/*
    Copyright (C) 2016  PencilBlue, LLC

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
'use strict';

//dependencies
var util = require('../../util.js');

module.exports = function RedisRegistrationProviderModule(pb) {

    /**
     * Implements the necessary functions in order to be able to create and manage
     * a service registry for PB processes in the cluster.  This provider uses Redis
     * as the storage.  In addition, it leverages Redis's expiry functionality to
     * expire entries automatically if they have not been touched.  In order to
     * retrieve all nodes/processes in the cluster the provider must execute
     * Redis's "keys" function which is an expensive operation.  To lessen the
     * impact on production systems the provider creates and manages its own Redis
     * client and switches to DB 2 in order to minimize the number of keys that
     * need to be scanned since the rest of the PB system leverages DB 0.
     * @class RedisRegistrationProvider
     * @constructor
     */
    function RedisRegistrationProvider(){}

    /**
     * The Redis DB used for storage
     * @private
     * @static
     * @readonly
     * @property REGISTRY_DB
     * @type {Integer}
     */
    var REGISTRY_DB = 0;

    /**
     * The character used to separate the registry key prefix from the unique value
     * that identifies the process/node.
     * @private
     * @static
     * @readonly
     * @property SEP
     * @type {String}
     */
    var SEP = '-';

    /**
     * The Redis client used to connect to the service registry
     * @private
     * @static
     * @readonly
     * @property CLIENT
     * @type {Integer}
     */
    var CLIENT = null;

    /**
     * Retrieves the entire cluster status as an array of status objects.  The '_id'
     * property uniquely identifies each process/node.
     * @method get
     * @param {Function} cb A callback that provides two parameters: cb(Error, Array)
     */
    RedisRegistrationProvider.prototype.get = function(cb) {

        var pattern = RedisRegistrationProvider.getPattern();
        CLIENT.keys(pattern, function(err, keys) {
            if (util.isError(err)) {
                cb(err);
                return;
            }

            CLIENT.mget(keys, function(err, statusObj) {

                //do data transform
                var statuses = [];
                if (util.isObject(statusObj)) {
                    for (var key in statusObj) {
                        try {
                            var status = JSON.parse(statusObj[key]);
                            status._id = status.id || key;
                            statuses.push(status);
                        }
                        catch(e){}
                    }
                }
                cb(err, statuses);
            });
        });
    };

    /**
     * Updates the status of a single node.
     * @method set
     * @param {String} id The unique identifier for the process/node
     * @param {Object} status The status information
     * @param {Function} cb A callback that provides two parameters: cb(Error, [RESULT])
     */
    RedisRegistrationProvider.prototype.set = function(id, status, cb) {
        if (!util.isObject(status)) {
            cb(new Error('The status parameter must be a valid object'));
            return;
        }

        var key    = RedisRegistrationProvider.getKey(id);
        var expiry = Math.floor(pb.config.registry.update_interval / util.TIME.MILLIS_PER_SEC);
        CLIENT.setex(key, expiry, JSON.stringify(status), cb);
    };

    /**
     * Purges all statuses from storage.
     * @method flush
     * @param {Function} cb A callback that provides two parameters: cb(Error, [RESULT])
     */
    RedisRegistrationProvider.prototype.flush = function(cb) {
        var pattern = RedisRegistrationProvider.getPattern();
        CLIENT.keys(pattern, function(err, keys) {
            if (util.isError(err)) {
                cb(err);
                return;
            }

            CLIENT.del(keys, cb);
        });
    };

    /**
     * This function should only be called once at startup.  It is responsible for
     * creating the Redis client that connects to the service registry.  It also
     * ensures the proper Redis DB is selected.
     * @method init
     * @param {Function} cb A callback that takes two parameters. cb(Error, [RESULT])
     */
    RedisRegistrationProvider.prototype.init = function(cb) {

        CLIENT = pb.CacheFactory.createInstance();
        CLIENT.select(REGISTRY_DB, cb);
    };

    /**
     * Should be called during shutdown.  It is responsible for removing the
     * process/node from the registry.
     * @method shutdown
     * @param {String} id The unique identifier for the node/process
     * @param {Function} cb A callback that takes two parameters: cb(Error, [RESULT])
     */
    RedisRegistrationProvider.prototype.shutdown = function(id, cb) {
        if (!id) {
            pb.log.error('RedisRegistrationProvider: A valid ID is needed in order to properly shutdown');
            cb(null, false);
        }

        var key = RedisRegistrationProvider.getKey(id);
        CLIENT.del(key, cb);
    };

    /**
     * Creates the cache key used to store the status update
     * @static
     * @method getKey
     * @param {String} id The unique identifier for the node/process
     * @return {String} The cache key to be used for storing the update
     */
    RedisRegistrationProvider.getKey = function(id) {
        return [pb.config.registry.key, id].join(SEP);
    };

    /**
     * Creates the glob pattern to be used to find service registry keys
     * @static
     * @method getPattern
     * @return {String} The glob patern to be used to find all status updates
     */
    RedisRegistrationProvider.getPattern = function() {
        return pb.config.registry.key + '*';
    };

    return RedisRegistrationProvider;
};