<!-- The <date-picker-sk> custom element declaration.

  A portable input element for dates, because Safari doesn't support "input type=date".

  Attributes:
    date - Unix date, number of seconds from the Epoch.

  Events:
    date-changed - The new value of 'date' is provided in the event details.

  Methods:
    None.
-->

<dom-module id=date-picker-sk>
  <template>
    <select on-change=_yearChange id=year name=year title=Year>
      <template is="dom-repeat" items="[[_years]]">
        <option selected$="{{_matches(item,_year)}}">[[ item ]]</option>
      </template>
    </select>
    <select on-change=_monthChange id=month name=month title=Month>
      <template is="dom-repeat" items="{{_months}}">
        <option selected$="{{_matches(index,_month)}}">[[ item ]]</option>
      </template>
    </select>
    <select on-change=_dayChange id=day name=day title=Day>
      <template is="dom-repeat" items="[[_days]]">
        <option selected$="{{_matches(item,_day)}}">[[ item ]]</option>
      </template>
    </select>
  </template>
</dom-module>

<script>
(function () {
  // The current year.
  let year = new Date().getFullYear();

  // The list of years to choose from.
  let years = Array(10).fill(0).map((_, i) => year-i)

  // How many days does Feb have in 'year'?
  function numFeb(year) {
    return ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0) ? 29 : 28;
  }

  // days per month.
  let days = [
    31, // Jan
    numFeb(year), // Feb
    31, // Mar
    30, // Apr
    31, // May
    30, // Jun
    31, // Jul
    31, // Aug
    30, // Sep
    31, // Oct
    30, // Nov
    31, // Dec
  ];

  let months = [
    "Jan",
    "Feb",
    "Mar",
    "Apr",
    "May",
    "Jun",
    "Jul",
    "Aug",
    "Sep",
    "Oct",
    "Nov",
    "Dec",
  ];

  Polymer({
    is: "date-picker-sk",

    properties: {
      date: {
        type: Number,
        value: Math.floor(Date.now()/1000),
        reflectToAttribute: true,
        observer: "_dateChanged",
      },
      _years: {
        type: Array,
        value: years,
        reflectToAttribute: false,
      },
      _months: {
        type: Array,
        value: months,
        reflectToAttribute: false,
      },
      _days: {
        type: Array,
        value: [],
        reflectToAttribute: false,
      },
    },

    _dateChanged: function() {
      let d = new Date();
      d.setTime(this.date *1000);
      this._setYear(d.getFullYear());
      this._setMonth(d.getMonth());
      this._setDay(d.getDate());
    },

    _setYear: function(year) {
      this._year = year;
      days[1] = numFeb(year);
      this._setMonth(this.$.month.selectedIndex);
    },

    _yearChange: function() {
      this._setYear(this.$.year.value);
      this._syncDate();
    },

    _setMonth: function(month) {
      this._month = month;
      this._days = Array(days[month]).fill(0).map((_, i) => i+1)
      // Fix up the day if necessary.
      if (this._day > days[month]) {
        this._day = days[month];
      }

    },

    _monthChange: function(e) {
      this._setMonth(this.$.month.selectedIndex);
      this._syncDate();
    },

    _setDay: function(day) {
      this._day = day;
    },

    _dayChange: function() {
      this._setDay(this.$.day.value);
      this._syncDate();
    },

    // Synchronize the values of _year, _month, _day to 'date'.
    //
    // Also fires the "date-changed" event.
    _syncDate() {
      let d = new Date();
      d.setYear(this._year);
      // Always set day before month. Otherwise Apr 31 => May 1.
      d.setDate(this._day);
      d.setMonth(this._month);
      this.date = Math.floor(d.getTime()/1000);
      this.fire("date-changed", {date: this.date, bubbles: true});
    },

    _matches: function(a, b) {
      return a === b;
    },

  });

})();
</script>