// Simulation tier system
// Implements D-026: Active/Background/State-saved/Ungenerated tiers
// Timestamp-based LRU eviction for simulation space management

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

// --- Zero-sized marker components (D-026) ---
// Tag-based tier identification. Systems query With<ActiveSim> to scope work
// to nearby NPCs only, avoiding full-world iteration every tick.

/// Marker: entity is in the Active simulation tier.
/// Full behavior systems (movement, perception, dialogue, monologue) run for
/// entities with this tag at 10–20 ticks/sec.
#[derive(Component, Debug, Clone, Copy, Default)]
pub struct ActiveSim;

/// Marker: entity is in the Background simulation tier.
/// Lightweight schedule-keeping only — no full perception or dialogue.
#[derive(Component, Debug, Clone, Copy, Default)]
pub struct BackgroundSim;

/// Marker: entity is in the State-saved tier.
/// ECS components preserved but no systems run. Re-promoted to Background
/// or Active when player approaches.
#[derive(Component, Debug, Clone, Copy, Default)]
pub struct StateSaved;

/// Plugin registering the tier marker components and associated resources.
/// Systems that filter by tier (With<ActiveSim>, etc.) require these markers
/// to exist in the type registry. Future: tier transition systems live here.
pub struct TierPlugin;

impl Plugin for TierPlugin {
    fn build(&self, _app: &mut App) {
        // Marker components are zero-sized — no resources to initialize.
        // Tier transition systems will be added here in ticket #99.
        tracing::debug!("TierPlugin initialized");
    }
}

#[derive(Component, Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum SimulationTier {
    Active,
    Background,
    StateSaved,
    Ungenerated,
}

#[derive(Component, Debug, Clone)]
pub struct LastInteraction {
    pub tick: u64,
}

#[derive(Component, Debug, Clone)]
pub struct ScopeTag {
    pub tags: Vec<ScopeKind>,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum ScopeKind {
    Neighborhood,
    ActiveQuest,
    Colleague,
    KnownContact,
}

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

    // --- SimulationTier enum tests ---

    #[test]
    fn tier_can_be_added_and_queried() {
        let mut world = World::new();
        let entity = world.spawn(SimulationTier::Active).id();
        assert_eq!(
            *world.get::<SimulationTier>(entity).unwrap(),
            SimulationTier::Active
        );
    }

    #[test]
    fn tier_can_transition() {
        let mut world = World::new();
        let entity = world.spawn(SimulationTier::Active).id();
        world.entity_mut(entity).insert(SimulationTier::Background);
        assert_eq!(
            *world.get::<SimulationTier>(entity).unwrap(),
            SimulationTier::Background
        );
    }

    #[test]
    fn all_tier_variants_are_distinct() {
        assert_ne!(SimulationTier::Active, SimulationTier::Background);
        assert_ne!(SimulationTier::Background, SimulationTier::StateSaved);
        assert_ne!(SimulationTier::StateSaved, SimulationTier::Ungenerated);
        assert_ne!(SimulationTier::Active, SimulationTier::Ungenerated);
    }

    // --- Marker component query correctness (D-026, #94) ---
    // These tests verify that With<ActiveSim> / With<BackgroundSim> / With<StateSaved>
    // filter correctly — the core guarantee that behavior systems only run for the
    // intended tier.

    #[test]
    fn with_active_sim_query_excludes_background_entities() {
        let mut world = World::new();
        let active = world.spawn(ActiveSim).id();
        let _background = world.spawn(BackgroundSim).id();
        let _state_saved = world.spawn(StateSaved).id();

        let mut query = world.query_filtered::<bevy_ecs::entity::Entity, With<ActiveSim>>();
        let results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();

        assert_eq!(results.len(), 1, "only one ActiveSim entity expected");
        assert_eq!(results[0], active);
    }

    #[test]
    fn with_background_sim_query_excludes_active_entities() {
        let mut world = World::new();
        let _active = world.spawn(ActiveSim).id();
        let background = world.spawn(BackgroundSim).id();
        let _state_saved = world.spawn(StateSaved).id();

        let mut query =
            world.query_filtered::<bevy_ecs::entity::Entity, With<BackgroundSim>>();
        let results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();

        assert_eq!(results.len(), 1, "only one BackgroundSim entity expected");
        assert_eq!(results[0], background);
    }

    #[test]
    fn with_state_saved_query_excludes_active_and_background() {
        let mut world = World::new();
        let _active = world.spawn(ActiveSim).id();
        let _background = world.spawn(BackgroundSim).id();
        let state_saved = world.spawn(StateSaved).id();

        let mut query =
            world.query_filtered::<bevy_ecs::entity::Entity, With<StateSaved>>();
        let results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();

        assert_eq!(results.len(), 1, "only one StateSaved entity expected");
        assert_eq!(results[0], state_saved);
    }

    #[test]
    fn multiple_active_sim_entities_all_returned() {
        let mut world = World::new();
        let a = world.spawn(ActiveSim).id();
        let b = world.spawn(ActiveSim).id();
        let _c = world.spawn(BackgroundSim).id();

        let mut query = world.query_filtered::<bevy_ecs::entity::Entity, With<ActiveSim>>();
        let mut results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();
        results.sort(); // deterministic comparison

        assert_eq!(results.len(), 2);
        assert!(results.contains(&a));
        assert!(results.contains(&b));
    }

    #[test]
    fn entity_without_tier_marker_not_returned_by_active_query() {
        let mut world = World::new();
        let _bare = world.spawn_empty().id();
        let active = world.spawn(ActiveSim).id();

        let mut query = world.query_filtered::<bevy_ecs::entity::Entity, With<ActiveSim>>();
        let results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();

        assert_eq!(results.len(), 1);
        assert_eq!(results[0], active);
    }

    // --- Tier transition tests (#99) ---

    #[test]
    fn promote_state_saved_to_active() {
        let mut world = World::new();
        let entity = world.spawn(StateSaved).id();

        // Transition: StateSaved → ActiveSim
        world
            .entity_mut(entity)
            .remove::<StateSaved>()
            .insert(ActiveSim);

        assert!(world.get::<ActiveSim>(entity).is_some(), "ActiveSim added");
        assert!(
            world.get::<StateSaved>(entity).is_none(),
            "StateSaved removed"
        );

        // Must appear in ActiveSim query after promotion
        let mut query = world.query_filtered::<bevy_ecs::entity::Entity, With<ActiveSim>>();
        let results: Vec<bevy_ecs::entity::Entity> = query.iter(&world).collect();
        assert_eq!(results.len(), 1);
        assert_eq!(results[0], entity);
    }

    #[test]
    fn demote_active_to_background() {
        let mut world = World::new();
        let entity = world.spawn(ActiveSim).id();

        // Transition: ActiveSim → BackgroundSim
        world
            .entity_mut(entity)
            .remove::<ActiveSim>()
            .insert(BackgroundSim);

        assert!(
            world.get::<BackgroundSim>(entity).is_some(),
            "BackgroundSim added"
        );
        assert!(world.get::<ActiveSim>(entity).is_none(), "ActiveSim removed");

        // Must NOT appear in ActiveSim query after demotion
        let mut active_query =
            world.query_filtered::<bevy_ecs::entity::Entity, With<ActiveSim>>();
        assert_eq!(
            active_query.iter(&world).count(),
            0,
            "demoted entity not in ActiveSim query"
        );
    }

    #[test]
    fn demote_active_to_state_saved() {
        let mut world = World::new();
        let entity = world.spawn(ActiveSim).id();

        world
            .entity_mut(entity)
            .remove::<ActiveSim>()
            .insert(StateSaved);

        assert!(world.get::<StateSaved>(entity).is_some());
        assert!(world.get::<ActiveSim>(entity).is_none());
    }

    // --- LastInteraction and ScopeTag ---

    #[test]
    fn last_interaction_records_tick() {
        let mut world = World::new();
        let entity = world.spawn(LastInteraction { tick: 42 }).id();

        let interaction = world.get::<LastInteraction>(entity).unwrap();
        assert_eq!(interaction.tick, 42);
    }

    #[test]
    fn last_interaction_tick_can_be_updated() {
        let mut world = World::new();
        let entity = world.spawn(LastInteraction { tick: 1 }).id();

        world.entity_mut(entity).insert(LastInteraction { tick: 100 });

        let interaction = world.get::<LastInteraction>(entity).unwrap();
        assert_eq!(interaction.tick, 100);
    }

    #[test]
    fn scope_tag_neighborhood_kind() {
        let mut world = World::new();
        let entity = world
            .spawn(ScopeTag {
                tags: vec![ScopeKind::Neighborhood],
            })
            .id();

        let tag = world.get::<ScopeTag>(entity).unwrap();
        assert!(tag.tags.contains(&ScopeKind::Neighborhood));
        assert!(!tag.tags.contains(&ScopeKind::ActiveQuest));
    }

    #[test]
    fn scope_tag_multiple_kinds() {
        let entity = ScopeTag {
            tags: vec![
                ScopeKind::Neighborhood,
                ScopeKind::Colleague,
                ScopeKind::KnownContact,
            ],
        };
        assert_eq!(entity.tags.len(), 3);
        assert!(entity.tags.contains(&ScopeKind::Colleague));
        assert!(entity.tags.contains(&ScopeKind::KnownContact));
        assert!(!entity.tags.contains(&ScopeKind::ActiveQuest));
    }

    // --- TierPlugin smoke test ---

    #[test]
    fn tier_plugin_builds_without_panic() {
        let mut app = bevy_app::App::new();
        app.add_plugins(TierPlugin);
        // Just verifying it doesn't panic on build
    }
}