Josep Piguillem
6fc600e6a1
Each field's original sits beside the field to write, and a translation that fell behind shows what the original said when it was translated and what it says now, word by word. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
100 lines
2.7 KiB
PHP
100 lines
2.7 KiB
PHP
<?php
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declare(strict_types=1);
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namespace App\Support;
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/**
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* What changed between two versions of a text, word by word, as HTML with
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* `<del>` and `<ins>` — enough to show a translator which sentence of the
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* original to look at again.
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*/
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final class TextDiff
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{
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/**
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* Above this many words on either side the comparison is skipped: it is
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* quadratic, and a text that long changed is better reread whole.
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*/
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protected const MAX_WORDS = 1500;
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public static function html(?string $old, ?string $new): ?string
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{
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$a = self::words($old);
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$b = self::words($new);
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if (count($a) > self::MAX_WORDS || count($b) > self::MAX_WORDS) {
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return null;
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}
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// Longest common subsequence, then walked back into runs.
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$m = count($a);
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$n = count($b);
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$lcs = array_fill(0, $m + 1, array_fill(0, $n + 1, 0));
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for ($i = $m - 1; $i >= 0; $i--) {
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for ($j = $n - 1; $j >= 0; $j--) {
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$lcs[$i][$j] = $a[$i] === $b[$j] ? $lcs[$i + 1][$j + 1] + 1 : max($lcs[$i + 1][$j], $lcs[$i][$j + 1]);
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}
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}
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$out = [];
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$i = $j = 0;
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while ($i < $m || $j < $n) {
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if ($i < $m && $j < $n && $a[$i] === $b[$j]) {
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$out[] = ['=', $a[$i]];
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$i++;
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$j++;
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} elseif ($i < $m && ($j === $n || $lcs[$i + 1][$j] >= $lcs[$i][$j + 1])) {
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// What went comes before what replaced it.
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$out[] = ['-', $a[$i]];
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$i++;
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} else {
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$out[] = ['+', $b[$j]];
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$j++;
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}
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}
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$html = '';
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$run = null;
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$buffer = [];
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$flush = function () use (&$html, &$run, &$buffer): void {
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if ($buffer === []) {
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return;
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}
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$text = e(implode(' ', $buffer));
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$html .= match ($run) {
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'+' => "<ins>{$text}</ins> ",
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'-' => "<del>{$text}</del> ",
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default => "{$text} ",
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};
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$buffer = [];
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};
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foreach ($out as [$op, $word]) {
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if ($op !== $run) {
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$flush();
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$run = $op;
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}
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$buffer[] = $word;
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}
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$flush();
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return trim($html);
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}
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/**
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* @return array<int, string>
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*/
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protected static function words(?string $text): array
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{
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$plain = trim((string) preg_replace('/\s+/u', ' ', html_entity_decode(strip_tags(str_replace(['</p>', '<br>', '<br/>', '<br />'], ' ', (string) $text)))));
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return $plain === '' ? [] : explode(' ', $plain);
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}
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}
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