<?php

/**
 * Math calculator. It handles the math operations.
 */
class VG_Math_Calculator {

	const PATTERN = '/(?:\-?\d+(?:\.?\d+)?[\+\-\*\/])+\-?\d+(?:\.?\d+)?/';
	const PARENTHESIS_DEPTH = 10;

	public function calculate($input) {
		if (strpos($input, '+') != null || strpos($input, '-') != null || strpos($input, '/') != null || strpos($input, '*') != null) {
			//  Remove white spaces and invalid math chars
			$input = str_replace(',', '.', $input);
			$input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input);

			//  Calculate each of the parenthesis from the top
			$i = 0;
			while (strpos($input, '(') || strpos($input, ')')) {
				$input = preg_replace_callback('/\(([^\(\)]+)\)/', 'self::callback', $input);

				$i++;
				if ($i > self::PARENTHESIS_DEPTH) {
					break;
				}
			}

			//  Calculate the result
			if (preg_match(self::PATTERN, $input, $match)) {
				return $this->compute($match[0]);
			}

			return 0;
		}

		return $input;
	}

	private function compute($input) {
		$compute = create_function('', 'return ' . $input . ';');

		return 0 + $compute();
	}

	private function callback($input) {
		if (is_numeric($input[1])) {
			return $input[1];
		} elseif (preg_match(self::PATTERN, $input[1], $match)) {
			return $this->compute($match[0]);
		}

		return 0;
	}

}