mx/utils/UIDUtil.as

////////////////////////////////////////////////////////////////////////////////
//
//  ADOBE SYSTEMS INCORPORATED
//  Copyright 2005-2007 Adobe Systems Incorporated
//  All Rights Reserved.
//
//  NOTICE: Adobe permits you to use, modify, and distribute this file
//  in accordance with the terms of the license agreement accompanying it.
//
////////////////////////////////////////////////////////////////////////////////

package mx.utils
{

import flash.utils.ByteArray;
import flash.utils.Dictionary;

import mx.core.IPropertyChangeNotifier;
import mx.core.IUIComponent;
import mx.core.IUID;
import mx.core.mx_internal;

use namespace mx_internal;

/**
 *  The UIDUtil class is an all-static class
 *  with methods for working with UIDs (unique identifiers) within Flex.
 *  You do not create instances of UIDUtil;
 *  instead you simply call static methods such as the
 *  <code>UIDUtil.createUID()</code> method.
 *
 *  <p><b>Note</b>: If you have a dynamic object that has no [Bindable] properties
 *  (which force the object to implement the IUID interface), Flex  adds an
 *  <code>mx_internal_uid</code> property that contains a UID to the object.
 *  To avoid having this field
 *  in your dynamic object, make it [Bindable], implement the IUID interface
 *  in the object class, or set a <coded>uid</coded> property with a value.</p>
 *
 *  @langversion 3.0
 *  @playerversion Flash 9
 *  @playerversion AIR 1.1
 *  @productversion Flex 3
 */
public class UIDUtil
{
    include "../core/Version.as";

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

    /**
     *  @private
     *  Char codes for 0123456789ABCDEF
     */
    private static const ALPHA_CHAR_CODES:Array = [48, 49, 50, 51, 52, 53, 54,
        55, 56, 57, 65, 66, 67, 68, 69, 70];

    //--------------------------------------------------------------------------
    //
    //  Class variables
    //
    //--------------------------------------------------------------------------

    /**
     *  This Dictionary records all generated uids for all existing items.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    private static var uidDictionary:Dictionary = new Dictionary(true);

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

    /**
     *  Generates a UID (unique identifier) based on ActionScript's
     *  pseudo-random number generator and the current time.
     *
     *  <p>The UID has the form
     *  <code>"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"</code>
     *  where X is a hexadecimal digit (0-9, A-F).</p>
     *
     *  <p>This UID will not be truly globally unique; but it is the best
     *  we can do without player support for UID generation.</p>
     *
     *  @return The newly-generated UID.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    public static function createUID():String
    {
        var uid:Array = new Array(36);
        var index:int = 0;

        var i:int;
        var j:int;

        for (i = 0; i < 8; i++)
        {
            uid[index++] = ALPHA_CHAR_CODES[Math.floor(Math.random() *  16)];
        }

        for (i = 0; i < 3; i++)
        {
            uid[index++] = 45; // charCode for "-"

            for (j = 0; j < 4; j++)
            {
                uid[index++] = ALPHA_CHAR_CODES[Math.floor(Math.random() *  16)];
            }
        }

        uid[index++] = 45; // charCode for "-"

        var time:Number = new Date().getTime();
        // Note: time is the number of milliseconds since 1970,
        // which is currently more than one trillion.
        // We use the low 8 hex digits of this number in the UID.
        // Just in case the system clock has been reset to
        // Jan 1-4, 1970 (in which case this number could have only
        // 1-7 hex digits), we pad on the left with 7 zeros
        // before taking the low digits.
        var timeString:String = ("0000000" + time.toString(16).toUpperCase()).substr(-8);

        for (i = 0; i < 8; i++)
        {
            uid[index++] = timeString.charCodeAt(i);
        }

        for (i = 0; i < 4; i++)
        {
            uid[index++] = ALPHA_CHAR_CODES[Math.floor(Math.random() *  16)];
        }

        return String.fromCharCode.apply(null, uid);
    }

    /**
     * Converts a 128-bit UID encoded as a ByteArray to a String representation.
     * The format matches that generated by createUID. If a suitable ByteArray
     * is not provided, null is returned.
     *
     * @param ba ByteArray 16 bytes in length representing a 128-bit UID.
     *
     * @return String representation of the UID, or null if an invalid
     * ByteArray is provided.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    public static function fromByteArray(ba:ByteArray):String
    {
        if (ba != null && ba.length >= 16 && ba.bytesAvailable >= 16)
        {
            var chars:Array = new Array(36);
            var index:uint = 0;
            for (var i:uint = 0; i < 16; i++)
            {
                if (i == 4 || i == 6 || i == 8 || i == 10)
                    chars[index++] = 45; // Hyphen char code

                var b:int = ba.readByte();
                chars[index++] = ALPHA_CHAR_CODES[(b & 0xF0) >>> 4];
                chars[index++] = ALPHA_CHAR_CODES[(b & 0x0F)];
            }
            return String.fromCharCode.apply(null, chars);
        }

        return null;
    }

    /**
     * A utility method to check whether a String value represents a
     * correctly formatted UID value. UID values are expected to be
     * in the format generated by createUID(), implying that only
     * capitalized A-F characters in addition to 0-9 digits are
     * supported.
     *
     * @param uid The value to test whether it is formatted as a UID.
     *
     * @return Returns true if the value is formatted as a UID.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    public static function isUID(uid:String):Boolean
    {
        if (uid != null && uid.length == 36)
        {
            for (var i:uint = 0; i < 36; i++)
            {
                var c:Number = uid.charCodeAt(i);

                // Check for correctly placed hyphens
                if (i == 8 || i == 13 || i == 18 || i == 23)
                {
                    if (c != 45)
                    {
                        return false;
                    }
                }
                // We allow capital alpha-numeric hex digits only
                else if (c < 48 || c > 70 || (c > 57 && c < 65))
                {
                    return false;
                }
            }

            return true;
        }

        return false;
    }

    /**
     * Converts a UID formatted String to a ByteArray. The UID must be in the
     * format generated by createUID, otherwise null is returned.
     *
     * @param String representing a 128-bit UID
     *
     * @return ByteArray 16 bytes in length representing the 128-bits of the
     * UID or null if the uid could not be converted.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    public static function toByteArray(uid:String):ByteArray
    {
        if (isUID(uid))
        {
            var result:ByteArray = new ByteArray();

            for (var i:uint = 0; i < uid.length; i++)
            {
                var c:String = uid.charAt(i);
                if (c == "-")
                    continue;
                var h1:uint = getDigit(c);
                i++;
                var h2:uint = getDigit(uid.charAt(i));
                result.writeByte(((h1 << 4) | h2) & 0xFF);
            }
            result.position = 0;
            return result;
        }

        return null;
    }

    /**
     *  Returns the UID (unique identifier) for the specified object.
     *  If the specified object doesn't have an UID
     *  then the method assigns one to it.
     *  If a map is specified this method will use the map
     *  to construct the UID.
     *  As a special case, if the item passed in is null,
     *  this method returns a null UID.
     *
     *  @param item Object that we need to find the UID for.
     *
     *  @return The UID that was either found or generated.
     *
     *  @langversion 3.0
     *  @playerversion Flash 9
     *  @playerversion AIR 1.1
     *  @productversion Flex 3
     */
    public static function getUID(item:Object):String
    {
        var result:String = null;

        if (item == null)
            return result;

        if (item is IUID)
        {
            result = IUID(item).uid;
            if (result == null || result.length == 0)
            {
                result = createUID();
                IUID(item).uid = result;
            }
        }
        else if ((item is IPropertyChangeNotifier) &&
                 !(item is IUIComponent))
        {
            result = IPropertyChangeNotifier(item).uid;
            if (result == null || result.length == 0)
            {
                result = createUID();
                IPropertyChangeNotifier(item).uid = result;
            }
        }
        else if (item is String)
        {
            return item as String;
        }
        else
        {
            try
            {
                // We don't create uids for XMLLists, but if
                // there's only a single XML node, we'll extract it.
                if (item is XMLList && item.length == 1)
                    item = item[0];

                if (item is XML)
                {
                    // XML nodes carry their UID on the
                    // function-that-is-a-hashtable they can carry around.
                    // To decorate an XML node with a UID,
                    // we need to first initialize it for notification.
                    // There is a potential performance issue here,
                    // since notification does have a cost,
                    // but most use cases for needing a UID on an XML node also
                    // require listening for change notifications on the node.
                    var xitem:XML = XML(item);
                    var nodeKind:String = xitem.nodeKind();
                    if (nodeKind == "text" || nodeKind == "attribute")
                        return xitem.toString();

                    var notificationFunction:Function = xitem.notification();
                    if (!(notificationFunction is Function))
                    {
                        // The xml node hasn't already been initialized
                        // for notification, so do so now.
                        notificationFunction =
                            XMLNotifier.initializeXMLForNotification();
                        xitem.setNotification(notificationFunction);
                    }

                    // Generate a new uid for the node if necessary.
                    if (notificationFunction["uid"] == undefined)
                        result = notificationFunction["uid"] = createUID();

                    result = notificationFunction["uid"];
                }
                else
                {
                    if ("mx_internal_uid" in item)
                        return item.mx_internal_uid;

                    if ("uid" in item)
                        return item.uid;

                    result = uidDictionary[item];

                    if (!result)
                    {
                        result = createUID();
                        try
                        {
                            item.mx_internal_uid = result;
                        }
                        catch(e:Error)
                        {
                            uidDictionary[item] = result;
                        }
                    }
                }
            }
            catch(e:Error)
            {
                result = item.toString();
            }
        }

        return result;
    }

    /**
     * Returns the decimal representation of a hex digit.
     * @private
     */
    private static function getDigit(hex:String):uint
    {
        switch (hex)
        {
            case "A":
            case "a":
                return 10;
            case "B":
            case "b":
                return 11;
            case "C":
            case "c":
                return 12;
            case "D":
            case "d":
                return 13;
            case "E":
            case "e":
                return 14;
            case "F":
            case "f":
                return 15;
            default:
                return new uint(hex);
        }
    }
}

}