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Filename : class-wc-eval-math.php
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<?php

use Automattic\Jetpack\Constants;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

if ( ! class_exists( 'WC_Eval_Math', false ) ) {
	/**
	 * Class WC_Eval_Math. Supports basic math only (removed eval function).
	 *
	 * Based on EvalMath by Miles Kaufman Copyright (C) 2005 Miles Kaufmann http://www.twmagic.com/.
	 */
	class WC_Eval_Math {

		/**
		 * Last error.
		 *
		 * @var string
		 */
		public static $last_error = null;

		/**
		 * Variables (and constants).
		 *
		 * @var array
		 */
		public static $v = array( 'e' => 2.71, 'pi' => 3.14 );

		/**
		 * User-defined functions.
		 *
		 * @var array
		 */
		public static $f = array();

		/**
		 * Constants.
		 *
		 * @var array
		 */
		public static $vb = array( 'e', 'pi' );

		/**
		 * Built-in functions.
		 *
		 * @var array
		 */
		public static $fb = array();

		/**
		 * Evaluate maths string.
		 *
		 * @param string  $expr
		 * @return mixed
		 */
		public static function evaluate( $expr ) {
			self::$last_error = null;
			$expr = trim( $expr );
			if ( substr( $expr, -1, 1 ) == ';' ) {
				$expr = substr( $expr, 0, strlen( $expr ) -1 ); // strip semicolons at the end
			}
			// ===============
			// is it a variable assignment?
			if ( preg_match( '/^\s*([a-z]\w*)\s*=\s*(.+)$/', $expr, $matches ) ) {
				if ( in_array( $matches[1], self::$vb ) ) { // make sure we're not assigning to a constant
					return self::trigger( "cannot assign to constant '$matches[1]'" );
				}
				if ( ( $tmp = self::pfx( self::nfx( $matches[2] ) ) ) === false ) {
					return false; // get the result and make sure it's good
				}
				self::$v[ $matches[1] ] = $tmp; // if so, stick it in the variable array
				return self::$v[ $matches[1] ]; // and return the resulting value
				// ===============
				// is it a function assignment?
			} elseif ( preg_match( '/^\s*([a-z]\w*)\s*\(\s*([a-z]\w*(?:\s*,\s*[a-z]\w*)*)\s*\)\s*=\s*(.+)$/', $expr, $matches ) ) {
				$fnn = $matches[1]; // get the function name
				if ( in_array( $matches[1], self::$fb ) ) { // make sure it isn't built in
					return self::trigger( "cannot redefine built-in function '$matches[1]()'" );
				}
				$args = explode( ",", preg_replace( "/\s+/", "", $matches[2] ) ); // get the arguments
				if ( ( $stack = self::nfx( $matches[3] ) ) === false ) {
					return false; // see if it can be converted to postfix
				}
				$stack_size = count( $stack );
				for ( $i = 0; $i < $stack_size; $i++ ) { // freeze the state of the non-argument variables
					$token = $stack[ $i ];
					if ( preg_match( '/^[a-z]\w*$/', $token ) and ! in_array( $token, $args ) ) {
						if ( array_key_exists( $token, self::$v ) ) {
							$stack[ $i ] = self::$v[ $token ];
						} else {
							return self::trigger( "undefined variable '$token' in function definition" );
						}
					}
				}
				self::$f[ $fnn ] = array( 'args' => $args, 'func' => $stack );
				return true;
				// ===============
			} else {
				return self::pfx( self::nfx( $expr ) ); // straight up evaluation, woo
			}
		}

		/**
		 * Convert infix to postfix notation.
		 *
		 * @param  string $expr
		 *
		 * @return array|string
		 */
		private static function nfx( $expr ) {

			$index = 0;
			$stack = new WC_Eval_Math_Stack;
			$output = array(); // postfix form of expression, to be passed to pfx()
			$expr = trim( $expr );

			$ops   = array( '+', '-', '*', '/', '^', '_' );
			$ops_r = array( '+' => 0, '-' => 0, '*' => 0, '/' => 0, '^' => 1 ); // right-associative operator?
			$ops_p = array( '+' => 0, '-' => 0, '*' => 1, '/' => 1, '_' => 1, '^' => 2 ); // operator precedence

			$expecting_op = false; // we use this in syntax-checking the expression
			// and determining when a - is a negation
			if ( preg_match( "/[^\w\s+*^\/()\.,-]/", $expr, $matches ) ) { // make sure the characters are all good
				return self::trigger( "illegal character '{$matches[0]}'" );
			}

			while ( 1 ) { // 1 Infinite Loop ;)
				$op = substr( $expr, $index, 1 ); // get the first character at the current index
				// find out if we're currently at the beginning of a number/variable/function/parenthesis/operand
				$ex = preg_match( '/^([A-Za-z]\w*\(?|\d+(?:\.\d*)?|\.\d+|\()/', substr( $expr, $index ), $match );
				// ===============
				if ( '-' === $op and ! $expecting_op ) { // is it a negation instead of a minus?
					$stack->push( '_' ); // put a negation on the stack
					$index++;
				} elseif ( '_' === $op ) { // we have to explicitly deny this, because it's legal on the stack
					return self::trigger( "illegal character '_'" ); // but not in the input expression
					// ===============
				} elseif ( ( in_array( $op, $ops ) or $ex ) and $expecting_op ) { // are we putting an operator on the stack?
					if ( $ex ) { // are we expecting an operator but have a number/variable/function/opening parenthesis?
						$op = '*';
						$index--; // it's an implicit multiplication
					}
					// heart of the algorithm:
					while ( $stack->count > 0 and ( $o2 = $stack->last() ) and in_array( $o2, $ops ) and ( $ops_r[ $op ] ? $ops_p[ $op ] < $ops_p[ $o2 ] : $ops_p[ $op ] <= $ops_p[ $o2 ] ) ) {
						$output[] = $stack->pop(); // pop stuff off the stack into the output
					}
					// many thanks: https://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail
					$stack->push( $op ); // finally put OUR operator onto the stack
					$index++;
					$expecting_op = false;
					// ===============
				} elseif ( ')' === $op && $expecting_op ) { // ready to close a parenthesis?
					while ( ( $o2 = $stack->pop() ) != '(' ) { // pop off the stack back to the last (
						if ( is_null( $o2 ) ) {
							return self::trigger( "unexpected ')'" );
						} else {
							$output[] = $o2;
						}
					}
					if ( preg_match( "/^([A-Za-z]\w*)\($/", $stack->last( 2 ), $matches ) ) { // did we just close a function?
						$fnn = $matches[1]; // get the function name
						$arg_count = $stack->pop(); // see how many arguments there were (cleverly stored on the stack, thank you)
						$output[] = $stack->pop(); // pop the function and push onto the output
						if ( in_array( $fnn, self::$fb ) ) { // check the argument count
							if ( $arg_count > 1 ) {
								return self::trigger( "too many arguments ($arg_count given, 1 expected)" );
							}
						} elseif ( array_key_exists( $fnn, self::$f ) ) {
							if ( count( self::$f[ $fnn ]['args'] ) != $arg_count ) {
								return self::trigger( "wrong number of arguments ($arg_count given, " . count( self::$f[ $fnn ]['args'] ) . " expected)" );
							}
						} else { // did we somehow push a non-function on the stack? this should never happen
							return self::trigger( "internal error" );
						}
					}
					$index++;
					// ===============
				} elseif ( ',' === $op and $expecting_op ) { // did we just finish a function argument?
					while ( ( $o2 = $stack->pop() ) != '(' ) {
						if ( is_null( $o2 ) ) {
							return self::trigger( "unexpected ','" ); // oops, never had a (
						} else {
							$output[] = $o2; // pop the argument expression stuff and push onto the output
						}
					}
					// make sure there was a function
					if ( ! preg_match( "/^([A-Za-z]\w*)\($/", $stack->last( 2 ), $matches ) ) {
						return self::trigger( "unexpected ','" );
					}
					$stack->push( $stack->pop() + 1 ); // increment the argument count
					$stack->push( '(' ); // put the ( back on, we'll need to pop back to it again
					$index++;
					$expecting_op = false;
					// ===============
				} elseif ( '(' === $op and ! $expecting_op ) {
					$stack->push( '(' ); // that was easy
					$index++;
					// ===============
				} elseif ( $ex and ! $expecting_op ) { // do we now have a function/variable/number?
					$expecting_op = true;
					$val = $match[1];
					if ( preg_match( "/^([A-Za-z]\w*)\($/", $val, $matches ) ) { // may be func, or variable w/ implicit multiplication against parentheses...
						if ( in_array( $matches[1], self::$fb ) or array_key_exists( $matches[1], self::$f ) ) { // it's a func
							$stack->push( $val );
							$stack->push( 1 );
							$stack->push( '(' );
							$expecting_op = false;
						} else { // it's a var w/ implicit multiplication
							$val = $matches[1];
							$output[] = $val;
						}
					} else { // it's a plain old var or num
						$output[] = $val;
					}
					$index += strlen( $val );
					// ===============
				} elseif ( ')' === $op ) { // miscellaneous error checking
					return self::trigger( "unexpected ')'" );
				} elseif ( in_array( $op, $ops ) and ! $expecting_op ) {
					return self::trigger( "unexpected operator '$op'" );
				} else { // I don't even want to know what you did to get here
					return self::trigger( "an unexpected error occurred" );
				}
				if ( strlen( $expr ) == $index ) {
					if ( in_array( $op, $ops ) ) { // did we end with an operator? bad.
						return self::trigger( "operator '$op' lacks operand" );
					} else {
						break;
					}
				}
				while ( substr( $expr, $index, 1 ) == ' ' ) { // step the index past whitespace (pretty much turns whitespace
					$index++;                             // into implicit multiplication if no operator is there)
				}
			}
			while ( ! is_null( $op = $stack->pop() ) ) { // pop everything off the stack and push onto output
				if ( '(' === $op ) {
					return self::trigger( "expecting ')'" ); // if there are (s on the stack, ()s were unbalanced
				}
				$output[] = $op;
			}
			return $output;
		}

		/**
		 * Evaluate postfix notation.
		 *
		 * @param  mixed $tokens
		 * @param  array $vars
		 *
		 * @return mixed
		 */
		private static function pfx( $tokens, $vars = array() ) {
			if ( false == $tokens ) {
				return false;
			}
			$stack = new WC_Eval_Math_Stack;

			foreach ( $tokens as $token ) { // nice and easy
				// if the token is a binary operator, pop two values off the stack, do the operation, and push the result back on
				if ( in_array( $token, array( '+', '-', '*', '/', '^' ) ) ) {
					if ( is_null( $op2 = $stack->pop() ) ) {
						return self::trigger( "internal error" );
					}
					if ( is_null( $op1 = $stack->pop() ) ) {
						return self::trigger( "internal error" );
					}
					switch ( $token ) {
						case '+':
							$stack->push( $op1 + $op2 );
							break;
						case '-':
							$stack->push( $op1 - $op2 );
							break;
						case '*':
							$stack->push( $op1 * $op2 );
							break;
						case '/':
							if ( 0 == $op2 ) {
								return self::trigger( 'division by zero' );
							}
							$stack->push( $op1 / $op2 );
							break;
						case '^':
							$stack->push( pow( $op1, $op2 ) );
							break;
					}
					// if the token is a unary operator, pop one value off the stack, do the operation, and push it back on
				} elseif ( '_' === $token ) {
					$stack->push( -1 * $stack->pop() );
					// if the token is a function, pop arguments off the stack, hand them to the function, and push the result back on
				} elseif ( ! preg_match( "/^([a-z]\w*)\($/", $token, $matches ) ) {
					if ( is_numeric( $token ) ) {
						$stack->push( $token );
					} elseif ( array_key_exists( $token, self::$v ) ) {
						$stack->push( self::$v[ $token ] );
					} elseif ( array_key_exists( $token, $vars ) ) {
						$stack->push( $vars[ $token ] );
					} else {
						return self::trigger( "undefined variable '$token'" );
					}
				}
			}
			// when we're out of tokens, the stack should have a single element, the final result
			if ( 1 != $stack->count ) {
				return self::trigger( "internal error" );
			}
			return $stack->pop();
		}

		/**
		 * Trigger an error, but nicely, if need be.
		 *
		 * @param  string $msg
		 *
		 * @return bool
		 */
		private static function trigger( $msg ) {
			self::$last_error = $msg;
			if ( ! Constants::is_true( 'DOING_AJAX' ) && Constants::is_true( 'WP_DEBUG' ) ) {
				echo "\nError found in:";
				self::debugPrintCallingFunction();
				trigger_error( $msg, E_USER_WARNING );
			}
			return false;
		}

		/**
		 * Prints the file name, function name, and
		 * line number which called your function
		 * (not this function, then one that  called
		 * it to begin with)
		 */
		private static function debugPrintCallingFunction() {
			$file = 'n/a';
			$func = 'n/a';
			$line = 'n/a';
			$debugTrace = debug_backtrace();
			if ( isset( $debugTrace[1] ) ) {
				$file = $debugTrace[1]['file'] ? $debugTrace[1]['file'] : 'n/a';
				$line = $debugTrace[1]['line'] ? $debugTrace[1]['line'] : 'n/a';
			}
			if ( isset( $debugTrace[2] ) ) {
				$func = $debugTrace[2]['function'] ? $debugTrace[2]['function'] : 'n/a';
			}
			echo "\n$file, $func, $line\n";
		}
	}

	/**
	 * Class WC_Eval_Math_Stack.
	 */
	class WC_Eval_Math_Stack {

		/**
		 * Stack array.
		 *
		 * @var array
		 */
		public $stack = array();

		/**
		 * Stack counter.
		 *
		 * @var integer
		 */
		public $count = 0;

		/**
		 * Push value into stack.
		 *
		 * @param  mixed $val
		 */
		public function push( $val ) {
			$this->stack[ $this->count ] = $val;
			$this->count++;
		}

		/**
		 * Pop value from stack.
		 *
		 * @return mixed
		 */
		public function pop() {
			if ( $this->count > 0 ) {
				$this->count--;
				return $this->stack[ $this->count ];
			}
			return null;
		}

		/**
		 * Get last value from stack.
		 *
		 * @param  int $n
		 *
		 * @return mixed
		 */
		public function last( $n=1 ) {
			$key = $this->count - $n;
			return array_key_exists( $key, $this->stack ) ? $this->stack[ $key ] : null;
		}
	}
}