/**
 * Lightweight EventBus for pub/sub communication between systems
 */
export const Events = {
  // Combat Events
  DAMAGE_DEALT: 'combat:damage_dealt',
  ENTITY_DIED: 'combat:entity_died',

  // Evolution Events
  EVOLVED: 'evolution:evolved',
  MUTATION_GAINED: 'evolution:mutation_gained',

  // Leveling Events
  EXP_GAINED: 'stats:exp_gained',
  LEVEL_UP: 'stats:level_up',

  // Skill Events
  SKILL_LEARNED: 'skills:learned',
  SKILL_COOLDOWN_STARTED: 'skills:cooldown_started'
};

export class EventBus {
  constructor() {
    this.listeners = new Map();
  }

  /**
     * Subscribe to an event
     */
  on(event, callback) {
    if (!this.listeners.has(event)) {
      this.listeners.set(event, []);
    }
    this.listeners.get(event).push(callback);
    return () => this.off(event, callback);
  }

  /**
     * Unsubscribe from an event
     */
  off(event, callback) {
    if (!this.listeners.has(event)) return;
    const callbacks = this.listeners.get(event);
    const index = callbacks.indexOf(callback);
    if (index > -1) {
      callbacks.splice(index, 1);
    }
  }

  /**
     * Emit an event
     */
  emit(event, data) {
    if (!this.listeners.has(event)) return;
    this.listeners.get(event).forEach(callback => callback(data));
  }
}