class PO extends Gettext_Translations {

		var $comments_before_headers = '';

		/**
		 * Exports headers to a PO entry
		 *
		 * @return string msgid/msgstr PO entry for this PO file headers, doesn't contain newline at the end
		 */
		function export_headers() {
			$header_string = '';
			foreach ( $this->headers as $header => $value ) {
				$header_string .= "$header: $value\n";
			}
			$poified = PO::poify( $header_string );
			if ( $this->comments_before_headers ) {
				$before_headers = $this->prepend_each_line( rtrim( $this->comments_before_headers ) . "\n", '# ' );
			} else {
				$before_headers = '';
			}
			return rtrim( "{$before_headers}msgid \"\"\nmsgstr $poified" );
		}

		/**
		 * Exports all entries to PO format
		 *
		 * @return string sequence of mgsgid/msgstr PO strings, doesn't containt newline at the end
		 */
		function export_entries() {
			//TODO sorting
			return implode( "\n\n", array_map( array( 'PO', 'export_entry' ), $this->entries ) );
		}

		/**
		 * Exports the whole PO file as a string
		 *
		 * @param bool $include_headers whether to include the headers in the export
		 * @return string ready for inclusion in PO file string for headers and all the enrtries
		 */
		function export( $include_headers = true ) {
			$res = '';
			if ( $include_headers ) {
				$res .= $this->export_headers();
				$res .= "\n\n";
			}
			$res .= $this->export_entries();
			return $res;
		}

		/**
		 * Same as {@link export}, but writes the result to a file
		 *
		 * @param string $filename where to write the PO string
		 * @param bool $include_headers whether to include tje headers in the export
		 * @return bool true on success, false on error
		 */
		function export_to_file( $filename, $include_headers = true ) {
			$fh = fopen( $filename, 'w' );
			if ( false === $fh ) {
				return false;
			}
			$export = $this->export( $include_headers );
			$res    = fwrite( $fh, $export );
			if ( false === $res ) {
				return false;
			}
			return fclose( $fh );
		}

		/**
		 * Text to include as a comment before the start of the PO contents
		 *
		 * Doesn't need to include # in the beginning of lines, these are added automatically
		 */
		function set_comment_before_headers( $text ) {
			$this->comments_before_headers = $text;
		}

		/**
		 * Formats a string in PO-style
		 *
		 * @param string $string the string to format
		 * @return string the poified string
		 */
		public static function poify( $string ) {
			$quote   = '"';
			$slash   = '\\';
			$newline = "\n";

			$replaces = array(
				"$slash" => "$slash$slash",
				"$quote" => "$slash$quote",
				"\t"     => '\t',
			);

			$string = str_replace( array_keys( $replaces ), array_values( $replaces ), $string );

			$po = $quote . implode( "${slash}n$quote$newline$quote", explode( $newline, $string ) ) . $quote;
			// add empty string on first line for readbility
			if ( false !== strpos( $string, $newline ) &&
				( substr_count( $string, $newline ) > 1 || ! ( $newline === substr( $string, -strlen( $newline ) ) ) ) ) {
				$po = "$quote$quote$newline$po";
			}
			// remove empty strings
			$po = str_replace( "$newline$quote$quote", '', $po );
			return $po;
		}

		/**
		 * Gives back the original string from a PO-formatted string
		 *
		 * @param string $string PO-formatted string
		 * @return string enascaped string
		 */
		public static function unpoify( $string ) {
			$escapes               = array(
				't'  => "\t",
				'n'  => "\n",
				'r'  => "\r",
				'\\' => '\\',
			);
			$lines                 = array_map( 'trim', explode( "\n", $string ) );
			$lines                 = array_map( array( 'PO', 'trim_quotes' ), $lines );
			$unpoified             = '';
			$previous_is_backslash = false;
			foreach ( $lines as $line ) {
				preg_match_all( '/./u', $line, $chars );
				$chars = $chars[0];
				foreach ( $chars as $char ) {
					if ( ! $previous_is_backslash ) {
						if ( '\\' == $char ) {
							$previous_is_backslash = true;
						} else {
							$unpoified .= $char;
						}
					} else {
						$previous_is_backslash = false;
						$unpoified            .= isset( $escapes[ $char ] ) ? $escapes[ $char ] : $char;
					}
				}
			}

			// Standardise the line endings on imported content, technically PO files shouldn't contain \r
			$unpoified = str_replace( array( "\r\n", "\r" ), "\n", $unpoified );

			return $unpoified;
		}

		/**
		 * Inserts $with in the beginning of every new line of $string and
		 * returns the modified string
		 *
		 * @param string $string prepend lines in this string
		 * @param string $with prepend lines with this string
		 */
		public static function prepend_each_line( $string, $with ) {
			$lines  = explode( "\n", $string );
			$append = '';
			if ( "\n" === substr( $string, -1 ) && '' === end( $lines ) ) {
				// Last line might be empty because $string was terminated
				// with a newline, remove it from the $lines array,
				// we'll restore state by re-terminating the string at the end
				array_pop( $lines );
				$append = "\n";
			}
			foreach ( $lines as &$line ) {
				$line = $with . $line;
			}
			unset( $line );
			return implode( "\n", $lines ) . $append;
		}

		/**
		 * Prepare a text as a comment -- wraps the lines and prepends #
		 * and a special character to each line
		 *
		 * @access private
		 * @param string $text the comment text
		 * @param string $char character to denote a special PO comment,
		 *  like :, default is a space
		 */
		public static function comment_block( $text, $char = ' ' ) {
			$text = wordwrap( $text, PO_MAX_LINE_LEN - 3 );
			return PO::prepend_each_line( $text, "#$char " );
		}

		/**
		 * Builds a string from the entry for inclusion in PO file
		 *
		 * @param Translation_Entry $entry the entry to convert to po string (passed by reference).
		 * @return false|string PO-style formatted string for the entry or
		 *  false if the entry is empty
		 */
		public static function export_entry( &$entry ) {
			if ( null === $entry->singular || '' === $entry->singular ) {
				return false;
			}
			$po = array();
			if ( ! empty( $entry->translator_comments ) ) {
				$po[] = PO::comment_block( $entry->translator_comments );
			}
			if ( ! empty( $entry->extracted_comments ) ) {
				$po[] = PO::comment_block( $entry->extracted_comments, '.' );
			}
			if ( ! empty( $entry->references ) ) {
				$po[] = PO::comment_block( implode( ' ', $entry->references ), ':' );
			}
			if ( ! empty( $entry->flags ) ) {
				$po[] = PO::comment_block( implode( ', ', $entry->flags ), ',' );
			}
			if ( $entry->context ) {
				$po[] = 'msgctxt ' . PO::poify( $entry->context );
			}
			$po[] = 'msgid ' . PO::poify( $entry->singular );
			if ( ! $entry->is_plural ) {
				$translation = empty( $entry->translations ) ? '' : $entry->translations[0];
				$translation = PO::match_begin_and_end_newlines( $translation, $entry->singular );
				$po[]        = 'msgstr ' . PO::poify( $translation );
			} else {
				$po[]         = 'msgid_plural ' . PO::poify( $entry->plural );
				$translations = empty( $entry->translations ) ? array( '', '' ) : $entry->translations;
				foreach ( $translations as $i => $translation ) {
					$translation = PO::match_begin_and_end_newlines( $translation, $entry->plural );
					$po[]        = "msgstr[$i] " . PO::poify( $translation );
				}
			}
			return implode( "\n", $po );
		}

		public static function match_begin_and_end_newlines( $translation, $original ) {
			if ( '' === $translation ) {
				return $translation;
			}

			$original_begin    = "\n" === substr( $original, 0, 1 );
			$original_end      = "\n" === substr( $original, -1 );
			$translation_begin = "\n" === substr( $translation, 0, 1 );
			$translation_end   = "\n" === substr( $translation, -1 );

			if ( $original_begin ) {
				if ( ! $translation_begin ) {
					$translation = "\n" . $translation;
				}
			} elseif ( $translation_begin ) {
				$translation = ltrim( $translation, "\n" );
			}

			if ( $original_end ) {
				if ( ! $translation_end ) {
					$translation .= "\n";
				}
			} elseif ( $translation_end ) {
				$translation = rtrim( $translation, "\n" );
			}

			return $translation;
		}

		/**
		 * @param string $filename
		 * @return boolean
		 */
		function import_from_file( $filename ) {
			$f = fopen( $filename, 'r' );
			if ( ! $f ) {
				return false;
			}
			$lineno = 0;
			while ( true ) {
				$res = $this->read_entry( $f, $lineno );
				if ( ! $res ) {
					break;
				}
				if ( $res['entry']->singular == '' ) {
					$this->set_headers( $this->make_headers( $res['entry']->translations[0] ) );
				} else {
					$this->add_entry( $res['entry'] );
				}
			}
			PO::read_line( $f, 'clear' );
			if ( false === $res ) {
				return false;
			}
			if ( ! $this->headers && ! $this->entries ) {
				return false;
			}
			return true;
		}

		/**
		 * Helper function for read_entry
		 *
		 * @param string $context
		 * @return bool
		 */
		protected static function is_final( $context ) {
			return ( $context === 'msgstr' ) || ( $context === 'msgstr_plural' );
		}

		/**
		 * @param resource $f
		 * @param int      $lineno
		 * @return null|false|array
		 */
		function read_entry( $f, $lineno = 0 ) {
			$entry = new Translation_Entry();
			// where were we in the last step
			// can be: comment, msgctxt, msgid, msgid_plural, msgstr, msgstr_plural
			$context      = '';
			$msgstr_index = 0;
			while ( true ) {
				$lineno++;
				$line = PO::read_line( $f );
				if ( ! $line ) {
					if ( feof( $f ) ) {
						if ( self::is_final( $context ) ) {
							break;
						} elseif ( ! $context ) { // we haven't read a line and eof came
							return null;
						} else {
							return false;
						}
					} else {
						return false;
					}
				}
				if ( $line == "\n" ) {
					continue;
				}
				$line = trim( $line );
				if ( preg_match( '/^#/', $line, $m ) ) {
					// the comment is the start of a new entry
					if ( self::is_final( $context ) ) {
						PO::read_line( $f, 'put-back' );
						$lineno--;
						break;
					}
					// comments have to be at the beginning
					if ( $context && $context != 'comment' ) {
						return false;
					}
					// add comment
					$this->add_comment_to_entry( $entry, $line );
				} elseif ( preg_match( '/^msgctxt\s+(".*")/', $line, $m ) ) {
					if ( self::is_final( $context ) ) {
						PO::read_line( $f, 'put-back' );
						$lineno--;
						break;
					}
					if ( $context && $context != 'comment' ) {
						return false;
					}
					$context         = 'msgctxt';
					$entry->context .= PO::unpoify( $m[1] );
				} elseif ( preg_match( '/^msgid\s+(".*")/', $line, $m ) ) {
					if ( self::is_final( $context ) ) {
						PO::read_line( $f, 'put-back' );
						$lineno--;
						break;
					}
					if ( $context && $context != 'msgctxt' && $context != 'comment' ) {
						return false;
					}
					$context          = 'msgid';
					$entry->singular .= PO::unpoify( $m[1] );
				} elseif ( preg_match( '/^msgid_plural\s+(".*")/', $line, $m ) ) {
					if ( $context != 'msgid' ) {
						return false;
					}
					$context          = 'msgid_plural';
					$entry->is_plural = true;
					$entry->plural   .= PO::unpoify( $m[1] );
				} elseif ( preg_match( '/^msgstr\s+(".*")/', $line, $m ) ) {
					if ( $context != 'msgid' ) {
						return false;
					}
					$context             = 'msgstr';
					$entry->translations = array( PO::unpoify( $m[1] ) );
				} elseif ( preg_match( '/^msgstr\[(\d+)\]\s+(".*")/', $line, $m ) ) {
					if ( $context != 'msgid_plural' && $context != 'msgstr_plural' ) {
						return false;
					}
					$context                      = 'msgstr_plural';
					$msgstr_index                 = $m[1];
					$entry->translations[ $m[1] ] = PO::unpoify( $m[2] );
				} elseif ( preg_match( '/^".*"$/', $line ) ) {
					$unpoified = PO::unpoify( $line );
					switch ( $context ) {
						case 'msgid':
							$entry->singular .= $unpoified;
							break;
						case 'msgctxt':
							$entry->context .= $unpoified;
							break;
						case 'msgid_plural':
							$entry->plural .= $unpoified;
							break;
						case 'msgstr':
							$entry->translations[0] .= $unpoified;
							break;
						case 'msgstr_plural':
							$entry->translations[ $msgstr_index ] .= $unpoified;
							break;
						default:
							return false;
					}
				} else {
					return false;
				}
			}

			$have_translations = false;
			foreach ( $entry->translations as $t ) {
				if ( $t || ( '0' === $t ) ) {
					$have_translations = true;
					break;
				}
			}
			if ( false === $have_translations ) {
				$entry->translations = array();
			}

			return array(
				'entry'  => $entry,
				'lineno' => $lineno,
			);
		}

		/**
		 * @staticvar string   $last_line
		 * @staticvar boolean  $use_last_line
		 *
		 * @param     resource $f
		 * @param     string   $action
		 * @return boolean
		 */
		function read_line( $f, $action = 'read' ) {
			static $last_line     = '';
			static $use_last_line = false;
			if ( 'clear' == $action ) {
				$last_line = '';
				return true;
			}
			if ( 'put-back' == $action ) {
				$use_last_line = true;
				return true;
			}
			$line          = $use_last_line ? $last_line : fgets( $f );
			$line          = ( "\r\n" == substr( $line, -2 ) ) ? rtrim( $line, "\r\n" ) . "\n" : $line;
			$last_line     = $line;
			$use_last_line = false;
			return $line;
		}

		/**
		 * @param Translation_Entry $entry
		 * @param string            $po_comment_line
		 */
		function add_comment_to_entry( &$entry, $po_comment_line ) {
			$first_two = substr( $po_comment_line, 0, 2 );
			$comment   = trim( substr( $po_comment_line, 2 ) );
			if ( '#:' == $first_two ) {
				$entry->references = array_merge( $entry->references, preg_split( '/\s+/', $comment ) );
			} elseif ( '#.' == $first_two ) {
				$entry->extracted_comments = trim( $entry->extracted_comments . "\n" . $comment );
			} elseif ( '#,' == $first_two ) {
				$entry->flags = array_merge( $entry->flags, preg_split( '/,\s*/', $comment ) );
			} else {
				$entry->translator_comments = trim( $entry->translator_comments . "\n" . $comment );
			}
		}

		/**
		 * @param string $s
		 * @return sring
		 */
		public static function trim_quotes( $s ) {
			if ( substr( $s, 0, 1 ) == '"' ) {
				$s = substr( $s, 1 );
			}
			if ( substr( $s, -1, 1 ) == '"' ) {
				$s = substr( $s, 0, -1 );
			}
			return $s;
		}
	}