import { extend as extend } from 'js-extend';

import PouchDB from "./constructor";
import inherits from 'inherits';
import collections from 'pouchdb-collections';
import { EventEmitter as EE } from 'events';
import hasLocalStorage from './deps/env/hasLocalStorage';

PouchDB.adapters = {};
PouchDB.preferredAdapters = [];

PouchDB.prefix = '_pouch_';

var eventEmitter = new EE();

function setUpEventEmitter(Pouch) {
  Object.keys(EE.prototype).forEach(function (key) {
    if (typeof EE.prototype[key] === 'function') {
      Pouch[key] = eventEmitter[key].bind(eventEmitter);
    }
  });

  // these are created in constructor.js, and allow us to notify each DB with
  // the same name that it was destroyed, via the constructor object
  var destructListeners = Pouch._destructionListeners = new collections.Map();
  Pouch.on('destroyed', function onConstructorDestroyed(name) {
    if (!destructListeners.has(name)) {
      return;
    }
    destructListeners.get(name).forEach(function (callback) {
      callback();
    });
    destructListeners.delete(name);
  });
}

setUpEventEmitter(PouchDB);

PouchDB.parseAdapter = function (name, opts) {
  var match = name.match(/([a-z\-]*):\/\/(.*)/);
  var adapter, adapterName;
  if (match) {
    // the http adapter expects the fully qualified name
    name = /http(s?)/.test(match[1]) ? match[1] + '://' + match[2] : match[2];
    adapter = match[1];
    /* istanbul ignore if */
    if (!PouchDB.adapters[adapter].valid()) {
      throw 'Invalid adapter';
    }
    return {name: name, adapter: match[1]};
  }

  // check for browsers that have been upgraded from websql-only to websql+idb
  var skipIdb = 'idb' in PouchDB.adapters && 'websql' in PouchDB.adapters &&
    hasLocalStorage() &&
    localStorage['_pouch__websqldb_' + PouchDB.prefix + name];


  if (opts.adapter) {
    adapterName = opts.adapter;
  } else if (typeof opts !== 'undefined' && opts.db) {
    adapterName = 'leveldb';
  } else { // automatically determine adapter
    for (var i = 0; i < PouchDB.preferredAdapters.length; ++i) {
      adapterName = PouchDB.preferredAdapters[i];
      if (adapterName in PouchDB.adapters) {
        /* istanbul ignore if */
        if (skipIdb && adapterName === 'idb') {
          // log it, because this can be confusing during development
          console.log('PouchDB is downgrading "' + name + '" to WebSQL to' +
            ' avoid data loss, because it was already opened with WebSQL.');
          continue; // keep using websql to avoid user data loss
        }
        break;
      }
    }
  }

  adapter = PouchDB.adapters[adapterName];

  // if adapter is invalid, then an error will be thrown later
  var usePrefix = (adapter && 'use_prefix' in adapter) ?
      adapter.use_prefix : true;

  return {
    name: usePrefix ? (PouchDB.prefix + name) : name,
    adapter: adapterName
  };
};

PouchDB.adapter = function (id, obj, addToPreferredAdapters) {
  if (obj.valid()) {
    PouchDB.adapters[id] = obj;
    if (addToPreferredAdapters) {
      PouchDB.preferredAdapters.push(id);
    }
  }
};

PouchDB.plugin = function (obj) {
  Object.keys(obj).forEach(function (id) {
    PouchDB.prototype[id] = obj[id];
  });

  return PouchDB;
};

PouchDB.defaults = function (defaultOpts) {
  function PouchAlt(name, opts, callback) {
    if (!(this instanceof PouchAlt)) {
      return new PouchAlt(name, opts, callback);
    }

    if (typeof opts === 'function' || typeof opts === 'undefined') {
      callback = opts;
      opts = {};
    }
    if (name && typeof name === 'object') {
      opts = name;
      name = undefined;
    }

    opts = extend({}, defaultOpts, opts);
    PouchDB.call(this, name, opts, callback);
  }

  inherits(PouchAlt, PouchDB);

  setUpEventEmitter(PouchAlt);

  PouchAlt.preferredAdapters = PouchDB.preferredAdapters.slice();
  Object.keys(PouchDB).forEach(function (key) {
    if (!(key in PouchAlt)) {
      PouchAlt[key] = PouchDB[key];
    }
  });

  return PouchAlt;
};

export default PouchDB;