//! Read-only source-line changes against Git HEAD or a single Jujutsu @- parent.
use crate::{
    blame::{git, git_without_literal_pathspecs, run, run_status},
    diff::line_hunks,
    editor::normalize_newlines,
    repository::{
        WorkingFileChange, WorkingFileReader, jj_command, jj_file_pattern, safe_path, store_for_jj,
    },
};
use serde::Deserialize;
use std::{
    fs, io,
    path::{Path, PathBuf},
    process::Command,
    sync::{
        Arc, Condvar, Mutex,
        atomic::{AtomicBool, AtomicU64, Ordering},
    },
    thread::{self, JoinHandle},
};

const FILE_LIMIT: usize = 16 * 1024 * 1024;
const BATCH_LIMIT: usize = 64 * 1024 * 1024;
const FILE_COUNT_LIMIT: usize = 1024;
type Files = Vec<(usize, PathBuf, Arc<str>)>;
type FileResult = Result<Vec<Option<Change>>, String>;
pub(crate) type ResultBatch = Vec<(usize, FileResult)>;
type PickerRequest = (PathBuf, Vec<(PathBuf, Arc<str>)>);
type Request = (u64, u64, Files, Option<PickerRequest>);

pub(crate) struct PickerChanges {
    pub(crate) root: PathBuf,
    pub(crate) result: Result<Vec<WorkingFileChange>, String>,
}

#[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum GutterStyle {
    #[default]
    Bar,
    Symbols,
    LineNumbers,
    None,
}

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub(crate) enum Change {
    Added,
    Removed,
    Modified,
}

#[derive(Default)]
struct State {
    request: Option<Request>,
    result: Option<(u64, ResultBatch, Option<PickerChanges>)>,
}
#[derive(Default)]
struct Shared {
    state: Mutex<State>,
    wake: Condvar,
    generation: AtomicU64,
    stopped: AtomicBool,
}
pub(crate) struct Worker {
    shared: Arc<Shared>,
    thread: Option<JoinHandle<()>>,
}
impl Worker {
    pub(crate) fn start() -> io::Result<Self> {
        let shared = Arc::new(Shared::default());
        let worker = Arc::clone(&shared);
        let thread = thread::Builder::new()
            .name("vamp-gutter".into())
            .spawn(move || {
                let mut picker_reader = WorkingFileReader::default();
                loop {
                    let Ok(mut state) = worker.state.lock() else {
                        return;
                    };
                    while state.request.is_none() && !worker.stopped.load(Ordering::Acquire) {
                        let Ok(next) = worker.wake.wait(state) else {
                            return;
                        };
                        state = next;
                    }
                    if worker.stopped.load(Ordering::Acquire) {
                        return;
                    }
                    let (generation, id, files, picker) = state.request.take().unwrap();
                    drop(state);
                    let cancelled = || {
                        worker.stopped.load(Ordering::Acquire)
                            || worker.generation.load(Ordering::Acquire) != generation
                    };
                    let mut results = Vec::with_capacity(files.len());
                    for (buffer, path, contents) in files {
                        if cancelled() {
                            break;
                        }
                        results.push((buffer, read_file(&path, &contents, &cancelled)));
                    }
                    let picker = picker.map(|(root, buffers)| PickerChanges {
                        result: picker_reader.read(&root, &buffers, &cancelled),
                        root,
                    });
                    let Ok(mut state) = worker.state.lock() else {
                        return;
                    };
                    if !cancelled() {
                        state.result = Some((id, results, picker));
                    }
                }
            })?;
        Ok(Self {
            shared,
            thread: Some(thread),
        })
    }

    pub(crate) fn request(
        &mut self,
        id: u64,
        files: Files,
        picker: Option<PickerRequest>,
    ) -> io::Result<()> {
        let size = files.iter().try_fold(0usize, |size, (_, path, text)| {
            size.checked_add(text.len())?
                .checked_add(path.as_os_str().len())
        });
        let picker_size = picker.as_ref().map_or(Some(0), |(root, buffers)| {
            buffers
                .iter()
                .try_fold(root.as_os_str().len(), |size, (path, text)| {
                    size.checked_add(text.len())?
                        .checked_add(path.as_os_str().len())
                })
        });
        let count = files.len() + picker.as_ref().map_or(0, |(_, buffers)| buffers.len());
        if count > FILE_COUNT_LIMIT
            || size
                .zip(picker_size)
                .and_then(|(files, picker)| files.checked_add(picker))
                .is_none_or(|size| size > BATCH_LIMIT)
        {
            return Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Gutter batch exceeds 64 MiB or 1024 files",
            ));
        }
        let mut state = self
            .shared
            .state
            .lock()
            .map_err(|_| io::Error::other("Gutter worker stopped"))?;
        let generation = self
            .shared
            .generation
            .fetch_add(1, Ordering::AcqRel)
            .wrapping_add(1);
        state.request = Some((generation, id, files, picker));
        state.result = None;
        self.shared.wake.notify_one();
        Ok(())
    }

    pub(crate) fn poll(&mut self) -> Option<(u64, ResultBatch, Option<PickerChanges>)> {
        self.shared.state.lock().ok()?.result.take()
    }
}
impl Drop for Worker {
    fn drop(&mut self) {
        let state = self.shared.state.lock();
        self.shared.stopped.store(true, Ordering::Release);
        self.shared.wake.notify_one();
        drop(state);
        if let Some(thread) = self.thread.take() {
            let _ = thread.join();
        }
    }
}

fn checked(command: Command, cancelled: &dyn Fn() -> bool) -> Result<Vec<u8>, String> {
    run(command, &[], cancelled)?.ok_or_else(|| "Cannot read gutter repository metadata".into())
}

fn read_file(path: &Path, contents: &str, cancelled: &dyn Fn() -> bool) -> FileResult {
    if contents.len() > FILE_LIMIT {
        return Err("Gutter file exceeds 16 MiB".into());
    }
    if contents.as_bytes().contains(&0) {
        return Ok(vec![]);
    }
    match fs::symlink_metadata(path) {
        Ok(metadata) if !metadata.file_type().is_file() => return Ok(vec![]),
        Ok(_) => {}
        Err(error) if error.kind() == io::ErrorKind::NotFound => {}
        Err(error) => return Err(error.to_string()),
    }
    // Check the lexical path before canonicalizing: metadata files and symlinked parents
    // must not acquire the markers of their target outside the checkout.
    let absolute = if path.is_absolute() {
        path.to_path_buf()
    } else {
        std::env::current_dir()
            .map_err(|e| e.to_string())?
            .join(path)
    };
    if absolute
        .components()
        .any(|part| part.as_os_str() == ".git" || part.as_os_str() == ".jj")
    {
        return Ok(vec![]);
    }
    let Some(root) = absolute.parent().and_then(|parent| {
        parent
            .ancestors()
            .find(|root| root.join(".jj").exists() || root.join(".git").exists())
    }) else {
        return Ok(vec![]);
    };
    if absolute
        .ancestors()
        .take_while(|part| *part != root)
        .any(|part| {
            fs::symlink_metadata(part).is_ok_and(|metadata| metadata.file_type().is_symlink())
        })
    {
        return Ok(vec![]);
    }
    let relative = absolute.strip_prefix(root).map_err(|e| e.to_string())?;
    if safe_path(relative).is_err() {
        return Ok(vec![]);
    }
    // Resolve ancestors above the checkout, preserving a missing named-buffer tail.
    let root = fs::canonicalize(root).map_err(|e| e.to_string())?;
    let baseline = if root.join(".jj").exists() {
        jj_baseline(&root, relative, cancelled)?
    } else {
        git_baseline(&root, relative, cancelled)?
    };
    let Some(baseline) = baseline else {
        return Ok(vec![]);
    };
    if baseline.contains(&0) {
        return Ok(vec![]);
    }
    let Ok(baseline) = std::str::from_utf8(&baseline) else {
        return Ok(vec![]);
    };
    if cancelled() {
        return Err("Gutter cancelled".into());
    }
    Ok(changes(baseline, contents))
}

fn eligible(
    root: &Path,
    relative: &Path,
    store: Option<&Path>,
    cancelled: &dyn Fn() -> bool,
) -> Result<bool, String> {
    let command = |literal_pathspecs| {
        let mut command = if literal_pathspecs {
            git(root)
        } else {
            git_without_literal_pathspecs(root)
        };
        if let Some(store) = store {
            command
                .arg("--git-dir")
                .arg(store)
                .arg("--work-tree")
                .arg(root);
        }
        command
    };
    let mut tracked = command(true);
    tracked
        .args(["ls-files", "--cached", "-z", "--"])
        .arg(relative);
    let bytes = checked(tracked, cancelled)?;
    if bytes
        .split(|byte| *byte == 0)
        .any(|entry| entry == relative.as_os_str().as_encoded_bytes())
    {
        return Ok(true);
    }
    let mut ignored = command(false);
    ignored
        .args(["check-ignore", "--no-index", "-q", "--"])
        .arg(relative);
    match run_status(ignored, &[], cancelled)?.0 {
        Some(0) => Ok(false),
        Some(1) => Ok(true),
        _ => Err("Cannot read gutter ignore rules".into()),
    }
}

fn git_baseline(
    root: &Path,
    relative: &Path,
    cancelled: &dyn Fn() -> bool,
) -> Result<Option<Vec<u8>>, String> {
    let mut head = git(root);
    head.args(["rev-parse", "--verify", "--quiet", "HEAD^{commit}"]);
    let (code, head) = run_status(head, &[], cancelled)?;
    if code == Some(1) {
        // An unborn repository still has an index and ignore rules.
        return Ok(eligible(root, relative, None, cancelled)?.then(Vec::new));
    }
    if code != Some(0) {
        return Err("Cannot resolve Git gutter HEAD".into());
    }
    let head = std::str::from_utf8(&head)
        .map_err(|_| "Invalid Git gutter HEAD")?
        .trim();
    let mut tree = git(root);
    tree.args(["ls-tree", "-z", "--full-tree", head, "--"])
        .arg(relative);
    let entries = checked(tree, cancelled)?;
    let Some(entry) = entries
        .split(|byte| *byte == 0)
        .find(|entry| !entry.is_empty())
    else {
        return Ok(eligible(root, relative, None, cancelled)?.then(Vec::new));
    };
    let tab = entry
        .iter()
        .position(|byte| *byte == b'\t')
        .ok_or("Invalid Git gutter tree")?;
    if &entry[tab + 1..] != relative.as_os_str().as_encoded_bytes() {
        return Err("Unexpected Git gutter path".into());
    }
    let fields = std::str::from_utf8(&entry[..tab]).map_err(|_| "Invalid Git gutter tree")?;
    let mut fields = fields.split(' ');
    if !matches!(fields.next(), Some("100644" | "100755")) || fields.next() != Some("blob") {
        return Ok(None);
    }
    let object = fields.next().ok_or("Missing Git gutter blob")?;
    let mut cat = git(root);
    cat.args(["cat-file", "blob", object]);
    checked(cat, cancelled).map(Some)
}

fn jj_file_kind(
    root: &Path,
    revision: &str,
    pattern: &str,
    cancelled: &dyn Fn() -> bool,
) -> Result<Option<String>, String> {
    let mut command = jj_command(root);
    command.args([
        "file",
        "list",
        "-r",
        revision,
        "-T",
        "json(file_type) ++ \"\\n\"",
        "--",
        pattern,
    ]);
    let bytes = checked(command, cancelled)?;
    if bytes.is_empty() {
        return Ok(None);
    }
    let kind =
        serde_json::from_slice(&bytes).map_err(|_| "Invalid Jujutsu gutter file metadata")?;
    Ok(Some(kind))
}

fn jj_baseline(
    root: &Path,
    relative: &Path,
    cancelled: &dyn Fn() -> bool,
) -> Result<Option<Vec<u8>>, String> {
    let Ok(store) = store_for_jj(root) else {
        return Ok(None);
    };
    let Some(path) = relative.to_str() else {
        return Ok(None);
    };
    let mut parents = jj_command(root);
    parents.args([
        "log",
        "--no-graph",
        "-r",
        "@-",
        "-T",
        "commit_id ++ \"\\n\"",
    ]);
    let bytes = checked(parents, cancelled)?;
    let ids = std::str::from_utf8(&bytes).map_err(|_| "Invalid Jujutsu gutter parents")?;
    let mut ids = ids.lines();
    let Some(parent) = ids.next() else {
        return Ok(None);
    };
    // ponytail: no merged-parent materializer exists here; hide markers on merges
    // rather than report changes against an arbitrary first parent.
    if ids.next().is_some() {
        return Ok(None);
    }
    let pattern = jj_file_pattern(path);
    let baseline_kind = if parent.bytes().all(|byte| byte == b'0') {
        None
    } else {
        jj_file_kind(root, parent, &pattern, cancelled)?
    };
    if let Some(kind) = baseline_kind {
        if !matches!(kind.as_str(), "file" | "conflict") {
            return Ok(None);
        }
        let mut show = jj_command(root);
        show.args(["file", "show", "-r", parent, "-T", "", "--", &pattern]);
        return checked(show, cancelled).map(Some);
    }
    if let Some(kind) = jj_file_kind(root, "@", &pattern, cancelled)? {
        return Ok(matches!(kind.as_str(), "file" | "conflict").then(Vec::new));
    }
    Ok(eligible(root, relative, Some(&store), cancelled)?.then(Vec::new))
}

fn changes(before: &str, after: &str) -> Vec<Option<Change>> {
    fn source(text: &str) -> (Vec<String>, bool) {
        (
            text.split_terminator('\n').map(str::to_owned).collect(),
            text.ends_with('\n'),
        )
    }
    let before = normalize_newlines(before);
    let after = normalize_newlines(after);
    if before == after {
        return vec![None; after.split('\n').count()];
    }
    let (before, before_eof) = source(&before);
    let (after_lines, after_eof) = source(&after);
    let mut markers = vec![None; after.split('\n').count()];
    for hunk in line_hunks(&before, before_eof, &after_lines, after_eof) {
        if hunk.after_len == 0 {
            let anchor = hunk.after_start.min(markers.len() - 1);
            // A deletion sharing a row with a replacement remains modified.
            if markers[anchor].is_none() {
                markers[anchor] = Some(Change::Removed);
            }
        } else {
            for offset in 0..hunk.after_len {
                markers[hunk.after_start + offset] = Some(if offset < hunk.before_len {
                    Change::Modified
                } else {
                    Change::Added
                });
            }
        }
    }
    markers
}

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