed
    // outcome, rather than leaving the UI believing nothing reached disk.
    let confirmation: Result<Checkout, String> = (|| {
        let before = identity(&workspace.root, cancelled)?;
        if before != workspace.checkout {
            return Err("Checkout changed after writing; jj confirmation was not attempted".into());
        }
        let mut command = Command::new("jj");
        command
            .arg("--repository")
            .arg(&workspace.root)
            .current_dir(&workspace.root)
            .args([
                "--no-pager",
                "--color=never",
                "--config=snapshot.auto-update-stale=false",
                "util",
                "snapshot",
            ]);
        run(command, cancelled)?;
        let checkout = identity(&workspace.root, cancelled)?;
        if checkout.change != workspace.checkout.change {
            return Err("Jujutsu changed checkout during confirmation".into());
        }
        let conflicts = entries(&workspace.root, &checkout.commit, cancelled)?;
        if identity(&workspace.root, cancelled)? != checkout {
            return Err("Jujutsu changed during conflict status confirmation".into());
        }
        if disk(&path, &mut (64 * 1024 * 1024), cancelled)? != saved.baseline {
            return Err(
                "Conflict file changed during jj confirmation; saved content cannot be confirmed"
                    .into(),
            );
        }
        saved.status = if conflicts.contains(&saved.path) {
            Status::Unresolved
        } else {
            Status::Resolved
        };
        Ok(checkout)
    })();
    match confirmation {
        Ok(checkout) => Ok(SaveOutcome {
            checkout,
            file: saved,
            confirmation: None,
        }),
        Err(error) => Ok(SaveOutcome {
            checkout: workspace.checkout.clone(),
            file: saved,
            confirmation: Some(format!("Saved; jj status unconfirmed: {error}")),
        }),
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Region {
    pub lines: Range<usize>,
    pub sides: Vec<String>,
    pub bases: Vec<String>,
}
impl Region {
    fn selected(&self, source: &Source) -> Result<&str, String> {
        if !matches!(source.kind, FileKind::Text | FileKind::Deleted) {
            return Err("Non-text sources require an explicit whole-file choice".into());
        }
        if self.sides.len() != source.sides || self.bases.len() != source.bases {
            return Err("Conflict region no longer has the original side/base count; edit it manually or choose a whole file".into());
        }
        let terms = if source.base {
            &self.bases
        } else {
            &self.sides
        };
        terms.get(source.term).map(String::as_str).ok_or_else(|| "Conflict region no longer matches this source; edit it manually or choose a whole file".into())
    }
    pub fn choose(&self, source: &Source) -> Result<String, String> {
        self.selected(source).map(str::to_owned)
    }
}
fn marker(line: &str) -> Option<(u8, usize)> {
    let bytes = line.as_bytes();
    let first = *bytes.first()?;
    if !b"<>+-%%|=^\\".contains(&first) {
        return None;
    }
    let width = bytes.iter().take_while(|b| **b == first).count();
    (width >= 7 && matches!(bytes.get(width), None | Some(b' ' | b'\r' | b'\n')))
        .then_some((first, width))
}
fn parse_region(lines: &[&str], width: usize) -> Option<(Vec<String>, Vec<String>)> {
    let mut sides = Vec::new();
    let mut bases = Vec::new();
    if lines.iter().any(|line| marker(line) == Some((b'|', width))) {
        let mut section = 0;
        sides.push(String::new());
        bases.push(String::new());
        sides.push(String::new());
        for line in lines {
            match marker(line) {
                Some((b'|', n)) if n == width && section == 0 => section = 1,
                Some((b'=', n)) if n == width && section == 1 => section = 2,
                _ => match section {
                    0 => sides[0].push_str(line),
                    1 => bases[0].push_str(line),
                    _ => sides[1].push_str(line),
                },
            }
        }
        return (section == 2).then_some((sides, bases));
    }
    let mut current = None;
    for line in lines {
        match marker(line) {
            Some((b'+', n)) if n == width => {
                sides.push(String::new());
                current = Some((b'+', sides.len() - 1, 0));
            }
            Some((b'-', n)) if n == width => {
                bases.push(String::new());
                current = Some((b'-', bases.len() - 1, 0));
            }
            Some((b'%', n)) if n == width => {
                bases.push(String::new());
                sides.push(String::new());
                current = Some((b'%', sides.len() - 1, bases.len() - 1));
            }
            Some((b'^' | b'\\', n))
                if n == width && current.is_some_and(|(kind, _, _)| kind == b'%') => {}
            _ => match current? {
                (b'+', side, _) => sides[side].push_str(line),
                (b'-', base, _) => bases[base].push_str(line),
                (b'%', side, base) => match line.as_bytes().first()? {
                    b' ' => {
                        sides[side].push_str(&line[1..]);
                        bases[base].push_str(&line[1..]);
                    }
                    b'+' => sides[side].push_str(&line[1..]),
                    b'-' => bases[base].push_str(&line[1..]),
                    _ => return None,
                },
                _ => return None,
            },
        }
    }
    (sides.len() >= 2 && bases.len() + 1 == sides.len()).then_some((sides, bases))
}
/// Recognize jj snapshot/diff/diff-experimental and Git diff3 markers at any
/// marker width. Recognition is local; jj alone decides saved resolution status.
pub fn regions(text: &str) -> Vec<Region> {
    let lines = text.split_inclusive('\n').collect::<Vec<_>>();
    let mut regions: Vec<Region> = Vec::new();
    let mut starts = Vec::new();
    for (row, line) in lines.iter().enumerate() {
        let width = match marker(line) {
            Some((b'<', width)) => {
                starts.push((row, width));
                continue;
            }
            Some((b'>', width)) => width,
            _ => continue,
        };
        let Some(position) = starts
            .iter()
            .rposition(|(_, candidate)| *candidate == width)
        else {
            continue;
        };
        let (start, _) = starts[position];
        starts.truncate(position);
        if let Some((mut sides, mut bases)) = parse_region(&lines[start + 1..row], width) {
            // jj adds a separator EOL to every term if any input lacks its final
            // newline; the end marker then has no EOL (jj conflicts.rs protocol).
            if !lines[row].ends_with('\n') {
                for term in sides.iter_mut().chain(bases.iter_mut()) {
                    if term.ends_with("\r\n") {
                        term.truncate(term.len() - 2);
                    } else if term.ends_with('\n') {
                        term.pop();
                    }
                }
            }
            regions.retain(|region| region.lines.start < start || region.lines.end > row + 1);
            regions.push(Region {
                lines: start..row + 1,
                sides,
                bases,
            });
        }
    }
    regions
}

/// Marker-free working text and the original choices, never historical full files.
/// Like jj-diffconflicts, replace marker sections in the working buffer, not
/// entire branch snapshots: https://github.com/rafikdraoui/jj-diffconflicts.
#[derive(Clone, Debug)]
pub struct Projection {
    seed_index: usize,
    alternatives: Vec<String>,
}
impl Projection {
    /// Freeze every choice from current working text. Indices are indices in
    /// `ConflictFile::sources`, including bases. Later draft edits are independent.
    pub fn new(raw: &str, sources: &[Source], seed_index: usize) -> Result<Self, String> {
        if seed_index >= sources.len() {
            return Err("No such conflict source".into());
        }
        let mut offsets = vec![0];
        for line in raw.split_inclusive('\n') {
            offsets.push(offsets.last().unwrap() + line.len());
        }
        let mut alternatives = sources
            .iter()
            .map(|_| String::with_capacity(raw.len()))
            .collect::<Vec<_>>();
        let mut end = 0;
        for region in regions(raw) {
            let outside = &raw[end..offsets[region.lines.start]];
            for (alternative, source) in alternatives.iter_mut().zip(sources) {
                alternative.push_str(outside);
                alternative.push_str(region.selected(source)?);
            }
            end = offsets[region.lines.end];
        }
        for alternative in &mut alternatives {
            alternative.push_str(&raw[end..]);
        }
        Ok(Self {
            seed_index,
            alternatives,
        })
    }

    pub fn seed(&self) -> &str {
        &self.alternatives[self.seed_index]
    }

    pub fn alternative(&self, index: usize) -> Result<&str, String> {
        self.alternatives
            .get(index)
            .map(String::as_str)
            .ok_or_else(|| "No such conflict source".into())
    }
}

/// Project the selected side/base through current materialized working text.
/// Bytes outside recognized marker regions, including the final EOL, are retained.
pub fn project(text: &str, source: &Source) -> Result<String, String> {
    Projection::new(text, std::slice::from_ref(source), 0)
        .map(|mut projection| projection.alternatives.pop().unwrap())
}

#[cfg(all(test, unix))]
#[path = "../tests/unit/resolve.rs"]
mod tests;

#[cfg(test)]
#[path = "../tests/unit/resolve_projection.rs"]
mod projection_tests;