<?php
/**
 * DjVu image handler.
 *
 * Copyright © 2006 Brion Vibber <brion@pobox.com>
 * https://www.mediawiki.org/
 *
 * 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; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Media
 */

/**
 * Support for detecting/validating DjVu image files and getting
 * some basic file metadata (resolution etc)
 *
 * File format docs are available in source package for DjVuLibre:
 * http://djvulibre.djvuzone.org/
 *
 * @ingroup Media
 */
class DjVuImage {
	/**
	 * @const DJVUTXT_MEMORY_LIMIT Memory limit for the DjVu description software
	 */
	const DJVUTXT_MEMORY_LIMIT = 300000;

	/**
	 * @param string $filename The DjVu file name.
	 */
	function __construct( $filename ) {
		$this->mFilename = $filename;
	}

	/**
	 * Check if the given file is indeed a valid DjVu image file
	 * @return bool
	 */
	public function isValid() {
		$info = $this->getInfo();

		return $info !== false;
	}

	/**
	 * Return data in the style of getimagesize()
	 * @return array|bool Array or false on failure
	 */
	public function getImageSize() {
		$data = $this->getInfo();

		if ( $data !== false ) {
			$width = $data['width'];
			$height = $data['height'];

			return [ $width, $height, 'DjVu',
				"width=\"$width\" height=\"$height\"" ];
		}

		return false;
	}

	// ---------

	/**
	 * For debugging; dump the IFF chunk structure
	 */
	function dump() {
		$file = fopen( $this->mFilename, 'rb' );
		$header = fread( $file, 12 );
		$arr = unpack( 'a4magic/a4chunk/NchunkLength', $header );
		$chunk = $arr['chunk'];
		$chunkLength = $arr['chunkLength'];
		echo "$chunk $chunkLength\n";
		$this->dumpForm( $file, $chunkLength, 1 );
		fclose( $file );
	}

	private function dumpForm( $file, $length, $indent ) {
		$start = ftell( $file );
		$secondary = fread( $file, 4 );
		echo str_repeat( ' ', $indent * 4 ) . "($secondary)\n";
		while ( ftell( $file ) - $start < $length ) {
			$chunkHeader = fread( $file, 8 );
			if ( $chunkHeader == '' ) {
				break;
			}
			$arr = unpack( 'a4chunk/NchunkLength', $chunkHeader );
			$chunk = $arr['chunk'];
			$chunkLength = $arr['chunkLength'];
			echo str_repeat( ' ', $indent * 4 ) . "$chunk $chunkLength\n";

			if ( $chunk == 'FORM' ) {
				$this->dumpForm( $file, $chunkLength, $indent + 1 );
			} else {
				fseek( $file, $chunkLength, SEEK_CUR );
				if ( $chunkLength & 1 == 1 ) {
					// Padding byte between chunks
					fseek( $file, 1, SEEK_CUR );
				}
			}
		}
	}

	function getInfo() {
		Wikimedia\suppressWarnings();
		$file = fopen( $this->mFilename, 'rb' );
		Wikimedia\restoreWarnings();
		if ( $file === false ) {
			wfDebug( __METHOD__ . ": missing or failed file read\n" );

			return false;
		}

		$header = fread( $file, 16 );
		$info = false;

		if ( strlen( $header ) < 16 ) {
			wfDebug( __METHOD__ . ": too short file header\n" );
		} else {
			$arr = unpack( 'a4magic/a4form/NformLength/a4subtype', $header );

			$subtype = $arr['subtype'];
			if ( $arr['magic'] != 'AT&T' ) {
				wfDebug( __METHOD__ . ": not a DjVu file\n" );
			} elseif ( $subtype == 'DJVU' ) {
				// Single-page document
				$info = $this->getPageInfo( $file );
			} elseif ( $subtype == 'DJVM' ) {
				// Multi-page document
				$info = $this->getMultiPageInfo( $file, $arr['formLength'] );
			} else {
				wfDebug( __METHOD__ . ": unrecognized DJVU file type '{$arr['subtype']}'\n" );
			}
		}
		fclose( $file );

		return $info;
	}

	private function readChunk( $file ) {
		$header = fread( $file, 8 );
		if ( strlen( $header ) < 8 ) {
			return [ false, 0 ];
		} else {
			$arr = unpack( 'a4chunk/Nlength', $header );

			return [ $arr['chunk'], $arr['length'] ];
		}
	}

	private function skipChunk( $file, $chunkLength ) {
		fseek( $file, $chunkLength, SEEK_CUR );

		if ( $chunkLength & 0x01 == 1 && !feof( $file ) ) {
			// padding byte
			fseek( $file, 1, SEEK_CUR );
		}
	}

	private function getMultiPageInfo( $file, $formLength ) {
		// For now, we'll just look for the first page in the file
		// and report its information, hoping others are the same size.
		$start = ftell( $file );
		do {
			list( $chunk, $length ) = $this->readChunk( $file );
			if ( !$chunk ) {
				break;
			}

			if ( $chunk == 'FORM' ) {
				$subtype = fread( $file, 4 );
				if ( $subtype == 'DJVU' ) {
					wfDebug( __METHOD__ . ": found first subpage\n" );

					return $this->getPageInfo( $file );
				}
				$this->skipChunk( $file, $length - 4 );
			} else {
				wfDebug( __METHOD__ . ": skipping '$chunk' chunk\n" );
				$this->skipChunk( $file, $length );
			}
		} while ( $length != 0 && !feof( $file ) && ftell( $file ) - $start < $formLength );

		wfDebug( __METHOD__ . ": multi-page DJVU file contained no pages\n" );

		return false;
	}

	private function getPageInfo( $file ) {
		list( $chunk, $length ) = $this->readChunk( $file );
		if ( $chunk != 'INFO' ) {
			wfDebug( __METHOD__ . ": expected INFO chunk, got '$chunk'\n" );

			return false;
		}

		if ( $length < 9 ) {
			wfDebug( __METHOD__ . ": INFO should be 9 or 10 bytes, found $length\n" );

			return false;
		}
		$data = fread( $file, $length );
		if ( strlen( $data ) < $length ) {
			wfDebug( __METHOD__ . ": INFO chunk cut off\n" );

			return false;
		}

		$arr = unpack(
			'nwidth/' .
			'nheight/' .
			'Cminor/' .
			'Cmajor/' .
			'vresolution/' .
			'Cgamma', $data );

		# Newer files have rotation info in byte 10, but we don't use it yet.

		return [
			'width' => $arr['width'],
			'height' => $arr['height'],
			'version' => "{$arr['major']}.{$arr['minor']}",
			'resolution' => $arr['resolution'],
			'gamma' => $arr['gamma'] / 10.0 ];
	}

	/**
	 * Return an XML string describing the DjVu image
	 * @return string|bool
	 */
	function retrieveMetaData() {
		global $wgDjvuToXML, $wgDjvuDump, $wgDjvuTxt;

		if ( !$this->isValid() ) {
			return false;
		}

		if ( isset( $wgDjvuDump ) ) {
			# djvudump is faster as of version 3.5
			# https://sourceforge.net/p/djvu/bugs/71/
			$cmd = wfEscapeShellArg( $wgDjvuDump ) . ' ' . wfEscapeShellArg( $this->mFilename );
			$dump = wfShellExec( $cmd );
			$xml = $this->convertDumpToXML( $dump );
		} elseif ( isset( $wgDjvuToXML ) ) {
			$cmd = wfEscapeShellArg( $wgDjvuToXML ) . ' --without-anno --without-text ' .
				wfEscapeShellArg( $this->mFilename );
			$xml = wfShellExec( $cmd );
		} else {
			$xml = null;
		}
		# Text layer
		if ( isset( $wgDjvuTxt ) ) {
			$cmd = wfEscapeShellArg( $wgDjvuTxt ) . ' --detail=page ' . wfEscapeShellArg( $this->mFilename );
			wfDebug( __METHOD__ . ": $cmd\n" );
			$retval = '';
			$txt = wfShellExec( $cmd, $retval, [], [ 'memory' => self::DJVUTXT_MEMORY_LIMIT ] );
			if ( $retval == 0 ) {
				# Strip some control characters
				$txt = preg_replace( "/[\013\035\037]/", "", $txt );
				$reg = <<<EOR
					/\(page\s[\d-]*\s[\d-]*\s[\d-]*\s[\d-]*\s*"
					((?>    # Text to match is composed of atoms of either:
						\\\\. # - any escaped character
						|     # - any character different from " and \
						[^"\\\\]+
					)*?)
					"\s*\)
					| # Or page can be empty ; in this case, djvutxt dumps ()
					\(\s*()\)/sx
EOR;
				$txt = preg_replace_callback( $reg, [ $this, 'pageTextCallback' ], $txt );
				$txt = "<DjVuTxt>\n<HEAD></HEAD>\n<BODY>\n" . $txt . "</BODY>\n</DjVuTxt>\n";
				$xml = preg_replace( "/<DjVuXML>/", "<mw-djvu><DjVuXML>", $xml, 1 );
				$xml = $xml . $txt . '</mw-djvu>';
			}
		}

		return $xml;
	}

	function pageTextCallback( $matches ) {
		# Get rid of invalid UTF-8, strip control characters
		$val = htmlspecialchars( UtfNormal\Validator::cleanUp( stripcslashes( $matches[1] ) ) );
		$val = str_replace( [ "\n", '�' ], [ '&#10;', '' ], $val );
		return '<PAGE value="' . $val . '" />';
	}

	/**
	 * Hack to temporarily work around djvutoxml bug
	 * @param string $dump
	 * @return string
	 */
	function convertDumpToXML( $dump ) {
		if ( strval( $dump ) == '' ) {
			return false;
		}

		$xml = <<<EOT
<?xml version="1.0" ?>
<!DOCTYPE DjVuXML PUBLIC "-//W3C//DTD DjVuXML 1.1//EN" "pubtext/DjVuXML-s.dtd">
<DjVuXML>
<HEAD></HEAD>
<BODY>
EOT;

		$dump = str_replace( "\r", '', $dump );
		$line = strtok( $dump, "\n" );
		$m = false;
		$good = false;
		if ( preg_match( '/^( *)FORM:DJVU/', $line, $m ) ) {
			# Single-page
			if ( $this->parseFormDjvu( $line, $xml ) ) {
				$good = true;
			} else {
				return false;
			}
		} elseif ( preg_match( '/^( *)FORM:DJVM/', $line, $m ) ) {
			# Multi-page
			$parentLevel = strlen( $m[1] );
			# Find DIRM
			$line = strtok( "\n" );
			while ( $line !== false ) {
				$childLevel = strspn( $line, ' ' );
				if ( $childLevel <= $parentLevel ) {
					# End of chunk
					break;
				}

				if ( preg_match( '/^ *DIRM.*indirect/', $line ) ) {
					wfDebug( "Indirect multi-page DjVu document, bad for server!\n" );

					return false;
				}
				if ( preg_match( '/^ *FORM:DJVU/', $line ) ) {
					# Found page
					if ( $this->parseFormDjvu( $line, $xml ) ) {
						$good = true;
					} else {
						return false;
					}
				}
				$line = strtok( "\n" );
			}
		}
		if ( !$good ) {
			return false;
		}

		$xml .= "</BODY>\n</DjVuXML>\n";

		return $xml;
	}

	function parseFormDjvu( $line, &$xml ) {
		$parentLevel = strspn( $line, ' ' );
		$line = strtok( "\n" );

		# Find INFO
		while ( $line !== false ) {
			$childLevel = strspn( $line, ' ' );
			if ( $childLevel <= $parentLevel ) {
				# End of chunk
				break;
			}

			if ( preg_match(
				'/^ *INFO *\[\d*\] *DjVu *(\d+)x(\d+), *\w*, *(\d+) *dpi, *gamma=([0-9.-]+)/',
				$line,
				$m
			) ) {
				$xml .= Xml::tags(
					'OBJECT',
					[
						# 'data' => '',
						# 'type' => 'image/x.djvu',
						'height' => $m[2],
						'width' => $m[1],
						# 'usemap' => '',
					],
					"\n" .
						Xml::element( 'PARAM', [ 'name' => 'DPI', 'value' => $m[3] ] ) . "\n" .
						Xml::element( 'PARAM', [ 'name' => 'GAMMA', 'value' => $m[4] ] ) . "\n"
				) . "\n";

				return true;
			}
			$line = strtok( "\n" );
		}

		# Not found
		return false;
	}
}
