//! Background tasks: CRDT-event bridge, auto-assign subscriber, unified tick
//! loop, gateway relay, and startup reconciliation.

use crate::agents::{AgentPool, ReconciliationEvent};
use crate::config;
use crate::gateway_relay;
use crate::io;
use crate::service;
use crate::service::status::StatusBroadcaster;
use std::path::PathBuf;
use std::sync::Arc;
use tokio::sync::broadcast;

/// Bridge CRDT state-transition events to the watcher broadcast channel and
/// spawn the auto-assign subscriber that triggers on active-stage transitions.
pub(crate) fn spawn_event_bridges(
    watcher_tx: broadcast::Sender<io::watcher::WatcherEvent>,
    project_root: Option<PathBuf>,
    agents: Arc<AgentPool>,
) {
    // Audit log subscriber: write one structured line per pipeline transition.
    crate::pipeline_state::spawn_audit_log_subscriber();

    // CRDT → watcher bridge: translate CRDT stage-transition events into
    // WatcherEvent::WorkItem so downstream consumers (WebSocket, auto-assign)
    // see a uniform stream regardless of whether the event originated from the
    // filesystem watcher or from a CRDT sync peer.
    {
        let crdt_watcher_tx = watcher_tx.clone();
        if let Some(mut crdt_rx) = crate::crdt_state::subscribe() {
            tokio::spawn(async move {
                while let Ok(evt) = crdt_rx.recv().await {
                    let (action, commit_msg) =
                        io::watcher::stage_metadata(&evt.to_stage, &evt.story_id);
                    let watcher_evt = io::watcher::WatcherEvent::WorkItem {
                        stage: evt.to_stage.dir_name().to_string(),
                        item_id: evt.story_id,
                        action: action.to_string(),
                        commit_msg,
                        from_stage: evt.from_stage.map(|s| s.dir_name().to_string()),
                    };
                    let _ = crdt_watcher_tx.send(watcher_evt);
                }
            });
        }
    }

    // Auto-assign: trigger `auto_assign_available_work` on every work-item
    // CRDT state-transition event.  auto_assign_available_work is idempotent
    // and noops where there is nothing to do, so firing on every transition
    // ensures that MergeFailure and other non-"active" stages are covered
    // without any per-stage special-casing.
    if let Some(root) = project_root {
        // Worktree lifecycle subscribers: create worktrees on Stage::Coding
        // and remove them on terminal stages (Done, Archived, Abandoned, Superseded).
        crate::agents::pool::worktree_lifecycle::spawn_worktree_create_subscriber(
            root.clone(),
            agents.port(),
        );
        crate::agents::pool::worktree_lifecycle::spawn_worktree_cleanup_subscriber(root.clone());

        // Mergemaster auto-spawn subscriber: reacts to TransitionFired events for
        // Stage::MergeFailure { kind: ConflictDetected } and spawns mergemaster
        // directly from the typed event, eliminating the predicate-mismatch
        // failure mode of the previous scan-loop approach (story 998).
        crate::agents::pool::auto_assign::spawn_merge_failure_subscriber(
            Arc::clone(&agents),
            root.clone(),
        );

        // Consecutive-failure auto-block subscriber: blocks stories after N
        // consecutive MergeFailure transitions (story 1018).
        crate::agents::pool::auto_assign::spawn_merge_failure_block_subscriber(root.clone());

        // Content-store GC subscriber: purges all ContentKey::* entries for a
        // story when it reaches a terminal stage, preventing zombie entries from
        // accumulating in the process heap (story 996).
        crate::db::gc::spawn_content_gc_subscriber();

        // Cost-rollup bootstrap: pre-populate the register from existing JSONL
        // so status renderers show correct costs after a server restart.
        crate::service::agents::cost_rollup::init_from_disk(&root);

        // Cost-rollup subscriber: snapshots per-story token costs into the
        // in-memory register whenever a story reaches a terminal stage.
        crate::agents::pool::cost_rollup_subscriber::spawn_cost_rollup_subscriber(root.clone());

        // Done→archived subscriber: archives Done stories after the configured
        // retention period. Fires on each Stage::Done TransitionFired event and
        // sleeps for the remaining retention time from merged_at before archiving.
        // Replaces the periodic sweep_done_to_archived scan that ran on every
        // sweep_interval_secs tick.
        {
            let done_retention = config::ProjectConfig::load(&root)
                .map(|c| std::time::Duration::from_secs(c.watcher.done_retention_secs))
                .unwrap_or_else(|_| std::time::Duration::from_secs(4 * 3600));
            io::watcher::spawn_done_to_archived_subscriber(done_retention);
        }

        let watcher_auto_rx = watcher_tx.subscribe();
        let watcher_auto_agents = Arc::clone(&agents);
        tokio::spawn(async move {
            let mut rx = watcher_auto_rx;
            while let Ok(event) = rx.recv().await {
                if let io::watcher::WatcherEvent::WorkItem { ref stage, .. } = event {
                    crate::slog!(
                        "[auto-assign] CRDT transition detected in {stage}/; \
                         triggering auto-assign."
                    );
                    watcher_auto_agents.auto_assign_available_work(&root).await;
                }
            }
        });
    }
}

/// Spawn the unified 1-second background tick loop.
///
/// Handles only genuinely time-based work:
/// - **Timer tick** (every second): fires due pipeline timers by comparing the
///   current wall-clock time against each timer's `due_at` field. Cannot be
///   reactive because timers encode absolute timestamps that only become
///   actionable when the clock reaches them.
/// - **Agent watchdog** (every 30 seconds): detects orphaned `Running` agents
///   by comparing elapsed time since the last heartbeat. Cannot be reactive
///   because the absence of an event (no heartbeat) is what signals a problem;
///   a `TransitionFired` subscriber would never fire for a silently crashed agent.
///
/// Stage-change-reactive work (done→archived archival, worktree cleanup) has
/// been moved to `TransitionFired` subscribers spawned from `spawn_event_bridges`.
pub(crate) fn spawn_tick_loop(
    agents: Arc<AgentPool>,
    timer_store: Arc<service::timer::TimerStore>,
    root: Option<PathBuf>,
) {
    let pending_count = timer_store.list().len();
    crate::slog!("[tick] Unified tick loop started; {pending_count} pending timer(s)");

    tokio::spawn(async move {
        let mut interval = tokio::time::interval(std::time::Duration::from_secs(1));
        let mut tick_count: u64 = 0;
        loop {
            interval.tick().await;
            tick_count = tick_count.wrapping_add(1);

            // Time-based: timers encode absolute due timestamps; only a
            // wall-clock comparison can determine when one is due.
            if let Some(ref r) = root {
                let result = service::timer::tick_once(&timer_store, &agents, r).await;
                if let Err(msg) = result {
                    crate::slog_error!("[tick] Timer tick panicked: {msg}");
                }
            }

            // Time-based: the watchdog detects silence (no heartbeat within a
            // timeout window). A `TransitionFired` subscriber cannot observe the
            // absence of events, so this must remain on a periodic tick.
            if tick_count.is_multiple_of(30) {
                let found = agents.run_watchdog_pass(root.as_deref());
                if found > 0 {
                    crate::slog!(
                        "[tick] {found} orphaned agent(s) detected; triggering auto-assign."
                    );
                    if let Some(ref r) = root {
                        agents.auto_assign_available_work(r).await;
                    }
                }
                agents.reap_stale_merge_jobs();
            }
        }
    });
}

/// Spawn the gateway relay task if `gateway_url` is configured in
/// `project.toml` or the `HUSKIES_GATEWAY_URL` environment variable.
pub(crate) fn spawn_gateway_relay(startup_root: &Option<PathBuf>, status: Arc<StatusBroadcaster>) {
    let relay_gateway_url = startup_root
        .as_ref()
        .and_then(|r| config::ProjectConfig::load(r).ok())
        .and_then(|c| c.gateway_url)
        .or_else(|| std::env::var("HUSKIES_GATEWAY_URL").ok())
        .unwrap_or_default();

    if !relay_gateway_url.is_empty() {
        let relay_project_name = startup_root
            .as_ref()
            .and_then(|r| config::ProjectConfig::load(r).ok())
            .and_then(|c| c.gateway_project)
            .or_else(|| std::env::var("HUSKIES_GATEWAY_PROJECT").ok())
            .or_else(|| {
                startup_root
                    .as_ref()
                    .and_then(|r| r.file_name())
                    .map(|n| n.to_string_lossy().into_owned())
            })
            .unwrap_or_else(|| "project".to_string());

        gateway_relay::spawn_relay_task(
            relay_gateway_url,
            relay_project_name,
            status,
            reqwest::Client::new(),
        );
    }
}

/// Spawn the startup reconstruction task: replay the current pipeline state
/// through the [`TransitionFired`][crate::pipeline_state::TransitionFired]
/// broadcast channel so that all existing subscribers (worktree lifecycle,
/// merge-failure auto-spawn, auto-assign) react identically to a live
/// transition, then trigger a full auto-assign pass.
///
/// Replaces the legacy scan-based `reconcile_on_startup` approach.  The CRDT
/// is the durable source of truth; replaying it as synthetic self-transitions
/// is cheaper, simpler, and idempotent: a second replay produces another burst
/// of events that subscribers safely ignore for already-assigned stories.
pub(crate) fn spawn_startup_reconciliation(
    startup_root: Option<PathBuf>,
    startup_agents: Arc<AgentPool>,
    startup_reconciliation_tx: broadcast::Sender<ReconciliationEvent>,
) {
    if let Some(root) = startup_root {
        tokio::spawn(async move {
            // Purge content-store entries for stories that reached terminal
            // stages in a previous session (before the GC subscriber was active).
            crate::db::gc::sweep_zombie_content_on_startup();
            crate::slog!(
                "[startup] Replaying current pipeline state through TransitionFired channel."
            );
            crate::pipeline_state::replay_current_pipeline_state();
            crate::slog!("[auto-assign] Scanning pipeline stages for unassigned work.");
            startup_agents.auto_assign_available_work(&root).await;
            let _ = startup_reconciliation_tx.send(ReconciliationEvent {
                story_id: String::new(),
                status: "done".to_string(),
                message: "Startup event replay complete.".to_string(),
            });
        });
    }
}