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[mediawiki.git] / languages / utils / CLDRPluralRuleEvaluator.php

<?php
/**
 * Parse and evaluate a plural rule.
 *
 * http://unicode.org/reports/tr35/#Language_Plural_Rules
 *
 * @author Niklas Laxstrom, Tim Starling
 *
 * @copyright Copyright © 2010-2012, Niklas Laxström
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License 2.0
 * or later
 *
 * 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
 * @since 1.20
 */

class CLDRPluralRuleEvaluator {
        /**
         * Evaluate a number against a set of plural rules. If a rule passes,
         * return the index of plural rule.
         *
         * @param int The number to be evaluated against the rules
         * @param array The associative array of plural rules in pluralform => rule format.
         * @return int The index of the plural form which passed the evaluation
         */
        public static function evaluate( $number, array $rules ) {
                $rules = self::compile( $rules );
                return self::evaluateCompiled( $number, $rules );
        }

        /**
         * Convert a set of rules to a compiled form which is optimised for
         * fast evaluation. The result will be an array of strings, and may be cached.
         *
         * @param $rules The rules to compile
         * @return An array of compile rules.
         */
        public static function compile( array $rules ) {
                // We can't use array_map() for this because it generates a warning if
                // there is an exception.
                foreach ( $rules as &$rule ) {
                        $rule = CLDRPluralRuleConverter::convert( $rule );
                }
                return $rules;
        }

        /**
         * Evaluate a compiled set of rules returned by compile(). Do not allow
         * the user to edit the compiled form, or else PHP errors may result.
         */
        public static function evaluateCompiled( $number, array $rules ) {
                // The compiled form is RPN, with tokens strictly delimited by
                // spaces, so this is a simple RPN evaluator.
                foreach ( $rules as $i => $rule ) {
                        $stack = array();
                        $zero = ord( '0' );
                        $nine = ord( '9' );
                        foreach ( StringUtils::explode( ' ', $rule ) as $token ) {
                                $ord = ord( $token );
                                if ( $token === 'n' ) {
                                        $stack[] = $number;
                                } elseif ( $ord >= $zero && $ord <= $nine ) {
                                        $stack[] = intval( $token );
                                } else {
                                        $right = array_pop( $stack );
                                        $left = array_pop( $stack );
                                        $result = self::doOperation( $token, $left, $right );
                                        $stack[] = $result;
                                }
                        }
                        if ( $stack[0] ) {
                                return $i;
                        }
                }
                // None of the provided rules match. The number belongs to caregory
                // 'other' which comes last.
                return count( $rules );
        }

        /**
         * Do a single operation
         *
         * @param $token string The token string
         * @param $left The left operand. If it is an object, its state may be destroyed.
         * @param $right The right operand
         * @throws CLDRPluralRuleError
         * @return mixed
         */
        private static function doOperation( $token, $left, $right ) {
                if ( in_array( $token, array( 'in', 'not-in', 'within', 'not-within' ) ) ) {
                        if ( !( $right instanceof CLDRPluralRuleEvaluator_Range ) ) {
                                $right = new CLDRPluralRuleEvaluator_Range( $right );
                        }
                }
                switch ( $token ) {
                        case 'or':
                                return $left || $right;
                        case 'and':
                                return $left && $right;
                        case 'is':
                                return $left == $right;
                        case 'is-not':
                                return $left != $right;
                        case 'in':
                                return $right->isNumberIn( $left );
                        case 'not-in':
                                return !$right->isNumberIn( $left );
                        case 'within':
                                return $right->isNumberWithin( $left );
                        case 'not-within':
                                return !$right->isNumberWithin( $left );
                        case 'mod':
                                if ( is_int( $left ) ) {
                                        return (int) fmod( $left, $right );
                                }
                                return fmod( $left, $right );
                        case ',':
                                if ( $left instanceof CLDRPluralRuleEvaluator_Range ) {
                                        $range = $left;
                                } else {
                                        $range = new CLDRPluralRuleEvaluator_Range( $left );
                                }
                                $range->add( $right );
                                return $range;
                        case '..':
                                return new CLDRPluralRuleEvaluator_Range( $left, $right );
                        default:
                                throw new CLDRPluralRuleError( "Invalid RPN token" );
                }
        }
}

/**
 * Evaluator helper class representing a range list.
 */
class CLDRPluralRuleEvaluator_Range {
        public $parts = array();

        function __construct( $start, $end = false ) {
                if ( $end === false ) {
                        $this->parts[] = $start;
                } else {
                        $this->parts[] = array( $start, $end );
                }
        }

        /**
         * Determine if the given number is inside the range. If $integerConstraint
         * is true, the number must additionally be an integer if it is to match
         * any interval part.
         */
        function isNumberIn( $number, $integerConstraint = true ) {
                foreach ( $this->parts as $part ) {
                        if ( is_array( $part ) ) {
                                if ( ( !$integerConstraint || floor( $number ) === (float)$number )
                                        && $number >= $part[0] && $number <= $part[1] )
                                {
                                        return true;
                                }
                        } else {
                                if ( $number == $part ) {
                                        return true;
                                }
                        }
                }
                return false;
        }

        /**
         * Readable alias for isNumberIn( $number, false ), and the implementation
         * of the "within" operator.
         */
        function isNumberWithin( $number ) {
                return $this->isNumberIn( $number, false );
        }

        /**
         * Add another part to this range. The supplied new part may either be a
         * range object itself, or a single number.
         */
        function add( $other ) {
                if ( $other instanceof self ) {
                        $this->parts = array_merge( $this->parts, $other->parts );
                } else {
                        $this->parts[] = $other;
                }
        }

        /**
         * For debugging
         */
        function __toString() {
                $s = 'Range(';
                foreach ( $this->parts as $i => $part ) {
                        if ( $i ) {
                                $s .= ', ';
                        }
                        if ( is_array( $part ) ) {
                                $s .= $part[0] . '..' . $part[1];
                        } else {
                                $s .= $part;
                        }
                }
                $s .= ')';
                return $s;
        }

}

/**
 * Helper class for converting rules to reverse polish notation (RPN).
 */
class CLDRPluralRuleConverter {
        public $rule, $pos, $end;
        public $operators = array();
        public $operands = array();

        /**
         * Precedence levels. Note that there's no need to worry about associativity
         * for the level 4 operators, since they return boolean and don't accept
         * boolean inputs.
         */
        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,
        );

        /**
         * A character list defining whitespace, for use in strspn() etc.
         */
        const WHITESPACE_CLASS = " \t\r\n";

        /**
         * Same for digits. Note that the grammar given in UTS #35 doesn't allow
         * negative numbers or decimals.
         */
        const NUMBER_CLASS = '0123456789';

        /**
         * An anchored regular expression which matches a word at the current offset.
         */
        const WORD_REGEX = '/[a-zA-Z]+/A';

        /**
         * Convert a rule to RPN. This is the only public entry point.
         */
        public static function convert( $rule ) {
                $parser = new self( $rule );
                return $parser->doConvert();
        }

        /**
         * Private constructor.
         */
        protected function __construct( $rule ) {
                $this->rule = $rule;
                $this->pos = 0;
                $this->end = strlen( $rule );
        }

        /**
         * Do the operation.
         */
        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 CLDRPluralRuleConverter_Expression ) {
                                // 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;
        }

        /**
         * Fetch the next token from the input string. Return it as a
         * CLDRPluralRuleConverter_Fragment object.
         */
        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;
                }

                // Comma
                if ( $this->rule[$this->pos] === ',' ) {
                        $token = $this->newOperator( ',', $this->pos, 1 );
                        $this->pos ++;
                        return $token;
                }

                // Dot dot
                if ( substr( $this->rule, $this->pos, 2 ) === '..' ) {
                        $token = $this->newOperator( '..', $this->pos, 2 );
                        $this->pos += 2;
                        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 special numerical keyword "n"
                if ( $word1 === 'n' ) {
                        $token = $this->newNumber( 'n', $this->pos );
                        $this->pos ++;
                        return $token;
                }

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

        /**
         * For the binary operator $op, pop its operands off the stack and push
         * a fragment with rpn and type members describing the result of that
         * operation.
         */
        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;
        }

        /**
         * Create a numerical expression object
         */
        protected function newNumber( $text, $pos ) {
                return new CLDRPluralRuleConverter_Expression( $this, 'number', $text, $pos, strlen( $text ) );
        }

        /**
         * Create a binary operator
         */
        protected function newOperator( $type, $pos, $length ) {
                return new CLDRPluralRuleConverter_Operator( $this, $type, $pos, $length );
        }

        /**
         * Throw an error
         */
        protected function error( $message ) {
                throw new CLDRPluralRuleError( $message );
        }
}

/**
 * Helper for CLDRPluralRuleConverter.
 * The base class for operators and expressions, describing a region of the input string.
 */
class CLDRPluralRuleConverter_Fragment {
        public $parser, $pos, $length, $end;

        function __construct( $parser, $pos, $length ) {
                $this->parser = $parser;
                $this->pos = $pos;
                $this->length = $length;
                $this->end = $pos + $length;
        }

        public function error( $message ) {
                $text = $this->getText();
                throw new CLDRPluralRuleError( "$message at position " . ( $this->pos + 1 ) . ": \"$text\"" );
        }

        public function getText() {
                return substr( $this->parser->rule, $this->pos, $this->length );
        }
}

/**
 * Helper for CLDRPluralRuleConverter.
 * An expression object, representing a region of the input string (for error
 * messages), the RPN notation used to evaluate it, and the result type for
 * validation.
 */
class CLDRPluralRuleConverter_Expression extends CLDRPluralRuleConverter_Fragment {
        public $type, $rpn;

        function __construct( $parser, $type, $rpn, $pos, $length ) {
                parent::__construct( $parser, $pos, $length );
                $this->type = $type;
                $this->rpn = $rpn;
        }

        public function isType( $type ) {
                if ( $type === 'range' && ( $this->type === 'range' || $this->type === 'number' ) ) {
                        return true;
                }
                if ( $type === $this->type ) {
                        return true;
                }
                return false;
        }
}

/**
 * Helper for CLDRPluralRuleConverter.
 * An operator object, representing a region of the input string (for error
 * messages), and the binary operator at that location.
 */
class CLDRPluralRuleConverter_Operator extends CLDRPluralRuleConverter_Fragment {
        public $name;

        /**
         * Each op type has three characters: left operand type, right operand type and result type
         *
         *   b = boolean
         *   n = number
         *   r = range
         *
         * A number is a kind of range.
         */
        static $opTypes = array(
                'or' => 'bbb',
                'and' => 'bbb',
                'is' => 'nnb',
                'is-not' => 'nnb',
                'in' => 'nrb',
                'not-in' => 'nrb',
                'within' => 'nrb',
                'not-within' => 'nrb',
                'mod' => 'nnn',
                ',' => 'rrr',
                '..' => 'nnr',
        );

        /**
         * Map converting from the abbrevation to the full form.
         */
        static $typeSpecMap = array(
                'b' => 'boolean',
                'n' => 'number',
                'r' => 'range',
        );

        function __construct( $parser, $name, $pos, $length ) {
                parent::__construct( $parser, $pos, $length );
                $this->name = $name;
        }

        public function operate( $left, $right ) {
                $typeSpec = self::$opTypes[$this->name];

                $leftType = self::$typeSpecMap[$typeSpec[0]];
                $rightType = self::$typeSpecMap[$typeSpec[1]];
                $resultType = self::$typeSpecMap[$typeSpec[2]];

                $start = min( $this->pos, $left->pos, $right->pos );
                $end = max( $this->end, $left->end, $right->end );
                $length = $end - $start;

                $newExpr = new CLDRPluralRuleConverter_Expression( $this->parser, $resultType,
                        "{$left->rpn} {$right->rpn} {$this->name}",
                        $start, $length );

                if ( !$left->isType( $leftType ) ) {
                        $newExpr->error( "invalid type for left operand: expected $leftType, got {$left->type}" );
                }

                if ( !$right->isType( $rightType ) ) {
                        $newExpr->error( "invalid type for right operand: expected $rightType, got {$right->type}" );
                }
                return $newExpr;
        }
}

/**
 * The exception class for all the classes in this file. This will be thrown
 * back to the caller if there is any validation error.
 */
class CLDRPluralRuleError extends MWException {
        function __construct( $message ) {
                parent::__construct( 'CLDR plural rule error: ' . $message );
        }
}