File class-wc-braintree-condition-evaluator.php

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<?php
defined( 'ABSPATH' ) || exit();

/**
 * @since 3.0.0
 * @package Braintree/Classes
 *
 */
class WC_Braintree_Condition_Evaluator {

    public $tokens = array();

    private $values = array();

    /**
     *
     * @var WC_Braintree_Context_Stack
     */
    private $stack = null;

    private $result_stack = null;

    public function condition_operators() {
        return array( '<', '>', '<=', '>=', 'AND', 'OR', 'IN', 'NOT_IN', 'EQ', 'NOT_EQ' );
    }

    public function condition_precedence() {
        return array(
            '<'      => 0,
            '>'      => 0,
            '<='     => 0,
            '>='     => 0,
            'AND'    => 1,
            'OR'     => 1,
            'IN'     => 0,
            'NOT_IN' => 0,
            'EQ'     => 0,
            'NOT_EQ' => 0,
        );
    }

    public function __construct() {
        $this->stack = new WC_Braintree_Context_Stack();
    }

    public function evaluate( $string, $values ) {
        $this->values = $values;
        if ( empty( $string ) ) {
            return true;
        }
        // make sure statement is converted to readable format.
        $string = html_entity_decode( $string );
        $output = $this->convert_exp_to_postfix( $string );
        return $this->evaluate_postfix( $output );
    }

    /**
     * Given a human readable expression, convert to postfix format.
     * <a href="https://en.wikipedia.org/wiki/Shunting-yard_algorithm">Shunting Yard Algorithm</a>
     *
     * @param string $string
     */
    public function convert_exp_to_postfix( $string ) {
        $string     = $this->get_values( trim( $string ) );
        $expression = '';
        // get the length of the string
        $output = array();
        $token  = '';

        // get all tokens from the expression.
        if ( ! preg_match_all( '/([\w.,]+)|(\[.+\])|(\()|(\))|(>=?)|(<=?)/', $string, $tokens ) ) {
            return self::trigger_error( 'invalid conditional statement.' );
        }
        $tokens = isset( $tokens[0] ) ? $tokens[0] : array();
        // loop through each character in the string.
        foreach ( $tokens as $token ) {
            if ( in_array( $token, self::condition_operators() ) ) {
                while ( ( $o2 = $this->stack->top() ) !== null && in_array( $o2, self::condition_operators() ) &&
                     self::condition_precedence()[ $token ] >= self::condition_precedence()[ $o2 ] ) {
                        $output[] = $this->stack->pop();
                }
                $this->stack->push( $token );
            } else {
                if ( $token === '(' ) {
                    $this->stack->push( $token );
                    $matched = true;
                } elseif ( $token === ')' ) {
                    while ( ( $o = $this->stack->pop() ) !== '(' ) {
                        if ( is_null( $o ) ) {
                            return self::trigger_error( 'invalid paranthesis in conditional statement.' );
                        } else {
                            $output[] = $o;
                        }
                    }
                } else {
                    $output[] = $token; // varable so push to output
                }
            }
        }
        while ( ( $o = $this->stack->pop() ) != null ) {
            $output[] = $o;
        }
        return $output;
    }

    /**
     * Evaluate the postfix expression and return the result.
     *
     * @param array $output
     * @return bool $result;
     */
    public function evaluate_postfix( $tokens ) {
        $stack = new WC_Braintree_Context_Stack();
        if ( ! $tokens ) {
            trigger_error( 'internal error evaluating conditional statement.' );
            return false;
        }
        foreach ( $tokens as $token ) {
            if ( in_array( $token, self::condition_operators() ) ) {
                if ( ( $op2 = $stack->pop() ) === null ) {
                    return self::trigger_error( 'internal error with conditional values' );
                }
                if ( ( $op1 = $stack->pop() ) === null ) {
                    return self::trigger_error( 'internal error with conditional values' );
                }
                switch ( $token ) {
                    case 'EQ':
                        $stack->push( $op1 == $op2 );
                        break;
                    case 'NOT_EQ':
                        $stack->push( $op1 != $op2 );
                        break;
                    case 'IN':
                        $array = explode( ',', preg_replace( '/\[|\]|\s+/', '', $op2 ) ); // remove brackets and white space
                        $stack->push( in_array( $op1, $array ) );
                        break;
                    case 'NOT_IN':
                        $array = explode( ',', preg_replace( '/\[|\]|\s+/', '', $op2 ) ); // remove brackets and white space
                        $stack->push( ! in_array( $op1, $array ) );
                        break;
                    case 'AND':
                        $stack->push( $op1 && $op2 );
                        break;
                    case 'OR':
                        $stack->push( $op1 || $op2 );
                        break;
                    case '<':
                        $stack->push( $op1 < $op2 );
                        break;
                    case '>':
                        $stack->push( $op1 > $op2 );
                        break;
                    case '<=':
                        $stack->push( $op1 <= $op2 );
                        break;
                    case '>=':
                        $stack->push( $op1 >= $op2 );
                        break;
                }
            } else {
                // token is a value
                $stack->push( $token );
            }
        }
        if ( $stack->size() > 1 ) {
            self::trigger_error( 'invalid condition statement. Check your syntax.' );
            return false;
        }
        // last result left in stack is the final result.
        return $stack->pop();
    }

    public static function trigger_error( $msg ) {
        if ( is_ajax() ) {
            return false;
        }
        if ( defined( 'WP_DEBUG' ) || is_admin() ) {
            trigger_error( $msg );
        }
        return false;
    }

    /**
     * Replace all values in the conditional string with formatted values.
     *
     * @param string $string
     * @return string $string
     */
    public function get_values( $string ) {
        $string = str_replace( array_keys( $this->values ), $this->values, $string );

        $string = str_replace(
            array( 'NOT EQ', 'NOT IN' ),
            array(
                'NOT EQ' => 'NOT_EQ',
                'NOT IN' => 'NOT_IN',
            ),
            $string
        );

        return $string;
    }
}

/**
 *
 * @since 3.0.0
 * @package Braintree/Classes
 *
 */
class WC_Braintree_Context_Stack {

    private $index = - 1;

    private $stack = array();

    public function push( $item ) {
        $this->index++;
        array_unshift( $this->stack, $item );
    }

    public function pop() {
        $this->index--;
        return array_shift( $this->stack );
    }

    public function top() {
        return ! empty( $this->stack ) ? $this->stack[0] : false;
    }

    public function is_empty() {
        return empty( $this->stack );
    }

    public function has_next() {
        $index = $this->index++;
        return isset( $this->stack[ $index ] );
    }

    public function size() {
        return count( $this->stack );
    }
}

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