//! Wave tracking state machine for concurrent hat execution.
//!
//! Tracks active waves, records results and failures, and determines
//! when all workers have reported back.

use ralph_proto::Event;
use std::collections::HashMap;
use std::time::{Duration, Instant};

/// Central state machine for tracking active waves.
#[derive(Debug, Default)]
pub struct WaveTracker {
    active_waves: HashMap<String, WaveState>,
}

/// State of a single active wave.
#[derive(Debug)]
pub(crate) struct WaveState {
    wave_id: String,
    expected_total: u32,
    results: Vec<WaveResult>,
    failures: Vec<WaveFailure>,
    started_at: Instant,
}

/// A successful result from a wave instance.
#[derive(Debug)]
pub struct WaveResult {
    pub index: u32,
    pub events: Vec<Event>,
}

/// A failure from a wave instance.
#[derive(Debug)]
pub struct WaveFailure {
    pub index: u32,
    pub error: String,
    pub duration: Duration,
}

/// A completed wave with all results and failures.
#[derive(Debug)]
pub struct CompletedWave {
    pub wave_id: String,
    pub results: Vec<WaveResult>,
    pub failures: Vec<WaveFailure>,
    pub duration: Duration,
}

/// Progress indicator returned by `record_result`.
#[derive(Debug, PartialEq, Eq)]
pub enum WaveProgress {
    /// More results expected.
    InProgress { received: u32, expected: u32 },
    /// All results received, wave complete.
    Complete,
}

impl WaveState {
    /// Returns the current progress of this wave.
    fn progress(&self) -> WaveProgress {
        let received = self.results.len() as u32 + self.failures.len() as u32;
        if received >= self.expected_total {
            WaveProgress::Complete
        } else {
            WaveProgress::InProgress {
                received,
                expected: self.expected_total,
            }
        }
    }

    /// Returns true if the given worker index has already submitted a result or failure.
    fn has_index(&self, index: u32) -> bool {
        self.results.iter().any(|r| r.index == index)
            || self.failures.iter().any(|f| f.index == index)
    }
}

impl WaveTracker {
    /// Creates a new empty wave tracker.
    pub fn new() -> Self {
        Self {
            active_waves: HashMap::new(),
        }
    }

    /// Register a new wave.
    ///
    /// Warns and overwrites if a wave with the same ID is already active.
    pub fn register_wave(&mut self, wave_id: String, expected_total: u32) {
        if self.active_waves.contains_key(&wave_id) {
            tracing::warn!(wave_id, "Overwriting existing active wave state");
        }
        let state = WaveState {
            wave_id: wave_id.clone(),
            expected_total,
            results: Vec::new(),
            failures: Vec::new(),
            started_at: Instant::now(),
        };
        self.active_waves.insert(wave_id, state);
    }

    /// Record result events for a wave instance.
    /// Returns the wave progress after recording.
    pub fn record_result(&mut self, wave_id: &str, index: u32, events: Vec<Event>) -> WaveProgress {
        let Some(state) = self.active_waves.get_mut(wave_id) else {
            tracing::warn!(wave_id, index, "Received result for unknown wave, ignoring");
            return WaveProgress::InProgress {
                received: 0,
                expected: 0,
            };
        };
        if state.has_index(index) {
            tracing::warn!(wave_id, index, "Duplicate worker index, ignoring");
            return state.progress();
        }
        state.results.push(WaveResult { index, events });
        state.progress()
    }

    /// Record a failure for a wave instance.
    /// Returns the wave progress after recording.
    pub fn record_failure(
        &mut self,
        wave_id: &str,
        index: u32,
        error: String,
        duration: Duration,
    ) -> WaveProgress {
        let Some(state) = self.active_waves.get_mut(wave_id) else {
            tracing::warn!(
                wave_id,
                index,
                "Failure recorded for unknown wave, ignoring"
            );
            return WaveProgress::InProgress {
                received: 0,
                expected: 0,
            };
        };
        if state.has_index(index) {
            tracing::warn!(
                wave_id,
                index,
                "Duplicate worker index in failure, ignoring"
            );
            return state.progress();
        }
        state.failures.push(WaveFailure {
            index,
            error,
            duration,
        });
        state.progress()
    }

    /// Check if a wave is complete (all results + failures == expected total).
    pub fn is_complete(&self, wave_id: &str) -> bool {
        self.active_waves
            .get(wave_id)
            .is_some_and(|state| state.progress() == WaveProgress::Complete)
    }

    /// Consume a completed wave, removing it from tracking.
    pub fn take_wave_results(&mut self, wave_id: &str) -> Option<CompletedWave> {
        let state = self.active_waves.remove(wave_id)?;
        Some(CompletedWave {
            wave_id: state.wave_id,
            results: state.results,
            failures: state.failures,
            duration: state.started_at.elapsed(),
        })
    }

    /// Check if any wave is currently active.
    pub fn has_active_waves(&self) -> bool {
        !self.active_waves.is_empty()
    }

    /// Returns wave IDs that have exceeded the given timeout since registration.
    ///
    /// Useful for enforcing aggregate timeouts — callers can force-complete
    /// these waves with partial results.
    pub fn timed_out_waves(&self, timeout: Duration) -> Vec<&str> {
        self.active_waves
            .values()
            .filter(|state| state.started_at.elapsed() > timeout)
            .map(|state| state.wave_id.as_str())
            .collect()
    }
}

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

    fn make_result_event(topic: &str, payload: &str) -> Event {
        Event::new(topic, payload)
    }

    #[test]
    fn test_register_and_record_results_until_complete() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-abc".into(), 3);

        assert!(tracker.has_active_waves());
        assert!(!tracker.is_complete("w-abc"));

        // Record first result
        let progress = tracker.record_result(
            "w-abc",
            0,
            vec![make_result_event("review.done", "result 0")],
        );
        assert_eq!(
            progress,
            WaveProgress::InProgress {
                received: 1,
                expected: 3
            }
        );
        assert!(!tracker.is_complete("w-abc"));

        // Record second result
        let progress = tracker.record_result(
            "w-abc",
            1,
            vec![make_result_event("review.done", "result 1")],
        );
        assert_eq!(
            progress,
            WaveProgress::InProgress {
                received: 2,
                expected: 3
            }
        );

        // Record third result — should be complete
        let progress = tracker.record_result(
            "w-abc",
            2,
            vec![make_result_event("review.done", "result 2")],
        );
        assert_eq!(progress, WaveProgress::Complete);
        assert!(tracker.is_complete("w-abc"));
    }

    #[test]
    fn test_record_results_and_failure_completes_wave() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-def".into(), 3);

        // Two successes
        tracker.record_result("w-def", 0, vec![make_result_event("review.done", "ok 0")]);
        tracker.record_result("w-def", 1, vec![make_result_event("review.done", "ok 1")]);

        assert!(!tracker.is_complete("w-def"));

        // One failure — should complete the wave (2 results + 1 failure = 3 total)
        let progress =
            tracker.record_failure("w-def", 2, "backend crashed".into(), Duration::from_secs(5));

        assert_eq!(progress, WaveProgress::Complete);
        assert!(tracker.is_complete("w-def"));
    }

    #[test]
    fn test_take_wave_results_returns_all_and_removes() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-take".into(), 3);

        tracker.record_result("w-take", 0, vec![make_result_event("review.done", "r0")]);
        tracker.record_result("w-take", 1, vec![make_result_event("review.done", "r1")]);
        tracker.record_failure("w-take", 2, "failed".into(), Duration::from_secs(3));

        let completed = tracker.take_wave_results("w-take").unwrap();
        assert_eq!(completed.wave_id, "w-take");
        assert_eq!(completed.results.len(), 2);
        assert_eq!(completed.failures.len(), 1);
        assert_eq!(completed.failures[0].index, 2);
        assert_eq!(completed.failures[0].error, "failed");

        // Wave should be removed
        assert!(!tracker.has_active_waves());
        assert!(tracker.take_wave_results("w-take").is_none());
    }

    #[test]
    fn test_multiple_concurrent_waves_tracked_independently() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-1".into(), 2);
        tracker.register_wave("w-2".into(), 3);

        assert!(tracker.has_active_waves());

        // Complete wave 1
        tracker.record_result("w-1", 0, vec![make_result_event("done", "a")]);
        tracker.record_result("w-1", 1, vec![make_result_event("done", "b")]);
        assert!(tracker.is_complete("w-1"));
        assert!(!tracker.is_complete("w-2"));

        // Take wave 1 results
        let w1 = tracker.take_wave_results("w-1").unwrap();
        assert_eq!(w1.results.len(), 2);

        // Wave 2 still active
        assert!(tracker.has_active_waves());
        assert!(!tracker.is_complete("w-2"));

        // Complete wave 2
        tracker.record_result("w-2", 0, vec![make_result_event("done", "x")]);
        tracker.record_failure("w-2", 1, "error".into(), Duration::from_secs(1));
        tracker.record_result("w-2", 2, vec![make_result_event("done", "z")]);

        assert!(tracker.is_complete("w-2"));
        let w2 = tracker.take_wave_results("w-2").unwrap();
        assert_eq!(w2.results.len(), 2);
        assert_eq!(w2.failures.len(), 1);

        assert!(!tracker.has_active_waves());
    }

    #[test]
    fn test_record_result_for_unknown_wave() {
        let mut tracker = WaveTracker::new();
        let progress =
            tracker.record_result("w-unknown", 0, vec![make_result_event("done", "orphan")]);
        assert_eq!(
            progress,
            WaveProgress::InProgress {
                received: 0,
                expected: 0
            }
        );
    }

    #[test]
    fn test_result_with_multiple_events() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-multi".into(), 1);

        // Worker emits multiple events
        let events = vec![
            make_result_event("review.done", "main review"),
            make_result_event("review.note", "additional note"),
        ];
        let progress = tracker.record_result("w-multi", 0, events);
        assert_eq!(progress, WaveProgress::Complete);

        let completed = tracker.take_wave_results("w-multi").unwrap();
        assert_eq!(completed.results.len(), 1);
        assert_eq!(completed.results[0].events.len(), 2);
    }

    #[test]
    fn test_default_impl() {
        let tracker = WaveTracker::default();
        assert!(!tracker.has_active_waves());
    }

    #[test]
    fn test_timed_out_waves_none_when_fresh() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-fresh".into(), 3);

        // Just registered — should not be timed out with any reasonable timeout
        let timed_out = tracker.timed_out_waves(Duration::from_mins(5));
        assert!(timed_out.is_empty());
    }

    #[test]
    fn test_timed_out_waves_returns_expired() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-old".into(), 2);

        // Zero-duration timeout means everything is timed out immediately
        let timed_out = tracker.timed_out_waves(Duration::ZERO);
        assert_eq!(timed_out.len(), 1);
        assert_eq!(timed_out[0], "w-old");
    }

    #[test]
    fn test_timed_out_waves_excludes_completed() {
        let mut tracker = WaveTracker::new();
        tracker.register_wave("w-done".into(), 1);
        tracker.record_result("w-done", 0, vec![make_result_event("done", "ok")]);
        tracker.take_wave_results("w-done");

        // Completed wave should not appear in timed_out_waves
        let timed_out = tracker.timed_out_waves(Duration::ZERO);
        assert!(timed_out.is_empty());
    }
}
