do a diff between files

PHPDiff.php

function PHPDiff ($old, $new) {

	$t1 = $old;
	$t2 = $new;

	# build a reverse-index array using the line as key and line number as value
	# don't store blank lines, so they won't be targets of the shortest distance
	# search
	foreach ($t1 as $i => $x) {
		if ($x>'') {
			$r1[$x][] = $i;
		}
	}
	foreach ($t2 as $i => $x) {
		if ($x>'') {
			$r2[$x][] = $i;
		}
	}

	$a1 = 0;
	$a2 = 0;   # start at beginning of each list
	$actions = array();

	# walk this loop until we reach the end of one of the lists
	while ($a1 < count($t1) && $a2 < count($t2)) {

		# if we have a common element, save it and go to the next
		if ($t1[$a1] == $t2[$a2]) {
			$actions[] = 4;
			$a1++;
			$a2++;
			continue;
		}

		# otherwise, find the shortest move (Manhattan-distance) from the
		# current location
		$best1 = count($t1);
		$best2 = count($t2);

		$s1 = $a1;
		$s2 = $a2;

		while(($s1 + $s2 - $a1 - $a2) < ($best1 + $best2 - $a1 - $a2)) {

			$d = -1;

			foreach((array) @$r1[$t2[$s2]] as $n) {
				if ($n >= $s1) {
					$d = $n;
					break;
				}
			}

			if ($d >= $s1 && ($d + $s2 - $a1 - $a2) < ($best1 + $best2 - $a1 - $a2)) {
				$best1 = $d;
				$best2 = $s2;
			}

			$d = -1;
			foreach((array) @$r2[$t1[$s1]] as $n) {
				if ($n >= $s2) {
					$d = $n;
					break;
				}
			}

			if ($d >= $s2 && ($s1 + $d - $a1 - $a2) < ($best1 + $best2 - $a1 - $a2)) {
				$best1 = $s1;
				$best2 = $d;
			}
			$s1++;
			$s2++;
		}

		// deleted elements
		while ($a1 < $best1) {
			$actions[] = 1;
			$a1++;
		}


		// added elements
		while ($a2 < $best2) {
			$actions[] = 2;
			$a2++;
		}
	}

	# we've reached the end of one list, now walk to the end of the other
	# deleted elements
	while($a1 < count($t1)) {
		$actions[] = 1;
		$a1 ++;
	}

	# added elements
	while($a2 < count($t2)) {
		$actions[] = 2;
		$a2 ++;
	}

	# and this marks our ending point
	$actions[] = 8;

	# now, let's follow the path we just took and report the added/deleted
	# elements into $out.
	$op = 0;
	$x0 = $x1 = $y0 = $y1 = 0;
	$changeCount = 0;

	$out = array();

	foreach($actions as $act) {

		if ($act == 1) {
			$op |= $act;
			$x1 ++;
			continue;
		}

		if ($act==2) {
			$op |= $act;
			$y1 ++;
			continue;
		}

		if ($op>0) {

			$xstr = ($x1 == ($x0 + 1)) ? $x1 : ($x0 + 1) . ', ' . $x1;
			$ystr = ($y1 == ($y0 + 1)) ? $y1 : ($y0 + 1) . ', ' . $y1;

			$out[] = '<li>';

			if ($op == 1) {
				$out[] = '<p><strong>Code deleted</strong> : lines ' . $xstr . '</p>';
			}
			if ($op == 3) {
				$out[] = '<p><strong>Code changed</strong> : lines ' . $xstr . ' &#8594; ' . $ystr . '</p>';
			}

			// deleted elems
			if ($x0 < $x1) {
				$out[] = "<pre>";
				while ($x0 < $x1) {
					if($t1[$x0] != "") {
						$out[] = str_replace("\n", "", str_replace("<", "&lt;", $t1[$x0]));
					}
					$x0++;
				}
				$out[] = "</pre>";
			}

			if ($op == 2) {
				//$out[] = "<p><strong>Lines added</strong> : " . $x1 . " to " . $ystr . "</p>";
				$out[] = "<p><strong>Lines added</strong> : " . $ystr . "</p>";
			}
			if ($op == 3) {
				$out[] = '<p>changed to : </p>';
			}

			# added elems
			if ($y0 < $y1) {
				$out[] = "<pre>";
				while ($y0 < $y1) {
					if($t2[$y0] != "") {
						$out[] = str_replace("\n", "", str_replace("<", "&lt;", $t2[$y0]));
					}
					$y0++;
				}
				$out[] = "</pre>";
			}

			$out[] = '</li>';
			$changeCount ++;

		}

		$x1++;
		$x0=$x1;

		$y1++;
		$y0=$y1;

		$op=0;
	}

	$ret["changes"] = join("\n", $out);
	$ret["changeCount"] = $changeCount;

	return $ret;
}