import * as I from 'immutable';
import mapValues from 'lodash.mapvalues';

import {compose} from '@avocado/core';
import {EventEmitter} from '@avocado/mixins';

import {create} from './index';

const decorate = compose(
  EventEmitter,
);

class EntityListBase {

  constructor() {
    this.entities_PRIVATE = {};
    this.state_PRIVATE = I.Map();
    this.uuidMap_PRIVATE = {};
  }

  *[Symbol.iterator]() {
    for (const uuid in this.entities_PRIVATE) {
      const entity = this.entities_PRIVATE[uuid];
      yield entity;
    }
  }

  acceptStateChange(change) {
    for (const uuid in change) {
      const localUuid = this.uuidMap_PRIVATE[uuid];
      const entity = this.entities_PRIVATE[localUuid];
      if (entity) {
        if (false === change[uuid]) {
          // Entity removed.
          this.removeEntity(entity);
        }
        else {
          entity.acceptStateChange(change[uuid]);
          this.state_PRIVATE = this.state_PRIVATE.set(localUuid, entity.state());
        }
      }
      else {
        // New entity. Create with change as traits.
        const newEntity = create().fromJSON({
          traits: change[uuid],
        });
        this.addEntity(newEntity);
        this.uuidMap_PRIVATE[uuid] = newEntity.instanceUuid;
      }
    }
  }

  addEntity(entity) {
    const uuid = entity.instanceUuid;
    this.entities_PRIVATE[uuid] = entity;
    this.state_PRIVATE = this.state_PRIVATE.set(uuid, entity.state());
    entity.on('destroyed', () => {
      this.removeEntity(entity);
    });
    this.emit('entityAdded', entity);
  }

  entity(uuid) {
    return this.entities_PRIVATE[uuid];
  }

  recomputeState() {
    for (const uuid in this.entities_PRIVATE) {
      const entity = this.entities_PRIVATE[uuid];
      this.state_PRIVATE = this.state_PRIVATE.set(uuid, entity.state());
    }
  }

  removeEntity(entity) {
    const uuid = entity.instanceUuid;
    delete this.entities_PRIVATE[uuid];
    this.state_PRIVATE = this.state_PRIVATE.delete(uuid);
    this.emit('entityRemoved', entity);
  }

  state() {
    return this.state_PRIVATE;
  }

  tick(elapsed) {
    for (const uuid in this.entities_PRIVATE) {
      const entity = this.entities_PRIVATE[uuid];
      if ('tick' in entity) {
        entity.tick(elapsed);
      }
    }
    this.recomputeState();
  }

}

export class EntityList extends decorate(EntityListBase) {}