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<?php declare(strict_types=1);
namespace PhpParser\Internal;
/**
* Implements the Myers diff algorithm.
*
* Myers, Eugene W. "An O (ND) difference algorithm and its variations."
* Algorithmica 1.1 (1986): 251-266.
*
* @template T
* @internal
*/
class Differ {
/** @var callable(T, T): bool */
private $isEqual;
/**
* Create differ over the given equality relation.
*
* @param callable(T, T): bool $isEqual Equality relation
*/
public function __construct(callable $isEqual) {
$this->isEqual = $isEqual;
}
/**
* Calculate diff (edit script) from $old to $new.
*
* @param T[] $old Original array
* @param T[] $new New array
*
* @return DiffElem[] Diff (edit script)
*/
public function diff(array $old, array $new): array {
$old = \array_values($old);
$new = \array_values($new);
list($trace, $x, $y) = $this->calculateTrace($old, $new);
return $this->extractDiff($trace, $x, $y, $old, $new);
}
/**
* Calculate diff, including "replace" operations.
*
* If a sequence of remove operations is followed by the same number of add operations, these
* will be coalesced into replace operations.
*
* @param T[] $old Original array
* @param T[] $new New array
*
* @return DiffElem[] Diff (edit script), including replace operations
*/
public function diffWithReplacements(array $old, array $new): array {
return $this->coalesceReplacements($this->diff($old, $new));
}
/**
* @param T[] $old
* @param T[] $new
* @return array{array<int, array<int, int>>, int, int}
*/
private function calculateTrace(array $old, array $new): array {
$n = \count($old);
$m = \count($new);
$max = $n + $m;
$v = [1 => 0];
$trace = [];
for ($d = 0; $d <= $max; $d++) {
$trace[] = $v;
for ($k = -$d; $k <= $d; $k += 2) {
if ($k === -$d || ($k !== $d && $v[$k - 1] < $v[$k + 1])) {
$x = $v[$k + 1];
} else {
$x = $v[$k - 1] + 1;
}
$y = $x - $k;
while ($x < $n && $y < $m && ($this->isEqual)($old[$x], $new[$y])) {
$x++;
$y++;
}
$v[$k] = $x;
if ($x >= $n && $y >= $m) {
return [$trace, $x, $y];
}
}
}
throw new \Exception('Should not happen');
}
/**
* @param array<int, array<int, int>> $trace
* @param T[] $old
* @param T[] $new
* @return DiffElem[]
*/
private function extractDiff(array $trace, int $x, int $y, array $old, array $new): array {
$result = [];
for ($d = \count($trace) - 1; $d >= 0; $d--) {
$v = $trace[$d];
$k = $x - $y;
if ($k === -$d || ($k !== $d && $v[$k - 1] < $v[$k + 1])) {
$prevK = $k + 1;
} else {
$prevK = $k - 1;
}
$prevX = $v[$prevK];
$prevY = $prevX - $prevK;
while ($x > $prevX && $y > $prevY) {
$result[] = new DiffElem(DiffElem::TYPE_KEEP, $old[$x - 1], $new[$y - 1]);
$x--;
$y--;
}
if ($d === 0) {
break;
}
while ($x > $prevX) {
$result[] = new DiffElem(DiffElem::TYPE_REMOVE, $old[$x - 1], null);
$x--;
}
while ($y > $prevY) {
$result[] = new DiffElem(DiffElem::TYPE_ADD, null, $new[$y - 1]);
$y--;
}
}
return array_reverse($result);
}
/**
* Coalesce equal-length sequences of remove+add into a replace operation.
*
* @param DiffElem[] $diff
* @return DiffElem[]
*/
private function coalesceReplacements(array $diff): array {
$newDiff = [];
$c = \count($diff);
for ($i = 0; $i < $c; $i++) {
$diffType = $diff[$i]->type;
if ($diffType !== DiffElem::TYPE_REMOVE) {
$newDiff[] = $diff[$i];
continue;
}
$j = $i;
while ($j < $c && $diff[$j]->type === DiffElem::TYPE_REMOVE) {
$j++;
}
$k = $j;
while ($k < $c && $diff[$k]->type === DiffElem::TYPE_ADD) {
$k++;
}
if ($j - $i === $k - $j) {
$len = $j - $i;
for ($n = 0; $n < $len; $n++) {
$newDiff[] = new DiffElem(
DiffElem::TYPE_REPLACE, $diff[$i + $n]->old, $diff[$j + $n]->new
);
}
} else {
for (; $i < $k; $i++) {
$newDiff[] = $diff[$i];
}
}
$i = $k - 1;
}
return $newDiff;
}
}
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