<!-- The <range-sel-sk> custom element declaration.

Allows selecting a sub-range. The full range is from [0, 100].

  [......(=====)........]

  Attributes:
    begin - Number - The start of the selected range.
    end   - Number - The end of the selected range.

  Events:
    range-change - Fired as the sliders move. The detail
       of the event contains the begin and end values:

         {
           begin: 15.0,
           end:   50.0,
         }

      Note that the element properties 'begin' and 'end' don't change
      until the sliders stop moving.

    range-change-end - Fired when the slider is done moving.

         {
           begin: 15.0,
           end:   50.0,
         }

  Methods:
    None.

-->

<dom-module id="range-sel-sk">
  <style>
    :host {
      display: block;
      width: 640px;
      height: 40px;
    }

    #wrapper {
      display: block;
      position: relative;
      width: 600px;
      height: 40px;
    }

    :host,
    div {
      user-select: none;
      -webkit-user-select: none;
    }

    #begin,
    #end {
      width: 15px;
      height: 38px;
      background: #1F78B4;
      border: solid 1px #eee;
      display: inline-block;
      position: absolute;
      border-radius: 5px;
    }

    #begin:hover,
    #end:hover {
      border: solid 1px black;
    }

    #fullrange,
    #range {
      width: 100%;
      height: 2px;
      background: #ccc;
      top: 20px;
      display: inline-block;
      position: absolute;
      left: 10px;
    }

    #range {
      background: #1F78B4;
      top: 20px;
      left: 15%;
      width: 36%;
    }

  </style>
  <template>
    <div id=wrapper>
      <div id=fullrange></div>
      <div id=range></div>
      <div id=begin on-track="_handleTrack"></div>
      <div id=end on-track="_handleTrack"></div>
    </div>
  </template>
</dom-module>

<script>
  Polymer({
    is: "range-sel-sk",

    properties: {
      begin: {
        type: Number,
        value: 0,
        reflectToAttribute: true,
        observer: "_beginChange",
      },
      end: {
        type: Number,
        value: 100,
        reflectToAttribute: true,
        observer: "_endChange",
      },
    },

    ready: function() {
      this._setSliderPos(this.$.begin, 0);
      this._setSliderPos(this.$.end, 0);
    },

    _beginChange: function() {
      this._setSliderPos(this.$.begin, 0);
      this._fireMsg(this.$.begin, 0, "range-change");
    },

    _endChange: function() {
      this._setSliderPos(this.$.end, 0);
      this._fireMsg(this.$.end, 0, "range-change");
    },

    // Clamps the dx so that the sliders don't move beyond
    // the ends of the range bar.
    _clamp: function(ele, dx) {
      if (ele.offsetLeft+dx > this.$.wrapper.clientWidth) {
        dx = this.$.wrapper.clientWidth - ele.offsetLeft;
      }
      if (ele.offsetLeft+dx < 0) {
        dx = -ele.offsetLeft;
      }
      return dx;
    },

    // Sets the position of slider 'ele' with a position delta of 'dx'.
    _setSliderPos: function(ele, dx) {
      dx = this._clamp(ele, dx);
      ele.style.left = this[ele.id] + "%";
      ele.style.transform = "translateX(" + dx + "px)";
      this.$.range.style.left = this.begin + "%";
      this.$.range.style.width = (this.end - this.begin) + "%";
    },

    // Fires the 'range-change' custom event with a detail section that
    // contains the new begin and end range.
    //
    // Returns the message detail that was sent.
    _fireMsg: function(ele, dx, eventName) {
      var msg = {
        begin: this.begin,
        end: this.end,
      };
      dx = this._clamp(ele, dx);
      msg[ele.id] = 100*(ele.offsetLeft+dx)/this.$.wrapper.clientWidth;
      if (msg.begin > msg.end) {
        var tmp = msg.begin;
        msg.begin = msg.end;
        msg.end = tmp;
      }
      this.fire(eventName, msg);
      return msg;
    },

    _handleTrack: function(e) {
      switch(e.detail.state) {
        case 'track':
          this._setSliderPos(e.target, e.detail.dx);
          this._fireMsg(e.target, e.detail.dx, "range-change");
          break;
        case 'end':
          var msg = this._fireMsg(e.target, e.detail.dx, "range-change");
          this._fireMsg(e.target, e.detail.dx, "range-change-end");
          this.begin = msg.begin;
          this.end = msg.end;
          this._setSliderPos(this.$.begin, 0);
          this._setSliderPos(this.$.end, 0);
          break;
      }
    },

  });
</script>