//! Filesystem watcher for `.story_kit/work/` and `.story_kit/project.toml`.
//!
//! Watches the work pipeline directories for file changes, infers the lifecycle
//! stage from the target directory name, auto-commits with a deterministic message,
//! and broadcasts a [`WatcherEvent`] to all connected WebSocket clients.
//!
//! Also watches `.story_kit/project.toml` for modifications and broadcasts
//! [`WatcherEvent::ConfigChanged`] so the frontend can reload the agent roster
//! without a server restart.
//!
//! # Debouncing
//! Events are buffered for 300 ms after the last activity. All changes within the
//! window are batched into a single `git add + commit`. This avoids double-commits
//! when `fs::rename` fires both a remove and a create event.
//!
//! # Race conditions
//! If a mutation handler (e.g. `move_story_to_current`) already committed the
//! change, `git commit` will return "nothing to commit". The watcher detects this
//! via exit-code inspection and silently skips the commit while still broadcasting
//! the event so connected clients stay in sync.

use crate::slog;
use notify::{EventKind, RecommendedWatcher, RecursiveMode, Watcher, recommended_watcher};
use serde::Serialize;
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::mpsc;
use std::time::{Duration, Instant};
use tokio::sync::broadcast;

/// A lifecycle event emitted by the filesystem watcher.
#[derive(Clone, Debug, Serialize)]
#[serde(tag = "type", rename_all = "snake_case")]
pub enum WatcherEvent {
    /// A work-pipeline file was created, modified, or deleted.
    WorkItem {
        /// Pipeline stage directory (e.g. `"2_current"`, `"5_archived"`).
        stage: String,
        /// Work item ID (filename stem without extension, e.g. `"42_story_my_feature"`).
        item_id: String,
        /// Semantic action inferred from the stage (e.g. `"start"`, `"accept"`).
        action: String,
        /// The deterministic git commit message used (or that would have been used).
        commit_msg: String,
    },
    /// `.story_kit/project.toml` was modified at the project root (not inside a worktree).
    ConfigChanged,
}

/// Return `true` if `path` is the root-level `.story_kit/project.toml`, i.e.
/// `{git_root}/.story_kit/project.toml`.
///
/// Returns `false` for paths inside worktree directories (paths containing
/// a `worktrees` component).
pub fn is_config_file(path: &Path, git_root: &Path) -> bool {
    // Reject any path that passes through the worktrees directory.
    if path.components().any(|c| c.as_os_str() == "worktrees") {
        return false;
    }
    let expected = git_root.join(".story_kit").join("project.toml");
    path == expected
}

/// Map a pipeline directory name to a (action, commit-message-prefix) pair.
fn stage_metadata(stage: &str, item_id: &str) -> Option<(&'static str, String)> {
    let (action, prefix) = match stage {
        "1_upcoming" => ("create", format!("story-kit: create {item_id}")),
        "2_current"  => ("start",  format!("story-kit: start {item_id}")),
        "3_qa"       => ("qa",     format!("story-kit: queue {item_id} for QA")),
        "4_merge"    => ("merge",  format!("story-kit: queue {item_id} for merge")),
        "5_archived" => ("accept", format!("story-kit: accept {item_id}")),
        _ => return None,
    };
    Some((action, prefix))
}

/// Return the pipeline stage name for a path if it is a `.md` file living
/// directly inside one of the known work subdirectories, otherwise `None`.
///
/// Explicitly returns `None` for any path under `.story_kit/worktrees/` so
/// that code changes made by agents in their isolated worktrees are never
/// auto-committed to master by the watcher.
fn stage_for_path(path: &Path) -> Option<String> {
    // Reject any path that passes through the worktrees directory.
    if path
        .components()
        .any(|c| c.as_os_str() == "worktrees")
    {
        return None;
    }

    if path.extension().is_none_or(|e| e != "md") {
        return None;
    }
    let stage = path
        .parent()
        .and_then(|p| p.file_name())
        .and_then(|n| n.to_str())?;
    matches!(stage, "1_upcoming" | "2_current" | "3_qa" | "4_merge" | "5_archived")
        .then(|| stage.to_string())
}

/// Stage all changes in the work directory and commit with the given message.
///
/// Uses `git add -A .story_kit/work/` to catch both additions and deletions in
/// a single commit. Returns `Ok(true)` if a commit was made, `Ok(false)` if
/// there was nothing to commit, and `Err` for unexpected failures.
fn git_add_work_and_commit(git_root: &Path, message: &str) -> Result<bool, String> {
    let work_rel = PathBuf::from(".story_kit").join("work");

    let add_out = std::process::Command::new("git")
        .args(["add", "-A"])
        .arg(&work_rel)
        .current_dir(git_root)
        .output()
        .map_err(|e| format!("git add: {e}"))?;
    if !add_out.status.success() {
        return Err(format!(
            "git add failed: {}",
            String::from_utf8_lossy(&add_out.stderr)
        ));
    }

    let commit_out = std::process::Command::new("git")
        .args(["commit", "-m", message])
        .current_dir(git_root)
        .output()
        .map_err(|e| format!("git commit: {e}"))?;

    if commit_out.status.success() {
        return Ok(true);
    }

    let stderr = String::from_utf8_lossy(&commit_out.stderr);
    let stdout = String::from_utf8_lossy(&commit_out.stdout);
    if stdout.contains("nothing to commit") || stderr.contains("nothing to commit") {
        return Ok(false);
    }

    Err(format!("git commit failed: {stderr}"))
}

/// Process a batch of pending (path → stage) entries: commit and broadcast.
///
/// Only files that still exist on disk are used to derive the commit message
/// (they represent the destination of a move or a new file). Deletions are
/// captured by `git add -A .story_kit/work/` automatically.
fn flush_pending(
    pending: &HashMap<PathBuf, String>,
    git_root: &Path,
    event_tx: &broadcast::Sender<WatcherEvent>,
) {
    // Separate into files that exist (additions) vs gone (deletions).
    let mut additions: Vec<(&PathBuf, &str)> = Vec::new();
    for (path, stage) in pending {
        if path.exists() {
            additions.push((path, stage.as_str()));
        }
    }

    // Pick the commit message from the first addition (the meaningful side of a move).
    // If there are only deletions, use a generic message.
    let (action, item_id, commit_msg) = if let Some((path, stage)) = additions.first() {
        let item = path.file_stem().and_then(|s| s.to_str()).unwrap_or("unknown");
        if let Some((act, msg)) = stage_metadata(stage, item) {
            (act, item.to_string(), msg)
        } else {
            return;
        }
    } else {
        // Only deletions — pick any pending path for the item name.
        let Some((path, _)) = pending.iter().next() else {
            return;
        };
        let item = path.file_stem().and_then(|s| s.to_str()).unwrap_or("unknown");
        ("remove", item.to_string(), format!("story-kit: remove {item}"))
    };

    slog!("[watcher] flush: {commit_msg}");
    match git_add_work_and_commit(git_root, &commit_msg) {
        Ok(committed) => {
            if committed {
                slog!("[watcher] committed: {commit_msg}");
            } else {
                slog!("[watcher] skipped (already committed): {commit_msg}");
            }
            let stage = additions.first().map_or("unknown", |(_, s)| s);
            let evt = WatcherEvent::WorkItem {
                stage: stage.to_string(),
                item_id,
                action: action.to_string(),
                commit_msg,
            };
            let _ = event_tx.send(evt);
        }
        Err(e) => {
            slog!("[watcher] git error: {e}");
        }
    }
}

/// Start the filesystem watcher on a dedicated OS thread.
///
/// `work_dir`  — absolute path to `.story_kit/work/` (watched recursively).
/// `git_root`  — project root (passed to `git` commands as cwd, and used to
///               derive the config file path `.story_kit/project.toml`).
/// `event_tx`  — broadcast sender; each connected WebSocket client holds a receiver.
pub fn start_watcher(
    work_dir: PathBuf,
    git_root: PathBuf,
    event_tx: broadcast::Sender<WatcherEvent>,
) {
    std::thread::spawn(move || {
        let (notify_tx, notify_rx) = mpsc::channel::<notify::Result<notify::Event>>();

        let mut watcher: RecommendedWatcher = match recommended_watcher(move |res| {
            let _ = notify_tx.send(res);
        }) {
            Ok(w) => w,
            Err(e) => {
                slog!("[watcher] failed to create watcher: {e}");
                return;
            }
        };

        if let Err(e) = watcher.watch(&work_dir, RecursiveMode::Recursive) {
            slog!("[watcher] failed to watch {}: {e}", work_dir.display());
            return;
        }

        // Also watch .story_kit/project.toml for hot-reload of agent config.
        let config_file = git_root.join(".story_kit").join("project.toml");
        if config_file.exists()
            && let Err(e) = watcher.watch(&config_file, RecursiveMode::NonRecursive)
        {
            slog!("[watcher] failed to watch config file {}: {e}", config_file.display());
        }

        slog!("[watcher] watching {}", work_dir.display());

        const DEBOUNCE: Duration = Duration::from_millis(300);

        // Map path → stage for pending (uncommitted) work-item changes.
        let mut pending: HashMap<PathBuf, String> = HashMap::new();
        // Whether a config file change is pending in the current debounce window.
        let mut config_changed_pending = false;
        let mut deadline: Option<Instant> = None;

        loop {
            // How long until the debounce window closes (or wait for next event).
            let timeout = deadline.map_or(Duration::from_secs(60), |d| {
                d.saturating_duration_since(Instant::now())
            });

            let flush = match notify_rx.recv_timeout(timeout) {
                Ok(Ok(event)) => {
                    // Track creates, modifies, AND removes. Removes are needed so
                    // that standalone deletions trigger a flush, and so that moves
                    // (which fire Remove + Create) land in the same debounce window.
                    let is_relevant_kind = matches!(
                        event.kind,
                        EventKind::Create(_) | EventKind::Modify(_) | EventKind::Remove(_)
                    );

                    if is_relevant_kind {
                        for path in event.paths {
                            if is_config_file(&path, &git_root) {
                                slog!("[watcher] config change detected: {}", path.display());
                                config_changed_pending = true;
                                deadline = Some(Instant::now() + DEBOUNCE);
                            } else if let Some(stage) = stage_for_path(&path) {
                                pending.insert(path, stage);
                                deadline = Some(Instant::now() + DEBOUNCE);
                            }
                        }
                    }
                    false
                }
                Ok(Err(e)) => {
                    slog!("[watcher] notify error: {e}");
                    false
                }
                // Debounce window expired — time to flush.
                Err(mpsc::RecvTimeoutError::Timeout) => true,
                Err(mpsc::RecvTimeoutError::Disconnected) => {
                    slog!("[watcher] channel disconnected, shutting down");
                    break;
                }
            };

            if flush {
                if !pending.is_empty() {
                    flush_pending(&pending, &git_root, &event_tx);
                    pending.clear();
                }
                if config_changed_pending {
                    slog!("[watcher] broadcasting agent_config_changed");
                    let _ = event_tx.send(WatcherEvent::ConfigChanged);
                    config_changed_pending = false;
                }
                deadline = None;
            }
        }
    });
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::HashMap;
    use std::fs;
    use tempfile::TempDir;

    /// Initialise a minimal git repo so commit operations work.
    fn init_git_repo(dir: &std::path::Path) {
        use std::process::Command;
        Command::new("git")
            .args(["init"])
            .current_dir(dir)
            .output()
            .expect("git init");
        Command::new("git")
            .args(["config", "user.email", "test@example.com"])
            .current_dir(dir)
            .output()
            .expect("git config email");
        Command::new("git")
            .args(["config", "user.name", "Test"])
            .current_dir(dir)
            .output()
            .expect("git config name");
        Command::new("git")
            .args(["commit", "--allow-empty", "-m", "init"])
            .current_dir(dir)
            .output()
            .expect("git initial commit");
    }

    /// Create the `.story_kit/work/{stage}/` dir tree inside `root`.
    fn make_stage_dir(root: &std::path::Path, stage: &str) -> PathBuf {
        let dir = root.join(".story_kit").join("work").join(stage);
        fs::create_dir_all(&dir).expect("create stage dir");
        dir
    }

    // ── git_add_work_and_commit ───────────────────────────────────────────────

    #[test]
    fn git_commit_returns_true_when_file_added() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        let stage_dir = make_stage_dir(tmp.path(), "2_current");
        fs::write(
            stage_dir.join("42_story_foo.md"),
            "---\nname: test\n---\n",
        )
        .unwrap();

        let result = git_add_work_and_commit(tmp.path(), "story-kit: start 42_story_foo");
        assert_eq!(result, Ok(true), "should return Ok(true) when a commit was made");
    }

    #[test]
    fn git_commit_returns_false_when_nothing_to_commit() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        let stage_dir = make_stage_dir(tmp.path(), "2_current");
        fs::write(
            stage_dir.join("42_story_foo.md"),
            "---\nname: test\n---\n",
        )
        .unwrap();

        // First commit — should succeed.
        git_add_work_and_commit(tmp.path(), "story-kit: start 42_story_foo").unwrap();

        // Second call with no changes — should return Ok(false).
        let result = git_add_work_and_commit(tmp.path(), "story-kit: start 42_story_foo");
        assert_eq!(
            result,
            Ok(false),
            "should return Ok(false) when nothing to commit"
        );
    }

    // ── flush_pending ─────────────────────────────────────────────────────────

    #[test]
    fn flush_pending_commits_and_broadcasts_work_item_for_addition() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        let stage_dir = make_stage_dir(tmp.path(), "2_current");
        let story_path = stage_dir.join("42_story_foo.md");
        fs::write(&story_path, "---\nname: test\n---\n").unwrap();

        let (tx, mut rx) = tokio::sync::broadcast::channel(16);
        let mut pending = HashMap::new();
        pending.insert(story_path, "2_current".to_string());

        flush_pending(&pending, tmp.path(), &tx);

        let evt = rx.try_recv().expect("expected a broadcast event");
        match evt {
            WatcherEvent::WorkItem {
                stage,
                item_id,
                action,
                commit_msg,
            } => {
                assert_eq!(stage, "2_current");
                assert_eq!(item_id, "42_story_foo");
                assert_eq!(action, "start");
                assert_eq!(commit_msg, "story-kit: start 42_story_foo");
            }
            other => panic!("unexpected event: {other:?}"),
        }
    }

    #[test]
    fn flush_pending_broadcasts_for_all_pipeline_stages() {
        let stages = [
            ("1_upcoming", "create", "story-kit: create 10_story_x"),
            ("3_qa", "qa", "story-kit: queue 10_story_x for QA"),
            ("4_merge", "merge", "story-kit: queue 10_story_x for merge"),
            ("5_archived", "accept", "story-kit: accept 10_story_x"),
        ];

        for (stage, expected_action, expected_msg) in stages {
            let tmp = TempDir::new().unwrap();
            init_git_repo(tmp.path());
            let stage_dir = make_stage_dir(tmp.path(), stage);
            let story_path = stage_dir.join("10_story_x.md");
            fs::write(&story_path, "---\nname: test\n---\n").unwrap();

            let (tx, mut rx) = tokio::sync::broadcast::channel(16);
            let mut pending = HashMap::new();
            pending.insert(story_path, stage.to_string());

            flush_pending(&pending, tmp.path(), &tx);

            let evt = rx.try_recv().expect("expected broadcast for stage {stage}");
            match evt {
                WatcherEvent::WorkItem {
                    action, commit_msg, ..
                } => {
                    assert_eq!(action, expected_action, "stage {stage}");
                    assert_eq!(commit_msg, expected_msg, "stage {stage}");
                }
                other => panic!("unexpected event for stage {stage}: {other:?}"),
            }
        }
    }

    #[test]
    fn flush_pending_deletion_only_broadcasts_remove_event() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        // Create the work dir tree but NOT the file (simulates a deletion).
        make_stage_dir(tmp.path(), "2_current");
        let deleted_path = tmp
            .path()
            .join(".story_kit")
            .join("work")
            .join("2_current")
            .join("42_story_foo.md");

        let (tx, mut rx) = tokio::sync::broadcast::channel(16);
        let mut pending = HashMap::new();
        pending.insert(deleted_path, "2_current".to_string());

        flush_pending(&pending, tmp.path(), &tx);

        // Even when nothing was committed (file never existed), an event is broadcast.
        let evt = rx.try_recv().expect("expected a broadcast event for deletion");
        match evt {
            WatcherEvent::WorkItem {
                action, item_id, ..
            } => {
                assert_eq!(action, "remove");
                assert_eq!(item_id, "42_story_foo");
            }
            other => panic!("unexpected event: {other:?}"),
        }
    }

    #[test]
    fn flush_pending_skips_unknown_stage_for_addition() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        // File sits in an unrecognised directory.
        let unknown_dir = tmp.path().join(".story_kit").join("work").join("9_unknown");
        fs::create_dir_all(&unknown_dir).unwrap();
        let path = unknown_dir.join("42_story_foo.md");
        fs::write(&path, "---\nname: test\n---\n").unwrap();

        let (tx, mut rx) = tokio::sync::broadcast::channel(16);
        let mut pending = HashMap::new();
        pending.insert(path, "9_unknown".to_string());

        flush_pending(&pending, tmp.path(), &tx);

        // No event should be broadcast because stage_metadata returns None for unknown stages.
        assert!(
            rx.try_recv().is_err(),
            "no event should be broadcast for unknown stage"
        );
    }

    #[test]
    fn flush_pending_empty_pending_does_nothing() {
        let tmp = TempDir::new().unwrap();
        init_git_repo(tmp.path());
        make_stage_dir(tmp.path(), "2_current");

        let (tx, mut rx) = tokio::sync::broadcast::channel(16);
        let pending: HashMap<PathBuf, String> = HashMap::new();

        // Should not panic and should not broadcast anything.
        flush_pending(&pending, tmp.path(), &tx);
        assert!(rx.try_recv().is_err(), "no event for empty pending map");
    }

    // ── stage_for_path (additional edge cases) ────────────────────────────────

    #[test]
    fn stage_for_path_recognises_pipeline_dirs() {
        let base = PathBuf::from("/proj/.story_kit/work");
        assert_eq!(
            stage_for_path(&base.join("2_current/42_story_foo.md")),
            Some("2_current".to_string())
        );
        assert_eq!(
            stage_for_path(&base.join("5_archived/10_bug_bar.md")),
            Some("5_archived".to_string())
        );
        assert_eq!(stage_for_path(&base.join("other/file.md")), None);
        assert_eq!(
            stage_for_path(&base.join("2_current/42_story_foo.txt")),
            None
        );
    }

    #[test]
    fn stage_for_path_ignores_worktree_paths() {
        let worktrees = PathBuf::from("/proj/.story_kit/worktrees");

        // Code changes inside a worktree must be ignored.
        assert_eq!(
            stage_for_path(&worktrees.join("42_story_foo/server/src/main.rs")),
            None,
        );

        // Even if a worktree happens to contain a path component that looks
        // like a pipeline stage, it must still be ignored.
        assert_eq!(
            stage_for_path(&worktrees.join("42_story_foo/.story_kit/work/2_current/42_story_foo.md")),
            None,
        );

        // A path that only contains the word "worktrees" as part of a longer
        // segment (not an exact component) must NOT be filtered out.
        assert_eq!(
            stage_for_path(&PathBuf::from("/proj/.story_kit/work/2_current/not_worktrees_story.md")),
            Some("2_current".to_string()),
        );
    }

    #[test]
    fn stage_metadata_returns_correct_actions() {
        let (action, msg) = stage_metadata("2_current", "42_story_foo").unwrap();
        assert_eq!(action, "start");
        assert_eq!(msg, "story-kit: start 42_story_foo");

        let (action, msg) = stage_metadata("5_archived", "42_story_foo").unwrap();
        assert_eq!(action, "accept");
        assert_eq!(msg, "story-kit: accept 42_story_foo");

        assert!(stage_metadata("unknown", "id").is_none());
    }

    #[test]
    fn is_config_file_identifies_root_project_toml() {
        let git_root = PathBuf::from("/proj");
        let config = git_root.join(".story_kit").join("project.toml");
        assert!(is_config_file(&config, &git_root));
    }

    #[test]
    fn is_config_file_rejects_worktree_copies() {
        let git_root = PathBuf::from("/proj");
        // project.toml inside a worktree must NOT be treated as the root config.
        let worktree_config = PathBuf::from(
            "/proj/.story_kit/worktrees/42_story_foo/.story_kit/project.toml",
        );
        assert!(!is_config_file(&worktree_config, &git_root));
    }

    #[test]
    fn is_config_file_rejects_other_files() {
        let git_root = PathBuf::from("/proj");
        // Random files must not match.
        assert!(!is_config_file(
            &PathBuf::from("/proj/.story_kit/work/2_current/42_story_foo.md"),
            &git_root
        ));
        assert!(!is_config_file(
            &PathBuf::from("/proj/.story_kit/README.md"),
            &git_root
        ));
    }

    #[test]
    fn is_config_file_rejects_wrong_root() {
        let git_root = PathBuf::from("/proj");
        let other_root_config = PathBuf::from("/other/.story_kit/project.toml");
        assert!(!is_config_file(&other_root_config, &git_root));
    }
}