<?php

/**
 *  PEL: PHP Exif Library.  A library with support for reading and
 *  writing all Exif headers in JPEG and TIFF images using PHP.
 *
 *  Copyright (C) 2004, 2005  Martin Geisler.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program in the file COPYING; if not, write to the
 *  Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 *  Boston, MA 02110-1301 USA
 */

/* $Id$ */


/**
 * Classes for dealing with Exif data.
 *
 * @author Martin Geisler <mgeisler@users.sourceforge.net>
 * @version $Revision$
 * @date $Date$
 * @license http://www.gnu.org/licenses/gpl.html GNU General Public
 * License (GPL)
 * @package PEL
 */

/**#@+ Required class definitions. */
require_once('PelJpegContent.php');
require_once('PelException.php');
require_once('PelFormat.php');
require_once('PelEntry.php');
require_once('PelTiff.php');
require_once('PelIfd.php');
require_once('PelTag.php');
require_once('Pel.php');
/**#@-*/


/**
 * Class representing Exif data.
 *
 * Exif data resides as {@link PelJpegContent data} and consists of a
 * header followed by a number of {@link PelJpegIfd IFDs}.
 *
 * The interesting method in this class is {@link getTiff()} which
 * will return the {@link PelTiff} object which really holds the data
 * which one normally think of when talking about Exif data.  This is
 * because Exif data is stored as an extension of the TIFF file
 * format.
 *
 * @author Martin Geisler <mgeisler@users.sourceforge.net>
 * @package PEL
 */
class PelExif extends PelJpegContent {

    /**
     * Exif header.
     *
     * The Exif data must start with these six bytes to be considered
     * valid.
     */
    const EXIF_HEADER = "Exif\0\0";

    /**
     * The PelTiff object contained within.
     *
     * @var PelTiff
     */
    private $tiff = null;


    /**
     * Construct a new Exif object.
     *
     * The new object will be empty --- use the {@link load()} method to
     * load Exif data from a {@link PelDataWindow} object, or use the
     * {@link setTiff()} to change the {@link PelTiff} object, which is
     * the true holder of the Exif {@link PelEntry entries}.
     */
    function __construct() {

    }


    /**
     * Load and parse Exif data.
     *
     * This will populate the object with Exif data, contained as a
     * {@link PelTiff} object.  This TIFF object can be accessed with
     * the {@link getTiff()} method.
     */
    function load(PelDataWindow $d) {
        Pel::debug('Parsing %d bytes of Exif data...', $d->getSize());

        /* There must be at least 6 bytes for the Exif header. */
        if ($d->getSize() < 6)
        throw new PelInvalidDataException('Expected at least 6 bytes of Exif ' .
                                        'data, found just %d bytes.',
        $d->getSize());

        /* Verify the Exif header */
        if ($d->strcmp(0, self::EXIF_HEADER)) {
            $d->setWindowStart(strlen(self::EXIF_HEADER));
        } else {
            throw new PelInvalidDataException('Exif header not found.');
        }

        /* The rest of the data is TIFF data. */
        $this->tiff = new PelTiff();
        $this->tiff->load($d);
    }


    /**
     * Change the TIFF information.
     *
     * Exif data is really stored as TIFF data, and this method can be
     * used to change this data from one {@link PelTiff} object to
     * another.
     *
     * @param PelTiff the new TIFF object.
     */
    function setTiff(PelTiff $tiff) {
        $this->tiff = $tiff;
    }


    /**
     * Get the underlying TIFF object.
     *
     * The actual Exif data is stored in a {@link PelTiff} object, and
     * this method provides access to it.
     *
     * @return PelTiff the TIFF object with the Exif data.
     */
    function getTiff() {
        return $this->tiff;
    }


    /**
     * Produce bytes for the Exif data.
     *
     * @return string bytes representing this object.
     */
    function getBytes() {
        return self::EXIF_HEADER . $this->tiff->getBytes();
    }


    /**
     * Return a string representation of this object.
     *
     * @return string a string describing this object.  This is mostly
     * useful for debugging.
     */
    function __toString() {
        return Pel::tra("Dumping Exif data...\n") .
        $this->tiff->__toString();
    }

}

