//! I/O side of the timer service: filesystem persistence, clock reads,
//! background task spawning, and story-ID resolution.
//!
//! This is the **only** place inside `service/timer/` that may perform side
//! effects (filesystem reads/writes, clock reads, `tokio::spawn`).

use chrono::{DateTime, Utc};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};

use super::persist::{TimerEntry, deserialize_timers, serialize_timers};
use super::schedule::next_occurrence_at;

// ── TimerStore ─────────────────────────────────────────────────────────────

/// Persistent store for pending timers, backed by a JSON file.
pub struct TimerStore {
    path: PathBuf,
    timers: Mutex<Vec<TimerEntry>>,
}

impl TimerStore {
    /// Load the timer store from `path`.  Returns an empty store if the file
    /// does not exist or cannot be parsed.
    pub fn load(path: PathBuf) -> Self {
        let timers = if path.exists() {
            std::fs::read_to_string(&path)
                .ok()
                .and_then(|s| deserialize_timers(&s))
                .unwrap_or_default()
        } else {
            Vec::new()
        };
        Self {
            path,
            timers: Mutex::new(timers),
        }
    }

    fn save_locked(path: &Path, timers: &[TimerEntry]) -> Result<(), String> {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .map_err(|e| format!("Failed to create directory: {e}"))?;
        }
        let content = serialize_timers(timers)?;
        std::fs::write(path, content).map_err(|e| format!("Failed to write timers: {e}"))
    }

    /// Add a timer and persist to disk.
    pub fn add(&self, story_id: String, scheduled_at: DateTime<Utc>) -> Result<(), String> {
        let mut timers = self.timers.lock().unwrap();
        timers.push(TimerEntry {
            story_id,
            scheduled_at,
        });
        Self::save_locked(&self.path, &timers)
    }

    /// Remove the timer for `story_id`.  Returns `true` if one was removed.
    pub fn remove(&self, story_id: &str) -> bool {
        let mut timers = self.timers.lock().unwrap();
        let before = timers.len();
        timers.retain(|t| t.story_id != story_id);
        let removed = timers.len() < before;
        if removed {
            let _ = Self::save_locked(&self.path, &timers);
        }
        removed
    }

    /// Return all pending timers (cloned).
    pub fn list(&self) -> Vec<TimerEntry> {
        self.timers.lock().unwrap().clone()
    }

    /// Add or update a timer for `story_id`.
    ///
    /// - If no timer exists for `story_id`, adds it.
    /// - If a timer already exists and `scheduled_at` is **later**, updates it.
    /// - If a timer already exists and `scheduled_at` is earlier or equal, no-op.
    ///
    /// Use this instead of [`add`] when auto-scheduling from rate-limit events to
    /// avoid creating duplicates and to always keep the latest reset time.
    pub fn upsert(&self, story_id: String, scheduled_at: DateTime<Utc>) -> Result<(), String> {
        let mut timers = self.timers.lock().unwrap();
        if let Some(existing) = timers.iter_mut().find(|t| t.story_id == story_id) {
            if scheduled_at > existing.scheduled_at {
                existing.scheduled_at = scheduled_at;
                Self::save_locked(&self.path, &timers)?;
            }
        } else {
            timers.push(TimerEntry {
                story_id,
                scheduled_at,
            });
            Self::save_locked(&self.path, &timers)?;
        }
        Ok(())
    }

    /// Remove and return all timers whose `scheduled_at` is ≤ `now`.
    /// Persists the updated list to disk if any timers were removed.
    pub fn take_due(&self, now: DateTime<Utc>) -> Vec<TimerEntry> {
        let mut timers = self.timers.lock().unwrap();
        let mut due = Vec::new();
        let mut remaining = Vec::new();
        for t in timers.drain(..) {
            if t.scheduled_at <= now {
                due.push(t);
            } else {
                remaining.push(t);
            }
        }
        *timers = remaining;
        if !due.is_empty() {
            let _ = Self::save_locked(&self.path, &timers);
        }
        due
    }
}

// ── Clock-reading wrapper ───────────────────────────────────────────────────

/// Parse `HH:MM` and return the next UTC instant at which the given timezone
/// (or the server-local clock when `timezone` is `None`) will read that time.
/// If the time has already passed today, returns tomorrow's occurrence.
///
/// This wrapper reads the current clock via `Utc::now()`.  For pure unit tests
/// use [`crate::service::timer::schedule::next_occurrence_at`] directly.
pub fn next_occurrence_of_hhmm(hhmm: &str, timezone: Option<&str>) -> Option<DateTime<Utc>> {
    next_occurrence_at(hhmm, timezone, Utc::now())
}

// ── Story-ID resolution ─────────────────────────────────────────────────────

/// Resolve a story ID from a numeric story number or a full ID string.
///
/// Searches all pipeline stages.  Returns `None` only when the input is
/// numeric but no matching file is found.
pub(super) fn resolve_story_id(number_or_id: &str, project_root: &Path) -> Option<String> {
    const STAGES: &[&str] = &[
        "1_backlog",
        "2_current",
        "3_qa",
        "4_merge",
        "5_done",
        "6_archived",
    ];

    // Full ID (contains underscores) — return as-is; validation happens at file-check time.
    if number_or_id.contains('_') {
        return Some(number_or_id.to_string());
    }

    // Numeric lookup.
    if !number_or_id.chars().all(|c| c.is_ascii_digit()) {
        return None;
    }

    // --- DB-first lookup ---
    for id in crate::db::all_content_ids() {
        let file_num = id.split('_').next().unwrap_or("");
        if file_num == number_or_id
            && crate::pipeline_state::read_typed(&id)
                .ok()
                .flatten()
                .is_some()
        {
            return Some(id);
        }
    }

    // --- Filesystem fallback ---
    for stage in STAGES {
        let dir = project_root.join(".huskies").join("work").join(stage);
        if !dir.exists() {
            continue;
        }
        if let Ok(entries) = std::fs::read_dir(&dir) {
            for entry in entries.flatten() {
                let path = entry.path();
                if path.extension().and_then(|e| e.to_str()) != Some("md") {
                    continue;
                }
                if let Some(stem) = path.file_stem().and_then(|s| s.to_str()) {
                    let file_num = stem
                        .split('_')
                        .next()
                        .filter(|s| !s.is_empty() && s.chars().all(|c| c.is_ascii_digit()))
                        .unwrap_or("");
                    if file_num == number_or_id {
                        return Some(stem.to_string());
                    }
                }
            }
        }
    }
    None
}

// ── Tick loop ───────────────────────────────────────────────────────────────

/// Execute one tick of the timer loop.
///
/// Called by the unified background tick loop every second.
/// Separated from the loop so we can catch panics at the call-site.
/// Returns `Err` only when the tick panicked (the panic message is returned).
pub async fn tick_once(
    store: &Arc<TimerStore>,
    agents: &Arc<crate::agents::AgentPool>,
    project_root: &Path,
) -> Result<(), String> {
    // take_due is sync and could panic (e.g. poisoned mutex) — catch it.
    let due = {
        let store_ref = Arc::clone(store);
        let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(move || {
            store_ref.take_due(Utc::now())
        }));
        match result {
            Ok(due) => due,
            Err(e) => return Err(panic_payload_to_string(&e)),
        }
    };

    if due.is_empty() {
        return Ok(());
    }

    let remaining = store.list().len();
    crate::slog!("[timer] Tick: {} due, {remaining} remaining", due.len());

    for entry in due {
        crate::slog!("[timer] Timer fired for story {}", entry.story_id);

        // Bug 501: Defense-in-depth check. If the story has already advanced
        // past the active-work stages (3_qa, 4_merge, 5_done, 6_archived),
        // there is nothing to resume — the timer is stale and should no-op.
        // The primary cancellation paths (move_story MCP → backlog, stop_agent)
        // remove the timer before it fires; this guard covers the case where
        // cancellation was not yet called or the story raced forward through
        // the pipeline while the timer was pending.
        if let Ok(Some(item)) = crate::pipeline_state::read_typed(&entry.story_id) {
            use crate::pipeline_state::Stage;
            match &item.stage {
                Stage::Qa | Stage::Merge { .. } | Stage::Done { .. } | Stage::Archived { .. } => {
                    crate::slog!(
                        "[timer] Skipping timer for story {} — currently in '{}', \
                         not in backlog/current; timer is stale",
                        entry.story_id,
                        item.stage.dir_name()
                    );
                    continue;
                }
                _ => {}
            }
        }

        // Move from backlog to current if needed — the auto-assign
        // watcher will then start an agent automatically.
        if let Err(e) =
            crate::agents::lifecycle::move_story_to_current(project_root, &entry.story_id)
        {
            crate::slog!(
                "[timer] Failed to move story {} to current: {e}",
                entry.story_id
            );
            continue;
        }

        match agents
            .start_agent(project_root, &entry.story_id, None, None, None)
            .await
        {
            Ok(info) => {
                crate::slog!(
                    "[timer] Started agent {} for story {}",
                    info.agent_name,
                    entry.story_id
                );
            }
            Err(e) => {
                crate::slog!(
                    "[timer] Failed to start agent for story {}: {e} \
                     (auto-assign may pick it up)",
                    entry.story_id
                );
            }
        }
    }
    Ok(())
}

fn panic_payload_to_string(payload: &Box<dyn std::any::Any + Send>) -> String {
    if let Some(s) = payload.downcast_ref::<&str>() {
        (*s).to_string()
    } else if let Some(s) = payload.downcast_ref::<String>() {
        s.clone()
    } else {
        "unknown panic".to_string()
    }
}

// ── Rate-limit auto-scheduler ───────────────────────────────────────────────

/// Spawn a background task that listens for [`WatcherEvent::RateLimitHardBlock`]
/// events and auto-schedules a timer for the blocked story.
///
/// When an OAuth account swap succeeds, emits [`WatcherEvent::OAuthAccountSwapped`]
/// so chat transports can notify the user which account took over.  When all
/// accounts are exhausted, emits [`WatcherEvent::OAuthAccountsExhausted`] with
/// the earliest reset time.
///
/// If a timer already exists for the story, it is updated to the later reset time
/// rather than creating a duplicate (via [`TimerStore::upsert`]).
pub fn spawn_rate_limit_auto_scheduler(
    store: Arc<TimerStore>,
    mut watcher_rx: tokio::sync::broadcast::Receiver<crate::io::watcher::WatcherEvent>,
    watcher_tx: tokio::sync::broadcast::Sender<crate::io::watcher::WatcherEvent>,
) {
    tokio::spawn(async move {
        loop {
            match watcher_rx.recv().await {
                Ok(crate::io::watcher::WatcherEvent::RateLimitHardBlock {
                    story_id,
                    agent_name,
                    reset_at,
                }) => {
                    // Skip short rate limits (≤10 min) — the CLI handles
                    // these internally.  Only schedule timers for long
                    // session-level blocks where the CLI will exit.
                    let until_reset = reset_at.signed_duration_since(chrono::Utc::now());
                    if until_reset.num_minutes() <= 10 {
                        crate::slog!(
                            "[timer] Skipping short rate limit for {story_id} \
                             ({} min); CLI will handle internally",
                            until_reset.num_minutes()
                        );
                        continue;
                    }

                    // Try to swap to the next available OAuth account.  On
                    // success the next agent start (via auto-assign) will use
                    // the freshly activated account — no long timer needed.
                    // On failure (no pool or all accounts exhausted) fall back
                    // to the existing timer-based retry path.
                    match crate::llm::oauth::swap_to_next_available_account(reset_at).await {
                        Ok(new_email) => {
                            crate::slog!(
                                "[timer] Account swap successful for story {story_id} \
                                 (agent {agent_name}): now using '{new_email}'. \
                                 Auto-assign will restart the agent with the new account."
                            );
                            let _ = watcher_tx.send(
                                crate::io::watcher::WatcherEvent::OAuthAccountSwapped { new_email },
                            );
                            // No timer needed — auto-assign picks up the story.
                            continue;
                        }
                        Err(swap_err) => {
                            crate::slog!(
                                "[timer] Account swap not possible for story {story_id}: \
                                 {swap_err}. Falling back to timer-based retry."
                            );
                            // Notify chat transports when all accounts are exhausted.
                            if swap_err.contains("All OAuth accounts are rate-limited") {
                                let _ = watcher_tx.send(
                                    crate::io::watcher::WatcherEvent::OAuthAccountsExhausted {
                                        earliest_reset_msg: swap_err.clone(),
                                    },
                                );
                            }
                        }
                    }

                    crate::slog!(
                        "[timer] Auto-scheduling timer for story {story_id} \
                         (agent {agent_name}) to resume at {reset_at}"
                    );
                    match store.upsert(story_id.clone(), reset_at) {
                        Ok(()) => {
                            crate::slog!(
                                "[timer] Timer upserted for story {story_id}; \
                                 scheduled at {reset_at}"
                            );
                        }
                        Err(e) => {
                            crate::slog!(
                                "[timer] Failed to upsert timer for story {story_id}: {e}"
                            );
                        }
                    }
                }
                Ok(_) => {}
                Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
                    crate::slog!("[timer] Rate-limit auto-scheduler lagged, skipped {n} events");
                }
                Err(tokio::sync::broadcast::error::RecvError::Closed) => {
                    crate::slog!(
                        "[timer] Watcher channel closed, stopping rate-limit auto-scheduler"
                    );
                    break;
                }
            }
        }
    });
}

// ── Tests ──────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;
    use chrono::Duration;
    use tempfile::TempDir;

    // ── next_occurrence_of_hhmm ─────────────────────────────────────────

    #[test]
    fn valid_hhmm_returns_some() {
        let result = next_occurrence_of_hhmm("14:30", None);
        assert!(result.is_some(), "valid HH:MM should return Some");
    }

    #[test]
    fn invalid_hhmm_missing_colon_returns_none() {
        assert!(next_occurrence_of_hhmm("1430", None).is_none());
    }

    #[test]
    fn invalid_hhmm_bad_hours_returns_none() {
        assert!(next_occurrence_of_hhmm("25:00", None).is_none());
    }

    #[test]
    fn invalid_hhmm_bad_minutes_returns_none() {
        assert!(next_occurrence_of_hhmm("12:60", None).is_none());
    }

    #[test]
    fn next_occurrence_is_in_the_future() {
        let result = next_occurrence_of_hhmm("14:30", None).unwrap();
        assert!(result > Utc::now(), "next occurrence must be in the future");
    }

    #[test]
    fn next_occurrence_with_named_timezone_is_in_the_future() {
        let result = next_occurrence_of_hhmm("14:30", Some("Europe/London")).unwrap();
        assert!(
            result > Utc::now(),
            "next occurrence (Europe/London) must be in the future"
        );
    }

    #[test]
    fn next_occurrence_with_invalid_timezone_falls_back_to_local() {
        // An unrecognised timezone name falls back to chrono::Local (returns Some).
        let result = next_occurrence_of_hhmm("14:30", Some("Invalid/Zone"));
        assert!(
            result.is_some(),
            "invalid timezone should fall back to local and return Some"
        );
    }

    // ── TimerStore ──────────────────────────────────────────────────────

    #[test]
    fn timer_store_empty_on_missing_file() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        assert!(store.list().is_empty());
    }

    #[test]
    fn timer_store_add_and_list() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let t = Utc::now() + Duration::hours(1);
        store.add("story_1".to_string(), t).unwrap();
        let list = store.list();
        assert_eq!(list.len(), 1);
        assert_eq!(list[0].story_id, "story_1");
    }

    #[test]
    fn timer_store_remove() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let t = Utc::now() + Duration::hours(1);
        store.add("story_1".to_string(), t).unwrap();
        assert!(store.remove("story_1"));
        assert!(!store.remove("story_1")); // already gone
        assert!(store.list().is_empty());
    }

    #[test]
    fn timer_store_persists_and_reloads() {
        let dir = TempDir::new().unwrap();
        let path = dir.path().join("timers.json");
        let t = Utc::now() + Duration::hours(2);
        {
            let store = TimerStore::load(path.clone());
            store.add("421_story_foo".to_string(), t).unwrap();
        }
        // Reload from disk.
        let store2 = TimerStore::load(path);
        let list = store2.list();
        assert_eq!(list.len(), 1);
        assert_eq!(list[0].story_id, "421_story_foo");
    }

    #[test]
    fn take_due_returns_only_past_entries() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let past = Utc::now() - Duration::minutes(1);
        let future = Utc::now() + Duration::hours(1);
        store.add("past_story".to_string(), past).unwrap();
        store.add("future_story".to_string(), future).unwrap();

        let due = store.take_due(Utc::now());
        assert_eq!(due.len(), 1);
        assert_eq!(due[0].story_id, "past_story");
        assert_eq!(store.list().len(), 1);
        assert_eq!(store.list()[0].story_id, "future_story");
    }

    // ── upsert ─────────────────────────────────────────────────────────

    #[test]
    fn upsert_adds_new_timer_when_none_exists() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let t = Utc::now() + Duration::hours(1);
        store.upsert("story_1".to_string(), t).unwrap();
        let list = store.list();
        assert_eq!(list.len(), 1);
        assert_eq!(list[0].story_id, "story_1");
        assert_eq!(list[0].scheduled_at, t);
    }

    #[test]
    fn upsert_updates_to_later_time() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let early = Utc::now() + Duration::hours(1);
        let later = Utc::now() + Duration::hours(2);
        store.upsert("story_1".to_string(), early).unwrap();
        store.upsert("story_1".to_string(), later).unwrap();
        let list = store.list();
        assert_eq!(list.len(), 1, "should not create duplicate");
        assert_eq!(list[0].scheduled_at, later, "should update to later time");
    }

    #[test]
    fn upsert_does_not_downgrade_to_earlier_time() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let later = Utc::now() + Duration::hours(2);
        let earlier = Utc::now() + Duration::hours(1);
        store.upsert("story_1".to_string(), later).unwrap();
        store.upsert("story_1".to_string(), earlier).unwrap();
        let list = store.list();
        assert_eq!(list.len(), 1);
        assert_eq!(
            list[0].scheduled_at, later,
            "should keep the later time, not downgrade"
        );
    }

    // ── spawn_rate_limit_auto_scheduler ─────────────────────────────────

    /// AC2: a RateLimitHardBlock event causes the auto-scheduler to add a timer.
    #[tokio::test]
    async fn rate_limit_auto_scheduler_adds_timer_on_hard_block() {
        use crate::io::watcher::WatcherEvent;

        let dir = TempDir::new().unwrap();
        let store = Arc::new(TimerStore::load(dir.path().join("timers.json")));
        let (watcher_tx, watcher_rx) = tokio::sync::broadcast::channel::<WatcherEvent>(16);

        spawn_rate_limit_auto_scheduler(Arc::clone(&store), watcher_rx, watcher_tx.clone());

        let reset_at = Utc::now() + Duration::hours(1);
        watcher_tx
            .send(WatcherEvent::RateLimitHardBlock {
                story_id: "423_story_test".to_string(),
                agent_name: "coder-1".to_string(),
                reset_at,
            })
            .unwrap();

        // Give the spawned task time to process the event.
        tokio::time::sleep(std::time::Duration::from_millis(100)).await;

        let list = store.list();
        assert_eq!(list.len(), 1, "expected one timer after hard block");
        assert_eq!(list[0].story_id, "423_story_test");
        assert_eq!(list[0].scheduled_at, reset_at);
    }

    /// AC3 integration: a second hard block with a later reset_at updates the
    /// existing timer rather than creating a duplicate.
    #[tokio::test]
    async fn rate_limit_auto_scheduler_upserts_on_repeated_hard_block() {
        use crate::io::watcher::WatcherEvent;

        let dir = TempDir::new().unwrap();
        let store = Arc::new(TimerStore::load(dir.path().join("timers.json")));
        let (watcher_tx, watcher_rx) = tokio::sync::broadcast::channel::<WatcherEvent>(16);

        spawn_rate_limit_auto_scheduler(Arc::clone(&store), watcher_rx, watcher_tx.clone());

        let first = Utc::now() + Duration::hours(1);
        let second = Utc::now() + Duration::hours(2);

        watcher_tx
            .send(WatcherEvent::RateLimitHardBlock {
                story_id: "423_story_test".to_string(),
                agent_name: "coder-1".to_string(),
                reset_at: first,
            })
            .unwrap();
        tokio::time::sleep(std::time::Duration::from_millis(50)).await;
        watcher_tx
            .send(WatcherEvent::RateLimitHardBlock {
                story_id: "423_story_test".to_string(),
                agent_name: "coder-1".to_string(),
                reset_at: second,
            })
            .unwrap();
        tokio::time::sleep(std::time::Duration::from_millis(100)).await;

        let list = store.list();
        assert_eq!(list.len(), 1, "should not create a duplicate timer");
        assert_eq!(list[0].scheduled_at, second, "should update to later time");
    }

    #[test]
    fn multiple_timers_same_time_all_returned() {
        let dir = TempDir::new().unwrap();
        let store = TimerStore::load(dir.path().join("timers.json"));
        let past = Utc::now() - Duration::minutes(1);
        store.add("story_a".to_string(), past).unwrap();
        store.add("story_b".to_string(), past).unwrap();

        let due = store.take_due(Utc::now());
        assert_eq!(due.len(), 2, "both timers at same time must fire");
    }

    // ── tick_once ───────────────────────────────────────────────────────

    /// Create a past-due timer, run tick_once, and assert the entry is
    /// consumed.  start_agent will fail (no real agent binary), but
    /// take_due must still drain the entry.
    #[tokio::test]
    async fn tick_once_consumes_past_due_entry() {
        use std::fs;

        let dir = TempDir::new().unwrap();
        let root = dir.path();
        let backlog = root.join(".huskies/work/1_backlog");
        let current = root.join(".huskies/work/2_current");
        fs::create_dir_all(&backlog).unwrap();
        fs::create_dir_all(&current).unwrap();
        let content = "---\nname: Foo\n---\n";
        fs::write(backlog.join("9905_story_foo.md"), content).unwrap();
        crate::db::ensure_content_store();
        crate::db::write_content("9905_story_foo", content);

        let store = Arc::new(TimerStore::load(root.join("timers.json")));
        let past = Utc::now() - Duration::seconds(5);
        store.add("9905_story_foo".to_string(), past).unwrap();
        assert_eq!(store.list().len(), 1, "precondition: one pending timer");

        let agents = Arc::new(crate::agents::AgentPool::new_test(19999));

        // tick_once should drain the due entry even though start_agent
        // will fail (no agent binary configured in the test pool).
        let result = super::tick_once(&store, &agents, root).await;
        assert!(result.is_ok(), "tick_once should not panic: {result:?}");
        assert!(
            store.list().is_empty(),
            "past-due timer must be consumed after tick_once"
        );
        // Story should still be accessible in the content store after the move.
        assert!(
            crate::db::read_content("9905_story_foo").is_some(),
            "story should be in the content store after tick fires"
        );
    }
}