<?php

namespace alveolata\algorithm;

require_once(DIR_ALVEOLATA . '/list/functions.php');


/**
 * @param array $order {map<§x,list<§x>>}
 * @return array {list<§x>}
 * @throw \Exception if not possible
 */
function topsort(
	array $order
) : array
{
	if (empty($order)) {
		return [];
	}
	else {
		foreach ($order as $member => $dependencies) {
			if (count($dependencies) <= 0) {
				$order_ = [];
				foreach ($order as $member_ => $dependencies_) {
					if ($member === $member_) {
						// do nothing
					}
					else {
						$order_[$member_] = \alveolata\list_\filter/*<§x,bool>*/(
							$dependencies_,
							function ($dependency_) use ($member) : bool {
								return (! ($member === $dependency_));
							}
						);
					}
				}
				return array_merge([$member], topsort($order_));
			}
		}
		throw (new \Exception('not sortable'));
	}
}


/**
 * calculates the levenshtein distance between two strings
 */
function levenshtein(string $x, string $y) : int
{
	$u = str_split($x);
	$v = str_split($y);
	
	// init
	$matrix = array_map(
		fn($i) => array_map(fn($j) => null, \alveolata\list_\sequence(count($u)+1)),
		\alveolata\list_\sequence(count($v)+1)
	);
	foreach (\alveolata\list_\sequence(count($u)+1) as $i) {$matrix[$i][0] = $i;}
	foreach (\alveolata\list_\sequence(count($v)+1) as $j) {$matrix[0][$j] = $j;}
	
	// feed
	foreach (\alveolata\list_\sequence(count($u)) as $i) {
		foreach (\alveolata\list_\sequence(count($v)) as $j) {
			$matrix[$i+1][$j+1] = min(
				min(
					($matrix[$i+1][$j+0] + 1),
					($matrix[$i+0][$j+1] + 1)
				),
				($matrix[$i+0][$j+0] + (($u[$i] === $v[$j]) ? 0 : 1))
			);
		}
	}
	
	// return
	return $matrix[count($u)][count($v)];
}


 ?>