<?php
/**
 * Permutator
 *
 * A functional class to perform tasks on each permutation of an array.
 *
 * @version 0.01
 * @author Shannon Wynter (http://fremnet.net/contact)
 * @license http://opensource.org/licenses/gpl-license.php GNU Public License
 * @copyright Copyright (c) 2010, Shannon Wynter
 */
class Permutator {
        /**
         * Storage for the original array passed to the constructor
         * @var array
         */
        private $source_array;
        /**
         * Storage for any valid callback (see {@link http://www.php.net/callback#callback PHP documentation})
         * @var callback
         */
        private $callback_function;
        /**
         * Storage for any arguments to pass to the callback if any
         * @var mixed
         */
        private $callback_argument;

        /**
         * Class constructor
         *
         * When calling the callback function the call is
         *      $callback_function($permutation, $callback_argument)
         *
         * @param array $source_array Array to permutate
         * @param callback $callback_function The function to call
         * @param mixed $callback_argument This parameter is passed to the callback function as the second argument
         */
        public function __construct($source_array, $callback_function, $callback_argument = null) {
                $this->source_array = $source_array;
                $this->callback_function = $callback_function;
                $this->callback_argument = $callback_argument;
        }

        /**
         * Factors
         *
         * Get the number of factors
         *
         * @return integer
         */
        public function factors() {
                return $this->factorial(count($this->source_array));
        }

        /**
         * Process
         *
         * Begin permutating the array
         */
        public function process() {
                $this->permutation($this->source_array);
        }

        /**
         * Factorial
         *
         * Calculate the factorial of a given number
         *
         * @param integer $number
         * @return integer
         */
        private function factorial($number) {
                if ($number == 0) return 1;
                return $number * $this->factorial($number - 1);
        }

        /**
         * Permutation
         *
         * Recursive function to find the permutations and eventually call
         * the callback function wrapper with the current permutation
         *
         * @param array $items
         * @param integer $depth
         * @param array $current
         */
        private function permutation($items, $depth = 0, $current = array()) {
                $count = count($items);
                if ($count == 0) {
                        call_user_func($this->callback_function, $current, $this->callback_argument);
                }
                else {
                        for ($i = 0; $i < $count; $i ++) {
                                $new_items = $items;
                                $current[$depth] = reset(array_splice($new_items, $i, 1));
                                $this->permutation($new_items, $depth + 1, $current);
                        }
                }
        }
}