import { System } from "../System";
import { type ECSWorld } from "../World";
import { type ComponentType } from "../components";
import { type EntityId } from "../../../core/types";
import { applyStatusEffect } from "./StatusEffectSystem";

/**
 * Processes trigger entities when other entities step on them.
 * Handles traps (damage), status effects, and one-shot triggers.
 * 
 * @example
 * registry.register(new TriggerSystem());
 * 
 * // Create a spike trap
 * world.addComponent(trapId, "trigger", {
 *   onEnter: true,
 *   damage: 15
 * });
 */
export class TriggerSystem extends System {
  readonly name = "Trigger";
  readonly requiredComponents: readonly ComponentType[] = ["trigger", "position"];
  readonly priority = 5; // Run before status effects

  /**
   * Track which entities are currently on which triggers.
   * Used to detect enter/exit events.
   */
  private entityPositions: Map<EntityId, { x: number; y: number }> = new Map();

  update(entities: EntityId[], world: ECSWorld, _dt?: number): void {
    // Get all entities with positions (potential activators)
    const allWithPosition = world.getEntitiesWith("position");
    
    for (const triggerId of entities) {
      const trigger = world.getComponent(triggerId, "trigger");
      const triggerPos = world.getComponent(triggerId, "position");

      if (!trigger || !triggerPos) continue;
      if (trigger.triggered && trigger.oneShot) continue; // Already triggered one-shot

      // Check for entities at this trigger's position
      for (const entityId of allWithPosition) {
        if (entityId === triggerId) continue; // Skip self

        const entityPos = world.getComponent(entityId, "position");
        if (!entityPos) continue;

        const isOnTrigger = entityPos.x === triggerPos.x && entityPos.y === triggerPos.y;
        const wasOnTrigger = this.wasEntityOnTrigger(entityId, triggerPos);

        // Handle enter
        if (trigger.onEnter && isOnTrigger && !wasOnTrigger) {
          this.activateTrigger(triggerId, entityId, trigger, world);
        }

        // Handle exit
        if (trigger.onExit && !isOnTrigger && wasOnTrigger) {
          this.eventBus?.emit({
            type: "trigger_activated",
            triggerId,
            activatorId: entityId
          });
        }
      }
    }

    // Update entity positions for next frame
    this.updateEntityPositions(allWithPosition, world);
  }

  /**
   * Activate a trigger on an entity.
   */
  private activateTrigger(
    triggerId: EntityId,
    activatorId: EntityId,
    trigger: { 
      damage?: number; 
      effect?: string; 
      effectDuration?: number; 
      oneShot?: boolean; 
      triggered?: boolean;
    },
    world: ECSWorld
  ): void {
    // Emit trigger event
    this.eventBus?.emit({
      type: "trigger_activated",
      triggerId,
      activatorId
    });

    // Apply damage if trap
    if (trigger.damage && trigger.damage > 0) {
      const stats = world.getComponent(activatorId, "stats");
      if (stats) {
        stats.hp = Math.max(0, stats.hp - trigger.damage);
        
        this.eventBus?.emit({
          type: "damage",
          entityId: activatorId,
          amount: trigger.damage,
          source: triggerId
        });
      }
    }

    // Apply status effect if specified
    if (trigger.effect) {
      applyStatusEffect(world, activatorId, {
        type: trigger.effect,
        duration: trigger.effectDuration ?? 3,
        source: triggerId
      });

      this.eventBus?.emit({
        type: "status_applied",
        entityId: activatorId,
        status: trigger.effect,
        duration: trigger.effectDuration ?? 3
      });
    }

    // Mark as triggered for one-shot triggers and update sprite
    if (trigger.oneShot) {
      trigger.triggered = true;
      
      // Change sprite to triggered appearance (dungeon sprite 23)
      const sprite = world.getComponent(triggerId, "sprite");
      if (sprite) {
        sprite.index = 23; // Triggered/spent trap appearance
      }
    }
  }

  /**
   * Check if an entity was previously on a trigger position.
   */
  private wasEntityOnTrigger(entityId: EntityId, triggerPos: { x: number; y: number }): boolean {
    const lastPos = this.entityPositions.get(entityId);
    if (!lastPos) return false;
    return lastPos.x === triggerPos.x && lastPos.y === triggerPos.y;
  }

  /**
   * Update cached entity positions for next frame comparison.
   */
  private updateEntityPositions(entities: EntityId[], world: ECSWorld): void {
    this.entityPositions.clear();
    for (const entityId of entities) {
      const pos = world.getComponent(entityId, "position");
      if (pos) {
        this.entityPositions.set(entityId, { x: pos.x, y: pos.y });
      }
    }
  }

  /**
   * Called when the system is registered - initialize position tracking.
   */
  onRegister(world: ECSWorld): void {
    const allWithPosition = world.getEntitiesWith("position");
    this.updateEntityPositions(allWithPosition, world);
  }
}