//! Stage transition notifications for Matrix rooms.
//!
//! Subscribes to [`WatcherEvent`] broadcasts and posts a notification to all
//! configured Matrix rooms whenever a work item moves between pipeline stages.

use crate::io::story_metadata::parse_front_matter;
use crate::io::watcher::WatcherEvent;
use crate::slog;
use crate::transport::ChatTransport;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use tokio::sync::broadcast;

/// Human-readable display name for a pipeline stage directory.
pub fn stage_display_name(stage: &str) -> &'static str {
    match stage {
        "1_backlog" => "Backlog",
        "2_current" => "Current",
        "3_qa" => "QA",
        "4_merge" => "Merge",
        "5_done" => "Done",
        "6_archived" => "Archived",
        _ => "Unknown",
    }
}

/// Infer the previous pipeline stage for a given destination stage.
///
/// Returns `None` for `1_backlog` since items are created there (not
/// transitioned from another stage).
pub fn inferred_from_stage(to_stage: &str) -> Option<&'static str> {
    match to_stage {
        "2_current" => Some("Backlog"),
        "3_qa" => Some("Current"),
        "4_merge" => Some("QA"),
        "5_done" => Some("Merge"),
        "6_archived" => Some("Done"),
        _ => None,
    }
}

/// Extract the numeric story number from an item ID like `"261_story_slug"`.
pub fn extract_story_number(item_id: &str) -> Option<&str> {
    item_id
        .split('_')
        .next()
        .filter(|s| !s.is_empty() && s.chars().all(|c| c.is_ascii_digit()))
}

/// Read the story name from the work item file's YAML front matter.
///
/// Returns `None` if the file doesn't exist or has no parseable name.
pub fn read_story_name(project_root: &Path, stage: &str, item_id: &str) -> Option<String> {
    let path = project_root
        .join(".storkit")
        .join("work")
        .join(stage)
        .join(format!("{item_id}.md"));
    let contents = std::fs::read_to_string(&path).ok()?;
    let meta = parse_front_matter(&contents).ok()?;
    meta.name
}

/// Format a stage transition notification message.
///
/// Returns `(plain_text, html)` suitable for `RoomMessageEventContent::text_html`.
pub fn format_stage_notification(
    item_id: &str,
    story_name: Option<&str>,
    from_stage: &str,
    to_stage: &str,
) -> (String, String) {
    let number = extract_story_number(item_id).unwrap_or(item_id);
    let name = story_name.unwrap_or(item_id);

    let prefix = if to_stage == "Done" { "\u{1f389} " } else { "" };
    let plain = format!("{prefix}#{number} {name} \u{2014} {from_stage} \u{2192} {to_stage}");
    let html = format!(
        "{prefix}<strong>#{number}</strong> <em>{name}</em> \u{2014} {from_stage} \u{2192} {to_stage}"
    );
    (plain, html)
}

/// Format an error notification message for a story failure.
///
/// Returns `(plain_text, html)` suitable for `RoomMessageEventContent::text_html`.
pub fn format_error_notification(
    item_id: &str,
    story_name: Option<&str>,
    reason: &str,
) -> (String, String) {
    let number = extract_story_number(item_id).unwrap_or(item_id);
    let name = story_name.unwrap_or(item_id);

    let plain = format!("\u{274c} #{number} {name} \u{2014} {reason}");
    let html = format!(
        "\u{274c} <strong>#{number}</strong> <em>{name}</em> \u{2014} {reason}"
    );
    (plain, html)
}

/// Spawn a background task that listens for watcher events and posts
/// stage-transition notifications to all configured rooms via the
/// [`ChatTransport`] abstraction.
pub fn spawn_notification_listener(
    transport: Arc<dyn ChatTransport>,
    room_ids: Vec<String>,
    watcher_rx: broadcast::Receiver<WatcherEvent>,
    project_root: PathBuf,
) {
    tokio::spawn(async move {
        let mut rx = watcher_rx;
        loop {
            match rx.recv().await {
                Ok(WatcherEvent::WorkItem {
                    ref stage,
                    ref item_id,
                    ..
                }) => {
                    // Only notify on stage transitions, not creations.
                    let Some(from_display) = inferred_from_stage(stage) else {
                        continue;
                    };
                    let to_display = stage_display_name(stage);

                    let story_name = read_story_name(&project_root, stage, item_id);
                    let (plain, html) = format_stage_notification(
                        item_id,
                        story_name.as_deref(),
                        from_display,
                        to_display,
                    );

                    slog!("[matrix-bot] Sending stage notification: {plain}");

                    for room_id in &room_ids {
                        if let Err(e) = transport.send_message(room_id, &plain, &html).await {
                            slog!(
                                "[matrix-bot] Failed to send notification to {room_id}: {e}"
                            );
                        }
                    }
                }
                Ok(WatcherEvent::MergeFailure {
                    ref story_id,
                    ref reason,
                }) => {
                    let story_name =
                        read_story_name(&project_root, "4_merge", story_id);
                    let (plain, html) = format_error_notification(
                        story_id,
                        story_name.as_deref(),
                        reason,
                    );

                    slog!("[matrix-bot] Sending error notification: {plain}");

                    for room_id in &room_ids {
                        if let Err(e) = transport.send_message(room_id, &plain, &html).await {
                            slog!(
                                "[matrix-bot] Failed to send error notification to {room_id}: {e}"
                            );
                        }
                    }
                }
                Ok(_) => {} // Ignore non-work-item events
                Err(broadcast::error::RecvError::Lagged(n)) => {
                    slog!(
                        "[matrix-bot] Notification listener lagged, skipped {n} events"
                    );
                }
                Err(broadcast::error::RecvError::Closed) => {
                    slog!(
                        "[matrix-bot] Watcher channel closed, stopping notification listener"
                    );
                    break;
                }
            }
        }
    });
}

#[cfg(test)]
mod tests {
    use super::*;

    // ── stage_display_name ──────────────────────────────────────────────────

    #[test]
    fn stage_display_name_maps_all_known_stages() {
        assert_eq!(stage_display_name("1_backlog"), "Backlog");
        assert_eq!(stage_display_name("2_current"), "Current");
        assert_eq!(stage_display_name("3_qa"), "QA");
        assert_eq!(stage_display_name("4_merge"), "Merge");
        assert_eq!(stage_display_name("5_done"), "Done");
        assert_eq!(stage_display_name("6_archived"), "Archived");
        assert_eq!(stage_display_name("unknown"), "Unknown");
    }

    // ── inferred_from_stage ─────────────────────────────────────────────────

    #[test]
    fn inferred_from_stage_returns_previous_stage() {
        assert_eq!(inferred_from_stage("2_current"), Some("Backlog"));
        assert_eq!(inferred_from_stage("3_qa"), Some("Current"));
        assert_eq!(inferred_from_stage("4_merge"), Some("QA"));
        assert_eq!(inferred_from_stage("5_done"), Some("Merge"));
        assert_eq!(inferred_from_stage("6_archived"), Some("Done"));
    }

    #[test]
    fn inferred_from_stage_returns_none_for_backlog() {
        assert_eq!(inferred_from_stage("1_backlog"), None);
    }

    #[test]
    fn inferred_from_stage_returns_none_for_unknown() {
        assert_eq!(inferred_from_stage("9_unknown"), None);
    }

    // ── extract_story_number ────────────────────────────────────────────────

    #[test]
    fn extract_story_number_parses_numeric_prefix() {
        assert_eq!(
            extract_story_number("261_story_bot_notifications"),
            Some("261")
        );
        assert_eq!(extract_story_number("42_bug_fix_thing"), Some("42"));
        assert_eq!(extract_story_number("1_spike_research"), Some("1"));
    }

    #[test]
    fn extract_story_number_returns_none_for_non_numeric() {
        assert_eq!(extract_story_number("abc_story_thing"), None);
        assert_eq!(extract_story_number(""), None);
    }

    // ── read_story_name ─────────────────────────────────────────────────────

    #[test]
    fn read_story_name_reads_from_front_matter() {
        let tmp = tempfile::tempdir().unwrap();
        let stage_dir = tmp
            .path()
            .join(".storkit")
            .join("work")
            .join("2_current");
        std::fs::create_dir_all(&stage_dir).unwrap();
        std::fs::write(
            stage_dir.join("42_story_my_feature.md"),
            "---\nname: My Cool Feature\n---\n# Story\n",
        )
        .unwrap();

        let name = read_story_name(tmp.path(), "2_current", "42_story_my_feature");
        assert_eq!(name.as_deref(), Some("My Cool Feature"));
    }

    #[test]
    fn read_story_name_returns_none_for_missing_file() {
        let tmp = tempfile::tempdir().unwrap();
        let name = read_story_name(tmp.path(), "2_current", "99_story_missing");
        assert_eq!(name, None);
    }

    #[test]
    fn read_story_name_returns_none_for_missing_name_field() {
        let tmp = tempfile::tempdir().unwrap();
        let stage_dir = tmp
            .path()
            .join(".storkit")
            .join("work")
            .join("2_current");
        std::fs::create_dir_all(&stage_dir).unwrap();
        std::fs::write(
            stage_dir.join("42_story_no_name.md"),
            "---\ncoverage_baseline: 50%\n---\n# Story\n",
        )
        .unwrap();

        let name = read_story_name(tmp.path(), "2_current", "42_story_no_name");
        assert_eq!(name, None);
    }

    // ── format_error_notification ────────────────────────────────────────────

    #[test]
    fn format_error_notification_with_story_name() {
        let (plain, html) =
            format_error_notification("262_story_bot_errors", Some("Bot error notifications"), "merge conflict in src/main.rs");
        assert_eq!(
            plain,
            "\u{274c} #262 Bot error notifications \u{2014} merge conflict in src/main.rs"
        );
        assert_eq!(
            html,
            "\u{274c} <strong>#262</strong> <em>Bot error notifications</em> \u{2014} merge conflict in src/main.rs"
        );
    }

    #[test]
    fn format_error_notification_without_story_name_falls_back_to_item_id() {
        let (plain, _html) =
            format_error_notification("42_bug_fix_thing", None, "tests failed");
        assert_eq!(
            plain,
            "\u{274c} #42 42_bug_fix_thing \u{2014} tests failed"
        );
    }

    #[test]
    fn format_error_notification_non_numeric_id_uses_full_id() {
        let (plain, _html) =
            format_error_notification("abc_story_thing", Some("Some Story"), "clippy errors");
        assert_eq!(
            plain,
            "\u{274c} #abc_story_thing Some Story \u{2014} clippy errors"
        );
    }

    // ── format_stage_notification ───────────────────────────────────────────

    #[test]
    fn format_notification_done_stage_includes_party_emoji() {
        let (plain, html) = format_stage_notification(
            "353_story_done",
            Some("Done Story"),
            "Merge",
            "Done",
        );
        assert_eq!(
            plain,
            "\u{1f389} #353 Done Story \u{2014} Merge \u{2192} Done"
        );
        assert_eq!(
            html,
            "\u{1f389} <strong>#353</strong> <em>Done Story</em> \u{2014} Merge \u{2192} Done"
        );
    }

    #[test]
    fn format_notification_non_done_stage_has_no_emoji() {
        let (plain, _html) = format_stage_notification(
            "42_story_thing",
            Some("Some Story"),
            "Backlog",
            "Current",
        );
        assert!(!plain.contains("\u{1f389}"));
    }

    #[test]
    fn format_notification_with_story_name() {
        let (plain, html) = format_stage_notification(
            "261_story_bot_notifications",
            Some("Bot notifications"),
            "Upcoming",
            "Current",
        );
        assert_eq!(
            plain,
            "#261 Bot notifications \u{2014} Upcoming \u{2192} Current"
        );
        assert_eq!(
            html,
            "<strong>#261</strong> <em>Bot notifications</em> \u{2014} Upcoming \u{2192} Current"
        );
    }

    #[test]
    fn format_notification_without_story_name_falls_back_to_item_id() {
        let (plain, _html) = format_stage_notification(
            "42_bug_fix_thing",
            None,
            "Current",
            "QA",
        );
        assert_eq!(
            plain,
            "#42 42_bug_fix_thing \u{2014} Current \u{2192} QA"
        );
    }

    #[test]
    fn format_notification_non_numeric_id_uses_full_id() {
        let (plain, _html) = format_stage_notification(
            "abc_story_thing",
            Some("Some Story"),
            "QA",
            "Merge",
        );
        assert_eq!(
            plain,
            "#abc_story_thing Some Story \u{2014} QA \u{2192} Merge"
        );
    }
}