/*
 * 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.
 */

/* $Id$ */

package org.apache.fop.afp.parser;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.apache.fop.afp.parser.UnparsedStructuredField.Introducer;

/**
 * An simple MO:DCA/AFP parser.
 */
public class MODCAParser {

    private static final Log LOG = LogFactory.getLog(MODCAParser.class);

    private static final int INTRODUCER_LENGTH = 8;

    /** The carriage control character (0x5A) used to indicate the start of a structured field. */
    public static final byte CARRIAGE_CONTROL_CHAR = (byte)(0x5A & 0xFF);

    private DataInputStream din;

    /**
     * Main constructor
     * @param in the {@link InputStream} to read the AFP file from.
     */
    public MODCAParser(InputStream in) {
        this.din = new DataInputStream(in);
    }


    /**
     * Reads the next structured field from the input stream.
     * <p>
     * No structure validation of the MO:DCA file is performed.
     * @return a new unparsed structured field (or null when parsing is finished).
     * @throws IOException if an I/O error occurs
     */
    public UnparsedStructuredField readNextStructuredField() throws IOException {

        //Find the SF delimiter
        do {
            //Exhausted streams and so no next SF
            //  - null return represents this case
            //  TODO should this happen?
            if (din.available() == 0) {
                return null;
            }
        } while (din.readByte() != CARRIAGE_CONTROL_CHAR);

        //Read introducer as byte array to preserve any data not parsed below
        byte[] introducerData = new byte[INTRODUCER_LENGTH]; //Length of introducer
        din.readFully(introducerData);

        Introducer introducer = new Introducer(introducerData);

        int dataLength = introducer.getLength() - INTRODUCER_LENGTH;

        //Handle optional extension
        byte[] extData = null;
        if (introducer.isExtensionPresent()) {
            short extLength = 0;
            extLength = (short)((din.readByte()) & 0xFF);
            if (extLength > 0) {
                extData = new byte[extLength - 1];
                din.readFully(extData);
                dataLength -= extLength;
            }
        }
        //Read payload
        byte[] data = new byte[dataLength];
        din.readFully(data);

        UnparsedStructuredField sf = new UnparsedStructuredField(introducer, data, extData);

        if (LOG.isTraceEnabled()) {
            LOG.trace(sf);
        }

        return sf;
    }
}