/*
Adobe Systems Incorporated(r) Source Code License Agreement
Copyright(c) 2005 Adobe Systems Incorporated. All rights reserved.
	
Please read this Source Code License Agreement carefully before using
the source code.
	
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THIS SOURCE CODE IS PROVIDED "AS IS" AND "WITH ALL FAULTS", WITHOUT
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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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*/

package com.adobe.serialization.json 
{

	import flash.utils.describeType;

	public class JSONEncoder {
	
		/** The string that is going to represent the object we're encoding */
		private var jsonString:String;
		
		/**
		 * Creates a new JSONEncoder.
		 *
		 * @param o The object to encode as a JSON string
		 * @langversion ActionScript 3.0
		 * @playerversion Flash 9.0
		 * @tiptext
		 */
		public function JSONEncoder( value:* ) {
			jsonString = convertToString( value );
		
		}
		
		/**
		 * Gets the JSON string from the encoder.
		 *
		 * @return The JSON string representation of the object
		 * 		that was passed to the constructor
		 * @langversion ActionScript 3.0
		 * @playerversion Flash 9.0
		 * @tiptext
		 */
		public function getString():String {
			return jsonString;
		}
		
		/**
		 * Converts a value to it's JSON string equivalent.
		 *
		 * @param value The value to convert.  Could be any 
		 *		type (object, number, array, etc)
		 */
		private function convertToString( value:* ):String {
			
			// determine what value is and convert it based on it's type
			if ( value is String ) {
				
				// escape the string so it's formatted correctly
				return escapeString( value as String );
				
			} else if ( value is Number ) {
				
				// only encode numbers that finate
				return isFinite( value as Number) ? value.toString() : "null";

			} else if ( value is Boolean ) {
				
				// convert boolean to string easily
				return value ? "true" : "false";

			} else if ( value is Array ) {
			
				// call the helper method to convert an array
				return arrayToString( value as Array );
			
			} else if ( value is Object && value != null ) {
			
				// call the helper method to convert an object
				return objectToString( value );
			}
            return "null";
		}
		
		/**
		 * Escapes a string accoding to the JSON specification.
		 *
		 * @param str The string to be escaped
		 * @return The string with escaped special characters
		 * 		according to the JSON specification
		 */
		private function escapeString( str:String ):String {
			// create a string to store the string's jsonstring value
			var s:String = "";
			// current character in the string we're processing
			var ch:String;
			// store the length in a local variable to reduce lookups
			var len:Number = str.length;
			
			// loop over all of the characters in the string
			for ( var i:int = 0; i < len; i++ ) {
			
				// examine the character to determine if we have to escape it
				ch = str.charAt( i );
				switch ( ch ) {
				
					case '"':	// quotation mark
						s += "\\\"";
						break;
						
					//case '/':	// solidus
					//	s += "\\/";
					//	break;
						
					case '\\':	// reverse solidus
						s += "\\\\";
						break;
						
					case '\b':	// bell
						s += "\\b";
						break;
						
					case '\f':	// form feed
						s += "\\f";
						break;
						
					case '\n':	// newline
						s += "\\n";
						break;
						
					case '\r':	// carriage return
						s += "\\r";
						break;
						
					case '\t':	// horizontal tab
						s += "\\t";
						break;
						
					default:	// everything else
						
						// check for a control character and escape as unicode
						if ( ch < ' ' ) {
							// get the hex digit(s) of the character (either 1 or 2 digits)
							var hexCode:String = ch.charCodeAt( 0 ).toString( 16 );
							
							// ensure that there are 4 digits by adjusting
							// the # of zeros accordingly.
							var zeroPad:String = hexCode.length == 2 ? "00" : "000";
							
							// create the unicode escape sequence with 4 hex digits
							s += "\\u" + zeroPad + hexCode;
						} else {
						
							// no need to do any special encoding, just pass-through
							s += ch;
							
						}
				}	// end switch
				
			}	// end for loop
						
			return "\"" + s + "\"";
		}
		
		/**
		 * Converts an array to it's JSON string equivalent
		 *
		 * @param a The array to convert
		 * @return The JSON string representation of <code>a</code>
		 */
		private function arrayToString( a:Array ):String {
			// create a string to store the array's jsonstring value
			var s:String = "";
			
			// loop over the elements in the array and add their converted
			// values to the string
			for ( var i:int = 0; i < a.length; i++ ) {
				// when the length is 0 we're adding the first element so
				// no comma is necessary
				if ( s.length > 0 ) {
					// we've already added an element, so add the comma separator
					s += ","
				}
				
				// convert the value to a string
				s += convertToString( a[i] );	
			}
			
			// KNOWN ISSUE:  In ActionScript, Arrays can also be associative
			// objects and you can put anything in them, ie:
			//		myArray["foo"] = "bar";
			//
			// These properties aren't picked up in the for loop above because
			// the properties don't correspond to indexes.  However, we're
			// sort of out luck because the JSON specification doesn't allow
			// these types of array properties.
			//
			// So, if the array was also used as an associative object, there
			// may be some values in the array that don't get properly encoded.
			//
			// A possible solution is to instead encode the Array as an Object
			// but then it won't get decoded correctly (and won't be an
			// Array instance)
						
			// close the array and return it's string value
			return "[" + s + "]";
		}
		
		/**
		 * Converts an object to it's JSON string equivalent
		 *
		 * @param o The object to convert
		 * @return The JSON string representation of <code>o</code>
		 */
		private function objectToString( o:Object ):String
		{
			// create a string to store the object's jsonstring value
			var s:String = "";
			
			// determine if o is a class instance or a plain object
			var classInfo:XML = describeType( o );
			if ( classInfo.@name.toString() == "Object" )
			{
				// the value of o[key] in the loop below - store this 
				// as a variable so we don't have to keep looking up o[key]
				// when testing for valid values to convert
				var value:Object;
				
				// loop over the keys in the object and add their converted
				// values to the string
				for ( var key:String in o )
				{
					// assign value to a variable for quick lookup
					value = o[key];
					
					// don't add function's to the JSON string
					if ( value is Function )
					{
						// skip this key and try another
						continue;
					}
					
					// when the length is 0 we're adding the first item so
					// no comma is necessary
					if ( s.length > 0 ) {
						// we've already added an item, so add the comma separator
						s += ","
					}
					
					s += escapeString( key ) + ":" + convertToString( value );
				}
			}
			else // o is a class instance
			{
				// Loop over all of the variables and accessors in the class and 
				// serialize them along with their values.
				for each ( var v:XML in classInfo..*.( name() == "variable" || name() == "accessor" ) )
				{
					// When the length is 0 we're adding the first item so
					// no comma is necessary
					if ( s.length > 0 ) {
						// We've already added an item, so add the comma separator
						s += ","
					}
					
					s += escapeString( v.@name.toString() ) + ":" 
							+ convertToString( o[ v.@name ] );
				}
				
			}
			
			return "{" + s + "}";
		}

		
	}
	
}