// Copyright 2007. Adobe Systems Incorporated. All Rights Reserved.
package fl.accessibility {
	
	import fl.controls.LabelButton;
	import fl.controls.CheckBox;
	import fl.core.UIComponent;

    /**
     *  The CheckBoxAccImpl class, also called the CheckBox Accessibility Implementation class,
     *  is used to make a CheckBox component accessible. This class enables communication 
     *  between a CheckBox component and a screen reader. Screen readers are used to translate
     *  screen content into synthesized speech or braille for visually impaired users. 
     * 
     * <p>The CheckBoxAccImpl class supports system roles, object-based events, and states.</p>
     * 
     * <p>A CheckBox reports the role <code>ROLE_SYSTEM_CHECKBUTTON</code> (0x2C) to a screen 
     * reader.</p>
     *
     * <p>A CheckBox reports the following states to a screen reader:</p>
     * <ul>
     *     <li><code>STATE_SYSTEM_NORMAL</code> (0x00000000)</li>
     *     <li><code>STATE_SYSTEM_UNAVAILABLE</code> (0x00000001)</li>
     *     <li><code>STATE_SYSTEM_FOCUSED</code> (0x00000004)</li>
     *     <li><code>STATE_SYSTEM_PRESSED</code> (0x00000008)</li>
     *     <li><code>STATE_SYSTEM_CHECKED</code> (0x00000010)</li>
     *     <li><code>STATE_SYSTEM_FOCUSABLE</code> (0x00100000)</li>
     * </ul>
     *
     * <p>A CheckBox dispatches the following events to a screen reader:</p>
     * <ul>
     *     <li><code>EVENT_OBJECT_STATECHANGE</code> (0x800A)</li>
     *     <li><code>EVENT_OBJECT_NAMECHANGE</code> (0x800C)</li>
     * </ul>
     * 
     * <p>Screen reader users can activate a Checkbox component with the spacebar or the Enter key.</p>
     *
     * @see fl.controls.CheckBox CheckBox
     *
     * @langversion 3.0
     * @playerversion Flash 9.0.28.0
     */
	public class CheckBoxAccImpl extends LabelButtonAccImpl {
        /**
         *  @private
         *  Static variable triggering the <code>hookAccessibility()</code> method.
         *  This is used for initializing CheckBoxAccImpl class to hook its
         *  <code>createAccessibilityImplementation()</code> method to CheckBox class 
         *  before it gets called from UIComponent.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
         */
		private static var accessibilityHooked:Boolean = hookAccessibility();

        /**
         *  @private
         *  Static method for swapping the <code>createAccessibilityImplementation()</code>
         *  method of CheckBox with the CheckBoxAccImpl class.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
         */
		private static function hookAccessibility():Boolean {
			CheckBox.createAccessibilityImplementation = createAccessibilityImplementation;
			return true;
		}

		//--------------------------------------------------------------------------
		//  Class constants
		//--------------------------------------------------------------------------

        /**
         *  @private
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
         */
		private static const STATE_SYSTEM_CHECKED:uint = 0x00000010;

		//--------------------------------------------------------------------------
		//  Class methods
		//--------------------------------------------------------------------------

        /**
         *  @private
         *  Method for creating the Accessibility class.
         *  This method is called from UIComponent.
         * 
         *  @param component The UIComponent instance that this AccImpl instance
         *  is making accessible.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
         */
		public static function createAccessibilityImplementation(component:UIComponent):void {
			component.accessibilityImplementation = new CheckBoxAccImpl(component);
		}
	
		/**
         *  Enables accessibility for a CheckBox component.
		 *  This method is required for the compiler to activate
         *  the accessibility classes for a component.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
		 */
		public static function enableAccessibility():void {
		}
	
		//--------------------------------------------------------------------------
		//  Constructor
		//--------------------------------------------------------------------------
	
        /**
         * @private
         * @internal Nivesh says: I don't think we should document the constructors 
         *           for the accessibility classes.  End-users just have to call the 
         *           static enableAccessibility method.  They don't really create an 
         *           instance of the classes.
         *
		 *  Creates a CheckBoxAccImpl instance for the specified CheckBox component.
		 *
		 *  @param component The CheckBox instance that this CheckBoxAccImpl instance
         *  makes accessible.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
		 */
		public function CheckBoxAccImpl(component:UIComponent) {
			super(component);
			role = 0x2C;
		}
	
		//--------------------------------------------------------------------------
		//  Overridden methods: AccessibilityImplementation
		//--------------------------------------------------------------------------
	
		/**
		 *  @private
		 *  IAccessible method for returning the state of the CheckBox.
		 *  States are predefined for all the components in MSAA.
		 *  Values are assigned to each state.
		 *  Depending upon whether the CheckBox is checked or unchecked,
		 *  a value is returned.
		 *
		 *  @param childID The child id.
		 *
         *  @return State.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
		 */
		override public function get_accState(childID:uint):uint {
			var accState:uint = getState(childID);
			if (LabelButton(master).selected) {
				accState |= STATE_SYSTEM_CHECKED;
			}
			return accState;
		}
	
		/**
		 *  @private
		 *  IAccessible method for returning the default action of
		 *  the CheckBox, which is Check or UnCheck depending on the state.
		 *
		 *  @param childID The child id.
		 *
         *  @return DefaultAction.
         *
         * @langversion 3.0
         * @playerversion Flash 9.0.28.0
		 */
		override public function get_accDefaultAction(childID:uint):String {
			return LabelButton(master).selected ? "UnCheck" : "Check";
		}
	}
}