//! Tolerance threshold monitoring system (#105).
//!
//! Monitors Active-tier NPCs each tick. When `current_stress >= threshold`,
//! emits a `ToleranceBreachEvent` (once per crossing) and marks the NPC with
//! `ToleranceBreached`. When stress drops below threshold, clears the marker.
//!
//! ## Integration
//! - `npc::mood::update_mood` reads `ToleranceThreshold` directly to derive
//!   `Hostile`/`Anxious` mood — no duplication needed here.
//! - Future #250 (Triangle escalation) consumes `ToleranceBreachEventQueue`.
//!
//! All arithmetic is integer-only (D-010 determinism).

use bevy_ecs::prelude::*;

use crate::npc::{Npc, ToleranceThreshold};
use crate::simulation::tier::ActiveSim;
use crate::simulation::time::SimulationTime;

// ---------------------------------------------------------------------------
// Event and queue
// ---------------------------------------------------------------------------

/// Emitted when an NPC's stress first crosses their tolerance threshold.
///
/// Produced once per crossing transition (not every tick while breached).
/// Consumed by future #250 (Triangle escalation system).
///
/// Threshold value comes from per-NPC generation seed — not hardcoded.
#[derive(Debug, Clone)]
pub struct ToleranceBreachEvent {
    /// The NPC entity that exceeded their threshold.
    pub entity: Entity,
    /// Tick when the breach occurred.
    pub tick: u64,
    /// Stress level at the moment of breach.
    pub stress_at_breach: i16,
    /// The NPC's tolerance threshold (per-NPC, seeded at generation).
    pub threshold: i16,
}

/// Resource: queue of tolerance breach events.
///
/// Drained once per tick by consumers. Multiple consumers may drain the queue
/// in sequence — the first consumer gets all events, subsequent consumers get
/// nothing (caller's responsibility to coordinate if multiple consumers exist).
#[derive(Resource, Default)]
pub struct ToleranceBreachEventQueue {
    pub events: Vec<ToleranceBreachEvent>,
}

impl ToleranceBreachEventQueue {
    /// Push a breach event into the queue.
    pub fn push(&mut self, event: ToleranceBreachEvent) {
        self.events.push(event);
    }

    /// Drain all pending events.
    pub fn drain(&mut self) -> Vec<ToleranceBreachEvent> {
        std::mem::take(&mut self.events)
    }

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

    /// Whether the queue is empty.
    pub fn is_empty(&self) -> bool {
        self.events.is_empty()
    }
}

// ---------------------------------------------------------------------------
// Marker component
// ---------------------------------------------------------------------------

/// Marker: NPC is currently in a tolerance breach state (stress >= threshold).
///
/// Inserted by `check_tolerance_threshold` on first breach.
/// Removed when stress drops below threshold.
/// Guards against duplicate events on consecutive breach ticks.
#[derive(Component, Debug, Clone, Copy)]
pub struct ToleranceBreached;

// ---------------------------------------------------------------------------
// System
// ---------------------------------------------------------------------------

/// System: monitor tolerance thresholds for Active-tier NPCs.
///
/// Runs once per tick. For each NPC with `ToleranceThreshold`:
/// - `stress >= threshold` and not yet marked: insert `ToleranceBreached`, emit event.
/// - `stress < threshold` and currently marked: remove `ToleranceBreached`.
/// - Already in correct state: no action.
///
/// Mood shift (Hostile/Anxious) is delegated to `npc::mood::update_mood`,
/// which reads `ToleranceThreshold` each tick. No duplication here.
///
/// Future behavioral reactions (confrontation-initiation, avoidance):
/// other systems should read `ToleranceBreachEventQueue` or query for
/// `ToleranceBreached` components.
///
/// Scoped to `ActiveSim` — Background-tier NPCs are not monitored per
/// tick (D-026). Background NPCs retain their last-known mood state.
pub fn check_tolerance_threshold(
    mut commands: Commands,
    time: Res<SimulationTime>,
    mut queue: ResMut<ToleranceBreachEventQueue>,
    npcs: Query<
        (Entity, &ToleranceThreshold, Option<&ToleranceBreached>),
        (With<Npc>, With<ActiveSim>),
    >,
) {
    let tick = time.tick;

    for (entity, tolerance, breach_opt) in npcs.iter() {
        let is_breached = tolerance.current_stress >= tolerance.threshold;
        let was_breached = breach_opt.is_some();

        match (is_breached, was_breached) {
            (true, false) => {
                // Transition: OK → Breached. Insert marker and emit event.
                commands.entity(entity).insert(ToleranceBreached);
                queue.push(ToleranceBreachEvent {
                    entity,
                    tick,
                    stress_at_breach: tolerance.current_stress,
                    threshold: tolerance.threshold,
                });
                tracing::debug!(
                    "Entity {:?}: tolerance breached (stress={}, threshold={}) at tick {}",
                    entity,
                    tolerance.current_stress,
                    tolerance.threshold,
                    tick
                );
            }
            (false, true) => {
                // Transition: Breached → OK. Remove marker.
                commands.entity(entity).remove::<ToleranceBreached>();
                tracing::debug!(
                    "Entity {:?}: tolerance breach resolved (stress={}, threshold={}) at tick {}",
                    entity,
                    tolerance.current_stress,
                    tolerance.threshold,
                    tick
                );
            }
            // (true, true): still breached — no action, no duplicate event.
            // (false, false): still fine — no action.
            _ => {}
        }
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;
    use crate::npc::{Npc, ToleranceThreshold};
    use crate::simulation::tier::{ActiveSim, BackgroundSim};
    use crate::simulation::time::SimulationTime;
    use bevy_ecs::world::World;

    fn setup_world() -> World {
        let mut world = World::new();
        world.init_resource::<SimulationTime>();
        world.init_resource::<ToleranceBreachEventQueue>();
        world
    }

    fn run_system(world: &mut World) {
        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(check_tolerance_threshold);
        schedule.run(world);
        world.flush();
    }

    // -----------------------------------------------------------------------
    // Breach event emission
    // -----------------------------------------------------------------------

    #[test]
    fn breach_event_emitted_when_stress_equals_threshold() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 50,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.len(), 1, "should emit exactly one breach event");
        assert_eq!(queue.events[0].stress_at_breach, 50);
        assert_eq!(queue.events[0].threshold, 50);
    }

    #[test]
    fn breach_event_emitted_when_stress_above_threshold() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 80,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.len(), 1);
        assert_eq!(queue.events[0].stress_at_breach, 80);
        assert_eq!(queue.events[0].threshold, 50);
    }

    #[test]
    fn no_breach_event_when_stress_below_threshold() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 49,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(queue.is_empty(), "stress=49 < threshold=50 should not breach");
    }

    #[test]
    fn no_breach_event_at_zero_stress() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 0,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(queue.is_empty());
    }

    // -----------------------------------------------------------------------
    // Breach event tick field
    // -----------------------------------------------------------------------

    #[test]
    fn breach_event_records_current_tick() {
        let mut world = setup_world();
        world.resource_mut::<SimulationTime>().tick = 42;
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 60,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.events[0].tick, 42);
    }

    // -----------------------------------------------------------------------
    // No duplicate events (ToleranceBreached marker)
    // -----------------------------------------------------------------------

    #[test]
    fn no_duplicate_event_on_consecutive_breach_ticks() {
        let mut world = setup_world();
        let entity = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 60,
                    threshold: 50,
                },
                ToleranceBreached, // Already marked — already breached
            ))
            .id();

        run_system(&mut world);

        // Still breached but marker was already present → no new event
        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(
            queue.is_empty(),
            "no duplicate event when already in breach state"
        );
        // Marker should still be present
        assert!(world.get::<ToleranceBreached>(entity).is_some());
    }

    // -----------------------------------------------------------------------
    // Breach resolution
    // -----------------------------------------------------------------------

    #[test]
    fn breach_marker_cleared_when_stress_drops_below_threshold() {
        let mut world = setup_world();
        let entity = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 30, // Dropped below threshold
                    threshold: 50,
                },
                ToleranceBreached, // Was breached
            ))
            .id();

        run_system(&mut world);

        assert!(
            world.get::<ToleranceBreached>(entity).is_none(),
            "marker should be removed when stress drops below threshold"
        );
        // No new breach event on resolution
        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(queue.is_empty(), "resolution should not emit a new event");
    }

    #[test]
    fn breach_event_emitted_again_after_recovery() {
        let mut world = setup_world();
        // Start: stress resolved (marker absent, stress below threshold)
        let entity = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 60, // Re-breached
                    threshold: 50,
                },
                // No ToleranceBreached — recovery had cleared it
            ))
            .id();

        run_system(&mut world);

        // Should emit new event after recovery
        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(
            queue.len(),
            1,
            "new breach event after recovery and re-breach"
        );
        assert!(world.get::<ToleranceBreached>(entity).is_some());
    }

    // -----------------------------------------------------------------------
    // Tier scoping
    // -----------------------------------------------------------------------

    #[test]
    fn background_npc_not_monitored() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            BackgroundSim, // Background tier — excluded
            ToleranceThreshold {
                current_stress: 100,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(
            queue.is_empty(),
            "Background-tier NPCs must not generate breach events"
        );
    }

    #[test]
    fn active_npc_without_tolerance_threshold_not_matched() {
        // Should not crash — query requires ToleranceThreshold, so entity is simply skipped
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            // No ToleranceThreshold component
        ));

        run_system(&mut world); // must not panic

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(queue.is_empty());
    }

    // -----------------------------------------------------------------------
    // Multiple NPCs
    // -----------------------------------------------------------------------

    #[test]
    fn multiple_npcs_breached_independently() {
        let mut world = setup_world();

        // NPC 1: will breach (stress >= threshold)
        let e1 = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 60,
                    threshold: 50,
                },
            ))
            .id();

        // NPC 2: fine (stress < threshold)
        let e2 = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 30,
                    threshold: 50,
                },
            ))
            .id();

        // NPC 3: will breach (different threshold — per-NPC, not hardcoded)
        let e3 = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 90,
                    threshold: 80,
                },
            ))
            .id();

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.len(), 2, "two NPCs should breach independently");

        let breached_entities: Vec<Entity> = queue.events.iter().map(|e| e.entity).collect();
        assert!(breached_entities.contains(&e1));
        assert!(!breached_entities.contains(&e2));
        assert!(breached_entities.contains(&e3));
    }

    #[test]
    fn breach_event_entity_field_matches_spawned_entity() {
        let mut world = setup_world();
        let entity = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 50,
                    threshold: 50,
                },
            ))
            .id();

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.events[0].entity, entity);
    }

    // -----------------------------------------------------------------------
    // Edge cases
    // -----------------------------------------------------------------------

    #[test]
    fn zero_threshold_with_zero_stress_breaches() {
        // 0 >= 0 → breach. Edge case: entity with threshold=0 is always breached.
        let mut world = setup_world();
        let entity = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 0,
                    threshold: 0,
                },
            ))
            .id();

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.len(), 1, "stress=0 >= threshold=0 must breach");
        assert!(world.get::<ToleranceBreached>(entity).is_some());
    }

    #[test]
    fn threshold_at_100_only_breaches_at_100() {
        let mut world = setup_world();
        world.spawn((
            Npc,
            ActiveSim,
            ToleranceThreshold {
                current_stress: 99,
                threshold: 100,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert!(queue.is_empty(), "stress=99 < threshold=100 should not breach");
    }

    #[test]
    fn mixed_active_and_background_npcs() {
        let mut world = setup_world();

        // Active NPC — should breach
        let active = world
            .spawn((
                Npc,
                ActiveSim,
                ToleranceThreshold {
                    current_stress: 60,
                    threshold: 50,
                },
            ))
            .id();

        // Background NPC — should NOT breach
        world.spawn((
            Npc,
            BackgroundSim,
            ToleranceThreshold {
                current_stress: 100,
                threshold: 50,
            },
        ));

        run_system(&mut world);

        let queue = world.resource::<ToleranceBreachEventQueue>();
        assert_eq!(queue.len(), 1);
        assert_eq!(queue.events[0].entity, active);
    }
}