settled-reach/server/src/npc/vision.rs

//! NPC vision system (#115, D-011).
//!
//! Active-tier NPCs use the same symmetric shadowcasting as the player.
//! Results stored in `NpcVisionState`; `NpcMemory` tracks last-known
//! positions and zone inferences ("saw you enter building → knows you're
//! inside").
//!
//! ## System ordering
//!
//! 1. `compute_npc_vision` — after movement/tier updates, before snapshot
//! 2. `emit_npc_vision_events` — after compute, before process_knowledge_events
//! 3. `degrade_npc_inferences` — once per game-minute (D-031)
//!
//! ## Performance
//!
//! 30–80 Active NPCs × symmetric shadowcast per tick. Confirmed within
//! D-026 Active tier budget by architecture review.

use std::collections::{BTreeMap, BTreeSet};

use bevy_ecs::prelude::*;
use serde::{Deserialize, Serialize};

use crate::knowledge::types::StableId;
use crate::knowledge::{
    EntityRegistry, KnowledgeEvent, KnowledgeEventQueue, KnowledgeEventType, KnowledgeGraph,
};
use crate::npc::Npc;
use crate::perception::shadowcast::compute_fov;
use crate::perception::vision_cone::{apply_vision_cone, Facing, VisionConeConfig};
use crate::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
use crate::simulation::spatial::{NaiveSpatialIndex, SpatialIndex};
use crate::simulation::tier::ActiveSim;
use crate::simulation::time::{SimulationTime, TICKS_PER_GAME_MINUTE};

/// NPC vision range in tiles (matches player forward range from VisionConeConfig).
pub const NPC_VISION_RANGE: i32 = 20;

/// Ticks before a zone inference degrades. 600 ticks = 60 game-minutes = 1 game-hour.
pub const INFERENCE_DEGRADE_TICKS: u64 = 600;

// ---------------------------------------------------------------------------
// Components
// ---------------------------------------------------------------------------

/// Current field-of-view results for an NPC.
/// Updated each tick for Active-tier NPCs. BTreeSet for determinism (D-010).
#[derive(Component, Debug, Clone, Default)]
pub struct NpcVisionState {
    /// StableIds of entities currently in this NPC's LOS.
    pub visible_entities: BTreeSet<StableId>,
    /// Whether the player character is currently visible.
    pub player_visible: bool,
}

/// Persistent memory of entities this NPC has seen.
/// Survives after entities leave LOS (D-011: "saw you enter building →
/// knows you're inside").
#[derive(Component, Debug, Clone, Default, Serialize, Deserialize)]
pub struct NpcMemory {
    /// Last known position + tick for entities this NPC has seen.
    /// Key: StableId of the observed entity.
    pub last_known: BTreeMap<StableId, LastKnownEntry>,
}

/// Record of last-known position for a single entity.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LastKnownEntry {
    /// Position where entity was last seen.
    pub position: TilePosition,
    /// Tick when the entity was last observed.
    pub observed_tick: u64,
    /// Zone inference: if entity was last seen before leaving LOS,
    /// the NPC infers they are still nearby.
    pub zone_inference: Option<ZoneInference>,
}

/// Inference that an entity is still near a position based on last observation.
/// Degrades after `degrades_at_tick`.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ZoneInference {
    /// The position where the entity was last seen.
    pub last_seen_position: TilePosition,
    /// Tick when the entity was seen at this position.
    pub observed_tick: u64,
    /// Tick at which this inference degrades (NPC stops assuming entity is here).
    pub degrades_at_tick: u64,
}

// ---------------------------------------------------------------------------
// Systems
// ---------------------------------------------------------------------------

/// Compute NPC field-of-view for all Active-tier NPCs.
///
/// For each NPC: run symmetric shadowcasting (same algorithm as player per D-011),
/// apply vision cone if the NPC has a `Facing` component, then check which entities
/// from the spatial index are at visible tiles.
pub fn compute_npc_vision(
    walkability: Option<Res<WalkabilityMap>>,
    registry: Res<EntityRegistry>,
    spatial_index: Res<NaiveSpatialIndex>,
    player_query: Query<Entity, With<PlayerCharacter>>,
    mut npc_query: Query<
        (Entity, &TilePosition, Option<&Facing>, &mut NpcVisionState),
        (With<Npc>, With<ActiveSim>),
    >,
    entity_positions: Query<&TilePosition>,
) {
    let Some(walkability) = walkability else {
        return;
    };
    let player_entity = player_query.iter().next();
    let player_stable_id = player_entity.and_then(|e| registry.to_stable(e));
    let config = VisionConeConfig::default();

    for (npc_entity, npc_pos, facing, mut vision_state) in npc_query.iter_mut() {
        let z = npc_pos.z;

        // Run symmetric shadowcasting — same algorithm as player (D-011, D-035)
        let fov = compute_fov(
            |x, y| !walkability.can_move_to(&TilePosition::new(x, y, z)),
            npc_pos.x,
            npc_pos.y,
            NPC_VISION_RANGE,
            z,
        );

        // Collect visible tile positions — apply vision cone if NPC has facing
        let visible_positions: BTreeSet<(i32, i32)> = if let Some(facing_comp) = facing {
            let cone_tiles = apply_vision_cone(&fov, npc_pos.x, npc_pos.y, facing_comp.0, &config);
            cone_tiles.into_iter().map(|(x, y, _)| (x, y)).collect()
        } else {
            // No facing → omnidirectional vision (full FOV)
            fov.visible_tiles().collect()
        };

        // Find entities at visible positions via spatial index
        let mut new_visible = BTreeSet::new();
        let mut player_vis = false;

        // Single-pass query: all entities within vision range including own tile
        let candidates = spatial_index.entities_within(npc_pos, NPC_VISION_RANGE as u32);

        for entity in candidates {
            if entity == npc_entity {
                continue;
            }
            let Ok(entity_pos) = entity_positions.get(entity) else {
                continue;
            };
            if entity_pos.z != z {
                continue;
            }
            if !visible_positions.contains(&(entity_pos.x, entity_pos.y)) {
                continue;
            }
            let Some(stable_id) = registry.to_stable(entity) else {
                continue;
            };

            new_visible.insert(stable_id);
            if Some(stable_id) == player_stable_id {
                player_vis = true;
            }
        }

        vision_state.visible_entities = new_visible;
        vision_state.player_visible = player_vis;
    }
}

/// Emit knowledge events when NPCs gain or lose sight of the player.
///
/// Mirrors the player's `emit_observation_events` pattern but scoped to
/// NPC→player tracking only. NPC-to-NPC vision is stored in `NpcVisionState`
/// for direct query by downstream systems (#244 awareness) without flooding
/// the knowledge event queue.
///
/// Also updates `NpcMemory` with last-known positions and zone inferences.
pub fn emit_npc_vision_events(
    time: Res<SimulationTime>,
    registry: Res<EntityRegistry>,
    mut event_queue: ResMut<KnowledgeEventQueue>,
    player_query: Query<(Entity, &TilePosition), With<PlayerCharacter>>,
    mut npc_query: Query<
        (
            Entity,
            &NpcVisionState,
            &mut NpcMemory,
            Option<&KnowledgeGraph>,
        ),
        (With<Npc>, With<ActiveSim>),
    >,
) {
    let Ok((player_entity, player_pos)) = player_query.single() else {
        return;
    };
    let Some(player_sid) = registry.to_stable(player_entity) else {
        return;
    };

    for (npc_entity, vision_state, mut memory, knowledge_graph) in npc_query.iter_mut() {
        if vision_state.player_visible {
            // Player is in LOS — update memory and emit DirectObservation
            memory.last_known.insert(
                player_sid,
                LastKnownEntry {
                    position: *player_pos,
                    observed_tick: time.tick,
                    zone_inference: None, // Active observation clears inference
                },
            );

            event_queue.push(KnowledgeEvent {
                observer: npc_entity,
                tick: time.tick,
                event_type: KnowledgeEventType::DirectObservation {
                    target: player_entity,
                    position: *player_pos,
                },
            });
        } else {
            // Player NOT in LOS — check if they WERE Direct (just left)
            let was_direct = knowledge_graph
                .and_then(|kg| {
                    kg.entity_knowledge(&player_sid)
                        .map(|k| k.confidence == crate::knowledge::KnowledgeConfidence::Direct)
                })
                .unwrap_or(false);

            if was_direct {
                // Player just left this NPC's LOS — emit LeftLOS
                event_queue.push(KnowledgeEvent {
                    observer: npc_entity,
                    tick: time.tick,
                    event_type: KnowledgeEventType::LeftLOS {
                        target: player_entity,
                    },
                });

                // Create zone inference — NPC remembers where they last saw the player
                if let Some(entry) = memory.last_known.get_mut(&player_sid) {
                    entry.zone_inference = Some(ZoneInference {
                        last_seen_position: entry.position,
                        observed_tick: entry.observed_tick,
                        degrades_at_tick: time.tick + INFERENCE_DEGRADE_TICKS,
                    });
                }
            }
        }
    }
}

/// Degrade stale zone inferences in NPC memory.
///
/// Runs once per game-minute (every 10 ticks per D-031). When a zone
/// inference passes its degradation tick, the inference is removed.
pub fn degrade_npc_inferences(
    time: Res<SimulationTime>,
    mut npc_query: Query<&mut NpcMemory, (With<Npc>, With<ActiveSim>)>,
) {
    if !time.tick.is_multiple_of(TICKS_PER_GAME_MINUTE) {
        return;
    }

    for mut memory in npc_query.iter_mut() {
        for entry in memory.last_known.values_mut() {
            if let Some(ref inference) = entry.zone_inference {
                if time.tick >= inference.degrades_at_tick {
                    entry.zone_inference = None;
                }
            }
        }
    }
}

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

#[cfg(test)]
mod tests {
    use super::*;
    use crate::knowledge::{EntityRegistry, KnowledgeGraph};
    use crate::perception::query::{ActivePerceptionMode, VisibilityGeometry};
    use bevy_ecs::world::World;

    fn setup_world(width: i32, height: i32) -> World {
        let mut world = World::new();
        world.insert_resource(SimulationTime::default());
        world.insert_resource(WalkabilityMap::new(width, height, 1));
        world.init_resource::<KnowledgeEventQueue>();
        world.init_resource::<EntityRegistry>();
        world.init_resource::<NaiveSpatialIndex>();
        world.init_resource::<VisibilityGeometry>();
        world.init_resource::<ActivePerceptionMode>();
        world
    }

    fn pos(x: i32, y: i32) -> TilePosition {
        TilePosition::new(x, y, 0)
    }

    // --- compute_npc_vision tests ---

    #[test]
    fn npc_sees_nearby_entity_in_open_field() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        // NPC at (16, 16), target at (16, 14) — 2 tiles away, clear LOS
        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        let npc_sid = registry.register(npc);
        spatial.update(npc, pos(16, 16));

        let target = world.spawn(pos(16, 14)).id();
        let target_sid = registry.register(target);
        spatial.update(target, pos(16, 14));

        // Player entity (required for player_stable_id lookup)
        let player = world.spawn((PlayerCharacter, pos(0, 0))).id();
        registry.register(player);

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            vision.visible_entities.contains(&target_sid),
            "NPC should see nearby entity in open field"
        );
        assert!(!vision.player_visible, "player is far away");
        let _ = npc_sid; // registered for completeness
    }

    #[test]
    fn npc_cannot_see_through_wall() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        // Target behind a wall
        let target = world.spawn(pos(16, 14)).id();
        let target_sid = registry.register(target);
        spatial.update(target, pos(16, 14));

        // Wall between NPC and target
        let mut walkability = world.resource_mut::<WalkabilityMap>();
        walkability.set_walkable(&pos(16, 15), false);
        drop(walkability);

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            !vision.visible_entities.contains(&target_sid),
            "NPC should not see entity behind wall"
        );
    }

    #[test]
    fn npc_detects_player_visible() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        let player = world.spawn((PlayerCharacter, pos(16, 14))).id();
        registry.register(player);
        spatial.update(player, pos(16, 14));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(vision.player_visible, "NPC should detect player in LOS");
    }

    #[test]
    fn npc_does_not_see_entity_on_different_z_level() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        // Target at same x/y but different z
        let target = world.spawn(TilePosition::new(16, 14, 1)).id();
        let target_sid = registry.register(target);
        spatial.update(target, TilePosition::new(16, 14, 1));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            !vision.visible_entities.contains(&target_sid),
            "NPC should not see entity on different z-level"
        );
    }

    #[test]
    fn npc_does_not_see_entity_beyond_range() {
        let mut world = setup_world(64, 64);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        // Target beyond NPC_VISION_RANGE (20 tiles)
        let target = world.spawn(pos(16 + NPC_VISION_RANGE + 5, 16)).id();
        let target_sid = registry.register(target);
        spatial.update(target, pos(16 + NPC_VISION_RANGE + 5, 16));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            !vision.visible_entities.contains(&target_sid),
            "NPC should not see entity beyond vision range"
        );
    }

    #[test]
    fn npc_does_not_see_self() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        let npc_sid = registry.register(npc);
        spatial.update(npc, pos(16, 16));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            !vision.visible_entities.contains(&npc_sid),
            "NPC should not include itself in visible entities"
        );
    }

    #[test]
    fn npc_sees_non_npc_entity_on_same_tile() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        // NPC at (16, 16)
        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), NpcVisionState::default()))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        // Non-NPC entity on the same tile (e.g. dropped item)
        let item = world.spawn(pos(16, 16)).id();
        let item_sid = registry.register(item);
        spatial.update(item, pos(16, 16));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            vision.visible_entities.contains(&item_sid),
            "NPC should see non-NPC entity sharing its tile"
        );
    }

    #[test]
    fn background_npc_not_processed() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);
        let mut spatial = NaiveSpatialIndex::new();

        // Background NPC — should NOT have its vision computed
        let npc = world
            .spawn((
                Npc,
                crate::simulation::tier::BackgroundSim,
                pos(16, 16),
                NpcVisionState::default(),
            ))
            .id();
        registry.register(npc);
        spatial.update(npc, pos(16, 16));

        let target = world.spawn(pos(16, 14)).id();
        let target_sid = registry.register(target);
        spatial.update(target, pos(16, 14));

        world.insert_resource(registry);
        world.insert_resource(spatial);

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

        let vision = world.get::<NpcVisionState>(npc).unwrap();
        assert!(
            vision.visible_entities.is_empty(),
            "Background NPC should not have vision computed"
        );
        let _ = target_sid;
    }

    // --- emit_npc_vision_events tests ---

    #[test]
    fn npc_seeing_player_emits_direct_observation() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);

        let player = world.spawn((PlayerCharacter, pos(16, 14))).id();
        let player_sid = registry.register(player);

        let mut vision = NpcVisionState::default();
        vision.visible_entities.insert(player_sid);
        vision.player_visible = true;

        let npc = world
            .spawn((
                Npc,
                ActiveSim,
                pos(16, 16),
                vision,
                NpcMemory::default(),
                KnowledgeGraph::new(),
            ))
            .id();
        registry.register(npc);

        world.insert_resource(registry);

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

        let queue = world.resource::<KnowledgeEventQueue>();
        assert!(
            !queue.is_empty(),
            "should emit DirectObservation for player"
        );

        let event = &queue.events[0];
        assert_eq!(event.observer, npc);
        assert!(matches!(
            event.event_type,
            KnowledgeEventType::DirectObservation { target, .. } if target == player
        ));
    }

    #[test]
    fn npc_losing_player_emits_left_los() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);

        let player = world.spawn((PlayerCharacter, pos(16, 14))).id();
        let player_sid = registry.register(player);

        // NPC that had Direct knowledge of player (player was just visible)
        let mut kg = KnowledgeGraph::new();
        kg.observe_entity(player_sid, pos(16, 14), 50);

        // Memory with last known position
        let mut memory = NpcMemory::default();
        memory.last_known.insert(
            player_sid,
            LastKnownEntry {
                position: pos(16, 14),
                observed_tick: 50,
                zone_inference: None,
            },
        );

        // Vision state: player NOT visible now
        let vision = NpcVisionState::default();

        let npc = world
            .spawn((Npc, ActiveSim, pos(16, 16), vision, memory, kg))
            .id();
        registry.register(npc);

        world.insert_resource(registry);

        let mut time = SimulationTime::default();
        time.tick = 60;
        world.insert_resource(time);

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

        let queue = world.resource::<KnowledgeEventQueue>();
        let has_left_los = queue.events.iter().any(|e| {
            matches!(
                e.event_type,
                KnowledgeEventType::LeftLOS { target } if target == player
            )
        });
        assert!(
            has_left_los,
            "should emit LeftLOS when player leaves NPC LOS"
        );

        // Check zone inference was created
        let npc_memory = world.get::<NpcMemory>(npc).unwrap();
        let entry = npc_memory.last_known.get(&player_sid).unwrap();
        assert!(
            entry.zone_inference.is_some(),
            "zone inference should be created when player leaves LOS"
        );
        assert_eq!(
            entry.zone_inference.as_ref().unwrap().degrades_at_tick,
            60 + INFERENCE_DEGRADE_TICKS
        );
    }

    #[test]
    fn npc_updates_memory_on_player_observation() {
        let mut world = setup_world(32, 32);
        let mut registry = EntityRegistry::new(0);

        let player = world.spawn((PlayerCharacter, pos(10, 10))).id();
        let player_sid = registry.register(player);

        let mut vision = NpcVisionState::default();
        vision.visible_entities.insert(player_sid);
        vision.player_visible = true;

        let npc = world
            .spawn((
                Npc,
                ActiveSim,
                pos(16, 16),
                vision,
                NpcMemory::default(),
                KnowledgeGraph::new(),
            ))
            .id();
        registry.register(npc);

        let mut time = SimulationTime::default();
        time.tick = 100;
        world.insert_resource(time);
        world.insert_resource(registry);

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

        let memory = world.get::<NpcMemory>(npc).unwrap();
        let entry = memory.last_known.get(&player_sid).unwrap();
        assert_eq!(entry.position, pos(10, 10));
        assert_eq!(entry.observed_tick, 100);
        assert!(
            entry.zone_inference.is_none(),
            "active observation = no inference"
        );
    }

    // --- degrade_npc_inferences tests ---

    #[test]
    fn inference_degrades_after_threshold() {
        let mut world = setup_world(32, 32);

        let player_sid = StableId(1);
        let mut memory = NpcMemory::default();
        memory.last_known.insert(
            player_sid,
            LastKnownEntry {
                position: pos(10, 10),
                observed_tick: 50,
                zone_inference: Some(ZoneInference {
                    last_seen_position: pos(10, 10),
                    observed_tick: 50,
                    degrades_at_tick: 100,
                }),
            },
        );

        let npc = world.spawn((Npc, ActiveSim, memory)).id();

        // Tick 90 (before degradation, on minute boundary)
        let mut time = SimulationTime::default();
        time.tick = 90;
        world.insert_resource(time);

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

        let mem = world.get::<NpcMemory>(npc).unwrap();
        assert!(
            mem.last_known[&player_sid].zone_inference.is_some(),
            "inference should survive before degradation tick"
        );

        // Tick 100 (degradation tick, on minute boundary)
        let mut time = SimulationTime::default();
        time.tick = 100;
        world.insert_resource(time);

        let mut schedule2 = bevy_ecs::schedule::Schedule::default();
        schedule2.add_systems(degrade_npc_inferences);
        schedule2.run(&mut world);

        let mem = world.get::<NpcMemory>(npc).unwrap();
        assert!(
            mem.last_known[&player_sid].zone_inference.is_none(),
            "inference should be removed at degradation tick"
        );
    }

    #[test]
    fn inference_degradation_skips_non_minute_ticks() {
        let mut world = setup_world(32, 32);

        let player_sid = StableId(1);
        let mut memory = NpcMemory::default();
        memory.last_known.insert(
            player_sid,
            LastKnownEntry {
                position: pos(10, 10),
                observed_tick: 50,
                zone_inference: Some(ZoneInference {
                    last_seen_position: pos(10, 10),
                    observed_tick: 50,
                    degrades_at_tick: 55, // already past
                }),
            },
        );

        let npc = world.spawn((Npc, ActiveSim, memory)).id();

        // Tick 57 — past degradation but NOT a minute boundary
        let mut time = SimulationTime::default();
        time.tick = 57;
        world.insert_resource(time);

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

        let mem = world.get::<NpcMemory>(npc).unwrap();
        assert!(
            mem.last_known[&player_sid].zone_inference.is_some(),
            "degradation should not run on non-minute ticks"
        );
    }

    #[test]
    fn no_events_when_no_player_entity() {
        let mut world = setup_world(32, 32);
        let registry = EntityRegistry::new(0);

        let vision = NpcVisionState::default();
        world.spawn((
            Npc,
            ActiveSim,
            pos(16, 16),
            vision,
            NpcMemory::default(),
            KnowledgeGraph::new(),
        ));

        world.insert_resource(registry);

        let mut schedule = bevy_ecs::schedule::Schedule::default();
        schedule.add_systems(emit_npc_vision_events);
        schedule.run(&mut world); // should not panic

        let queue = world.resource::<KnowledgeEventQueue>();
        assert!(queue.is_empty(), "no events when no player entity exists");
    }
}