YUI.add('datatype-date-math', function (Y, NAME) {

/**
 * Date Math submodule.
 *
 * @module datatype-date
 * @submodule datatype-date-math
 * @for Date
 */
var LANG = Y.Lang;

Y.mix(Y.namespace("Date"), {

    /**
     * Checks whether a native JavaScript Date contains a valid value.
     * @for Date
     * @method isValidDate
     * @param oDate {Date} Date in the month for which the number of days is desired.
     * @return {Boolean} True if the date argument contains a valid value.
     */
     isValidDate : function (oDate) {
        if(LANG.isDate(oDate) && (isFinite(oDate)) && (oDate != "Invalid Date") && !isNaN(oDate) && (oDate != null)) {
            return true;
        }
        else {
            return false;
        }
    },

    /**
     * Checks whether two dates correspond to the same date and time.
     * @for Date
     * @method areEqual
     * @param aDate {Date} The first date to compare.
     * @param bDate {Date} The second date to compare.
     * @return {Boolean} True if the two dates correspond to the same
     * date and time.
     */
    areEqual : function (aDate, bDate) {
        return (this.isValidDate(aDate) && this.isValidDate(bDate) && (aDate.getTime() == bDate.getTime()));
    },

    /**
     * Checks whether the first date comes later than the second.
     * @for Date
     * @method isGreater
     * @param aDate {Date} The first date to compare.
     * @param bDate {Date} The second date to compare.
     * @return {Boolean} True if the first date is later than the second.
     */
    isGreater : function (aDate, bDate) {
        return (this.isValidDate(aDate) && this.isValidDate(bDate) && (aDate.getTime() > bDate.getTime()));
    },

    /**
     * Checks whether the first date comes later than or is the same as
     * the second.
     * @for Date
     * @method isGreaterOrEqual
     * @param aDate {Date} The first date to compare.
     * @param bDate {Date} The second date to compare.
     * @return {Boolean} True if the first date is later than or
     * the same as the second.
     */
    isGreaterOrEqual : function (aDate, bDate) {
        return (this.isValidDate(aDate) && this.isValidDate(bDate) && (aDate.getTime() >= bDate.getTime()));
    },


    /**
     * Checks whether the date is between two other given dates.
     * @for Date
     * @method isInRange
     * @param aDate {Date} The date to check
     * @param bDate {Date} Lower bound of the range.
     * @param cDate {Date} Higher bound of the range.
     * @return {Boolean} True if the date is between the two other given dates.
     */
    isInRange : function (aDate, bDate, cDate) {
        return (this.isGreaterOrEqual(aDate, bDate) && this.isGreaterOrEqual(cDate, aDate));
    },

    /**
     * Adds a specified number of days to the given date.
     * @for Date
     * @method addDays
     * @param oDate {Date} The date to add days to.
     * @param numDays {Number} The number of days to add (can be negative)
     * @return {Date} A new Date with the specified number of days
     * added to the original date.
     */
    addDays : function (oDate, numDays) {
        return new Date(oDate.getTime() + 86400000*numDays);
    },


    /**
     * Adds a specified number of months to the given date.
     * @for Date
     * @method addMonths
     * @param oDate {Date} The date to add months to.
     * @param numMonths {Number} The number of months to add (can be negative)
     * @return {Date} A new Date with the specified number of months
     * added to the original date.
     */
    addMonths : function (oDate, numMonths) {
        var newYear = oDate.getFullYear();
        var newMonth = oDate.getMonth() + numMonths;

        newYear  = Math.floor(newYear + newMonth / 12);
        newMonth = (newMonth % 12 + 12) % 12;

        var newDate = new Date (oDate.getTime());
        newDate.setFullYear(newYear);
        newDate.setMonth(newMonth);

        return newDate;
    },

    /**
     * Adds a specified number of years to the given date.
     * @for Date
     * @method addYears
     * @param oDate {Date} The date to add years to.
     * @param numYears {Number} The number of years to add (can be negative)
     * @return {Date} A new Date with the specified number of years
     * added to the original date.
     */
    addYears : function (oDate, numYears) {
        var newYear = oDate.getFullYear() + numYears;
        var newDate = new Date(oDate.getTime());

        newDate.setFullYear(newYear);
        return newDate;
    },

    /**
     * Lists all dates in a given month.
     * @for Date
     * @method listOfDatesInMonth
     * @param oDate {Date} The date corresponding to the month for
     * which a list of dates is required.
     * @return {Array} An `Array` of `Date`s from a given month.
     */
    listOfDatesInMonth : function (oDate) {
       if (!this.isValidDate(oDate)) {
         return [];
       }

       var daysInMonth = this.daysInMonth(oDate),
           year        = oDate.getFullYear(),
           month       = oDate.getMonth(),
           output      = [];

       for (var day = 1; day <= daysInMonth; day++) {
           output.push(new Date(year, month, day, 12, 0, 0));
       }

       return output;
    },

    /**
     * Takes a native JavaScript Date and returns the number of days
     * in the month that the given date belongs to.
     * @for Date
     * @method daysInMonth
     * @param oDate {Date} Date in the month for which the number
     * of days is desired.
     * @return {Number} A number (either 28, 29, 30 or 31) of days
     * in the given month.
     */
     daysInMonth : function (oDate) {
        if (!this.isValidDate(oDate)) {
            return 0;
        }

        var mon = oDate.getMonth();
        var lengths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

        if (mon != 1) {
            return lengths[mon];
        }
        else {

            var year = oDate.getFullYear();
            if (year%400 === 0) {
                   return 29;
            }
            else if (year%100 === 0) {
                   return 28;
            }
            else if (year%4 === 0) {
                   return 29;
            }
            else {
                   return 28;
            }
       }
    }

});

Y.namespace("DataType");
Y.DataType.Date = Y.Date;


}, '@VERSION@', {"requires": ["yui-base"]});
