//! Cognitive delay system for fog recognition (#423, D-060).
//!
//! Recognition is NOT instant. When the observer first perceives an entity
//! not yet in their knowledge graph, recognition is buffered through a
//! cognitive delay: 0.6s (6 ticks) normal, 0.3s (3 ticks) urgent.
//!
//! Flow: observation.rs detects new entity -> CognitiveDelay buffers ->
//! process_cognitive_delay drains on expiry -> KnowledgeEvent emitted.
//!
//! Client-facing: ObserverSnapshot.pending_recognitions lists entities
//! undergoing recognition (grey blobs with no identity until delay expires).

use bevy_ecs::prelude::*;

use crate::knowledge::types::StableId;
use crate::knowledge::{KnowledgeEvent, KnowledgeEventQueue, KnowledgeEventType};
use crate::simulation::movement::TilePosition;
use crate::simulation::time::SimulationTime;

/// Base cognitive delay: 0.6 seconds = 6 ticks at 10 tps (D-031, D-060).
/// Tunable: expect playtesting adjustments.
pub const NORMAL_DELAY_TICKS: u64 = 6;

/// Urgent cognitive delay: 0.3 seconds = 3 ticks at 10 tps (D-031, D-060).
/// Triggered when observe_anomaly context is active.
pub const URGENT_DELAY_TICKS: u64 = 3;

/// How the recognition was triggered, determines delay duration.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RecognitionTrigger {
    /// Standard perception event. 0.6s = 6 ticks.
    Normal,
    /// Urgent context (observe_anomaly). 0.3s = 3 ticks.
    Urgent,
}

impl RecognitionTrigger {
    /// Delay in simulation ticks for this trigger type.
    pub fn delay_ticks(self) -> u64 {
        match self {
            Self::Normal => NORMAL_DELAY_TICKS,
            Self::Urgent => URGENT_DELAY_TICKS,
        }
    }
}

/// A single pending recognition in the cognitive delay pipeline.
#[derive(Debug, Clone)]
pub struct PendingRecognition {
    /// Bevy entity being recognized.
    pub target: Entity,
    /// Stable entity ID (for KG and wire format).
    pub stable_id: StableId,
    /// Position where the entity was perceived.
    pub position: TilePosition,
    /// Tick when recognition will complete.
    pub delay_until_tick: u64,
    /// What triggered this recognition.
    pub trigger: RecognitionTrigger,
}

/// Component: cognitive delay buffer for entity recognition (D-060).
///
/// Attached to entities with a KnowledgeGraph (player character, NPCs in future).
/// Tracks pending recognitions -- entities that have been perceived but not yet
/// identified. Drained by `process_cognitive_delay` each tick.
#[derive(Component, Debug, Default)]
pub struct CognitiveDelay {
    pending: Vec<PendingRecognition>,
}

impl CognitiveDelay {
    /// Queue a new pending recognition.
    pub fn push(&mut self, recognition: PendingRecognition) {
        self.pending.push(recognition);
    }

    /// Check if an entity is already pending recognition.
    pub fn is_pending(&self, stable_id: &StableId) -> bool {
        self.pending.iter().any(|p| p.stable_id == *stable_id)
    }

    /// Cancel a pending recognition (e.g., entity left perception range).
    /// Returns the cancelled entry if it existed.
    pub fn cancel(&mut self, stable_id: &StableId) -> Option<PendingRecognition> {
        if let Some(idx) = self.pending.iter().position(|p| p.stable_id == *stable_id) {
            Some(self.pending.swap_remove(idx))
        } else {
            None
        }
    }

    /// Drain all recognitions whose delay has expired (delay_until_tick <= current_tick).
    pub fn drain_ready(&mut self, current_tick: u64) -> Vec<PendingRecognition> {
        let mut ready = Vec::new();
        self.pending.retain(|p| {
            if current_tick >= p.delay_until_tick {
                ready.push(p.clone());
                false
            } else {
                true
            }
        });
        ready
    }

    /// Read-only access to pending recognitions (for snapshot assembly).
    pub fn pending(&self) -> &[PendingRecognition] {
        &self.pending
    }

    /// Number of pending recognitions.
    pub fn len(&self) -> usize {
        self.pending.len()
    }

    /// Whether there are any pending recognitions.
    pub fn is_empty(&self) -> bool {
        self.pending.is_empty()
    }
}

/// System: drain expired cognitive delays and emit KnowledgeEvents (#423, D-060).
///
/// Each tick, checks CognitiveDelay components for expired recognition timers.
/// Expired recognitions are converted to DirectObservation KnowledgeEvents.
///
/// System ordering: after emit_observation_events, before process_knowledge_events.
pub fn process_cognitive_delay(
    time: Res<SimulationTime>,
    mut query: Query<(Entity, &mut CognitiveDelay)>,
    mut event_queue: ResMut<KnowledgeEventQueue>,
) {
    for (observer, mut delay) in query.iter_mut() {
        let ready = delay.drain_ready(time.tick);
        for recognition in ready {
            event_queue.push(KnowledgeEvent {
                observer,
                tick: time.tick,
                event_type: KnowledgeEventType::DirectObservation {
                    target: recognition.target,
                    position: recognition.position,
                },
            });
            tracing::debug!(
                "Cognitive delay resolved: target={:?}, stable_id={}, trigger={:?}, tick={}",
                recognition.target,
                recognition.stable_id.0,
                recognition.trigger,
                time.tick,
            );
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::knowledge::registry::EntityRegistry;
    use crate::knowledge::KnowledgeGraph;
    use bevy_ecs::world::World;

    // --- RecognitionTrigger ---

    #[test]
    fn trigger_delay_values() {
        assert_eq!(RecognitionTrigger::Normal.delay_ticks(), NORMAL_DELAY_TICKS);
        assert_eq!(RecognitionTrigger::Urgent.delay_ticks(), URGENT_DELAY_TICKS);
        assert_eq!(NORMAL_DELAY_TICKS, 6);
        assert_eq!(URGENT_DELAY_TICKS, 3);
    }

    // --- CognitiveDelay component ---

    #[test]
    fn default_is_empty() {
        let delay = CognitiveDelay::default();
        assert!(delay.is_empty());
        assert_eq!(delay.len(), 0);
        assert!(delay.pending().is_empty());
    }

    #[test]
    fn push_adds_pending() {
        let mut world = World::new();
        let target = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        assert_eq!(delay.len(), 1);
        assert!(delay.is_pending(&StableId(1)));
        assert!(!delay.is_pending(&StableId(2)));
    }

    #[test]
    fn cancel_removes_and_returns_entry() {
        let mut world = World::new();
        let target = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        let cancelled = delay.cancel(&StableId(1));
        assert!(cancelled.is_some());
        assert_eq!(cancelled.unwrap().stable_id, StableId(1));
        assert!(delay.is_empty());
    }

    #[test]
    fn cancel_missing_returns_none() {
        let mut delay = CognitiveDelay::default();
        assert!(delay.cancel(&StableId(999)).is_none());
    }

    #[test]
    fn drain_ready_before_delay() {
        let mut world = World::new();
        let target = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        let ready = delay.drain_ready(105);
        assert!(ready.is_empty());
        assert_eq!(delay.len(), 1, "entry should remain pending");
    }

    #[test]
    fn drain_ready_at_exact_tick() {
        let mut world = World::new();
        let target = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        let ready = delay.drain_ready(106);
        assert_eq!(ready.len(), 1);
        assert_eq!(ready[0].stable_id, StableId(1));
        assert!(delay.is_empty());
    }

    #[test]
    fn drain_ready_past_tick() {
        let mut world = World::new();
        let target = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        let ready = delay.drain_ready(200);
        assert_eq!(ready.len(), 1);
        assert!(delay.is_empty());
    }

    #[test]
    fn drain_ready_partial_mixed_triggers() {
        let mut world = World::new();
        let t1 = world.spawn_empty().id();
        let t2 = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target: t1,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 103, // Urgent: 3 ticks from tick 100
            trigger: RecognitionTrigger::Urgent,
        });
        delay.push(PendingRecognition {
            target: t2,
            stable_id: StableId(2),
            position: TilePosition::new(10, 10, 0),
            delay_until_tick: 106, // Normal: 6 ticks from tick 100
            trigger: RecognitionTrigger::Normal,
        });

        // Tick 103: only urgent should drain
        let ready = delay.drain_ready(103);
        assert_eq!(ready.len(), 1);
        assert_eq!(ready[0].stable_id, StableId(1));
        assert_eq!(delay.len(), 1);

        // Tick 106: normal should drain
        let ready = delay.drain_ready(106);
        assert_eq!(ready.len(), 1);
        assert_eq!(ready[0].stable_id, StableId(2));
        assert!(delay.is_empty());
    }

    #[test]
    fn is_pending_checks_stable_id() {
        let mut world = World::new();
        let t1 = world.spawn_empty().id();
        let t2 = world.spawn_empty().id();

        let mut delay = CognitiveDelay::default();
        delay.push(PendingRecognition {
            target: t1,
            stable_id: StableId(1),
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        assert!(delay.is_pending(&StableId(1)));
        assert!(!delay.is_pending(&StableId(2)));

        delay.push(PendingRecognition {
            target: t2,
            stable_id: StableId(2),
            position: TilePosition::new(10, 10, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });

        assert!(delay.is_pending(&StableId(1)));
        assert!(delay.is_pending(&StableId(2)));
    }

    // --- process_cognitive_delay system ---

    #[test]
    fn process_emits_knowledge_event_on_expiry() {
        let mut world = World::new();
        let mut registry = EntityRegistry::new(0);

        let target = world.spawn_empty().id();
        let target_sid = registry.register(target);

        let mut cd = CognitiveDelay::default();
        cd.push(PendingRecognition {
            target,
            stable_id: target_sid,
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });
        world.spawn((KnowledgeGraph::new(), cd));

        world.insert_resource(registry);
        world.init_resource::<KnowledgeEventQueue>();
        world.insert_resource({
            let mut t = SimulationTime::default();
            t.tick = 106;
            t
        });

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(process_cognitive_delay);
        schedule.run(&mut world);

        let queue = world.resource::<KnowledgeEventQueue>();
        assert_eq!(queue.len(), 1, "should emit one KnowledgeEvent on expiry");
    }

    #[test]
    fn process_does_not_emit_before_delay() {
        let mut world = World::new();
        let mut registry = EntityRegistry::new(0);

        let target = world.spawn_empty().id();
        let target_sid = registry.register(target);

        let mut cd = CognitiveDelay::default();
        cd.push(PendingRecognition {
            target,
            stable_id: target_sid,
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });
        world.spawn((KnowledgeGraph::new(), cd));

        world.insert_resource(registry);
        world.init_resource::<KnowledgeEventQueue>();
        world.insert_resource({
            let mut t = SimulationTime::default();
            t.tick = 105;
            t
        });

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(process_cognitive_delay);
        schedule.run(&mut world);

        let queue = world.resource::<KnowledgeEventQueue>();
        assert!(queue.is_empty(), "should not emit before delay expires");
    }

    #[test]
    fn process_urgent_resolves_faster() {
        let mut world = World::new();
        let mut registry = EntityRegistry::new(0);

        let t1 = world.spawn_empty().id();
        let t1_sid = registry.register(t1);
        let t2 = world.spawn_empty().id();
        let t2_sid = registry.register(t2);

        let mut cd = CognitiveDelay::default();
        cd.push(PendingRecognition {
            target: t1,
            stable_id: t1_sid,
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 103, // Urgent
            trigger: RecognitionTrigger::Urgent,
        });
        cd.push(PendingRecognition {
            target: t2,
            stable_id: t2_sid,
            position: TilePosition::new(10, 10, 0),
            delay_until_tick: 106, // Normal
            trigger: RecognitionTrigger::Normal,
        });
        world.spawn((KnowledgeGraph::new(), cd));

        world.insert_resource(registry);
        world.init_resource::<KnowledgeEventQueue>();
        world.insert_resource({
            let mut t = SimulationTime::default();
            t.tick = 103;
            t
        });

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(process_cognitive_delay);
        schedule.run(&mut world);

        let queue = world.resource::<KnowledgeEventQueue>();
        assert_eq!(queue.len(), 1, "only urgent should resolve at tick 103");
    }

    #[test]
    fn process_no_crash_without_pending() {
        let mut world = World::new();
        world.spawn((KnowledgeGraph::new(), CognitiveDelay::default()));
        world.init_resource::<KnowledgeEventQueue>();
        world.init_resource::<SimulationTime>();

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(process_cognitive_delay);
        schedule.run(&mut world); // Should not panic
    }

    #[test]
    fn process_clears_pending_after_drain() {
        let mut world = World::new();
        let mut registry = EntityRegistry::new(0);

        let target = world.spawn_empty().id();
        let target_sid = registry.register(target);

        let mut cd = CognitiveDelay::default();
        cd.push(PendingRecognition {
            target,
            stable_id: target_sid,
            position: TilePosition::new(5, 5, 0),
            delay_until_tick: 106,
            trigger: RecognitionTrigger::Normal,
        });
        let observer = world.spawn((KnowledgeGraph::new(), cd)).id();

        world.insert_resource(registry);
        world.init_resource::<KnowledgeEventQueue>();
        world.insert_resource({
            let mut t = SimulationTime::default();
            t.tick = 106;
            t
        });

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(process_cognitive_delay);
        schedule.run(&mut world);

        let cd = world.entity(observer).get::<CognitiveDelay>().unwrap();
        assert!(cd.is_empty(), "pending should be cleared after drain");
    }
}