//! Content hot-reload via timestamp polling (dev-only).
//!
//! Periodically checks content YAML files for modifications and triggers
//! a full reload when changes are detected. Designed for the authoring
//! workflow — not enabled in production builds.
//!
//! Check interval: every 20 ticks (~2s at 10 tps per D-031).
//! Failures are non-critical: previous content is preserved on reload error.

use std::collections::BTreeMap;
use std::path::{Path, PathBuf};
use std::time::SystemTime;

use bevy_ecs::prelude::*;

use crate::content::line_pool::LinePoolIndex;
use crate::content::loader;
use crate::content::{ContentConfig, ContentStoreResource, LinePoolIndexResource};

/// How often to check for content changes (in system ticks).
/// At 10 tps (D-031), 20 ticks = 2 seconds.
const CHECK_INTERVAL_TICKS: u64 = 20;

/// Consecutive reload failures before escalating to a warning.
const FAILURE_WARN_THRESHOLD: u32 = 5;

/// Resource tracking content file timestamps for change detection.
#[derive(Resource, Debug)]
pub struct ContentWatcher {
    file_timestamps: BTreeMap<PathBuf, SystemTime>,
    ticks_since_check: u64,
    /// Consecutive reload failures. Resets on success.
    consecutive_failures: u32,
}

impl ContentWatcher {
    /// Create a new watcher and perform initial timestamp scan.
    /// Returns a watcher with no tracked files if content_root is invalid.
    pub fn new(content_root: &Path) -> Self {
        let mut watcher = Self {
            file_timestamps: BTreeMap::new(),
            ticks_since_check: 0,
            consecutive_failures: 0,
        };
        if content_root.as_os_str().is_empty() || !content_root.is_dir() {
            tracing::warn!(
                "ContentWatcher: invalid content root {:?}, hot-reload disabled",
                content_root,
            );
            return watcher;
        }
        watcher.scan(content_root);
        watcher
    }

    /// Scan content directory tree and record all YAML file timestamps.
    fn scan(&mut self, content_root: &Path) {
        self.file_timestamps.clear();
        walk_yaml(content_root, &mut self.file_timestamps, 0);
        tracing::debug!(
            "ContentWatcher: tracking {} content files",
            self.file_timestamps.len()
        );
    }

    /// Check for changes and rescan. Returns true if any files changed.
    fn check_and_rescan(&mut self, content_root: &Path) -> bool {
        let mut new_timestamps = BTreeMap::new();
        walk_yaml(content_root, &mut new_timestamps, 0);
        let changed = new_timestamps != self.file_timestamps;
        if changed {
            self.file_timestamps = new_timestamps;
        }
        changed
    }

    /// Number of tracked files (for diagnostics).
    pub fn tracked_file_count(&self) -> usize {
        self.file_timestamps.len()
    }
}

/// Maximum recursion depth for directory walking (guards against symlink loops).
const MAX_WALK_DEPTH: usize = 100;

/// Recursively walk a directory, recording .yaml file modification timestamps.
/// Stops recursing at MAX_WALK_DEPTH to guard against symlink loops.
fn walk_yaml(dir: &Path, timestamps: &mut BTreeMap<PathBuf, SystemTime>, depth: usize) {
    if depth >= MAX_WALK_DEPTH {
        tracing::warn!("walk_yaml: max depth {} reached at {:?}, stopping", MAX_WALK_DEPTH, dir);
        return;
    }
    let Ok(entries) = std::fs::read_dir(dir) else {
        return;
    };
    for entry in entries.filter_map(|e| e.ok()) {
        let path = entry.path();
        if path.is_dir() {
            walk_yaml(&path, timestamps, depth + 1);
        } else if path.extension().and_then(|e| e.to_str()) == Some("yaml") {
            if let Ok(meta) = std::fs::metadata(&path) {
                if let Ok(modified) = meta.modified() {
                    timestamps.insert(path, modified);
                }
            }
        }
    }
}

/// System: periodically check for content file changes and reload.
///
/// Only runs when a ContentWatcher resource exists (hot-reload enabled).
/// Runs in PostUpdate to avoid interfering with the current tick.
pub fn hot_reload_content(
    config: Res<ContentConfig>,
    watcher: Option<ResMut<ContentWatcher>>,
    store_res: Option<ResMut<ContentStoreResource>>,
    index_res: Option<ResMut<LinePoolIndexResource>>,
) {
    let Some(mut watcher) = watcher else {
        return;
    };
    let Some(mut store_res) = store_res else {
        return;
    };
    let Some(mut index_res) = index_res else {
        return;
    };

    watcher.ticks_since_check += 1;
    if watcher.ticks_since_check < CHECK_INTERVAL_TICKS {
        return;
    }
    watcher.ticks_since_check = 0;

    if !watcher.check_and_rescan(&config.content_root) {
        return;
    }

    tracing::info!("Content files changed, reloading...");

    match loader::load_content(&config.content_root) {
        Ok(store) => {
            let index = LinePoolIndex::build(&store);
            let d_count = index.dialogue_line_count();
            let m_count = index.monologue_line_count();
            store_res.0 = store;
            index_res.0 = index;
            watcher.consecutive_failures = 0;
            tracing::info!(
                "Content hot-reloaded: {} dialogue lines, {} monologue lines",
                d_count,
                m_count
            );
        }
        Err(e) => {
            watcher.consecutive_failures += 1;
            if watcher.consecutive_failures >= FAILURE_WARN_THRESHOLD {
                tracing::warn!(
                    "Content hot-reload failed {} consecutive times (keeping previous): {}",
                    watcher.consecutive_failures,
                    e,
                );
            } else {
                tracing::warn!("Content hot-reload failed (keeping previous): {}", e);
            }
        }
    }
}

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

    #[test]
    fn watcher_tracks_yaml_files() {
        let dir = std::env::temp_dir().join("sr_hotreload_test_track");
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).unwrap();

        fs::write(dir.join("test.yaml"), "key: value\n").unwrap();
        fs::write(dir.join("other.txt"), "ignored\n").unwrap();

        let watcher = ContentWatcher::new(&dir);
        assert_eq!(watcher.tracked_file_count(), 1);

        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn watcher_detects_new_file() {
        let dir = std::env::temp_dir().join("sr_hotreload_test_new");
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).unwrap();

        fs::write(dir.join("a.yaml"), "key: a\n").unwrap();

        let mut watcher = ContentWatcher::new(&dir);
        assert!(!watcher.check_and_rescan(&dir)); // no change yet

        fs::write(dir.join("b.yaml"), "key: b\n").unwrap();
        assert!(watcher.check_and_rescan(&dir)); // new file detected

        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn watcher_detects_deleted_file() {
        let dir = std::env::temp_dir().join("sr_hotreload_test_del");
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).unwrap();

        fs::write(dir.join("a.yaml"), "key: a\n").unwrap();
        fs::write(dir.join("b.yaml"), "key: b\n").unwrap();

        let mut watcher = ContentWatcher::new(&dir);
        assert_eq!(watcher.tracked_file_count(), 2);

        fs::remove_file(dir.join("b.yaml")).unwrap();
        assert!(watcher.check_and_rescan(&dir));

        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn watcher_detects_modification() {
        let dir = std::env::temp_dir().join("sr_hotreload_test_mod");
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).unwrap();

        fs::write(dir.join("a.yaml"), "key: a\n").unwrap();

        let mut watcher = ContentWatcher::new(&dir);

        // Sleep briefly to ensure modification time differs
        std::thread::sleep(std::time::Duration::from_millis(50));
        fs::write(dir.join("a.yaml"), "key: modified\n").unwrap();

        assert!(watcher.check_and_rescan(&dir));

        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn watcher_recurses_subdirectories() {
        let dir = std::env::temp_dir().join("sr_hotreload_test_recurse");
        let _ = fs::remove_dir_all(&dir);
        let sub = dir.join("sub/deep");
        fs::create_dir_all(&sub).unwrap();

        fs::write(dir.join("root.yaml"), "key: root\n").unwrap();
        fs::write(sub.join("deep.yaml"), "key: deep\n").unwrap();

        let watcher = ContentWatcher::new(&dir);
        assert_eq!(watcher.tracked_file_count(), 2);

        let _ = fs::remove_dir_all(&dir);
    }
}