(function() {
  'use strict';

  /**
   * Utility for performing date calculations to facilitate operation of the calendar and
   * datepicker.
   */
  angular.module('material.components.datepicker').factory('$$mdDateUtil', function() {
    return {
      getFirstDateOfMonth: getFirstDateOfMonth,
      getNumberOfDaysInMonth: getNumberOfDaysInMonth,
      getDateInNextMonth: getDateInNextMonth,
      getDateInPreviousMonth: getDateInPreviousMonth,
      isInNextMonth: isInNextMonth,
      isInPreviousMonth: isInPreviousMonth,
      getDateMidpoint: getDateMidpoint,
      isSameMonthAndYear: isSameMonthAndYear,
      getWeekOfMonth: getWeekOfMonth,
      incrementDays: incrementDays,
      incrementMonths: incrementMonths,
      getLastDateOfMonth: getLastDateOfMonth,
      isSameDay: isSameDay,
      getMonthDistance: getMonthDistance,
      isValidDate: isValidDate,
      setDateTimeToMidnight: setDateTimeToMidnight,
      createDateAtMidnight: createDateAtMidnight,
      isDateWithinRange: isDateWithinRange
    };

    /**
     * Gets the first day of the month for the given date's month.
     * @param {Date} date
     * @returns {Date}
     */
    function getFirstDateOfMonth(date) {
      return new Date(date.getFullYear(), date.getMonth(), 1);
    }

    /**
     * Gets the number of days in the month for the given date's month.
     * @param date
     * @returns {number}
     */
    function getNumberOfDaysInMonth(date) {
      return new Date(date.getFullYear(), date.getMonth() + 1, 0).getDate();
    }

    /**
     * Get an arbitrary date in the month after the given date's month.
     * @param date
     * @returns {Date}
     */
    function getDateInNextMonth(date) {
      return new Date(date.getFullYear(), date.getMonth() + 1, 1);
    }

    /**
     * Get an arbitrary date in the month before the given date's month.
     * @param date
     * @returns {Date}
     */
    function getDateInPreviousMonth(date) {
      return new Date(date.getFullYear(), date.getMonth() - 1, 1);
    }

    /**
     * Gets whether two dates have the same month and year.
     * @param {Date} d1
     * @param {Date} d2
     * @returns {boolean}
     */
    function isSameMonthAndYear(d1, d2) {
      return d1.getFullYear() === d2.getFullYear() && d1.getMonth() === d2.getMonth();
    }

    /**
     * Gets whether two dates are the same day (not not necesarily the same time).
     * @param {Date} d1
     * @param {Date} d2
     * @returns {boolean}
     */
    function isSameDay(d1, d2) {
      return d1.getDate() == d2.getDate() && isSameMonthAndYear(d1, d2);
    }

    /**
     * Gets whether a date is in the month immediately after some date.
     * @param {Date} startDate The date from which to compare.
     * @param {Date} endDate The date to check.
     * @returns {boolean}
     */
    function isInNextMonth(startDate, endDate) {
      var nextMonth = getDateInNextMonth(startDate);
      return isSameMonthAndYear(nextMonth, endDate);
    }

    /**
     * Gets whether a date is in the month immediately before some date.
     * @param {Date} startDate The date from which to compare.
     * @param {Date} endDate The date to check.
     * @returns {boolean}
     */
    function isInPreviousMonth(startDate, endDate) {
      var previousMonth = getDateInPreviousMonth(startDate);
      return isSameMonthAndYear(endDate, previousMonth);
    }

    /**
     * Gets the midpoint between two dates.
     * @param {Date} d1
     * @param {Date} d2
     * @returns {Date}
     */
    function getDateMidpoint(d1, d2) {
      return createDateAtMidnight((d1.getTime() + d2.getTime()) / 2);
    }

    /**
     * Gets the week of the month that a given date occurs in.
     * @param {Date} date
     * @returns {number} Index of the week of the month (zero-based).
     */
    function getWeekOfMonth(date) {
      var firstDayOfMonth = getFirstDateOfMonth(date);
      return Math.floor((firstDayOfMonth.getDay() + date.getDate() - 1) / 7);
    }

    /**
     * Gets a new date incremented by the given number of days. Number of days can be negative.
     * @param {Date} date
     * @param {number} numberOfDays
     * @returns {Date}
     */
    function incrementDays(date, numberOfDays) {
      return new Date(date.getFullYear(), date.getMonth(), date.getDate() + numberOfDays);
    }

    /**
     * Gets a new date incremented by the given number of months. Number of months can be negative.
     * If the date of the given month does not match the target month, the date will be set to the
     * last day of the month.
     * @param {Date} date
     * @param {number} numberOfMonths
     * @returns {Date}
     */
    function incrementMonths(date, numberOfMonths) {
      // If the same date in the target month does not actually exist, the Date object will
      // automatically advance *another* month by the number of missing days.
      // For example, if you try to go from Jan. 30 to Feb. 30, you'll end up on March 2.
      // So, we check if the month overflowed and go to the last day of the target month instead.
      var dateInTargetMonth = new Date(date.getFullYear(), date.getMonth() + numberOfMonths, 1);
      var numberOfDaysInMonth = getNumberOfDaysInMonth(dateInTargetMonth);
      if (numberOfDaysInMonth < date.getDate()) {
        dateInTargetMonth.setDate(numberOfDaysInMonth);
      } else {
        dateInTargetMonth.setDate(date.getDate());
      }

      return dateInTargetMonth;
    }

    /**
     * Get the integer distance between two months. This *only* considers the month and year
     * portion of the Date instances.
     *
     * @param {Date} start
     * @param {Date} end
     * @returns {number} Number of months between `start` and `end`. If `end` is before `start`
     *     chronologically, this number will be negative.
     */
    function getMonthDistance(start, end) {
      return (12 * (end.getFullYear() - start.getFullYear())) + (end.getMonth() - start.getMonth());
    }

    /**
     * Gets the last day of the month for the given date.
     * @param {Date} date
     * @returns {Date}
     */
    function getLastDateOfMonth(date) {
      return new Date(date.getFullYear(), date.getMonth(), getNumberOfDaysInMonth(date));
    }

    /**
     * Checks whether a date is valid.
     * @param {Date} date
     * @return {boolean} Whether the date is a valid Date.
     */
    function isValidDate(date) {
      return date != null && date.getTime && !isNaN(date.getTime());
    }

    /**
     * Sets a date's time to midnight.
     * @param {Date} date
     */
    function setDateTimeToMidnight(date) {
      date.setHours(0, 0, 0, 0);
    }

    /**
     * Creates a date with the time set to midnight.
     * Drop-in replacement for two forms of the Date constructor:
     * 1. No argument for Date representing now.
     * 2. Single-argument value representing number of seconds since Unix Epoch.
     * @param {number=} opt_value
     * @return {Date} New date with time set to midnight.
     */
    function createDateAtMidnight(opt_value) {
      var date;
      if (angular.isUndefined(opt_value)) {
        date = new Date();
      } else {
        date = new Date(opt_value);
      }
      setDateTimeToMidnight(date);
      return date;
    }

     /**
      * Checks if a date is within a min and max range.
      * If minDate or maxDate are not dates, they are ignored.
      * @param {Date} date
      * @param {Date} minDate
      * @param {Date} maxDate
      */
     function isDateWithinRange(date, minDate, maxDate) {
       return (!angular.isDate(minDate) || minDate <= date) &&
           (!angular.isDate(maxDate) || maxDate >= date);
     }
  });
})();
