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/**
 * 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 {
 Y.log("Could not validate data as type Date", "warn", "date");
 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;