//! Headless build-agent mode for distributed, rendezvous-based story processing.
/// Headless build agent mode.
///
/// When invoked via `huskies agent --rendezvous ws://host:3001/crdt-sync`, this
/// module runs a headless loop that:
///
/// 1. Syncs CRDT state with the rendezvous peer.
/// 2. Writes a heartbeat to the CRDT `nodes` list.
/// 3. Scans for unclaimed stories in `2_current` and claims them via CRDT.
/// 4. Spawns Claude Code locally for each claimed story.
/// 5. Pushes the feature branch to the git remote when done.
/// 6. Reports completion by advancing the story stage via CRDT.
/// 7. Handles offline/reconnect: CRDT merges on reconnect, interrupted work
///    is reclaimed after a timeout.
///
/// No web UI, HTTP server, or chat interface is started.
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use tokio::sync::broadcast;

use crate::agents::AgentPool;
use crate::config::ProjectConfig;
use crate::crdt_state;
use crate::io::watcher;
use crate::slog;

/// Default claim timeout in seconds. If a node has not updated its heartbeat
/// within this window, other nodes may reclaim the story.
const CLAIM_TIMEOUT_SECS: f64 = 600.0; // 10 minutes

/// Interval between heartbeat writes and work scans.
const SCAN_INTERVAL_SECS: u64 = 15;

/// Run the headless build agent loop.
///
/// This function never returns under normal operation — it runs until the
/// process is terminated (SIGINT/SIGTERM).
///
/// If `join_token` and `gateway_url` are both provided the agent will register
/// itself with the gateway on startup using the one-time token.
pub async fn run(
    project_root: Option<PathBuf>,
    rendezvous_url: String,
    port: u16,
    join_token: Option<String>,
    gateway_url: Option<String>,
) -> Result<(), std::io::Error> {
    let project_root = match project_root {
        Some(r) => r,
        None => {
            eprintln!("error: agent mode requires a project root (no .huskies/ found)");
            std::process::exit(1);
        }
    };

    println!("\x1b[96;1m[agent-mode]\x1b[0m Starting headless build agent");
    println!("\x1b[96;1m[agent-mode]\x1b[0m Rendezvous: {rendezvous_url}");
    println!(
        "\x1b[96;1m[agent-mode]\x1b[0m Project: {}",
        project_root.display()
    );

    // Validate project config.
    let config = ProjectConfig::load(&project_root).unwrap_or_else(|e| {
        eprintln!("error: invalid project config: {e}");
        std::process::exit(1);
    });
    slog!(
        "[agent-mode] Loaded config with {} agents",
        config.agent.len()
    );

    // Event bus for pipeline lifecycle events.
    let (watcher_tx, _) = broadcast::channel::<watcher::WatcherEvent>(1024);
    let agents = Arc::new(AgentPool::new(port, watcher_tx.clone()));

    // Start filesystem watcher for config hot-reload.
    watcher::start_watcher(project_root.clone(), watcher_tx.clone());

    // Bridge CRDT events to watcher channel (same as main server).
    {
        let crdt_watcher_tx = watcher_tx.clone();
        let crdt_prune_root = Some(project_root.clone());
        if let Some(mut crdt_rx) = crdt_state::subscribe() {
            tokio::spawn(async move {
                while let Ok(evt) = crdt_rx.recv().await {
                    if evt.to_stage == "6_archived"
                        && let Some(root) = crdt_prune_root.as_ref().cloned()
                    {
                        let story_id = evt.story_id.clone();
                        tokio::task::spawn_blocking(move || {
                            if let Err(e) = crate::worktree::prune_worktree_sync(&root, &story_id) {
                                slog!("[agent-mode] worktree prune failed for {story_id}: {e}");
                            }
                        });
                    }
                    let (action, commit_msg) =
                        watcher::stage_metadata(&evt.to_stage, &evt.story_id)
                            .unwrap_or(("update", format!("huskies: update {}", evt.story_id)));
                    let watcher_evt = watcher::WatcherEvent::WorkItem {
                        stage: evt.to_stage,
                        item_id: evt.story_id,
                        action: action.to_string(),
                        commit_msg,
                        from_stage: evt.from_stage,
                    };
                    let _ = crdt_watcher_tx.send(watcher_evt);
                }
            });
        }
    }

    // Subscribe to watcher events to trigger auto-assign on stage transitions.
    {
        let auto_rx = watcher_tx.subscribe();
        let auto_agents = Arc::clone(&agents);
        let auto_root = project_root.clone();
        tokio::spawn(async move {
            let mut rx = auto_rx;
            while let Ok(event) = rx.recv().await {
                if let watcher::WatcherEvent::WorkItem { ref stage, .. } = event
                    && matches!(stage.as_str(), "2_current" | "3_qa" | "4_merge")
                {
                    slog!("[agent-mode] CRDT transition in {stage}/; triggering auto-assign.");
                    auto_agents.auto_assign_available_work(&auto_root).await;
                }
            }
        });
    }

    // Write initial heartbeat.
    write_heartbeat(&rendezvous_url, port);

    // Register with gateway if a join token and gateway URL were provided.
    if let (Some(token), Some(url)) = (join_token, gateway_url) {
        let node_id = crdt_state::our_node_id().unwrap_or_else(|| "unknown".to_string());
        let label = format!("build-agent-{}", &node_id[..node_id.len().min(8)]);
        let address = format!("ws://0.0.0.0:{port}/crdt-sync");
        register_with_gateway(&url, &token, &label, &address).await;
    }

    // Reconcile any committed work from a previous session.
    {
        let recon_agents = Arc::clone(&agents);
        let recon_root = project_root.clone();
        let (recon_tx, _) = broadcast::channel(64);
        slog!("[agent-mode] Reconciling completed worktrees from previous session.");
        recon_agents
            .reconcile_on_startup(&recon_root, &recon_tx)
            .await;
    }

    // Run initial auto-assign.
    slog!("[agent-mode] Initial auto-assign scan.");
    agents.auto_assign_available_work(&project_root).await;

    // Track which stories we've claimed so we can detect conflicts.
    let mut our_claims: HashMap<String, f64> = HashMap::new();

    // Main loop: heartbeat, scan, claim, detect conflicts.
    let mut interval = tokio::time::interval(std::time::Duration::from_secs(SCAN_INTERVAL_SECS));
    loop {
        interval.tick().await;

        // Write heartbeat.
        write_heartbeat(&rendezvous_url, port);

        // Scan CRDT for claimable work.
        scan_and_claim(&agents, &project_root, &mut our_claims).await;

        // Detect claim conflicts: if another node overwrote our claim, stop our agent.
        detect_conflicts(&agents, &project_root, &mut our_claims).await;

        // Reclaim timed-out work from dead nodes.
        reclaim_timed_out_work(&project_root);

        // Check for completed agents and push their branches.
        check_completions_and_push(&agents, &project_root).await;
    }
}

/// Write this node's heartbeat to the CRDT `nodes` list.
fn write_heartbeat(rendezvous_url: &str, port: u16) {
    let Some(node_id) = crdt_state::our_node_id() else {
        return;
    };
    let now = chrono::Utc::now().timestamp() as f64;
    // Advertise our crdt-sync endpoint.
    let address = format!("ws://0.0.0.0:{port}/crdt-sync");
    crdt_state::write_node_presence(&node_id, &address, now, true);
    slog!(
        "[agent-mode] Heartbeat written: node={:.12}… rendezvous={rendezvous_url}",
        &node_id
    );
}

/// Scan CRDT pipeline for unclaimed stories and claim them.
async fn scan_and_claim(
    agents: &AgentPool,
    project_root: &Path,
    our_claims: &mut HashMap<String, f64>,
) {
    let Some(items) = crdt_state::read_all_items() else {
        return;
    };
    let Some(our_node) = crdt_state::our_node_id() else {
        return;
    };

    for item in &items {
        // Only claim stories in active stages.
        if !matches!(item.stage.as_str(), "2_current" | "3_qa" | "4_merge") {
            continue;
        }

        // Skip blocked stories.
        if item.blocked == Some(true) {
            continue;
        }

        // If already claimed by us, skip.
        if item.claimed_by.as_deref() == Some(&our_node) {
            continue;
        }

        // If claimed by another alive node and claim is fresh, skip.
        if let Some(ref claimer) = item.claimed_by
            && !claimer.is_empty()
            && claimer != &our_node
            && let Some(claimed_at) = item.claimed_at
        {
            let now = chrono::Utc::now().timestamp() as f64;
            if now - claimed_at < CLAIM_TIMEOUT_SECS && is_node_alive(claimer) {
                continue;
            }
        }

        // Try to claim this story.
        slog!(
            "[agent-mode] Claiming story '{}' for this node",
            item.story_id
        );
        if crdt_state::write_claim(&item.story_id) {
            let now = chrono::Utc::now().timestamp() as f64;
            our_claims.insert(item.story_id.clone(), now);
        }
    }

    // Trigger auto-assign to start agents for newly claimed work.
    agents.auto_assign_available_work(project_root).await;
}

/// Detect if another node overwrote our claims (CRDT conflict resolution).
/// If so, stop our local agent for that story.
async fn detect_conflicts(
    agents: &AgentPool,
    project_root: &Path,
    our_claims: &mut HashMap<String, f64>,
) {
    let lost: Vec<String> = our_claims
        .keys()
        .filter(|story_id| !crdt_state::is_claimed_by_us(story_id))
        .cloned()
        .collect();

    for story_id in lost {
        slog!(
            "[agent-mode] Lost claim on '{}' to another node; stopping local agent.",
            story_id
        );
        our_claims.remove(&story_id);

        // Stop any local agent for this story by looking up its name.
        if let Ok(agent_list) = agents.list_agents() {
            for info in agent_list {
                if info.story_id == story_id {
                    let _ = agents
                        .stop_agent(project_root, &story_id, &info.agent_name)
                        .await;
                    break;
                }
            }
        }

        // Release our claim (in case it wasn't fully overwritten).
        crdt_state::release_claim(&story_id);
    }
}

/// Reclaim work from nodes that have timed out (stale heartbeat).
fn reclaim_timed_out_work(_project_root: &Path) {
    let Some(items) = crdt_state::read_all_items() else {
        return;
    };
    let now = chrono::Utc::now().timestamp() as f64;

    for item in &items {
        if !matches!(item.stage.as_str(), "2_current" | "3_qa" | "4_merge") {
            continue;
        }

        // Check if the claim has timed out.
        if let Some(ref claimer) = item.claimed_by {
            if claimer.is_empty() {
                continue;
            }
            if let Some(claimed_at) = item.claimed_at
                && now - claimed_at >= CLAIM_TIMEOUT_SECS
                && !is_node_alive(claimer)
            {
                slog!(
                    "[agent-mode] Reclaiming timed-out story '{}' from dead node {:.12}…",
                    item.story_id,
                    claimer
                );
                crdt_state::release_claim(&item.story_id);
            }
        }
    }
}

/// Check if a node is alive according to the CRDT nodes list.
fn is_node_alive(node_id: &str) -> bool {
    let Some(nodes) = crdt_state::read_all_node_presence() else {
        return false;
    };
    let now = chrono::Utc::now().timestamp() as f64;

    for node in &nodes {
        if node.node_id == node_id {
            // Node is considered alive if it's marked alive AND its heartbeat
            // is within the timeout window.
            return node.alive && (now - node.last_seen) < CLAIM_TIMEOUT_SECS;
        }
    }
    false
}

/// Check for completed agents, push their feature branches to the remote,
/// and report completion via CRDT.
async fn check_completions_and_push(agents: &AgentPool, _project_root: &Path) {
    let Ok(agent_list) = agents.list_agents() else {
        return;
    };

    for info in agent_list {
        if !matches!(
            info.status,
            crate::agents::AgentStatus::Completed | crate::agents::AgentStatus::Failed
        ) {
            continue;
        }

        let story_id = &info.story_id;

        // Only push if this node still owns the claim.
        if !crdt_state::is_claimed_by_us(story_id) {
            continue;
        }

        slog!(
            "[agent-mode] Agent {} for '{}'; pushing feature branch.",
            if matches!(info.status, crate::agents::AgentStatus::Completed) {
                "completed"
            } else {
                "failed"
            },
            story_id
        );

        // Push the feature branch to the remote.
        if let Some(ref wt) = info.worktree_path {
            let push_result = push_feature_branch(wt, story_id);
            match push_result {
                Ok(()) => {
                    slog!("[agent-mode] Pushed feature branch for '{story_id}' to remote.");
                }
                Err(e) => {
                    slog!("[agent-mode] Failed to push '{story_id}': {e}");
                }
            }
        }

        // Release the claim now that work is done.
        crdt_state::release_claim(story_id);
    }
}

/// Push the feature branch of a worktree to the git remote.
fn push_feature_branch(worktree_path: &str, story_id: &str) -> Result<(), String> {
    let branch = format!("feature/story-{story_id}");

    // Try to push to 'origin'. If origin doesn't exist, try the first remote.
    let output = std::process::Command::new("git")
        .args(["push", "origin", &branch])
        .current_dir(worktree_path)
        .output()
        .map_err(|e| format!("Failed to run git push: {e}"))?;

    if output.status.success() {
        Ok(())
    } else {
        let stderr = String::from_utf8_lossy(&output.stderr);
        // If 'origin' doesn't exist, try to find any remote.
        if stderr.contains("does not appear to be a git repository")
            || stderr.contains("No such remote")
        {
            let remotes = std::process::Command::new("git")
                .args(["remote"])
                .current_dir(worktree_path)
                .output()
                .map_err(|e| format!("Failed to list remotes: {e}"))?;

            let remote_list = String::from_utf8_lossy(&remotes.stdout);
            let first_remote = remote_list.lines().next();

            if let Some(remote) = first_remote {
                let retry = std::process::Command::new("git")
                    .args(["push", remote.trim(), &branch])
                    .current_dir(worktree_path)
                    .output()
                    .map_err(|e| format!("Failed to push to {remote}: {e}"))?;

                if retry.status.success() {
                    return Ok(());
                }
                return Err(format!(
                    "git push to '{remote}' failed: {}",
                    String::from_utf8_lossy(&retry.stderr)
                ));
            }

            // No remotes configured — not an error in agent mode, just skip.
            slog!("[agent-mode] No git remote configured; skipping push for '{story_id}'.");
            Ok(())
        } else {
            Err(format!("git push failed: {stderr}"))
        }
    }
}

// ── Gateway registration ──────────────────────────────────────────────────

/// Register this build agent with a gateway using a one-time join token.
///
/// POSTs `{ token, label, address }` to `{gateway_url}/gateway/register`. On
/// success the gateway stores the agent and it will appear in the gateway UI.
async fn register_with_gateway(gateway_url: &str, token: &str, label: &str, address: &str) {
    let client = reqwest::Client::new();
    let url = format!("{}/gateway/register", gateway_url.trim_end_matches('/'));
    let body = serde_json::json!({
        "token": token,
        "label": label,
        "address": address,
    });
    match client.post(&url).json(&body).send().await {
        Ok(resp) if resp.status().is_success() => {
            slog!("[agent-mode] Registered with gateway at {gateway_url}");
        }
        Ok(resp) => {
            slog!(
                "[agent-mode] Gateway registration failed: HTTP {}",
                resp.status()
            );
        }
        Err(e) => {
            slog!("[agent-mode] Gateway registration error: {e}");
        }
    }
}

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

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

    #[test]
    fn is_node_alive_returns_false_for_unknown_node() {
        // Without CRDT init, should return false.
        assert!(!is_node_alive("nonexistent_node_id"));
    }

    #[test]
    fn push_feature_branch_handles_missing_worktree() {
        let result = push_feature_branch("/nonexistent/path", "test_story");
        assert!(result.is_err());
    }

    #[test]
    fn claim_timeout_is_ten_minutes() {
        assert_eq!(CLAIM_TIMEOUT_SECS, 600.0);
    }
}