const debug = require('debug')('@avocado/entity:traits');
import without from 'lodash.without';
import * as I from 'immutable';

import {Resource} from '@avocado/resource';
import {Synchronized} from '@avocado/state';

import {hasTrait, lookupTrait, registerTrait} from './trait-registry';

function enumerateProperties(prototype) {
  const result = {};
  do {
    Object.getOwnPropertyNames(prototype).forEach((property) => {
      const descriptor = Object.getOwnPropertyDescriptor(prototype, property);
      if (typeof descriptor.get === 'function') {
        result[property] = result[property] || {};
        result[property].get = true;
      }
      if (typeof descriptor.set === 'function') {
        result[property] = result[property] || {};
        result[property].set = true;
      }
    });
  } while (Object.prototype !== (prototype = Object.getPrototypeOf(prototype)));
  return result;
}

export class Traits extends Synchronized {

  constructor(entity) {
    super();
    this._methods = {};
    this._entity = entity;
    this._hooks = {};
    this._properties = {};
    this._traits = {};
    entity.once('destroyed', () => {
      this.removeAllTraits();
    });
  }

  allInstances() {
    return this._traits;
  }

  allTypes() {
    return Object.keys(this._traits);
  }

  addTrait(type, json = {}) {
    if (this.hasTrait(type)) {
      debug(`Tried to add trait "${type}" when it already exists!`);
      return;
    }
    if (!hasTrait(type)) {
      debug(`Tried to add trait "${type}" which isn't registered!`);
      return;
    }
    const Trait = lookupTrait(type);
    // Ensure dependencies.
    const dependencies = Trait.dependencies();
    const allTypes = this.allTypes();
    const lacking = without(dependencies, ...allTypes);
    if (lacking.length > 0) {
      debug(
        `Tried to add trait "${type}" but lack one or more dependents: "${
          lacking.join('", "')
        }"!`
      );
      return;
    }
    // Instantiate.
    const {params, state} = json;
    const instance = new Trait(this._entity, params, state);
    // Proxy properties.
    const properties = enumerateProperties(Trait.prototype);
    for (const key in properties) {
      properties[key].instance = instance;
      this._properties[key] = properties[key];
    }
    // Let the Trait do its initialization.
    instance.initialize();
    // Attach listeners.
    const listeners = instance.listeners();
    for (const eventName in listeners) {
      this._entity.on(
        `${eventName}.trait-${type}`,
        listeners[eventName]
      );
    }
    // Proxy methods.
    const methods = instance.methods();
    for (const key in methods) {
      this._methods[key] = methods[key];
    }
    // Register hook listeners.
    const hooks = instance.hooks();
    for (const key in hooks) {
      this._hooks[key] = this._hooks[key] || [];
      this._hooks[key].push({
        fn: hooks[key],
        type: Trait.type(),
      });
    }
    // Add state.
    this._setInstanceState(type, instance);
    // Track trait.
    this._traits[type] = instance;
    this._entity.emit('traitAdded', type, instance);
  }

  addTraits(traits) {
    const allTypes = this.allTypes();
    for (const type in traits) {
      this.addTrait(type, traits[type]);
    }
  }

  fromJSON(json) {
    this.addTraits(json);
    return this;
  }

  getProperty(property) {
    if (property in this._methods) {
      return this._methods[property];
    }
    if (property in this._properties) {
      const instance = this._properties[property].instance;
      if (!this._properties[property].get) {
        const type = instance.constructor.type();
        throw new ReferenceError(
          `Property '${property}' from Trait '${type}' has no getter`
        );
      }
      return instance[property];
    }
  }

  hasProperty(property) {
    if (property in this._methods) {
      return true;
    }
    if (property in this._properties) {
      return true;
    }
    return false;
  }

  hasTrait(type) {
    return type in this._traits;
  }

  hydrate() {
    const promises = [];
    for (const type in this._traits) {
      const instance = this._traits[type];
      promises.push(instance.hydrate());
    }
    return Promise.all(promises);
  }

  instance(type) {
    return this._traits[type];
  }

  invokeHook(hook, ...args) {
    const results = {};
    if (!(hook in this._hooks)) {
      return results;
    }
    for (const {fn, type} of this._hooks[hook]) {
      results[type] = fn(...args);
    }
    return results;
  }

  invokeHookFlat(hook, ...args) {
    const invokeResults = this.invokeHook(hook, ...args);
    const results = [];
    for (const type in invokeResults) {
      results.push(invokeResults[type]);
    }
    return results;
  }

  patchStateStep(type, step) {
    let instance = this._traits[type];
    // New trait requested?
    if (!this._traits[type]) {
      // Doesn't exist?
      if (!hasTrait(type)) {
        return;
      }
      this.addTrait(type, step.value);
      instance = this._traits[type];
    }
    else {
      // Accept state.
      instance.patchState([step]);
    }
    this._setInstanceState(type, instance);
  }

  removeAllTraits() {
    const types = this.allTypes();
    this.removeTraits(types);
  }

  removeTrait(type) {
    if (!this.hasTrait(type)) {
      debug(`Tried to remove trait "${type}" when it doesn't exist!`);
      return;
    }

    const instance = this._traits[type];
    instance.destroy();

    const methods = instance.methods();
    for (const key in methods) {
      delete this._methods[key];
    }

    const hooks = instance.hooks();
    for (const key in hooks) {
      delete this._hooks[key];
    }

    const Trait = lookupTrait(type);
    const properties = enumerateProperties(Trait.prototype);
    for (const key in properties) {
      delete this._properties[key];
    }

    this._entity.off(`.trait-${type}`);

    this.state = this.state.delete(type);
    delete this._traits[type];
  }

  removeTraits(types) {
    types.forEach((type) => this.removeTrait(type));
  }

  _setInstanceState(type, instance) {
    const state = this.state;
    let map = state.has(type) ? state.get(type) : I.Map();
    map = map.set('state', instance.state);
    map = map.set('params', instance.params);
    this.state = this.state.set(type, map);
  }

  setProperty(property, value, receiver) {
    if (property in this._properties) {
      const instance = this._properties[property].instance;
      const type = instance.constructor.type();
      if (!this._properties[property].set) {
        throw new ReferenceError(
          `Property '${property}' from Trait '${type}' has no setter`
        );
      }
      instance[property] = value;
      this._setInstanceState(type, instance);
      return true;
    }
    return false;
  }

  toJSON() {
    const json = {};
    for (const type in this._traits) {
      json[type] = this._traits[type].toJSON();
    }
    return json;
  }

}