import * as I from 'immutable';
import D from 'debug';
import without from 'lodash.without';

import {compose, EventEmitter} from '@avocado/core';
import {Resource} from '@avocado/resource';
import {Synchronized} from '@avocado/state';

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

const debug = D('@avocado:entity:traits');

function copyTraitProperties(from, to, instance) {
  do {
    Object.getOwnPropertyNames(from).forEach((property) => {
      // Nooope.
      switch (property) {
        case 'state':
          return;
      }
      // Make sure it's actually a property.
      let descriptor = Object.getOwnPropertyDescriptor(from, property);
      if (!descriptor.get && !descriptor.set) {
        return;
      }
      // Bind properties to trait instance.
      if (descriptor.get) {
        descriptor.get = descriptor.get.bind(instance);
      }
      if (descriptor.set) {
        descriptor.set = descriptor.set.bind(instance);
      }
      Object.defineProperty(to, property, descriptor);
    });
  } while (Object.prototype !== (from = Object.getPrototypeOf(from)));
}

function enumerateTraitProperties(prototype) {
  const keys = [];
  do {
    Object.getOwnPropertyNames(prototype).forEach((property) => {
      let descriptor = Object.getOwnPropertyDescriptor(prototype, property);
      if (!descriptor.get && !descriptor.set) {
        return;
      }
      keys.push(property);
    });
  } while (Object.prototype !== (prototype = Object.getPrototypeOf(prototype)));
  return keys;
}

const decorate = compose(
  EventEmitter,
  Synchronized,
);

export class Entity extends decorate(Resource) {

  constructor() {
    super();
    this._hooks = {};
    this.isDirty = true;
    this._traits = {};
    this.once('destroyed', () => {
      this.removeAllTraits();
    });
  }

  acceptPacket(packet) {
    for (const type in this._traits) {
      const instance = this._traits[type];
      instance.acceptPacket(packet);
    }
  }

  addTrait(type, json = {}) {
    if (this.is(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.allTraitTypes();
    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, params, state);
    // Proxy properties.
    copyTraitProperties(Trait.prototype, this, instance);
    // Let the Trait do its initialization.
    instance.initialize();
    // Attach listeners.
    const listeners = instance.memoizedListeners();
    for (const eventName in listeners) {
      this.on(eventName, listeners[eventName]);
    }
    // Proxy methods.
    const methods = instance.methods();
    for (const key in methods) {
      this[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.state = this._setInstanceState(this.state, type, instance);
    // Track trait.
    this._traits[type] = instance;
    this.emit('traitAdded', type, instance);
  }

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

  allTraitInstances() {
    return this._traits;
  }

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

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

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

  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;
  }

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

  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.state = this._setInstanceState(this.state, type, instance);
  }

  renderTick(elapsed) {
    for (const type in this._traits) {
      const instance = this._traits[type];
      instance.renderTick(elapsed);
    }
  }

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

  removeTrait(type) {
    if (!this.is(type)) {
      debug(`Tried to remove trait "${type}" when it doesn't exist!`);
      return;
    }
    // Destroy instance.
    const instance = this._traits[type];
    instance.destroy();
    // Remove methods, hooks, and properties.
    const methods = instance.methods();
    for (const key in methods) {
      delete this[key];
    }
    const hooks = instance.hooks();
    for (const key in hooks) {
      delete this._hooks[key];
    }
    const Trait = lookupTrait(type);
    const properties = enumerateTraitProperties(Trait.prototype);
    for (let i = 0; i < properties.length; ++i) {
      const property = properties[i];
      delete this[property];
    }
    // Remove all event listeners.
    const listeners = instance.memoizedListeners();
    for (const eventName in listeners) {
      this.off(eventName, listeners[eventName]);
    }
    // Remove state.
    this.state = this.state.delete(type);
    // Remove instance.
    delete this._traits[type];
    // Unloop.
    // instance.entity = undefined;
  }

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

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

  tick(elapsed) {
    for (const type in this._traits) {
      const instance = this._traits[type];
      instance.tick(elapsed);
    }
    if (AVOCADO_SERVER) {
      this.state = this.state.withMutations((state) => {
        for (const type in this._traits) {
          const instance = this._traits[type];
          if (!instance.isDirty) {
            continue;
          }
          instance.isDirty = false;
          this.isDirty = true;
          this._setInstanceState(state, type, instance);
        }
      });
    }
  }

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

}

export {EntityPacket} from './entity.packet';

export {EntityList, EntityListView} from './list';

export {EntityPacketSynchronizer} from './packet-synchronizer';

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

export {StateProperty, Trait} from './trait';