<!--
    @license
    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
    Code distributed by Google as part of the polymer project is also
    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->

<!--
`core-a11y-keys` provides a normalized interface for processing keyboard commands that pertain to [WAI-ARIA best
practices](http://www.w3.org/TR/wai-aria-practices/#kbd_general_binding). The element takes care of browser differences
with respect to Keyboard events and uses an expressive syntax to filter key presses.

Use the `keys` attribute to express what combination of keys will trigger the event to fire.

Use the `target` attribute to set up event handlers on a specific node.
The `keys-pressed` event will fire when one of the key combinations set with the `keys` attribute is pressed.

Example:

This element will call `arrowHandler` on all arrow keys:

    <core-a11y-keys target="{{}}" keys="up down left right" on-keys-pressed="{{arrowHandler}}"></core-a11y-keys>

Keys Syntax:

The `keys` attribute can accepts a space seprated, `+` concatenated set of modifier keys and some common keyboard keys.

The common keys are `a-z`, `0-9` (top row and number pad), `*` (shift 8 and number pad), `F1-F12`, `Page Up`, `Page
Down`, `Left Arrow`, `Right Arrow`, `Down Arrow`, `Up Arrow`, `Home`, `End`, `Escape`, `Space`, `Tab`, and `Enter` keys.

The modifier keys are `Shift`, `Control`, and `Alt`.

All keys are expected to be lowercase and shortened:
`Left Arrow` is `left`, `Page Down` is `pagedown`, `Control` is `ctrl`, `F1` is `f1`, `Escape` is `esc` etc.

Keys Syntax Example:

Given the `keys` attribute value "ctrl+shift+f7 up pagedown esc space alt+m", the `<core-a11y-keys>` element will send
the `keys-pressed` event if any of the follow key combos are pressed: Control and Shift and F7 keys, Up Arrow key, Page
Down key, Escape key, Space key, Alt and M key.

Slider Example:

The following is an example of the set of keys that fulfil the WAI-ARIA "slider" role [best
practices](http://www.w3.org/TR/wai-aria-practices/#slider):

    <core-a11y-keys target="{{}}" keys="left pagedown down" on-keys-pressed="{{decrement}}"></core-a11y-keys>
    <core-a11y-keys target="{{}}" keys="right pageup up" on-keys-pressed="{{increment}}"></core-a11y-keys>
    <core-a11y-keys target="{{}}" keys="home" on-keys-pressed="{{setMin}}"></core-a11y-keys>
    <core-a11y-keys target="{{}}" keys="end" on-keys-pressed="{{setMax}}"></core-a11y-keys>

The `increment` function will move the slider a set amount toward the maximum value.
The `decrement` function will move the slider a set amount toward the minimum value.
The `setMin` function will move the slider to the minimum value.
The `setMax` function will move the slider to the maximum value.

Keys Syntax Grammar:

[EBNF](http://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_Form) Grammar of the `keys` attribute.

    modifier = "shift" | "ctrl" | "alt";
    ascii = ? /[a-z0-9]/ ? ;
    fnkey = ? f1 through f12 ? ;
    arrow = "up" | "down" | "left" | "right" ;
    key = "tab" | "esc" | "space" | "*" | "pageup" | "pagedown" | "home" | "end" | arrow | ascii | fnkey ;
    keycombo = { modifier, "+" }, key ;
    keys = keycombo, { " ", keycombo } ;

@group Core Elements
@element core-a11y-keys
@homepage github.io
-->

<!--
Fired when a keycombo in `keys` is pressed.

@event keys-pressed
@param {Object} detail
  @param {boolean} detail.shift true if shift key is pressed
  @param {boolean} detail.ctrl true if ctrl key is pressed
  @param {boolean} detail.meta true if meta key is pressed
  @param {boolean} detail.alt true if alt key is pressed
  @param {String} detail.key the normalized key
-->

<link rel="import" href="../polymer/polymer.html">

<style shim-shadowdom>
  html /deep/ core-a11y-keys {
    display: none;
  }
</style>

<polymer-element name="core-a11y-keys">
<script>
  (function() {
    /*
     * Chrome uses an older version of DOM Level 3 Keyboard Events
     *
     * Most keys are labeled as text, but some are Unicode codepoints.
     * Values taken from: http://www.w3.org/TR/2007/WD-DOM-Level-3-Events-20071221/keyset.html#KeySet-Set
     */
    var KEY_IDENTIFIER = {
      'U+0009': 'tab',
      'U+001B': 'esc',
      'U+0020': 'space',
      'U+002A': '*',
      'U+0030': '0',
      'U+0031': '1',
      'U+0032': '2',
      'U+0033': '3',
      'U+0034': '4',
      'U+0035': '5',
      'U+0036': '6',
      'U+0037': '7',
      'U+0038': '8',
      'U+0039': '9',
      'U+0041': 'a',
      'U+0042': 'b',
      'U+0043': 'c',
      'U+0044': 'd',
      'U+0045': 'e',
      'U+0046': 'f',
      'U+0047': 'g',
      'U+0048': 'h',
      'U+0049': 'i',
      'U+004A': 'j',
      'U+004B': 'k',
      'U+004C': 'l',
      'U+004D': 'm',
      'U+004E': 'n',
      'U+004F': 'o',
      'U+0050': 'p',
      'U+0051': 'q',
      'U+0052': 'r',
      'U+0053': 's',
      'U+0054': 't',
      'U+0055': 'u',
      'U+0056': 'v',
      'U+0057': 'w',
      'U+0058': 'x',
      'U+0059': 'y',
      'U+005A': 'z',
      'U+007F': 'del'
    };

    /*
     * Special table for KeyboardEvent.keyCode.
     * KeyboardEvent.keyIdentifier is better, and KeyBoardEvent.key is even better than that
     *
     * Values from: https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent.keyCode#Value_of_keyCode
     */
    var KEY_CODE = {
      9: 'tab',
      13: 'enter',
      27: 'esc',
      33: 'pageup',
      34: 'pagedown',
      35: 'end',
      36: 'home',
      32: 'space',
      37: 'left',
      38: 'up',
      39: 'right',
      40: 'down',
      46: 'del',
      106: '*'
    };

    /*
     * KeyboardEvent.key is mostly represented by printable character made by the keyboard, with unprintable keys labeled
     * nicely.
     *
     * However, on OS X, Alt+char can make a Unicode character that follows an Apple-specific mapping. In this case, we
     * fall back to .keyCode.
     */
    var KEY_CHAR = /[a-z0-9*]/;

    function transformKey(key) {
      var validKey = '';
      if (key) {
        var lKey = key.toLowerCase();
        if (lKey.length == 1) {
          if (KEY_CHAR.test(lKey)) {
            validKey = lKey;
          }
        } else if (lKey == 'multiply') {
          // numpad '*' can map to Multiply on IE/Windows
          validKey = '*';
        } else {
          validKey = lKey;
        }
      }
      return validKey;
    }

    var IDENT_CHAR = /U\+/;
    function transformKeyIdentifier(keyIdent) {
      var validKey = '';
      if (keyIdent) {
        if (IDENT_CHAR.test(keyIdent)) {
          validKey = KEY_IDENTIFIER[keyIdent];
        } else {
          validKey = keyIdent.toLowerCase();
        }
      }
      return validKey;
    }

    function transformKeyCode(keyCode) {
      var validKey = '';
      if (Number(keyCode)) {
        if (keyCode >= 65 && keyCode <= 90) {
          // ascii a-z
          // lowercase is 32 offset from uppercase
          validKey = String.fromCharCode(32 + keyCode);
        } else if (keyCode >= 112 && keyCode <= 123) {
          // function keys f1-f12
          validKey = 'f' + (keyCode - 112);
        } else if (keyCode >= 48 && keyCode <= 57) {
          // top 0-9 keys
          validKey = String(48 - keyCode);
        } else if (keyCode >= 96 && keyCode <= 105) {
          // num pad 0-9
          validKey = String(96 - keyCode);
        } else {
          validKey = KEY_CODE[keyCode];
        }
      }
      return validKey;
    }

    function keyboardEventToKey(ev) {
      // fall back from .key, to .keyIdentifier, to .keyCode, and then to .detail.key to support artificial keyboard events
      var normalizedKey = transformKey(ev.key) || transformKeyIdentifier(ev.keyIdentifier) || transformKeyCode(ev.keyCode) || transformKey(ev.detail.key) || '';
      return {
        shift: ev.shiftKey,
        ctrl: ev.ctrlKey,
        meta: ev.metaKey,
        alt: ev.altKey,
        key: normalizedKey
      };
    }

    /*
     * Input: ctrl+shift+f7 => {ctrl: true, shift: true, key: 'f7'}
     * ctrl/space => {ctrl: true} || {key: space}
     */
    function stringToKey(keyCombo) {
      var keys = keyCombo.split('+');
      var keyObj = Object.create(null);
      keys.forEach(function(key) {
        if (key == 'shift') {
          keyObj.shift = true;
        } else if (key == 'ctrl') {
          keyObj.ctrl = true;
        } else if (key == 'alt') {
          keyObj.alt = true;
        } else {
          keyObj.key = key;
        }
      });
      return keyObj;
    }

    function keyMatches(a, b) {
      return Boolean(a.alt) == Boolean(b.alt) && Boolean(a.ctrl) == Boolean(b.ctrl) && Boolean(a.shift) == Boolean(b.shift) && a.key === b.key;
    }

    function processKeys(ev) {
      var current = keyboardEventToKey(ev);
      for (var i = 0, dk; i < this._desiredKeys.length; i++) {
        dk = this._desiredKeys[i];
        if (keyMatches(dk, current)) {
          ev.preventDefault();
          ev.stopPropagation();
          this.fire('keys-pressed', current, this, false);
          break;
        }
      }
    }

    function listen(node, handler) {
      if (node && node.addEventListener) {
        node.addEventListener('keydown', handler);
      }
    }

    function unlisten(node, handler) {
      if (node && node.removeEventListener) {
        node.removeEventListener('keydown', handler);
      }
    }

    Polymer('core-a11y-keys', {
      created: function() {
        this._keyHandler = processKeys.bind(this);
      },
      attached: function() {
        if (!this.target) {
          this.target = this.parentNode;
        }
        listen(this.target, this._keyHandler);
      },
      detached: function() {
        unlisten(this.target, this._keyHandler);
      },
      publish: {
        /**
         * The set of key combinations that will be matched (in keys syntax).
         *
         * @attribute keys
         * @type string
         * @default ''
         */
        keys: '',
        /**
         * The node that will fire keyboard events.
         * Default to this element's parentNode unless one is assigned
         *
         * @attribute target
         * @type Node
         * @default this.parentNode
         */
        target: null
      },
      keysChanged: function() {
        // * can have multiple mappings: shift+8, * on numpad or Multiply on numpad
        var normalized = this.keys.replace('*', '* shift+*');
        this._desiredKeys = normalized.toLowerCase().split(' ').map(stringToKey);
      },
      targetChanged: function(oldTarget) {
        unlisten(oldTarget, this._keyHandler);
        listen(this.target, this._keyHandler);
      }
    });
  })();
</script>
</polymer-element>