var CronTime = exports.CronTime = function CronTime(time){
  this.source = time;

  this.map= ['second', 'minute', 'hour', 'dayOfMonth', 'month', 'dayOfWeek'];
	this.constraints = [[0,59],[0,59],[0,23],[1,31],[0,11],[1,7]];
	this.aliases = {
	   jan:1,feb:2,mar:3,apr:4,may:5,jun:6,jul:7,aug:8,sep:9,oct:10,nov:11,dec:12,
	   sun:0,mon:1,tue:2,wed:3,thu:4,fri:5,sat:6
	};

	this.second = {};
	this.minute = {};
	this.hour = {};
	this.dayOfMonth = {};
	this.month = {};
	this.dayOfWeek = {};

	this._parse();
}

CronTime.prototype = {

  _parse: function(){
    var aliases = this.aliases,
        cur,
        len=6;

    var source = this.source.replace(/[a-z]/i, function(alias){
      alias = alias.toLowerCase();

      if(alias in aliases){
        return aliases[alias];
      }

      throw new Error('Unknown alias: ' + alias);
    });
    var split = this.source.replace(/^\s\s*|\s\s*$/g, '').split(/\s+/);


    while(len--){
      cur = split[len] || '*';
      this._parseField(cur, this.map[len], this.constraints[len]);
    }
  },

  _parseField: function(field, type, constraints){
    var rangePattern = /(\d+?)(?:-(\d+?))?(?:\/(\d+?))?(?:,|$)/g,
        typeObj = this[type],
        diff,
        low = constraints[0],
        high = constraints[1];

    // * is a shortcut to [lower-upper] range
    field = field.replace(/\*/g,  low + '-' + high);

    if(field.match(rangePattern)){
      field.replace(rangePattern, function($0, lower, upper, step){
        step = step || 1;

        // Positive integer higher than constraints[0]
        lower = Math.max(low, ~~Math.abs(lower));

        // Positive integer lower than constraints[1]
        upper = upper ? Math.min(high, ~~Math.abs(upper)) : lower;

        diff = step+upper-lower;
        while((diff -= step) > -1){
          typeObj[diff+lower] = true;
        }
      });
    }
    else{
      throw new Error('Field (' + field + ') cannot be parsed');
    }
  }
};