462 lines
15 KiB
PHP
462 lines
15 KiB
PHP
<?php
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/*
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Copyright (c) 2020 Sunil Mohan Adapa <sunil at medhas dot org>
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Drop in replacement for native gettext.
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This file is part of PHP-gettext.
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PHP-gettext is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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PHP-gettext is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with PHP-gettext; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/**
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* Lexical analyzer for gettext plurals expression. Takes a string to parse
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* during construction and returns a single token every time peek() or
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* fetch_token() are called. The special string '__END__' is returned if there
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* are no more tokens to be read. Spaces are ignored during tokenization.
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*/
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class PluralsLexer {
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private $string;
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private $position;
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/**
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* Constructor
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*
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* @param string string Contains the value gettext plurals expression to
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* analyze.
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*/
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public function __construct(string $string) {
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$this->string = $string;
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$this->position = 0;
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}
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/**
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* Return the next token and the length to advance the read position without
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* actually advancing the read position. Tokens for operators and variables
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* are simple strings containing the operator or variable. If there are no
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* more token to provide, the special value ['__END__', 0] is returned. If
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* there was an unexpected input an Exception is raised.
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*
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* @access private
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* @throws Exception If there is unexpected input in the provided string.
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* @return array The next token and length to advance the current position.
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*/
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private function _tokenize() {
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$buf = $this->string;
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// Consume all spaces until the next token
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$index = $this->position;
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while ($index < strlen($buf) && $buf[$index] == ' ') {
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$index++;
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}
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$this->position = $index;
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// Return special token if next of the string is reached.
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if (strlen($buf) - $index == 0) {
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return ['__END__', 0];
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}
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// Operators with two characters
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$doubles = ['==', '!=', '>=', '<=', '&&', '||'];
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$next = substr($buf, $index, 2);
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if (in_array($next, $doubles)) {
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return [$next, 2];
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}
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// Operators with single character or variable 'n'.
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$singles = [
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'n', '(', ')', '?', ':', '+', '-', '*', '/', '%', '!', '>', '<'];
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if (in_array($buf[$index], $singles)) {
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return [$buf[$index], 1];
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}
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// Whole number constants, return an integer.
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$digits = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
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$pos = $index;
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while ($pos < strlen($buf) && in_array($buf[$pos], $digits)) {
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$pos++;
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}
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if ($pos != $index) {
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$length = $pos - $index;
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return [(int)substr($buf, $index, $length), $length];
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}
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// Throw and exception for all other unexpected input in the string.
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throw new Exception('Lexical analysis failed');
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}
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/**
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* Return the next token without actually advancing the read position.
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* Tokens for operators and variables are simple strings containing the
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* operator or variable. If there are no more tokens to provide, the special
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* value '__END__' is returned. If there was an unexpected input an
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* Exception is raised.
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*
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* @throws Exception If there is unexpected input in the provided string.
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* @return string The next token.
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*/
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public function peek() {
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list($token, $length) = $this->_tokenize();
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return $token;
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}
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/**
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* Return the next token after advancing the read position. Tokens for
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* operators and variables are simple strings containing the operator or
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* variable. If there are no more token to provide, the special value
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* '__END__' is returned. If there was an unexpected input an Exception is
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* raised.
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*
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* @throws Exception If there is unexpected input in the provided string.
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* @return string The next token.
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*/
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public function fetch_token() {
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list($token, $length) = $this->_tokenize();
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$this->position += $length;
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return $token;
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}
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}
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/**
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* A parsed representation of the gettext plural expression. This is a tree
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* containing further expressions depending on how nested the given input is.
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* Calling the evaluate() function computes the value of the expression if the
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* variable 'n' is set a certain value. This is used to decide which plural
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* string translation to use based on the number items at hand.
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*/
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class PluralsExpression {
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private $operator;
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private $operands;
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const BINARY_OPERATORS = [
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'==', '!=', '>=', '<=', '&&', '||', '+', '-', '*', '/', '%', '>', '<'];
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const UNARY_OPERATORS = ['!'];
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/**
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* Constructor
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*
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* @param string Operator for the expression.
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* @param (int|string|PuralsExpression)[] Variable number of operands of the
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* expression. One int operand is expected in case the operator is 'const'.
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* One string operand with value 'n' is expected in case the operator is
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* 'var'. For all other operators, the operands much be objects of type
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* PluralExpression. Unary operators expect one operand, binary operators
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* expect two operands and trinary operators expect three operands.
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*/
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public function __construct($operator, ...$operands) {
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$this->operator = $operator;
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$this->operands = $operands;
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}
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/**
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* Return a parenthesized string representation of the expression for
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* debugging purposes.
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*
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* @return string A string representation of the expression.
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*/
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public function to_string() {
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if ($this->operator == 'const' || $this->operator == 'var') {
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return $this->operands[0];
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} elseif (in_array($this->operator, self::BINARY_OPERATORS)) {
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return sprintf(
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"(%s %s %s)", $this->operands[0]->to_string(), $this->operator,
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$this->operands[1]->to_string());
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} elseif (in_array($this->operator, self::UNARY_OPERATORS)) {
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return sprintf(
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"(%s %s)", $this->operator, $this->operands[0]->to_string());
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} elseif ($this->operator == '?') {
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return sprintf(
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"(%s ? %s : %s)", $this->operands[0]->to_string(),
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$this->operands[1]->to_string(),
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$this->operands[2]->to_string());
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}
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}
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/**
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* Return the computed value of the expression if the variable 'n' is set to
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* a certain value.
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*
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* @param int The value of the variable n to use when evaluating.
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* @throws Exception If the expression has been constructed incorrectly.
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* @return int The value of the expression after evaluation.
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*/
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public function evaluate($n) {
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if (!in_array($this->operator, ['const', 'var'])) {
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$operand1 = $this->operands[0]->evaluate($n);
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}
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if (in_array($this->operator, self::BINARY_OPERATORS) ||
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$this->operator == '?') {
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$operand2 = $this->operands[1]->evaluate($n);
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}
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if ($this->operator == '?') {
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$operand3 = $this->operands[2]->evaluate($n);
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}
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switch ($this->operator) {
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case 'const':
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return $this->operands[0];
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case 'var':
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return $n;
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case '!':
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return !($operand1);
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case '==':
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return $operand1 == $operand2;
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case '!=':
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return $operand1 != $operand2;
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case '>=':
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return $operand1 >= $operand2;
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case '<=':
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return $operand1 <= $operand2;
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case '>':
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return $operand1 > $operand2;
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case '<':
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return $operand1 < $operand2;
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case '&&':
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return $operand1 && $operand2;
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case '||':
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return $operand1 || $operand2;
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case '+':
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return $operand1 + $operand2;
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case '-':
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return $operand1 - $operand2;
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case '*':
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return $operand1 * $operand2;
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case '/':
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return (int)($operand1 / $operand2);
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case '%':
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return $operand1 % $operand2;
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case '?':
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return $operand1 ? $operand2 : $operand3;
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default:
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throw new Exception('Invalid expression');
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}
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}
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}
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/**
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* A simple operator-precedence parser for gettext plural expressions. Takes a
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* string during construction and returns a PluralsExpression tree when
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* parse() is called.
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*/
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class PluralsParser {
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private $lexer;
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/*
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* Operator precedence. The parsing only happens with minimum precedence of
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* 0. However, ':' and ')' exist here to make sure that parsing does not
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* proceed beyond them when they are not to be parsed.
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*/
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const PREC = [
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':' => -1, '?' => 0, '||' => 1, '&&' => 2, '==' => 3, '!=' => 3,
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'>' => 4, '<' => 4, '>=' => 4, '<=' => 4, '+' => 5, '-' => 5, '*' => 6,
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'/' => 6, '%' => 6, '!' => 7, '__END__' => -1, ')' => -1
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];
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// List of right associative operators
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const RIGHT_ASSOC = ['?'];
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/**
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* Constructor
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*
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* @param string string the plural expression to be parsed.
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*/
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public function __construct(string $string) {
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$this->lexer = new PluralsLexer($string);
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}
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/**
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* Expect a primary next for parsing and return a PluralsExpression or throw
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* and exception otherwise. A primary can be the variable 'n', an whole
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* number constant, a unary operator expression string with '!', or a
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* parenthesis expression.
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*
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* @throws Exception If the next token is not a primary or if parenthesis
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* expression is not closes properly with ')'.
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* @return PluralsExpression That is constructed from the parsed primary.
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*/
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private function _parse_primary() {
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$token = $this->lexer->fetch_token();
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if ($token === 'n') {
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return new PluralsExpression('var', 'n');
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} elseif (is_int($token)) {
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return new PluralsExpression('const', (int)$token);
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} elseif ($token === '!') {
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return new PluralsExpression('!', $this->_parse_primary());
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} elseif ($token === '(') {
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$result = $this->_parse($this->_parse_primary(), 0);
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if ($this->lexer->fetch_token() != ')') {
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throw new Exception('Mismatched parenthesis');
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}
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return $result;
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}
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throw new Exception('Primary expected');
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}
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/**
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* Fetch an operator from the lexical analyzer and test for it. Optionally
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* advance the position of the lexical analyzer to next token. Raise
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* exception if the token retrieved is not an operator.
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*
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* @access private
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* @param bool peek A flag to indicate whether the position of the lexical
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* analyzer should *not* be advanced. If false, the lexical analyzer is
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* advanced by one token.
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* @throws Exception If the token read is not an operator.
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* @return string The operator that has been fetched from the lexical
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* analyzer.
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*/
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private function _parse_operator($peek) {
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if ($peek) {
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$token = $this->lexer->peek();
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} else {
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$token = $this->lexer->fetch_token();
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}
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if ($token !== null && !array_key_exists($token, self::PREC)) {
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throw new Exception('Operator expected');
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}
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return $token;
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}
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/**
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* A parsing method suitable for recursion.
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*
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* @access private
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* @param ParserExpression left_side A pre-parsed left-hand side expression
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* of the file expression to be constructed. This helps with recursion.
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* @param int min_precedence The minimum value of precedence for the
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* operators to be considered for parsing. Parsing will stop and current
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* expression is returned if an operator of a lower precedence is
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* encountered.
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* @throws Exception If the input string does not conform to the grammar of
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* the gettext plural expression.
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* @return ParserExpression A complete expression after parsing.
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*/
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private function _parse($left_side, $min_precedence) {
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$next_token = $this->_parse_operator(true);
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while (self::PREC[$next_token] >= $min_precedence) {
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$operator = $this->_parse_operator(false);
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$right_side = $this->_parse_primary();
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$next_token = $this->_parse_operator(true);
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/*
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* Consume (recursively) into right hand side all expressions of higher
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* precedence.
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*/
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while ((self::PREC[$operator] < self::PREC[$next_token]) ||
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((self::PREC[$operator] == self::PREC[$next_token]) &&
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in_array($operator, self::RIGHT_ASSOC))) {
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$right_side = $this->_parse(
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$right_side, self::PREC[$next_token]);
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$next_token = $this->_parse_operator(true);
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}
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if ($operator != '?') {
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/*
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* Handling for all binary operators. Consume into left hand side all
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* expressions of equal precedence.
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*/
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$left_side = new PluralsExpression($operator, $left_side, $right_side);
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} else {
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// Special handling for (a ? b : c) expression
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$operator = $this->lexer->fetch_token();
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if ($operator != ':') {
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throw new Exception('Invalid ? expression');
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}
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$right_side2 = $this->_parse(
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$this->_parse_primary(), self::PREC[$operator] + 1);
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$next_token = $this->_parse_operator(true);
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$left_side = new PluralsExpression(
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'?', $left_side, $right_side, $right_side2);
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}
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}
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return $left_side;
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}
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/**
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* A simple implementation of an operator-precedence parser. See:
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* https://en.wikipedia.org/wiki/Operator-precedence_parser for an analysis
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* of the algorithm.
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*
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* @throws Exception If the input string does not conform to the grammar of
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* the gettext plural expression.
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* @return ParserExpression A complete expression after parsing.
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*/
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public function parse() {
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$expression = $this->_parse($this->_parse_primary(), 0);
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// Special handling for an extra ')' at the end.
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if ($this->lexer->peek() != '__END__') {
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throw new Exception('Could not parse completely');
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}
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return $expression;
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}
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}
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/**
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* Provides a class to parse the value of the 'Plural-Forms:' header in the
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* gettext translation files. Holds the expression tree and the number of
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* plurals after parsing. Parsing happens during construction which takes as
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* its only argument the string to parse. Error during parsing are silently
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* suppressed and the fallback behavior is used with the value for Germanic
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* languages as follows: "nplurals=2; plural=n == 1 ? 0 : 1;".
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*/
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class PluralHeader {
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public $total;
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public $expression;
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/**
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* Constructor
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*
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* @param string The value of the Plural-Forms: header as seen in .po files.
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*/
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function __construct($string) {
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try {
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list($total, $expression) = $this->parse($string);
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} catch (Exception $e) {
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$string = "nplurals=2; plural=n == 1 ? 0 : 1;";
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list($total, $expression) = $this->parse($string);
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}
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$this->total = $total;
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$this->expression = $expression;
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}
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/**
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* Return the number of plural forms and the parsed expression tree.
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*
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* @access private
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* @param string string The value of the Plural-Forms: header.
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* @throws Exception If the string could not be parsed.
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* @return array The number of plural forms and parsed expression tree.
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*/
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private function parse($string) {
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$regex = "/^\s*nplurals\s*=\s*(\d+)\s*;\s*plural\s*=([^;]+);/i";
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if (preg_match($regex, $string, $matches)) {
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$total = (int)$matches[1];
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$expression_string = $matches[2];
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} else {
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throw new Exception('Invalid header value');
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}
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$parser = new PluralsParser($expression_string);
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$expression = $parser->parse();
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return [$total, $expression];
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}
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}
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