define(function(require) {
    'use strict';

    var config = require('js/app-config').config;


    /**
     * Update handler for transition database version 3 -> 4
     *
     * In database version 4, we need to add a "provider" flag to the
     * indexeddb. only gmail was allowed as a mail service provider before,
     * so let's add this...
     */
    function update(options, callback) {
        var VERSION_DB_TYPE = 'dbVersion',
            EMAIL_ADDR_DB_KEY = 'emailaddress',
            USERNAME_DB_KEY = 'username',
            PROVIDER_DB_KEY = 'provider',
            IMAP_DB_KEY = 'imap',
            SMTP_DB_KEY = 'smtp',
            REALNAME_DB_KEY = 'realname',
            POST_UPDATE_DB_VERSION = 4;


        var imap = config.gmail.imap,
            smtp = config.gmail.smtp;

        // load the email address (if existing)
        loadFromDB(EMAIL_ADDR_DB_KEY, function(err, emailAddress) {
            if (err) {
                return callback(err);
            }

            // load the provider (if existing)
            loadFromDB(PROVIDER_DB_KEY, function(err, provider) {
                if (err) {
                    return callback(err);
                }

                // if there is an email address without a provider, we need to add the missing provider entry
                // for any other situation, we're good.

                if (!(emailAddress && !provider)) {
                    // update the database version to POST_UPDATE_DB_VERSION
                    return options.appConfigStorage.storeList([POST_UPDATE_DB_VERSION], VERSION_DB_TYPE, callback);
                }

                // add the missing provider key
                options.appConfigStorage.storeList(['gmail'], PROVIDER_DB_KEY, function(err) {
                    if (err) {
                        return callback(err);
                    }

                    // add the missing user name key
                    options.appConfigStorage.storeList([emailAddress], USERNAME_DB_KEY, function(err) {
                        if (err) {
                            return callback(err);
                        }

                        // add the missing imap host info key
                        options.appConfigStorage.storeList([imap], IMAP_DB_KEY, function(err) {
                            if (err) {
                                return callback(err);
                            }

                            // add the missing empty real name
                            options.appConfigStorage.storeList([''], REALNAME_DB_KEY, function(err) {
                                if (err) {
                                    return callback(err);
                                }

                                // add the missing smtp host info key
                                options.appConfigStorage.storeList([smtp], SMTP_DB_KEY, function(err) {
                                    if (err) {
                                        return callback(err);
                                    }

                                    // reload the credentials
                                    options.auth.initialized = false;
                                    options.auth._loadCredentials(function(err) {
                                        if (err) {
                                            return callback(err);
                                        }


                                        // update the database version to POST_UPDATE_DB_VERSION
                                        options.appConfigStorage.storeList([POST_UPDATE_DB_VERSION], VERSION_DB_TYPE, callback);
                                    });
                                });
                            });
                        });
                    });
                });
            });
        });

        function loadFromDB(key, callback) {
            options.appConfigStorage.listItems(key, 0, null, function(err, cachedItems) {
                callback(err, (!err && cachedItems && cachedItems[0]));
            });
        }
    }

    return update;
});