CLDRPluralRuleConverter.php

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<?php
class CLDRPluralRuleConverter {
    public $rule;

    public $pos;

    public $end;

    public $operators = array();

    public $operands = array();

    private static $precedence = array(
        'or' => 2,
        'and' => 3,
        'is' => 4,
        'is-not' => 4,
        'in' => 4,
        'not-in' => 4,
        'within' => 4,
        'not-within' => 4,
        'mod' => 5,
        ',' => 6,
        '..' => 7,
    );

    const WHITESPACE_CLASS = " \t\r\n";

    const NUMBER_CLASS = '0123456789';

    const OPERAND_SYMBOLS = 'nivwft';

    const WORD_REGEX = '/[a-zA-Z@]+/A';

    public static function convert( $rule ) {
        $parser = new self( $rule );

        return $parser->doConvert();
    }

    protected function __construct( $rule ) {
        $this->rule = $rule;
        $this->pos = 0;
        $this->end = strlen( $rule );
    }

    protected function doConvert() {
        $expectOperator = true;

        // Iterate through all tokens, saving the operators and operands to a
        // stack per Dijkstra's shunting yard algorithm.
        while ( false !== ( $token = $this->nextToken() ) ) {
            // In this grammar, there are only binary operators, so every valid
            // rule string will alternate between operator and operand tokens.
            $expectOperator = !$expectOperator;

            if ( $token instanceof CLDRPluralRuleConverterExpression ) {
                // Operand
                if ( $expectOperator ) {
                    $token->error( 'unexpected operand' );
                }
                $this->operands[] = $token;
                continue;
            } else {
                // Operator
                if ( !$expectOperator ) {
                    $token->error( 'unexpected operator' );
                }
                // Resolve higher precedence levels
                $lastOp = end( $this->operators );
                while ( $lastOp && self::$precedence[$token->name] <= self::$precedence[$lastOp->name] ) {
                    $this->doOperation( $lastOp, $this->operands );
                    array_pop( $this->operators );
                    $lastOp = end( $this->operators );
                }
                $this->operators[] = $token;
            }
        }

        // Finish off the stack
        while ( $op = array_pop( $this->operators ) ) {
            $this->doOperation( $op, $this->operands );
        }

        // Make sure the result is sane. The first case is possible for an empty
        // string input, the second should be unreachable.
        if ( !count( $this->operands ) ) {
            $this->error( 'condition expected' );
        } elseif ( count( $this->operands ) > 1 ) {
            $this->error( 'missing operator or too many operands' );
        }

        $value = $this->operands[0];
        if ( $value->type !== 'boolean' ) {
            $this->error( 'the result must have a boolean type' );
        }

        return $this->operands[0]->rpn;
    }

    protected function nextToken() {
        if ( $this->pos >= $this->end ) {
            return false;
        }

        // Whitespace
        $length = strspn( $this->rule, self::WHITESPACE_CLASS, $this->pos );
        $this->pos += $length;

        if ( $this->pos >= $this->end ) {
            return false;
        }

        // Number
        $length = strspn( $this->rule, self::NUMBER_CLASS, $this->pos );
        if ( $length !== 0 ) {
            $token = $this->newNumber( substr( $this->rule, $this->pos, $length ), $this->pos );
            $this->pos += $length;

            return $token;
        }

        // Two-character operators
        $op2 = substr( $this->rule, $this->pos, 2 );
        if ( $op2 === '..' || $op2 === '!=' ) {
            $token = $this->newOperator( $op2, $this->pos, 2 );
            $this->pos += 2;

            return $token;
        }

        // Single-character operators
        $op1 = $this->rule[$this->pos];
        if ( $op1 === ',' || $op1 === '=' || $op1 === '%' ) {
            $token = $this->newOperator( $op1, $this->pos, 1 );
            $this->pos++;

            return $token;
        }

        // Word
        if ( !preg_match( self::WORD_REGEX, $this->rule, $m, 0, $this->pos ) ) {
            $this->error( 'unexpected character "' . $this->rule[$this->pos] . '"' );
        }
        $word1 = strtolower( $m[0] );
        $word2 = '';
        $nextTokenPos = $this->pos + strlen( $word1 );
        if ( $word1 === 'not' || $word1 === 'is' ) {
            // Look ahead one word
            $nextTokenPos += strspn( $this->rule, self::WHITESPACE_CLASS, $nextTokenPos );
            if ( $nextTokenPos < $this->end
                && preg_match( self::WORD_REGEX, $this->rule, $m, 0, $nextTokenPos )
            ) {
                $word2 = strtolower( $m[0] );
                $nextTokenPos += strlen( $word2 );
            }
        }

        // Two-word operators like "is not" take precedence over single-word operators like "is"
        if ( $word2 !== '' ) {
            $bothWords = "{$word1}-{$word2}";
            if ( isset( self::$precedence[$bothWords] ) ) {
                $token = $this->newOperator( $bothWords, $this->pos, $nextTokenPos - $this->pos );
                $this->pos = $nextTokenPos;

                return $token;
            }
        }

        // Single-word operators
        if ( isset( self::$precedence[$word1] ) ) {
            $token = $this->newOperator( $word1, $this->pos, strlen( $word1 ) );
            $this->pos += strlen( $word1 );

            return $token;
        }

        // The single-character operand symbols
        if ( strpos( self::OPERAND_SYMBOLS, $word1 ) !== false ) {
            $token = $this->newNumber( $word1, $this->pos );
            $this->pos++;

            return $token;
        }

        // Samples
        if ( $word1 === '@integer' || $word1 === '@decimal' ) {
            // Samples are like comments, they have no effect on rule evaluation.
            // They run from the first sample indicator to the end of the string.
            $this->pos = $this->end;

            return false;
        }

        $this->error( 'unrecognised word' );
    }

    protected function doOperation( $op ) {
        if ( count( $this->operands ) < 2 ) {
            $op->error( 'missing operand' );
        }
        $right = array_pop( $this->operands );
        $left = array_pop( $this->operands );
        $result = $op->operate( $left, $right );
        $this->operands[] = $result;
    }

    protected function newNumber( $text, $pos ) {
        return new CLDRPluralRuleConverterExpression( $this, 'number', $text, $pos, strlen( $text ) );
    }

    protected function newOperator( $type, $pos, $length ) {
        return new CLDRPluralRuleConverterOperator( $this, $type, $pos, $length );
    }

    protected function error( $message ) {
        throw new CLDRPluralRuleError( $message );
    }
}