// Copyright IBM Corp. 2014,2016. All Rights Reserved.
  // Node module: loopback
  // This file is licensed under the MIT License.
  // License text available at https://opensource.org/licenses/MIT
  
  /**
   * Module Dependencies.
   */
  
  var assert = require('assert');
  
  /**
   * Checkpoint list entry.
   *
   * @property id {Number} the sequencial identifier of a checkpoint
   * @property time {Number} the time when the checkpoint was created
   * @property sourceId {String}  the source identifier
   *
   * @class Checkpoint
   * @inherits {PersistedModel}
   */
  
  module.exports = function(Checkpoint) {
  
    // Workaround for https://github.com/strongloop/loopback/issues/292
    Checkpoint.definition.rawProperties.time.default =
      Checkpoint.definition.properties.time.default = function() {
        return new Date();
      };
  
    /**
     * Get the current checkpoint id
     * @callback {Function} callback
     * @param {Error} err
     * @param {Number} checkpoint The current checkpoint seq
     */
    Checkpoint.current = function(cb) {
      var Checkpoint = this;
      Checkpoint._getSingleton(function(err, cp) {
        cb(err, cp.seq);
      });
    };
  
    Checkpoint._getSingleton = function(cb) {
      var query = {limit: 1}; // match all instances, return only one
      var initialData = {seq: 1};
      this.findOrCreate(query, initialData, cb);
    };
  
    /**
     * Increase the current checkpoint if it already exists otherwise initialize it
     * @callback {Function} callback
     * @param {Error} err
     * @param {Object} checkpoint The current checkpoint
     */
    Checkpoint.bumpLastSeq = function(cb) {
      var Checkpoint = this;
      Checkpoint._getSingleton(function(err, cp) {
        if (err) return cb(err);
        var originalSeq = cp.seq;
        cp.seq++;
        // Update the checkpoint but only if it was not changed under our hands
        Checkpoint.updateAll({id: cp.id, seq: originalSeq}, {seq: cp.seq}, function(err, info) {
          if (err) return cb(err);
          // possible outcomes
          // 1) seq was updated to seq+1 - exactly what we wanted!
          // 2) somebody else already updated seq to seq+1 and our call was a no-op.
          //   That should be ok, checkpoints are time based, so we reuse the one created just now
          //  3) seq was bumped more than once, so we will be using a value that is behind the latest seq.
          //    @bajtos is not entirely sure if this is ok, but since it wasn't handled by the current implementation either,
          //    he thinks we can keep it this way.
          cb(null, cp);
        });
      });
    };
  };