//! Polling manager for periodic repository change detection.
//!
//! Spawns background tasks for sites with `poll_interval` configured.
//! Integrates with SIGHUP reload to restart polling tasks on config change.

use crate::build_guard::BuildGuard;
use crate::config::SiteConfig;
use crate::git;
use crate::server::AppState;
use std::collections::HashMap;
use std::hash::{Hash as _, Hasher as _};
use std::sync::Arc;
use std::time::Duration;
use tokio::sync::RwLock;
use tokio_util::sync::CancellationToken;
use tracing::{debug, error, info};

/// Manages polling tasks for all sites.
pub struct PollingManager {
    /// Map of `site_name` -> cancellation token for active polling tasks
    tasks: Arc<RwLock<HashMap<String, CancellationToken>>>,
}

impl PollingManager {
    #[must_use]
    pub fn new() -> Self {
        Self {
            tasks: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Start polling tasks for sites with `poll_interval` configured.
    /// Call this on startup and after SIGHUP reload.
    pub async fn start_polling(&self, state: AppState) {
        let config = state.config.read().await;

        for site in &config.sites {
            if let Some(interval) = site.poll_interval {
                self.spawn_poll_task(state.clone(), site.clone(), interval)
                    .await;
            }
        }
    }

    /// Stop all currently running polling tasks.
    /// Call this before starting new tasks on SIGHUP.
    pub async fn stop_all(&self) {
        let mut tasks = self.tasks.write().await;

        for (site_name, token) in tasks.drain() {
            info!(site = %site_name, "stopping polling task");
            token.cancel();
        }
    }

    /// Spawn a single polling task for a site.
    async fn spawn_poll_task(&self, state: AppState, site: SiteConfig, interval: Duration) {
        let site_name = site.name.clone();
        let token = CancellationToken::new();

        // Store the cancellation token
        {
            let mut tasks = self.tasks.write().await;
            tasks.insert(site_name.clone(), token.clone());
        }

        info!(
            site = %site_name,
            interval_secs = interval.as_secs(),
            "starting polling task"
        );

        // Spawn the polling loop
        let tasks = Arc::clone(&self.tasks);
        tokio::spawn(async move {
            #[allow(clippy::large_futures)]
            poll_loop(state, site, interval, token.clone()).await;

            // Remove from active tasks when done
            tasks.write().await.remove(&site_name);
            debug!(site = %site_name, "polling task ended");
        });
    }
}

impl Default for PollingManager {
    fn default() -> Self {
        Self::new()
    }
}

/// The main polling loop for a single site.
async fn poll_loop(
    state: AppState,
    site: SiteConfig,
    interval: Duration,
    cancel_token: CancellationToken,
) {
    let site_name = &site.name;

    // Initial delay before first poll (avoid thundering herd on startup)
    let initial_delay = calculate_initial_delay(site_name, interval);
    debug!(site = %site_name, delay_secs = initial_delay.as_secs(), "initial poll delay");

    tokio::select! {
        () = tokio::time::sleep(initial_delay) => {}
        () = cancel_token.cancelled() => return,
    }

    loop {
        debug!(site = %site_name, "polling for changes");

        // 1. Acquire build lock before any git operation
        let Some(guard) = BuildGuard::try_acquire(site_name.clone(), &state.build_scheduler) else {
            debug!(site = %site_name, "build in progress, skipping poll cycle");
            tokio::select! {
                () = tokio::time::sleep(interval) => {}
                () = cancel_token.cancelled() => {
                    info!(site = %site_name, "polling cancelled");
                    return;
                }
            }
            continue;
        };

        // Get current config (might have changed via SIGHUP)
        let (base_dir, git_timeout) = {
            let config = state.config.read().await;
            (
                config.base_dir.clone(),
                config.git_timeout.unwrap_or(git::GIT_TIMEOUT_DEFAULT),
            )
        };
        let clone_dir = base_dir.join("clones").join(site_name);

        // 2. Check for changes (guard held — no concurrent git ops possible)
        let has_changes = match git::has_remote_changes(
            &clone_dir,
            &site.branch,
            git_timeout,
            site.git_depth.unwrap_or(git::GIT_DEPTH_DEFAULT),
        )
        .await
        {
            Ok(changed) => changed,
            Err(e) => {
                error!(site = %site_name, error = %e, "failed to check for changes");
                false
            }
        };

        if has_changes {
            // 3a. Keep guard alive — move into build pipeline
            info!(site = %site_name, "new commits detected, triggering build");
            #[allow(clippy::large_futures)]
            crate::server::run_build_pipeline(
                state.clone(),
                site_name.clone(),
                site.clone(),
                guard,
            )
            .await;
        } else {
            // 3b. Explicit drop BEFORE sleep — release lock immediately
            drop(guard);
        }

        // 4. Sleep (lock is NOT held here in either branch)
        tokio::select! {
            () = tokio::time::sleep(interval) => {}
            () = cancel_token.cancelled() => {
                info!(site = %site_name, "polling cancelled");
                return;
            }
        }
    }
}

/// Calculate staggered initial delay to avoid all sites polling at once.
/// Uses a simple hash of the site name to distribute start times.
fn calculate_initial_delay(site_name: &str, interval: Duration) -> Duration {
    use std::collections::hash_map::DefaultHasher;

    let mut hasher = DefaultHasher::new();
    site_name.hash(&mut hasher);
    let hash = hasher.finish();

    // Spread across 0 to interval/2
    let max_delay_secs = interval.as_secs() / 2;
    let delay_secs = if max_delay_secs > 0 {
        hash % max_delay_secs
    } else {
        0
    };

    Duration::from_secs(delay_secs)
}

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

    #[test]
    fn initial_delay_zero_interval() {
        // interval=0 → max_delay_secs=0 → delay=0
        let delay = calculate_initial_delay("site", Duration::from_secs(0));
        assert_eq!(delay, Duration::from_secs(0));
    }

    #[test]
    fn initial_delay_one_second_interval() {
        // interval=1s → max_delay_secs=0 → delay=0
        let delay = calculate_initial_delay("site", Duration::from_secs(1));
        assert_eq!(delay, Duration::from_secs(0));
    }

    #[test]
    fn initial_delay_within_half_interval() {
        let interval = Duration::from_secs(600); // 10 min
        let delay = calculate_initial_delay("my-site", interval);
        // Must be < interval/2 (300s)
        assert!(delay < Duration::from_secs(300));
    }

    #[test]
    fn initial_delay_deterministic() {
        let interval = Duration::from_secs(600);
        let d1 = calculate_initial_delay("my-site", interval);
        let d2 = calculate_initial_delay("my-site", interval);
        assert_eq!(d1, d2);
    }

    #[test]
    fn initial_delay_different_sites_differ() {
        let interval = Duration::from_secs(3600);
        let d1 = calculate_initial_delay("site-alpha", interval);
        let d2 = calculate_initial_delay("site-beta", interval);
        // Different names should (almost certainly) produce different delays
        assert_ne!(d1, d2);
    }
}