/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

var Guacamole = Guacamole || {};

/**
 * Simple Guacamole protocol parser that invokes an oninstruction event when
 * full instructions are available from data received via receive().
 * 
 * @constructor
 */
Guacamole.Parser = function() {

    /**
     * Reference to this parser.
     * @private
     */
    var parser = this;

    /**
     * Current buffer of received data. This buffer grows until a full
     * element is available. After a full element is available, that element
     * is flushed into the element buffer.
     * 
     * @private
     */
    var buffer = "";

    /**
     * Buffer of all received, complete elements. After an entire instruction
     * is read, this buffer is flushed, and a new instruction begins.
     * 
     * @private
     */
    var element_buffer = [];

    // The location of the last element's terminator
    var element_end = -1;

    // Where to start the next length search or the next element
    var start_index = 0;

    /**
     * Appends the given instruction data packet to the internal buffer of
     * this Guacamole.Parser, executing all completed instructions at
     * the beginning of this buffer, if any.
     *
     * @param {String} packet The instruction data to receive.
     */
    this.receive = function(packet) {

        // Truncate buffer as necessary
        if (start_index > 4096 && element_end >= start_index) {

            buffer = buffer.substring(start_index);

            // Reset parse relative to truncation
            element_end -= start_index;
            start_index = 0;

        }

        // Append data to buffer
        buffer += packet;

        // While search is within currently received data
        while (element_end < buffer.length) {

            // If we are waiting for element data
            if (element_end >= start_index) {

                // We now have enough data for the element. Parse.
                var element = buffer.substring(start_index, element_end);
                var terminator = buffer.substring(element_end, element_end+1);

                // Add element to array
                element_buffer.push(element);

                // If last element, handle instruction
                if (terminator == ";") {

                    // Get opcode
                    var opcode = element_buffer.shift();

                    // Call instruction handler.
                    if (parser.oninstruction != null)
                        parser.oninstruction(opcode, element_buffer);

                    // Clear elements
                    element_buffer.length = 0;

                }
                else if (terminator != ',')
                    throw new Error("Illegal terminator.");

                // Start searching for length at character after
                // element terminator
                start_index = element_end + 1;

            }

            // Search for end of length
            var length_end = buffer.indexOf(".", start_index);
            if (length_end != -1) {

                // Parse length
                var length = parseInt(buffer.substring(element_end+1, length_end));
                if (isNaN(length))
                    throw new Error("Non-numeric character in element length.");

                // Calculate start of element
                start_index = length_end + 1;

                // Calculate location of element terminator
                element_end = start_index + length;

            }
            
            // If no period yet, continue search when more data
            // is received
            else {
                start_index = buffer.length;
                break;
            }

        } // end parse loop

    };

    /**
     * Fired once for every complete Guacamole instruction received, in order.
     * 
     * @event
     * @param {String} opcode The Guacamole instruction opcode.
     * @param {Array} parameters The parameters provided for the instruction,
     *                           if any.
     */
    this.oninstruction = null;

};