WebCompDev / COMPONENTS

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

<script>
  (function() {
    'use strict';

    /**
     * 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: '*'
    };

    /**
     * MODIFIER_KEYS maps the short name for modifier keys used in a key
     * combo string to the property name that references those same keys
     * in a KeyboardEvent instance.
     */
    var MODIFIER_KEYS = {
      'shift': 'shiftKey',
      'ctrl': 'ctrlKey',
      'alt': 'altKey',
      'meta': 'metaKey'
    };

    /**
     * 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*]/;

    /**
     * Matches a keyIdentifier string.
     */
    var IDENT_CHAR = /U\+/;

    /**
     * Matches arrow keys in Gecko 27.0+
     */
    var ARROW_KEY = /^arrow/;

    /**
     * Matches space keys everywhere (notably including IE10's exceptional name
     * `spacebar`).
     */
    var SPACE_KEY = /^space(bar)?/;

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

    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 normalizedKeyForEvent(keyEvent) {
      // fall back from .key, to .keyIdentifier, to .keyCode, and then to
      // .detail.key to support artificial keyboard events
      return transformKey(keyEvent.key) ||
        transformKeyIdentifier(keyEvent.keyIdentifier) ||
        transformKeyCode(keyEvent.keyCode) ||
        transformKey(keyEvent.detail.key) || '';
    }

    function keyComboMatchesEvent(keyCombo, keyEvent) {
      return normalizedKeyForEvent(keyEvent) === keyCombo.key &&
        !!keyEvent.shiftKey === !!keyCombo.shiftKey &&
        !!keyEvent.ctrlKey === !!keyCombo.ctrlKey &&
        !!keyEvent.altKey === !!keyCombo.altKey &&
        !!keyEvent.metaKey === !!keyCombo.metaKey;
    }

    function parseKeyComboString(keyComboString) {
      return keyComboString.split('+').reduce(function(parsedKeyCombo, keyComboPart) {
        var eventParts = keyComboPart.split(':');
        var keyName = eventParts[0];
        var event = eventParts[1];

        if (keyName in MODIFIER_KEYS) {
          parsedKeyCombo[MODIFIER_KEYS[keyName]] = true;
        } else {
          parsedKeyCombo.key = keyName;
          parsedKeyCombo.event = event || 'keydown';
        }

        return parsedKeyCombo;
      }, {
        combo: keyComboString.split(':').shift()
      });
    }

    function parseEventString(eventString) {
      return eventString.split(' ').map(function(keyComboString) {
        return parseKeyComboString(keyComboString);
      });
    }


    /**
     * `Polymer.IronA11yKeysBehavior` 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 `keyBindings` prototype property to express what combination of keys
     * will trigger the event to fire.
     *
     * Use the `key-event-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` property is pressed.
     *
     * @demo demo/index.html
     * @polymerBehavior
     */
    Polymer.IronA11yKeysBehavior = {
      properties: {
        /**
         * The HTMLElement that will be firing relevant KeyboardEvents.
         */
        keyEventTarget: {
          type: Object,
          value: function() {
            return this;
          }
        },

        _boundKeyHandlers: {
          type: Array,
          value: function() {
            return [];
          }
        },

        // We use this due to a limitation in IE10 where instances will have
        // own properties of everything on the "prototype".
        _imperativeKeyBindings: {
          type: Object,
          value: function() {
            return {};
          }
        }
      },

      observers: [
        '_resetKeyEventListeners(keyEventTarget, _boundKeyHandlers)'
      ],

      keyBindings: {},

      registered: function() {
        this._prepKeyBindings();
      },

      attached: function() {
        this._listenKeyEventListeners();
      },

      detached: function() {
        this._unlistenKeyEventListeners();
      },

      /**
       * Can be used to imperatively add a key binding to the implementing
       * element. This is the imperative equivalent of declaring a keybinding
       * in the `keyBindings` prototype property.
       */
      addOwnKeyBinding: function(eventString, handlerName) {
        this._imperativeKeyBindings[eventString] = handlerName;
        this._prepKeyBindings();
        this._resetKeyEventListeners();
      },

      /**
       * When called, will remove all imperatively-added key bindings.
       */
      removeOwnKeyBindings: function() {
        this._imperativeKeyBindings = {};
        this._prepKeyBindings();
        this._resetKeyEventListeners();
      },

      keyboardEventMatchesKeys: function(event, eventString) {
        var keyCombos = parseEventString(eventString);
        var index;

        for (index = 0; index < keyCombos.length; ++index) {
          if (keyComboMatchesEvent(keyCombos[index], event)) {
            return true;
          }
        }

        return false;
      },

      _collectKeyBindings: function() {
        var keyBindings = this.behaviors.map(function(behavior) {
          return behavior.keyBindings;
        });

        if (keyBindings.indexOf(this.keyBindings) === -1) {
          keyBindings.push(this.keyBindings);
        }

        return keyBindings;
      },

      _prepKeyBindings: function() {
        this._keyBindings = {};

        this._collectKeyBindings().forEach(function(keyBindings) {
          for (var eventString in keyBindings) {
            this._addKeyBinding(eventString, keyBindings[eventString]);
          }
        }, this);

        for (var eventString in this._imperativeKeyBindings) {
          this._addKeyBinding(eventString, this._imperativeKeyBindings[eventString]);
        }
      },

      _addKeyBinding: function(eventString, handlerName) {
        parseEventString(eventString).forEach(function(keyCombo) {
          this._keyBindings[keyCombo.event] =
            this._keyBindings[keyCombo.event] || [];

          this._keyBindings[keyCombo.event].push([
            keyCombo,
            handlerName
          ]);
        }, this);
      },

      _resetKeyEventListeners: function() {
        this._unlistenKeyEventListeners();

        if (this.isAttached) {
          this._listenKeyEventListeners();
        }
      },

      _listenKeyEventListeners: function() {
        Object.keys(this._keyBindings).forEach(function(eventName) {
          var keyBindings = this._keyBindings[eventName];
          var boundKeyHandler = this._onKeyBindingEvent.bind(this, keyBindings);

          this._boundKeyHandlers.push([this.keyEventTarget, eventName, boundKeyHandler]);

          this.keyEventTarget.addEventListener(eventName, boundKeyHandler);
        }, this);
      },

      _unlistenKeyEventListeners: function() {
        var keyHandlerTuple;
        var keyEventTarget;
        var eventName;
        var boundKeyHandler;

        while (this._boundKeyHandlers.length) {
          // My kingdom for block-scope binding and destructuring assignment..
          keyHandlerTuple = this._boundKeyHandlers.pop();
          keyEventTarget = keyHandlerTuple[0];
          eventName = keyHandlerTuple[1];
          boundKeyHandler = keyHandlerTuple[2];

          keyEventTarget.removeEventListener(eventName, boundKeyHandler);
        }
      },

      _onKeyBindingEvent: function(keyBindings, event) {
        keyBindings.forEach(function(keyBinding) {
          var keyCombo = keyBinding[0];
          var handlerName = keyBinding[1];

          if (!event.defaultPrevented && keyComboMatchesEvent(keyCombo, event)) {
            this._triggerKeyHandler(keyCombo, handlerName, event);
          }
        }, this);
      },

      _triggerKeyHandler: function(keyCombo, handlerName, keyboardEvent) {
        var detail = Object.create(keyCombo);
        detail.keyboardEvent = keyboardEvent;

        this[handlerName].call(this, new CustomEvent(keyCombo.event, {
          detail: detail
        }));
      }
    };
  })();
</script>