/*
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.
    
Adobe Systems Incorporated grants to you a perpetual, worldwide, non-exclusive,
no-charge, royalty-free, irrevocable copyright license, to reproduce,
prepare derivative works of, publicly display, publicly perform, and
distribute this source code and such derivative works in source or
object code form without any attribution requirements.
    
The name "Adobe Systems Incorporated" must not be used to endorse or promote products
derived from the source code without prior written permission.
    
You agree to indemnify, hold harmless and defend Adobe Systems Incorporated from and
against any loss, damage, claims or lawsuits, including attorney's
fees that arise or result from your use or distribution of the source
code.
    
THIS SOURCE CODE IS PROVIDED "AS IS" AND "WITH ALL FAULTS", WITHOUT
ANY TECHNICAL SUPPORT OR ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. ALSO, THERE IS NO WARRANTY OF
NON-INFRINGEMENT, TITLE OR QUIET ENJOYMENT. IN NO EVENT SHALL MACROMEDIA
OR ITS SUPPLIERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOURCE CODE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package com.adobe.serialization.json {

    public class JSONTokenizer {
    
        /** The object that will get parsed from the JSON string */
        private var obj:Object;
        
        /** The JSON string to be parsed */
        private var jsonString:String;
        
        /** The current parsing location in the JSON string */
        private var loc:int;
        
        /** The current character in the JSON string during parsing */
        private var ch:String;
        
        /**
         * Constructs a new JSONDecoder to parse a JSON string 
         * into a native object.
         *
         * @param s The JSON string to be converted
         *        into a native object
         */
        public function JSONTokenizer( s:String ) {
            jsonString = s;
            loc = 0;
            
            // prime the pump by getting the first character
            nextChar();
        }
        
        /**
         * Gets the next token in the input sting and advances
        * the character to the next character after the token
         */
        public function getNextToken():JSONToken {
            var token:JSONToken = new JSONToken();
            
            // skip any whitespace / comments since the last 
            // token was read
            skipIgnored();
                        
            // examine the new character and see what we have...
            switch ( ch ) {
                
                case '{':
                    token.type = JSONTokenType.LEFT_BRACE;
                    token.value = '{';
                    nextChar();
                    break
                    
                case '}':
                    token.type = JSONTokenType.RIGHT_BRACE;
                    token.value = '}';
                    nextChar();
                    break
                    
                case '[':
                    token.type = JSONTokenType.LEFT_BRACKET;
                    token.value = '[';
                    nextChar();
                    break
                    
                case ']':
                    token.type = JSONTokenType.RIGHT_BRACKET;
                    token.value = ']';
                    nextChar();
                    break
                
                case ',':
                    token.type = JSONTokenType.COMMA;
                    token.value = ',';
                    nextChar();
                    break
                    
                case ':':
                    token.type = JSONTokenType.COLON;
                    token.value = ':';
                    nextChar();
                    break;
                    
                case 't': // attempt to read true
                    var possibleTrue:String = "t" + nextChar() + nextChar() + nextChar();
                    
                    if ( possibleTrue == "true" ) {
                        token.type = JSONTokenType.TRUE;
                        token.value = true;
                        nextChar();
                    } else {
                        parseError( "Expecting 'true' but found " + possibleTrue );
                    }
                    
                    break;
                    
                case 'f': // attempt to read false
                    var possibleFalse:String = "f" + nextChar() + nextChar() + nextChar() + nextChar();
                    
                    if ( possibleFalse == "false" ) {
                        token.type = JSONTokenType.FALSE;
                        token.value = false;
                        nextChar();
                    } else {
                        parseError( "Expecting 'false' but found " + possibleFalse );
                    }
                    
                    break;
                    
                case 'n': // attempt to read null
                
                    var possibleNull:String = "n" + nextChar() + nextChar() + nextChar();
                    
                    if ( possibleNull == "null" ) {
                        token.type = JSONTokenType.NULL;
                        token.value = null;
                        nextChar();
                    } else {
                        parseError( "Expecting 'null' but found " + possibleNull );
                    }
                    
                    break;
                    
                case '"': // the start of a string
                    token = readString();
                    break;
                    
                default: 
                    // see if we can read a number
                    if ( isDigit( ch ) || ch == '-' ) {
                        token = readNumber();
                    } else if ( ch == '' ) {
                        // check for reading past the end of the string
                        return null;
                    } else {                        
                        // not sure what was in the input string - it's not
                        // anything we expected
                        parseError( "Unexpected " + ch + " encountered" );
                    }
            }
            
            return token;
        }
        
        /**
         * Attempts to read a string from the input string.  Places
         * the character location at the first character after the
         * string.  It is assumed that ch is " before this method is called.
         *
         * @return the JSONToken with the string value if a string could
         *        be read.  Throws an error otherwise.
         */
        private function readString():JSONToken {
            // the token for the string we'll try to read
            var token:JSONToken = new JSONToken();
            token.type = JSONTokenType.STRING;
            
            // the string to store the string we'll try to read
            var string:String = "";
            
            // advance past the first "
            nextChar();
            
            while ( ch != '"' && ch != '' ) {
                                
                // unescape the escape sequences in the string
                if ( ch == '\\' ) {
                    
                    // get the next character so we know what
                    // to unescape
                    nextChar();
                    
                    switch ( ch ) {
                        
                        case '"': // quotation mark
                            string += '"';
                            break;
                        
                        case '/':    // solidus
                            string += "/";
                            break;
                            
                        case '\\':    // reverse solidus
                            string += '\\';
                            break;
                            
                        case 'b':    // bell
                            string += '\b';
                            break;
                            
                        case 'f':    // form feed
                            string += '\f';
                            break;
                            
                        case 'n':    // newline
                            string += '\n';
                            break;
                            
                        case 'r':    // carriage return
                            string += '\r';
                            break;
                            
                        case 't':    // horizontal tab
                            string += '\t'
                            break;
                        
                        case 'u':
                            // convert a unicode escape sequence
                            // to it's character value - expecting
                            // 4 hex digits
                            
                            // save the characters as a string we'll convert to an int
                            var hexValue:String = "";
                            
                            // try to find 4 hex characters
                            for ( var i:int = 0; i < 4; i++ ) {
                                // get the next character and determine
                                // if it's a valid hex digit or not
                                if ( !isHexDigit( nextChar() ) ) {
                                    parseError( " Excepted a hex digit, but found: " + ch );
                                }
                                // valid, add it to the value
                                hexValue += ch;
                            }
                            
                            // convert hexValue to an integer, and use that
                            // integrer value to create a character to add
                            // to our string.
                            string += String.fromCharCode( parseInt( hexValue, 16 ) );
                            
                            break;
                    
                        default:
                            // couldn't unescape the sequence, so just
                            // pass it through
                            string += '\\' + ch;
                        
                    }
                    
                } else {
                    // didn't have to unescape, so add the character to the string
                    string += ch;
                    
                }
                
                // move to the next character
                nextChar();
                
            }
            
            // we read past the end of the string without closing it, which
            // is a parse error
            if ( ch == '' ) {
                parseError( "Unterminated string literal" );
            }
            
            // move past the closing " in the input string
            nextChar();
            
            // attach to the string to the token so we can return it
            token.value = string;
            
            return token;
        }
        
        /**
         * Attempts to read a number from the input string.  Places
         * the character location at the first character after the
         * number.
         * 
         * @return The JSONToken with the number value if a number could
         *         be read.  Throws an error otherwise.
         */
        private function readNumber():JSONToken {
            // the token for the number we'll try to read
            var token:JSONToken = new JSONToken();
            token.type = JSONTokenType.NUMBER;
            
            // the string to accumulate the number characters
            // into that we'll convert to a number at the end
            var input:String = "";
            
            // check for a negative number
            if ( ch == '-' ) {
                input += '-';
                nextChar();
            }
            
            // the number must start with a digit
            if ( !isDigit( ch ) )
            {
                parseError( "Expecting a digit" );
            }
            
            // 0 can only be the first digit if it
            // is followed by a decimal point
            if ( ch == '0' )
            {
                input += ch;
                nextChar();
                
                // make sure no other digits come after 0
                if ( isDigit( ch ) )
                {
                    parseError( "A digit cannot immediately follow 0" );
                }
            }
            else
            {
                // read numbers while we can
                while ( isDigit( ch ) ) {
                    input += ch;
                    nextChar();
                }
            }
            
            // check for a decimal value
            if ( ch == '.' ) {
                input += '.';
                nextChar();
                
                // after the decimal there has to be a digit
                if ( !isDigit( ch ) )
                {
                    parseError( "Expecting a digit" );
                }
                
                // read more numbers to get the decimal value
                while ( isDigit( ch ) ) {
                    input += ch;
                    nextChar();
                }
            }
            
            // check for scientific notation
            if ( ch == 'e' || ch == 'E' )
            {
                input += "e"
                nextChar();
                // check for sign
                if ( ch == '+' || ch == '-' )
                {
                    input += ch;
                    nextChar();
                }
                
                // require at least one number for the exponent
                // in this case
                if ( !isDigit( ch ) )
                {
                    parseError( "Scientific notation number needs exponent value" );
                }
                            
                // read in the exponent
                while ( isDigit( ch ) )
                {
                    input += ch;
                    nextChar();
                }
            }
            
            // convert the string to a number value
            var num:Number = Number( input );
            
            if ( isFinite( num ) && !isNaN( num ) ) {
                token.value = num;
                return token;
            } else {
                parseError( "Number " + num + " is not valid!" );
            }
            return null;
        }

        /**
         * Reads the next character in the input
         * string and advances the character location.
         *
         * @return The next character in the input string, or
         *        null if we've read past the end.
         */
        private function nextChar():String {
            return ch = jsonString.charAt( loc++ );
        }
        
        /**
         * Advances the character location past any
         * sort of white space and comments
         */
        private function skipIgnored():void {
            skipWhite();
            skipComments();
            skipWhite();
        }
        
        /**
         * Skips comments in the input string, either
         * single-line or multi-line.  Advances the character
         * to the first position after the end of the comment.
         */
        private function skipComments():void {
            if ( ch == '/' ) {
                // Advance past the first / to find out what type of comment
                nextChar();
                switch ( ch ) {
                    case '/': // single-line comment, read through end of line
                        
                        // Loop over the characters until we find
                        // a newline or until there's no more characters left
                        do {
                            nextChar();
                        } while ( ch != '\n' && ch != '' )
                        
                        // move past the \n
                        nextChar();
                        
                        break;
                    
                    case '*': // multi-line comment, read until closing */

                        // move past the opening *
                        nextChar();
                        
                        // try to find a trailing */
                        while ( true ) {
                            if ( ch == '*' ) {
                                // check to see if we have a closing /
                                nextChar();
                                if ( ch == '/') {
                                    // move past the end of the closing */
                                    nextChar();
                                    break;
                                }
                            } else {
                                // move along, looking if the next character is a *
                                nextChar();
                            }
                            
                            // when we're here we've read past the end of 
                            // the string without finding a closing */, so error
                            if ( ch == '' ) {
                                parseError( "Multi-line comment not closed" );
                            }
                        }

                        break;
                    
                    // Can't match a comment after a /, so it's a parsing error
                    default:
                        parseError( "Unexpected " + ch + " encountered (expecting '/' or '*' )" );
                }
            }
            
        }
        
        
        /**
         * Skip any whitespace in the input string and advances
         * the character to the first character after any possible
         * whitespace.
         */
        private function skipWhite():void {
            
            // As long as there are spaces in the input 
            // stream, advance the current location pointer
            // past them
            while ( isWhiteSpace( ch ) ) {
                nextChar();
            }
            
        }
        
        /**
         * Determines if a character is whitespace or not.
         *
         * @return True if the character passed in is a whitespace
         *    character
         */
        private function isWhiteSpace( ch:String ):Boolean {
            return ( ch == ' ' || ch == '\t' || ch == '\n' );
        }
        
        /**
         * Determines if a character is a digit [0-9].
         *
         * @return True if the character passed in is a digit
         */
        private function isDigit( ch:String ):Boolean {
            return ( ch >= '0' && ch <= '9' );
        }
        
        /**
         * Determines if a character is a digit [0-9].
         *
         * @return True if the character passed in is a digit
         */
        private function isHexDigit( ch:String ):Boolean {
            // get the uppercase value of ch so we only have
            // to compare the value between 'A' and 'F'
            var uc:String = ch.toUpperCase();
            
            // a hex digit is a digit of A-F, inclusive ( using
            // our uppercase constraint )
            return ( isDigit( ch ) || ( uc >= 'A' && uc <= 'F' ) );
        }
    
        /**
         * Raises a parsing error with a specified message, tacking
         * on the error location and the original string.
         *
         * @param message The message indicating why the error occurred
         */
        public function parseError( message:String ):void {
            throw new JSONParseError( message, loc, jsonString );
        }
    }
    
}