<?php

/**
* A gettext Plural-Forms parser.
*
* @since 4.9.0
*/
if ( ! class_exists( 'Plural_Forms', false ) ) :
#[AllowDynamicProperties]
class Plural_Forms {
/**
* Operator characters.
*
* @since 4.9.0
* @var string OP_CHARS Operator characters.
*/
const OP_CHARS = '|&><!=%?:';

/**
* Valid number characters.
*
* @since 4.9.0
* @var string NUM_CHARS Valid number characters.
*/
const NUM_CHARS = '0123456789';

/**
* Operator precedence.
*
* Operator precedence from highest to lowest. Higher numbers indicate
* higher precedence, and are executed first.
*
* @see https://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence
*
* @since 4.9.0
* @var array $op_precedence Operator precedence from highest to lowest.
*/
protected static $op_precedence = array(
'%' => 6,

'<' => 5,
'<=' => 5,
'>' => 5,
'>=' => 5,

'==' => 4,
'!=' => 4,

'&&' => 3,

'||' => 2,

'?:' => 1,
'?' => 1,

'(' => 0,
')' => 0,
);

/**
* Tokens generated from the string.
*
* @since 4.9.0
* @var array $tokens List of tokens.
*/
protected $tokens = array();

/**
* Cache for repeated calls to the function.
*
* @since 4.9.0
* @var array $cache Map of $n => $result
*/
protected $cache = array();

/**
* Constructor.
*
* @since 4.9.0
*
* @param string $str Plural function (just the bit after `plural=` from Plural-Forms)
*/
public function __construct( $str ) {
$this->parse( $str );
}

/**
* Parse a Plural-Forms string into tokens.
*
* Uses the shunting-yard algorithm to convert the string to Reverse Polish
* Notation tokens.
*
* @since 4.9.0
*
* @throws Exception If there is a syntax or parsing error with the string.
*
* @param string $str String to parse.
*/
protected function parse( $str ) {
$pos = 0;
$len = strlen( $str );

// Convert infix operators to postfix using the shunting-yard algorithm.
$output = array();
$stack = array();
while ( $pos < $len ) {
$next = substr( $str, $pos, 1 );

switch ( $next ) {
// Ignore whitespace.
case ' ':
case "\t":
++$pos;
break;

// Variable (n).
case 'n':
$output[] = array( 'var' );
++$pos;
break;

// Parentheses.
case '(':
$stack[] = $next;
++$pos;
break;

case ')':
$found = false;
while ( ! empty( $stack ) ) {
$o2 = $stack[ count( $stack ) - 1 ];
if ( '(' !== $o2 ) {
$output[] = array( 'op', array_pop( $stack ) );
continue;
}

// Discard open paren.
array_pop( $stack );
$found = true;
break;
}

if ( ! $found ) {
throw new Exception( 'Mismatched parentheses' );
}

++$pos;
break;

// Operators.
case '|':
case '&':
case '>':
case '<':
case '!':
case '=':
case '%':
case '?':
$end_operator = strspn( $str, self::OP_CHARS, $pos );
$operator = substr( $str, $pos, $end_operator );
if ( ! array_key_exists( $operator, self::$op_precedence ) ) {
throw new Exception( sprintf( 'Unknown operator "%s"', $operator ) );
}

while ( ! empty( $stack ) ) {
$o2 = $stack[ count( $stack ) - 1 ];

// Ternary is right-associative in C.
if ( '?:' === $operator || '?' === $operator ) {
if ( self::$op_precedence[ $operator ] >= self::$op_precedence[ $o2 ] ) {
break;
}
} elseif ( self::$op_precedence[ $operator ] > self::$op_precedence[ $o2 ] ) {
break;
}

$output[] = array( 'op', array_pop( $stack ) );
}
$stack[] = $operator;

$pos += $end_operator;
break;

// Ternary "else".
case ':':
$found = false;
$s_pos = count( $stack ) - 1;
while ( $s_pos >= 0 ) {
$o2 = $stack[ $s_pos ];
if ( '?' !== $o2 ) {
$output[] = array( 'op', array_pop( $stack ) );
--$s_pos;
continue;
}

// Replace.
$stack[ $s_pos ] = '?:';
$found = true;
break;
}

if ( ! $found ) {
throw new Exception( 'Missing starting "?" ternary operator' );
}
++$pos;
break;

// Default - number or invalid.
default:
if ( $next >= '0' && $next <= '9' ) {
$span = strspn( $str, self::NUM_CHARS, $pos );
$output[] = array( 'value', intval( substr( $str, $pos, $span ) ) );
$pos += $span;
break;
}

throw new Exception( sprintf( 'Unknown symbol "%s"', $next ) );
}
}

while ( ! empty( $stack ) ) {
$o2 = array_pop( $stack );
if ( '(' === $o2 || ')' === $o2 ) {
throw new Exception( 'Mismatched parentheses' );
}

$output[] = array( 'op', $o2 );
}

$this->tokens = $output;
}

/**
* Get the plural form for a number.
*
* Caches the value for repeated calls.
*
* @since 4.9.0
*
* @param int $num Number to get plural form for.
* @return int Plural form value.
*/
public function get( $num ) {
if ( isset( $this->cache[ $num ] ) ) {
return $this->cache[ $num ];
}
$this->cache[ $num ] = $this->execute( $num );
return $this->cache[ $num ];
}

/**
* Execute the plural form function.
*
* @since 4.9.0
*
* @throws Exception If the plural form value cannot be calculated.
*
* @param int $n Variable "n" to substitute.
* @return int Plural form value.
*/
public function execute( $n ) {
$stack = array();
$i = 0;
$total = count( $this->tokens );
while ( $i < $total ) {
$next = $this->tokens[ $i ];
++$i;
if ( 'var' === $next[0] ) {
$stack[] = $n;
continue;
} elseif ( 'value' === $next[0] ) {
$stack[] = $next[1];
continue;
}

// Only operators left.
switch ( $next[1] ) {
case '%':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 % $v2;
break;

case '||':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 || $v2;
break;

case '&&':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 && $v2;
break;

case '<':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 < $v2;
break;

case '<=':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 <= $v2;
break;

case '>':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 > $v2;
break;

case '>=':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 >= $v2;
break;

case '!=':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 !== $v2;
break;

case '==':
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 === $v2;
break;

case '?:':
$v3 = array_pop( $stack );
$v2 = array_pop( $stack );
$v1 = array_pop( $stack );
$stack[] = $v1 ? $v2 : $v3;
break;

default:
throw new Exception( sprintf( 'Unknown operator "%s"', $next[1] ) );
}
}

if ( count( $stack ) !== 1 ) {
throw new Exception( 'Too many values remaining on the stack' );
}

return (int) $stack[0];
}
}
endif;