class MO extends Gettext_Translations {

		var $_nplurals = 2;

		/**
		 * Loaded MO file.
		 *
		 * @var string
		 */
		private $filename = '';

		/**
		 * Returns the loaded MO file.
		 *
		 * @return string The loaded MO file.
		 */
		public function get_filename() {
			return $this->filename;
		}

		/**
		 * Fills up with the entries from MO file $filename
		 *
		 * @param string $filename MO file to load
		 * @return bool True if the import from file was successful, otherwise false.
		 */
		function import_from_file( $filename ) {
			$reader = new POMO_FileReader( $filename );

			if ( ! $reader->is_resource() ) {
				return false;
			}

			$this->filename = (string) $filename;

			return $this->import_from_reader( $reader );
		}

		/**
		 * @param string $filename
		 * @return bool
		 */
		function export_to_file( $filename ) {
			$fh = fopen( $filename, 'wb' );
			if ( ! $fh ) {
				return false;
			}
			$res = $this->export_to_file_handle( $fh );
			fclose( $fh );
			return $res;
		}

		/**
		 * @return string|false
		 */
		function export() {
			$tmp_fh = fopen( 'php://temp', 'r+' );
			if ( ! $tmp_fh ) {
				return false;
			}
			$this->export_to_file_handle( $tmp_fh );
			rewind( $tmp_fh );
			return stream_get_contents( $tmp_fh );
		}

		/**
		 * @param Translation_Entry $entry
		 * @return bool
		 */
		function is_entry_good_for_export( $entry ) {
			if ( empty( $entry->translations ) ) {
				return false;
			}

			if ( ! array_filter( $entry->translations ) ) {
				return false;
			}

			return true;
		}

		/**
		 * @param resource $fh
		 * @return true
		 */
		function export_to_file_handle( $fh ) {
			$entries = array_filter( $this->entries, array( $this, 'is_entry_good_for_export' ) );
			ksort( $entries );
			$magic                     = 0x950412de;
			$revision                  = 0;
			$total                     = count( $entries ) + 1; // all the headers are one entry
			$originals_lenghts_addr    = 28;
			$translations_lenghts_addr = $originals_lenghts_addr + 8 * $total;
			$size_of_hash              = 0;
			$hash_addr                 = $translations_lenghts_addr + 8 * $total;
			$current_addr              = $hash_addr;
			fwrite(
				$fh,
				pack(
					'V*',
					$magic,
					$revision,
					$total,
					$originals_lenghts_addr,
					$translations_lenghts_addr,
					$size_of_hash,
					$hash_addr
				)
			);
			fseek( $fh, $originals_lenghts_addr );

			// headers' msgid is an empty string
			fwrite( $fh, pack( 'VV', 0, $current_addr ) );
			$current_addr++;
			$originals_table = "\0";

			$reader = new POMO_Reader();

			foreach ( $entries as $entry ) {
				$originals_table .= $this->export_original( $entry ) . "\0";
				$length           = $reader->strlen( $this->export_original( $entry ) );
				fwrite( $fh, pack( 'VV', $length, $current_addr ) );
				$current_addr += $length + 1; // account for the NULL byte after
			}

			$exported_headers = $this->export_headers();
			fwrite( $fh, pack( 'VV', $reader->strlen( $exported_headers ), $current_addr ) );
			$current_addr      += strlen( $exported_headers ) + 1;
			$translations_table = $exported_headers . "\0";

			foreach ( $entries as $entry ) {
				$translations_table .= $this->export_translations( $entry ) . "\0";
				$length              = $reader->strlen( $this->export_translations( $entry ) );
				fwrite( $fh, pack( 'VV', $length, $current_addr ) );
				$current_addr += $length + 1;
			}

			fwrite( $fh, $originals_table );
			fwrite( $fh, $translations_table );
			return true;
		}

		/**
		 * @param Translation_Entry $entry
		 * @return string
		 */
		function export_original( $entry ) {
			//TODO: warnings for control characters
			$exported = $entry->singular;
			if ( $entry->is_plural ) {
				$exported .= "\0" . $entry->plural;
			}
			if ( $entry->context ) {
				$exported = $entry->context . "\4" . $exported;
			}
			return $exported;
		}

		/**
		 * @param Translation_Entry $entry
		 * @return string
		 */
		function export_translations( $entry ) {
			//TODO: warnings for control characters
			return $entry->is_plural ? implode( "\0", $entry->translations ) : $entry->translations[0];
		}

		/**
		 * @return string
		 */
		function export_headers() {
			$exported = '';
			foreach ( $this->headers as $header => $value ) {
				$exported .= "$header: $value\n";
			}
			return $exported;
		}

		/**
		 * @param int $magic
		 * @return string|false
		 */
		function get_byteorder( $magic ) {
			// The magic is 0x950412de

			// bug in PHP 5.0.2, see https://savannah.nongnu.org/bugs/?func=detailitem&item_id=10565
			$magic_little    = (int) - 1794895138;
			$magic_little_64 = (int) 2500072158;
			// 0xde120495
			$magic_big = ( (int) - 569244523 ) & 0xFFFFFFFF;
			if ( $magic_little == $magic || $magic_little_64 == $magic ) {
				return 'little';
			} elseif ( $magic_big == $magic ) {
				return 'big';
			} else {
				return false;
			}
		}

		/**
		 * @param POMO_FileReader $reader
		 * @return bool True if the import was successful, otherwise false.
		 */
		function import_from_reader( $reader ) {
			$endian_string = MO::get_byteorder( $reader->readint32() );
			if ( false === $endian_string ) {
				return false;
			}
			$reader->setEndian( $endian_string );

			$endian = ( 'big' == $endian_string ) ? 'N' : 'V';

			$header = $reader->read( 24 );
			if ( $reader->strlen( $header ) != 24 ) {
				return false;
			}

			// parse header
			$header = unpack( "{$endian}revision/{$endian}total/{$endian}originals_lenghts_addr/{$endian}translations_lenghts_addr/{$endian}hash_length/{$endian}hash_addr", $header );
			if ( ! is_array( $header ) ) {
				return false;
			}

			// support revision 0 of MO format specs, only
			if ( $header['revision'] != 0 ) {
				return false;
			}

			// seek to data blocks
			$reader->seekto( $header['originals_lenghts_addr'] );

			// read originals' indices
			$originals_lengths_length = $header['translations_lenghts_addr'] - $header['originals_lenghts_addr'];
			if ( $originals_lengths_length != $header['total'] * 8 ) {
				return false;
			}

			$originals = $reader->read( $originals_lengths_length );
			if ( $reader->strlen( $originals ) != $originals_lengths_length ) {
				return false;
			}

			// read translations' indices
			$translations_lenghts_length = $header['hash_addr'] - $header['translations_lenghts_addr'];
			if ( $translations_lenghts_length != $header['total'] * 8 ) {
				return false;
			}

			$translations = $reader->read( $translations_lenghts_length );
			if ( $reader->strlen( $translations ) != $translations_lenghts_length ) {
				return false;
			}

			// transform raw data into set of indices
			$originals    = $reader->str_split( $originals, 8 );
			$translations = $reader->str_split( $translations, 8 );

			// skip hash table
			$strings_addr = $header['hash_addr'] + $header['hash_length'] * 4;

			$reader->seekto( $strings_addr );

			$strings = $reader->read_all();
			$reader->close();

			for ( $i = 0; $i < $header['total']; $i++ ) {
				$o = unpack( "{$endian}length/{$endian}pos", $originals[ $i ] );
				$t = unpack( "{$endian}length/{$endian}pos", $translations[ $i ] );
				if ( ! $o || ! $t ) {
					return false;
				}

				// adjust offset due to reading strings to separate space before
				$o['pos'] -= $strings_addr;
				$t['pos'] -= $strings_addr;

				$original    = $reader->substr( $strings, $o['pos'], $o['length'] );
				$translation = $reader->substr( $strings, $t['pos'], $t['length'] );

				if ( '' === $original ) {
					$this->set_headers( $this->make_headers( $translation ) );
				} else {
					$entry                          = &$this->make_entry( $original, $translation );
					$this->entries[ $entry->key() ] = &$entry;
				}
			}
			return true;
		}

		/**
		 * Build a Translation_Entry from original string and translation strings,
		 * found in a MO file
		 *
		 * @static
		 * @param string $original original string to translate from MO file. Might contain
		 *  0x04 as context separator or 0x00 as singular/plural separator
		 * @param string $translation translation string from MO file. Might contain
		 *  0x00 as a plural translations separator
		 * @return Translation_Entry Entry instance.
		 */
		function &make_entry( $original, $translation ) {
			$entry = new Translation_Entry();
			// Look for context, separated by \4.
			$parts = explode( "\4", $original );
			if ( isset( $parts[1] ) ) {
				$original       = $parts[1];
				$entry->context = $parts[0];
			}
			// look for plural original
			$parts           = explode( "\0", $original );
			$entry->singular = $parts[0];
			if ( isset( $parts[1] ) ) {
				$entry->is_plural = true;
				$entry->plural    = $parts[1];
			}
			// plural translations are also separated by \0
			$entry->translations = explode( "\0", $translation );
			return $entry;
		}

		/**
		 * @param int $count
		 * @return string
		 */
		function select_plural_form( $count ) {
			return $this->gettext_select_plural_form( $count );
		}

		/**
		 * @return int
		 */
		function get_plural_forms_count() {
			return $this->_nplurals;
		}
	}