aria2-core 0.2.1

use serde::{Deserialize, Serialize};
use std::sync::atomic::{AtomicU32, AtomicU64, Ordering};
use std::time::{SystemTime, UNIX_EPOCH};

const EMA_ALPHA: f64 = 0.7;

/// Serializable snapshot of ServerStat for persistence.
///
/// This struct contains all the persistent fields of ServerStat in a
/// serde-compatible format (no atomic types). Used for saving and loading
/// server performance statistics across restarts.
///
/// # Example
///
/// ```
/// use aria2_core::selector::server_stat::{ServerStat, ServerStatSnapshot};
///
/// let stat = ServerStat::new("mirror.example.com");
/// stat.update_speed(5000, false);
///
/// let snapshot = stat.to_snapshot();
/// let restored = ServerStat::from_snapshot(&snapshot);
///
/// assert_eq!(restored.host, stat.host);
/// ```
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ServerStatSnapshot {
    /// Server hostname (e.g., "mirror1.example.com")
    pub host: String,
    /// Current download speed in bytes/sec
    pub download_speed: u64,
    /// Exponential moving average of single-connection download speed
    pub single_connection_avg_speed: u64,
    /// Exponential moving average of multi-connection download speed
    pub multi_connection_avg_speed: u64,
    /// Unix timestamp of last update
    pub last_updated: u64,
    /// Server status: 0 = OK, 1 = Error
    pub status: u32,
    /// Usage counter (number of times this server was selected)
    pub counter: u32,
    /// Unix timestamp of last error (None if never failed)
    pub last_error_time: Option<u64>,
    /// HTTP error code of last error (0 if never failed)
    pub last_error_code: u16,
    /// Number of consecutive failures (reset on success)
    pub consecutive_failures: u32,
}

#[derive(Debug)]
pub struct ServerStat {
    pub host: String,
    download_speed: AtomicU64,
    single_connection_avg_speed: AtomicU64,
    multi_connection_avg_speed: AtomicU64,
    last_updated: AtomicU64,
    status: AtomicU32,
    counter: AtomicU32,
    // Fields for failure tracking and availability cooldown
    // Note: These use plain types (not atomic) because ServerStat is already
    // protected by RwLock in ServerStatMan's internal HashMap
    pub last_error_time: Option<SystemTime>,
    pub last_error_code: Option<u16>,
    pub consecutive_failures: u32,
}

impl Clone for ServerStat {
    fn clone(&self) -> Self {
        Self {
            host: self.host.clone(),
            download_speed: AtomicU64::new(self.download_speed.load(Ordering::Relaxed)),
            single_connection_avg_speed: AtomicU64::new(
                self.single_connection_avg_speed.load(Ordering::Relaxed),
            ),
            multi_connection_avg_speed: AtomicU64::new(
                self.multi_connection_avg_speed.load(Ordering::Relaxed),
            ),
            last_updated: AtomicU64::new(self.last_updated.load(Ordering::Relaxed)),
            status: AtomicU32::new(self.status.load(Ordering::Relaxed)),
            counter: AtomicU32::new(self.counter.load(Ordering::Relaxed)),
            // Clone new fields
            last_error_time: self.last_error_time,
            last_error_code: self.last_error_code,
            consecutive_failures: self.consecutive_failures,
        }
    }
}

impl ServerStat {
    pub fn new(host: &str) -> Self {
        Self {
            host: host.to_string(),
            download_speed: AtomicU64::new(0),
            single_connection_avg_speed: AtomicU64::new(0),
            multi_connection_avg_speed: AtomicU64::new(0),
            last_updated: AtomicU64::new(0),
            status: AtomicU32::new(0),
            counter: AtomicU32::new(0),
            // Initialize new fields
            last_error_time: None,
            last_error_code: None,
            consecutive_failures: 0,
        }
    }

    pub fn update_speed(&self, speed: u64, is_multi: bool) {
        self.download_speed.store(speed, Ordering::Relaxed);
        if is_multi {
            let old = self.multi_connection_avg_speed.load(Ordering::Relaxed);
            let new_val = ema(old, speed);
            self.multi_connection_avg_speed
                .store(new_val, Ordering::Relaxed);
        } else {
            let old = self.single_connection_avg_speed.load(Ordering::Relaxed);
            let new_val = ema(old, speed);
            self.single_connection_avg_speed
                .store(new_val, Ordering::Relaxed);
        }
        self.touch();
    }

    pub fn get_download_speed(&self) -> u64 {
        self.download_speed.load(Ordering::Relaxed)
    }

    pub fn get_single_avg_speed(&self) -> u64 {
        self.single_connection_avg_speed.load(Ordering::Relaxed)
    }

    pub fn get_multi_avg_speed(&self) -> u64 {
        self.multi_connection_avg_speed.load(Ordering::Relaxed)
    }

    pub fn get_avg_speed(&self) -> u64 {
        let s = self.single_connection_avg_speed.load(Ordering::Relaxed);
        let m = self.multi_connection_avg_speed.load(Ordering::Relaxed);
        if s > 0 && m > 0 {
            (s + m) / 2
        } else {
            s.max(m)
        }
    }

    pub fn is_ok(&self) -> bool {
        self.status.load(Ordering::Relaxed) == 0
    }

    pub fn set_error(&self) {
        self.status.store(1, Ordering::Relaxed);
    }

    pub fn reset_status(&self) {
        self.status.store(0, Ordering::Relaxed);
    }

    pub fn increment_counter(&self) -> u32 {
        self.counter.fetch_add(1, Ordering::Relaxed).wrapping_add(1)
    }

    pub fn get_counter(&self) -> u32 {
        self.counter.load(Ordering::Relaxed)
    }

    pub fn reset_counter(&self) {
        self.counter.store(0, Ordering::Relaxed);
    }

    pub fn is_fresh(&self, duration_secs: u64) -> bool {
        let last = self.last_updated.load(Ordering::Relaxed);
        if last == 0 {
            return false;
        }
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();
        now.saturating_sub(last) < duration_secs
    }

    /// Get the last update timestamp as unix timestamp (0 if never updated).
    pub fn get_last_updated(&self) -> u64 {
        self.last_updated.load(Ordering::Relaxed)
    }

    fn touch(&self) {
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();
        self.last_updated.store(now, Ordering::Relaxed);
    }

    /// Check if server is available (not in cooldown due to consecutive failures)
    pub fn is_available(&self) -> bool {
        if self.consecutive_failures >= 3
            && let Some(error_time) = self.last_error_time
            && let Ok(elapsed) = error_time.elapsed()
        {
            return elapsed.as_secs() > 60; // cooldown expired?
        }
        true
    }

    /// Get the last error time as unix timestamp (0 if never failed)
    pub fn get_last_error_time(&self) -> u64 {
        self.last_error_time
            .map(|t| t.duration_since(UNIX_EPOCH).unwrap_or_default().as_secs())
            .unwrap_or(0)
    }

    /// Get the last error code (0 if never failed)
    pub fn get_last_error_code(&self) -> u16 {
        self.last_error_code.unwrap_or(0)
    }

    /// Get consecutive failure count
    pub fn get_consecutive_failures(&self) -> u32 {
        self.consecutive_failures
    }

    /// Set error tracking fields (for use by ServerStatMan::mark_failure)
    /// Note: Requires &mut self because these fields are not atomic
    pub fn set_failure_info(&mut self, error_code: u16) {
        self.last_error_time = Some(SystemTime::now());
        self.last_error_code = Some(error_code);
        self.consecutive_failures += 1;
    }

    // ==================== Persistence Methods ====================

    /// Convert to a serializable snapshot for persistence.
    ///
    /// Extracts all atomic values into a plain struct suitable for
    /// JSON serialization. The snapshot captures the current state
    /// of all performance metrics and error tracking.
    ///
    /// # Example
    ///
    /// ```
    /// use aria2_core::selector::server_stat::ServerStat;
    ///
    /// let stat = ServerStat::new("fast.mirror.com");
    /// stat.update_speed(10000, false);
    /// stat.increment_counter();
    ///
    /// let snapshot = stat.to_snapshot();
    /// assert_eq!(snapshot.host, "fast.mirror.com");
    /// assert_eq!(snapshot.counter, 1);
    /// ```
    pub fn to_snapshot(&self) -> ServerStatSnapshot {
        ServerStatSnapshot {
            host: self.host.clone(),
            download_speed: self.download_speed.load(Ordering::Relaxed),
            single_connection_avg_speed: self.single_connection_avg_speed.load(Ordering::Relaxed),
            multi_connection_avg_speed: self.multi_connection_avg_speed.load(Ordering::Relaxed),
            last_updated: self.last_updated.load(Ordering::Relaxed),
            status: self.status.load(Ordering::Relaxed),
            counter: self.counter.load(Ordering::Relaxed),
            last_error_time: self
                .last_error_time
                .and_then(|t| t.duration_since(UNIX_EPOCH).ok().map(|d| d.as_secs())),
            last_error_code: self.last_error_code.unwrap_or(0),
            consecutive_failures: self.consecutive_failures,
        }
    }

    /// Restore from a serialized snapshot.
    ///
    /// Creates a new ServerStat instance with all fields initialized
    /// from the snapshot data. Atomic fields are set to the snapshot values.
    ///
    /// # Arguments
    ///
    /// * `snapshot` - The serialized server statistics to restore from
    ///
    /// # Example
    ///
    /// ```
    /// use aria2_core::selector::server_stat::{ServerStat, ServerStatSnapshot};
    ///
    /// let snapshot = ServerStatSnapshot {
    ///     host: "restored.mirror.com".to_string(),
    ///     download_speed: 5000,
    ///     single_connection_avg_speed: 4500,
    ///     multi_connection_avg_speed: 8000,
    ///     last_updated: 1700000000,
    ///     status: 0,
    ///     counter: 10,
    ///     last_error_time: None,
    ///     last_error_code: 0,
    ///     consecutive_failures: 0,
    /// };
    ///
    /// let stat = ServerStat::from_snapshot(&snapshot);
    /// assert_eq!(stat.host, "restored.mirror.com");
    /// assert_eq!(stat.get_counter(), 10);
    /// ```
    pub fn from_snapshot(snapshot: &ServerStatSnapshot) -> Self {
        Self {
            host: snapshot.host.clone(),
            download_speed: AtomicU64::new(snapshot.download_speed),
            single_connection_avg_speed: AtomicU64::new(snapshot.single_connection_avg_speed),
            multi_connection_avg_speed: AtomicU64::new(snapshot.multi_connection_avg_speed),
            last_updated: AtomicU64::new(snapshot.last_updated),
            status: AtomicU32::new(snapshot.status),
            counter: AtomicU32::new(snapshot.counter),
            last_error_time: snapshot
                .last_error_time
                .and_then(|ts| UNIX_EPOCH.checked_add(std::time::Duration::from_secs(ts))),
            last_error_code: if snapshot.last_error_code > 0 {
                Some(snapshot.last_error_code)
            } else {
                None
            },
            consecutive_failures: snapshot.consecutive_failures,
        }
    }
}

fn ema(old: u64, new: u64) -> u64 {
    (old as f64 * (1.0 - EMA_ALPHA) + new as f64 * EMA_ALPHA) as u64
}

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

    #[test]
    fn test_creation() {
        let stat = ServerStat::new("example.com");
        assert_eq!(stat.host, "example.com");
        assert_eq!(stat.get_download_speed(), 0);
        assert_eq!(stat.get_single_avg_speed(), 0);
        assert!(stat.is_ok());
        assert_eq!(stat.get_counter(), 0);
    }

    #[test]
    fn test_update_single_speed() {
        let stat = ServerStat::new("example.com");
        stat.update_speed(1000, false);
        assert_eq!(stat.get_download_speed(), 1000);
        assert_eq!(stat.get_single_avg_speed(), 700); // 0*0.3 + 1000*0.7

        stat.update_speed(2000, false);
        assert_eq!(stat.get_single_avg_speed(), 1610); // 700*0.3 + 2000*0.7
    }

    #[test]
    fn test_update_multi_speed_independent() {
        let stat = ServerStat::new("example.com");
        stat.update_speed(1000, true);
        assert_eq!(stat.get_multi_avg_speed(), 700);
        assert_eq!(stat.get_single_avg_speed(), 0);

        stat.update_speed(500, false);
        assert_eq!(stat.get_single_avg_speed(), 350);
        assert_eq!(stat.get_multi_avg_speed(), 700);
    }

    #[test]
    fn test_get_avg_speed_combines_both() {
        let stat = ServerStat::new("example.com");
        stat.update_speed(1000, false);
        stat.update_speed(2000, true);
        let avg = stat.get_avg_speed();
        assert!(avg > 0);
        assert!((350..=1400).contains(&avg));
    }

    #[test]
    fn test_status_toggle() {
        let stat = ServerStat::new("example.com");
        assert!(stat.is_ok());

        stat.set_error();
        assert!(!stat.is_ok());

        stat.reset_status();
        assert!(stat.is_ok());
    }

    #[test]
    fn test_counter_operations() {
        let stat = ServerStat::new("example.com");
        assert_eq!(stat.get_counter(), 0);

        let c1 = stat.increment_counter();
        assert_eq!(c1, 1);
        assert_eq!(stat.get_counter(), 1);

        let c2 = stat.increment_counter();
        assert_eq!(c2, 2);

        stat.reset_counter();
        assert_eq!(stat.get_counter(), 0);
    }

    #[test]
    fn test_is_fresh_after_update() {
        let stat = ServerStat::new("example.com");
        assert!(!stat.is_fresh(60));

        stat.update_speed(1000, false);
        assert!(stat.is_fresh(60));
        assert!(!stat.is_fresh(0));
    }

    #[test]
    fn test_concurrent_updates() {
        use std::sync::Arc;
        use std::thread;

        let stat = Arc::new(ServerStat::new("concurrent.test"));
        let mut handles = Vec::new();

        for i in 0..10u64 {
            let s = Arc::clone(&stat);
            handles.push(thread::spawn(move || {
                s.update_speed((i + 1) * 1000, i % 2 == 0);
            }));
        }

        for h in handles {
            h.join().unwrap();
        }

        assert!(stat.get_download_speed() > 0);
        assert!(stat.is_fresh(60));
    }

    // ======================================================================
    // Tests for Availability Cooldown
    // ======================================================================

    #[test]
    fn test_server_available_initially() {
        let stat = ServerStat::new("fresh.server");
        assert!(stat.is_available(), "New server should be available");
    }

    #[test]
    fn test_server_available_with_few_failures() {
        let mut stat = ServerStat::new("some.failures");
        stat.consecutive_failures = 2;
        stat.last_error_time = Some(SystemTime::now());
        assert!(
            stat.is_available(),
            "Server with <3 failures should still be available"
        );
    }

    #[test]
    fn test_server_unavailable_after_3_failures() {
        let mut stat = ServerStat::new("cooldown.server");
        stat.consecutive_failures = 3;
        stat.last_error_time = Some(SystemTime::now());
        assert!(
            !stat.is_available(),
            "Server with 3+ recent failures should be unavailable"
        );
    }

    #[test]
    fn test_server_available_after_cooldown_expires() {
        let mut stat = ServerStat::new("recovered.server");
        stat.consecutive_failures = 5;
        // Simulate error that happened more than 60 seconds ago
        stat.last_error_time = Some(SystemTime::now() - std::time::Duration::from_secs(61));
        assert!(
            stat.is_available(),
            "Server should become available after cooldown expires"
        );
    }

    #[test]
    fn test_set_failure_info() {
        let mut stat = ServerStat::new("failure.test");

        // Initially no failures
        assert_eq!(stat.get_consecutive_failures(), 0);
        assert_eq!(stat.get_last_error_code(), 0);
        assert_eq!(stat.get_last_error_time(), 0);

        // Set failure info
        stat.set_failure_info(500);

        assert_eq!(stat.get_consecutive_failures(), 1);
        assert_eq!(stat.get_last_error_code(), 500);
        assert!(stat.get_last_error_time() > 0);

        // Set another failure
        stat.set_failure_info(503);
        assert_eq!(stat.get_consecutive_failures(), 2);
        assert_eq!(stat.get_last_error_code(), 503);
    }

    // ======================================================================
    // Tests for Persistence (Snapshot Roundtrip)
    // ======================================================================

    #[test]
    fn test_snapshot_roundtrip_basic() {
        let stat = ServerStat::new("snapshot.test");
        stat.update_speed(5000, false);
        stat.update_speed(10000, true);
        stat.increment_counter();
        stat.increment_counter();

        let snapshot = stat.to_snapshot();
        let restored = ServerStat::from_snapshot(&snapshot);

        assert_eq!(restored.host, "snapshot.test");
        assert_eq!(restored.get_download_speed(), 10000);
        assert_eq!(restored.get_counter(), 2);
        assert!(restored.get_single_avg_speed() > 0);
        assert!(restored.get_multi_avg_speed() > 0);
    }

    #[test]
    fn test_snapshot_roundtrip_with_failures() {
        let mut stat = ServerStat::new("failed.snapshot.test");
        stat.update_speed(3000, false);
        stat.set_failure_info(500);
        stat.set_failure_info(503);

        let snapshot = stat.to_snapshot();
        assert_eq!(snapshot.consecutive_failures, 2);
        assert_eq!(snapshot.last_error_code, 503);
        assert!(snapshot.last_error_time.is_some());

        let restored = ServerStat::from_snapshot(&snapshot);
        assert_eq!(restored.get_consecutive_failures(), 2);
        assert_eq!(restored.get_last_error_code(), 503);
        assert!(restored.get_last_error_time() > 0);
    }

    #[test]
    fn test_snapshot_preserves_all_fields() {
        let mut stat = ServerStat::new("complete.snapshot.test");
        stat.update_speed(12345, false);
        stat.update_speed(67890, true);
        for _ in 0..5 {
            stat.increment_counter();
        }
        stat.set_error();
        stat.set_failure_info(502);

        let snapshot = stat.to_snapshot();

        // Verify all fields are captured
        assert_eq!(snapshot.host, "complete.snapshot.test");
        assert_eq!(snapshot.download_speed, 67890);
        assert!(snapshot.single_connection_avg_speed > 0);
        assert!(snapshot.multi_connection_avg_speed > 0);
        assert!(snapshot.last_updated > 0);
        assert_eq!(snapshot.status, 1); // Error status
        assert_eq!(snapshot.counter, 5);
        assert!(snapshot.last_error_time.is_some());
        assert_eq!(snapshot.last_error_code, 502);
        assert_eq!(snapshot.consecutive_failures, 1);

        // Verify restoration preserves all fields
        let restored = ServerStat::from_snapshot(&snapshot);
        assert_eq!(restored.host, snapshot.host);
        assert_eq!(restored.get_download_speed(), snapshot.download_speed);
        assert_eq!(
            restored.get_single_avg_speed(),
            snapshot.single_connection_avg_speed
        );
        assert_eq!(
            restored.get_multi_avg_speed(),
            snapshot.multi_connection_avg_speed
        );
        assert_eq!(restored.get_counter(), snapshot.counter);
        assert!(!restored.is_ok()); // Should have error status
    }

    #[test]
    fn test_snapshot_json_serialization() {
        let stat = ServerStat::new("json.test");
        stat.update_speed(10000, false);
        stat.increment_counter();

        let snapshot = stat.to_snapshot();

        // Serialize to JSON
        let json = serde_json::to_string(&snapshot).expect("Should serialize to JSON");
        assert!(json.contains("json.test"));
        assert!(json.contains("10000"));

        // Deserialize from JSON
        let deserialized: ServerStatSnapshot =
            serde_json::from_str(&json).expect("Should deserialize from JSON");
        assert_eq!(deserialized.host, "json.test");
        assert_eq!(deserialized.download_speed, 10000);
        assert_eq!(deserialized.counter, 1);
    }

    #[test]
    fn test_snapshot_zero_values() {
        let stat = ServerStat::new("zero.test");
        // No updates - all values should be zero/default

        let snapshot = stat.to_snapshot();
        assert_eq!(snapshot.download_speed, 0);
        assert_eq!(snapshot.single_connection_avg_speed, 0);
        assert_eq!(snapshot.multi_connection_avg_speed, 0);
        assert_eq!(snapshot.counter, 0);
        assert_eq!(snapshot.status, 0);
        assert!(snapshot.last_error_time.is_none());
        assert_eq!(snapshot.last_error_code, 0);
        assert_eq!(snapshot.consecutive_failures, 0);

        let restored = ServerStat::from_snapshot(&snapshot);
        assert_eq!(restored.get_download_speed(), 0);
        assert!(restored.is_ok());
    }
}