WP-LIT-MCP/src/Integrations/Divi/Release/LineDiff.php

<?php

declare(strict_types=1);

namespace LIT\MCP\Integrations\Divi\Release;

defined('ABSPATH') || exit;

/** A small line diff (longest common subsequence) for wp lit-mcp divi-check --diff. */
final class LineDiff
{
    /**
     * @param list<string> $old
     * @param list<string> $new
     * @return list<string> "  kept", "- removed", "+ added"; "…" between changes more than 2 × $context lines apart.
     */
    public static function lines(array $old, array $new, int $context = 2): array
    {
        $operations = self::operations($old, $new);
        $keep = [];
        foreach ($operations as $i => [$op]) {
            if ($op === ' ') {
                continue;
            }
            for ($j = max(0, $i - $context); $j <= min(count($operations) - 1, $i + $context); ++$j) {
                $keep[$j] = true;
            }
        }

        $lines = [];
        $last = null;
        foreach ($operations as $i => [$op, $line]) {
            if (! isset($keep[$i])) {
                continue;
            }
            if ($last !== null && $i > $last + 1) {
                $lines[] = '…';
            }
            $lines[] = $op . ' ' . $line;
            $last = $i;
        }

        return $lines;
    }

    /**
     * @param list<string> $a
     * @param list<string> $b
     * @return list<array{0: string, 1: string}>
     */
    private static function operations(array $a, array $b): array
    {
        $n = count($a);
        $m = count($b);
        $lcs = array_fill(0, $n + 1, array_fill(0, $m + 1, 0));
        for ($i = $n - 1; $i >= 0; --$i) {
            for ($j = $m - 1; $j >= 0; --$j) {
                $lcs[$i][$j] = $a[$i] === $b[$j] ? $lcs[$i + 1][$j + 1] + 1 : max($lcs[$i + 1][$j], $lcs[$i][$j + 1]);
            }
        }

        $operations = [];
        $i = 0;
        $j = 0;
        while ($i < $n && $j < $m) {
            if ($a[$i] === $b[$j]) {
                $operations[] = [' ', $a[$i]];
                ++$i;
                ++$j;
            } elseif ($lcs[$i + 1][$j] >= $lcs[$i][$j + 1]) {
                $operations[] = ['-', $a[$i++]];
            } else {
                $operations[] = ['+', $b[$j++]];
            }
        }
        while ($i < $n) {
            $operations[] = ['-', $a[$i++]];
        }
        while ($j < $m) {
            $operations[] = ['+', $b[$j++]];
        }

        return $operations;
    }
}