1<?php
2/*
3 * Paste $v3.2 2025/09/08 https://github.com/boxlabss/PASTE
4 * demo: https://paste.boxlabs.uk/
5 *
6 * https://phpaste.sourceforge.io/
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version 3
11 * of the License, or (at your option) any later version.
12 * 
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16 * GNU General Public License in LICENCE for more details.
17 */
18declare(strict_types=1);
19
20require_once __DIR__ . '/includes/session.php';
21require_once __DIR__ . '/config.php';
22require_once __DIR__ . '/includes/functions.php';
23// Error handling
24paste_enable_themed_errors();
25
26// Highlighter bootstrap + language lists
27require_once __DIR__ . '/includes/hlbootstrap.php';
28require_once __DIR__ . '/includes/list_languages.php';
29
30ini_set('display_errors','0');
31ini_set('log_errors','1');
32date_default_timezone_set('UTC');
33
34// Load paste by ID, decrypting as needed. Returns ['title','content','code'] or null
35function load_paste(PDO $pdo, int $id): ?array {
36    try {
37        $st = $pdo->prepare("SELECT id,title,content,code,encrypt FROM pastes WHERE id=? LIMIT 1");
38        $st->execute([$id]);
39        $r = $st->fetch();
40        if (!$r) return null;
41
42        $title   = (string)$r['title'];
43        $content = (string)$r['content'];
44
45        if ((string)$r['encrypt'] === "1" && defined('SECRET')) {
46            $title   = decrypt($title,   hex2bin(SECRET))   ?? $title;
47            $content = decrypt($content, hex2bin(SECRET))   ?? $content;
48        }
49
50        // Stored content is HTML-escaped before encrypt; decode for diffing
51        $content = html_entity_decode($content, ENT_QUOTES|ENT_SUBSTITUTE, 'UTF-8');
52
53        return [
54            'title'   => $title,
55            'content' => $content,
56            'code'    => (string)($r['code'] ?? 'text'),
57        ];
58    } catch (Throwable $e) {
59        error_log("diff.php load_paste($id): ".$e->getMessage());
60        return null;
61    }
62}
63
64// Inline (word/char) diff > [leftHTML, rightHTML] with <span class="diff-inside-...">
65function inline_diff(string $a, string $b): array {
66    $split = static function(string $s): array {
67        preg_match_all('/\s+|[^\s]+/u', $s, $m);
68        return $m[0] ?: [$s];
69    };
70    $Aw = $split($a); $Bw = $split($b);
71    $useChar = (count($Aw) <= 4 || count($Bw) <= 4);
72    if ($useChar) {
73        $Aw = preg_split('//u', $a, -1, PREG_SPLIT_NO_EMPTY);
74        $Bw = preg_split('//u', $b, -1, PREG_SPLIT_NO_EMPTY);
75    }
76    $n=count($Aw); $m=count($Bw);
77    $L = array_fill(0,$n+1,array_fill(0,$m+1,0));
78    for($i=$n-1;$i>=0;$i--) for($j=$m-1;$j>=0;$j--) {
79        $L[$i][$j]=($Aw[$i]===$Bw[$j])?($L[$i+1][$j+1]+1):max($L[$i+1][$j],$L[$i][$j+1]);
80    }
81    $i=0;$j=0;$left='';$right='';
82    $esc = static fn($s)=>htmlspecialchars($s, ENT_QUOTES|ENT_SUBSTITUTE, 'UTF-8');
83    while($i<$n && $j<$m){
84        if($Aw[$i]===$Bw[$j]){ $left.=$esc($Aw[$i]); $right.=$esc($Bw[$j]); $i++; $j++; }
85        elseif($L[$i+1][$j] >= $L[$i][$j+1]){ $left.='<span class="diff-inside-del">'.$esc($Aw[$i]).'</span>'; $i++; }
86        else { $right.='<span class="diff-inside-add">'.$esc($Bw[$j]).'</span>'; $j++; }
87    }
88    while($i<$n){ $left.='<span class="diff-inside-del">'.$esc($Aw[$i]).'</span>'; $i++; }
89    while($j<$m){ $right.='<span class="diff-inside-add">'.$esc($Bw[$j]).'</span>'; $j++; }
90    return [$left,$right];
91}
92
93/**
94 * Index-based diff at line level > opcodes referencing original arrays.
95 * Opcodes:
96 *   - ['op'=>'eq','ai'=>i,'bi'=>j]
97 *   - ['op'=>'del','ai'=>i]
98 *   - ['op'=>'add','bi'=>j]
99 *
100 *   1) xdiff accelerator (parse unified diff) if available
101 *   2) Myers O((N+M)D) fallback in pure PHP
102 */
103function diff_lines_idx(array $A, array $B, ?callable $normalizer=null): array {
104    $An = $normalizer ? array_map($normalizer, $A) : $A;
105    $Bn = $normalizer ? array_map($normalizer, $B) : $B;
106
107    if (function_exists('xdiff_string_diff')) {
108        return _diff_idx_via_xdiff($An, $Bn);
109    }
110    return _diff_idx_via_myers($An, $Bn);
111}
112
113/* ---------- Fast path: use xdiff to compute unified diff, parse to opcodes ---------- */
114function _diff_idx_via_xdiff(array $A, array $B): array {
115    $N = count($A); $M = count($B);
116
117    // Join as text; add trailing newline to stabilize EOF handling
118    $left  = ($N ? implode("\n", $A) : '') . "\n";
119    $right = ($M ? implode("\n", $B) : '') . "\n";
120
121    // Use context for stable headers + ' ' lines; non-minimal for speed
122    $ctx = 3;
123    $ud = xdiff_string_diff($left, $right, $ctx, false);
124    if ($ud === false) {
125        // Trivial fallback: align common prefix, then tail adds/dels
126        $ops = [];
127        $eq = min($N, $M);
128        for ($i=0; $i<$eq; $i++) $ops[] = ['op'=>'eq','ai'=>$i,'bi'=>$i];
129        for ($i=$eq; $i<$N; $i++) $ops[] = ['op'=>'del','ai'=>$i];
130        for ($j=$eq; $j<$M; $j++) $ops[] = ['op'=>'add','bi'=>$j];
131        return $ops;
132    }
133    if ($ud === '') {
134        $ops = [];
135        for ($i=0; $i<min($N,$M); $i++) $ops[] = ['op'=>'eq','ai'=>$i,'bi'=>$i];
136        for ($i=$M; $i<$N; $i++) $ops[] = ['op'=>'del','ai'=>$i];
137        for ($j=$N; $j<$M; $j++) $ops[] = ['op'=>'add','bi'=>$j];
138        return $ops;
139    }
140
141    $ops = [];
142    $ai = 0; $bi = 0;
143
144    $lines = preg_split("/\R/u", $ud);
145    foreach ($lines as $ln) {
146        if ($ln === '' && $ln !== '0') continue;
147
148        // Hunk header: @@ -aStart,aLen +bStart,bLen @@
149        if (($ln[0] ?? '') === '@' &&
150            preg_match('/^@@\s+-([0-9]+)(?:,([0-9]+))?\s+\+([0-9]+)(?:,([0-9]+))?\s+@@/', $ln, $m)) {
151
152            $startA = max(0, (int)$m[1] - 1);  // convert to 0-based
153            $startB = max(0, (int)$m[3] - 1);
154
155            // Between hunks: move forward by equal lines only
156            $gap = min(max(0, $startA - $ai), max(0, $startB - $bi));
157            for ($k=0; $k<$gap; $k++) { $ops[] = ['op'=>'eq','ai'=>$ai,'bi'=>$bi]; $ai++; $bi++; }
158            continue;
159        }
160
161        $tag = $ln[0] ?? '';
162        if ($tag === ' ') {                   // context (equal)
163            $ops[] = ['op'=>'eq','ai'=>$ai,'bi'=>$bi];  $ai++; $bi++;
164        } elseif ($tag === '-') {             // deletion
165            $ops[] = ['op'=>'del','ai'=>$ai];           $ai++;
166        } elseif ($tag === '+') {             // addition
167            $ops[] = ['op'=>'add','bi'=>$bi];                    $bi++;
168        } elseif ($tag === '\\') {
169            // "\ No newline at end of file" > ignore
170        } else {
171            // headers '---' / '+++' or noise > ignore
172        }
173    }
174
175    // Trailing equals after the last hunk
176    $tailEq = min($N - $ai, $M - $bi);
177    for ($k=0; $k<$tailEq; $k++) { $ops[] = ['op'=>'eq','ai'=>$ai,'bi'=>$bi]; $ai++; $bi++; }
178    for (; $ai<$N; $ai++) $ops[] = ['op'=>'del','ai'=>$ai];
179    for (; $bi<$M; $bi++) $ops[] = ['op'=>'add','bi'=>$bi];
180
181    return $ops;
182}
183
184/* ---------- Fallback: Myers O((N+M)D) with path reconstruction ---------- */
185function _diff_idx_via_myers(array $A, array $B): array {
186    $N = count($A); $M = count($B);
187
188    if ($N === 0 && $M === 0) return [];
189    if ($N === 0) { $ops=[]; for($j=0;$j<$M;$j++) $ops[]=['op'=>'add','bi'=>$j]; return $ops; }
190    if ($M === 0) { $ops=[]; for($i=0;$i<$N;$i++) $ops[]=['op'=>'del','ai'=>$i]; return $ops; }
191
192    $max = $N + $M;
193    $off = $max;
194    $V = array_fill(0, 2 * $max + 1, 0);
195    $trace = [];
196
197    $Dend = 0;
198    for ($d = 0; $d <= $max; $d++) {
199        $trace[$d] = $V;
200
201        for ($k = -$d; $k <= $d; $k += 2) {
202            if ($k == -$d || ($k != $d && $V[$off + $k - 1] < $V[$off + $k + 1])) {
203                $x = $V[$off + $k + 1];       // down (insert B)
204            } else {
205                $x = $V[$off + $k - 1] + 1;   // right (delete A)
206            }
207            $y = $x - $k;
208
209            while ($x < $N && $y < $M && $A[$x] === $B[$y]) { $x++; $y++; }
210
211            $V[$off + $k] = $x;
212
213            if ($x >= $N && $y >= $M) {
214                $trace[$d] = $V;
215                $Dend = $d;
216                break 2;
217            }
218        }
219    }
220
221    $ops = [];
222    $x = $N; $y = $M;
223    for ($d = $Dend; $d > 0; $d--) {
224        $Vprev = $trace[$d-1];
225        $k  = $x - $y;
226
227        $down = ($k == -$d) || ($k != $d && $Vprev[$off + $k - 1] < $Vprev[$off + $k + 1]);
228        $kPrev   = $down ? $k + 1 : $k - 1;
229        $xStart  = $down ? $Vprev[$off + $kPrev] : $Vprev[$off + $kPrev] + 1;
230        $yStart  = $xStart - $kPrev;
231
232        while ($x > $xStart && $y > $yStart) { $x--; $y--; $ops[] = ['op'=>'eq','ai'=>$x,'bi'=>$y]; }
233
234        if ($down) {
235            $yStart--;
236            $ops[] = ['op'=>'add','bi'=>$yStart];
237        } else {
238            $xStart--;
239            $ops[] = ['op'=>'del','ai'=>$xStart];
240        }
241
242        $x = $xStart; $y = $yStart;
243    }
244
245    while ($x > 0 && $y > 0) { $x--; $y--; $ops[] = ['op'=>'eq','ai'=>$x,'bi'=>$y]; }
246    while ($x > 0) { $x--; $ops[] = ['op'=>'del','ai'=>$x]; }
247    while ($y > 0) { $y--; $ops[] = ['op'=>'add','bi'=>$y]; }
248
249    return array_reverse($ops);
250}
251
252// Build side-by-side & unified row arrays from ops (index-based).
253function build_tables_idx(array $ops, array $leftLines, array $rightLines): array {
254    $side=[]; $uni=[]; $li=1; $ri=1;
255    foreach ($ops as $op) {
256        if ($op['op']==='eq') {
257            $L=(string)($leftLines[$op['ai']] ?? '');
258            $R=(string)($rightLines[$op['bi']] ?? '');
259            $side[]=['lno'=>$li,'rno'=>$ri,'lclass'=>'ctx','rclass'=>'ctx','lhtml'=>$L,'rhtml'=>$R,'l_intra'=>false,'r_intra'=>false];
260            $uni[] =['lno'=>$li,'rno'=>$ri,'class'=>'ctx','html'=>$L,'intra'=>false];
261            $li++; $ri++;
262        } elseif ($op['op']==='del') {
263            $L=(string)($leftLines[$op['ai']] ?? '');
264            $side[]=['lno'=>$li,'rno'=>'','lclass'=>'del','rclass'=>'empty','lhtml'=>$L,'rhtml'=>'','l_intra'=>false,'r_intra'=>false];
265            $uni[] =['lno'=>$li,'rno'=>'','class'=>'del','html'=>$L,'intra'=>false];
266            $li++;
267        } else { // add
268            $R=(string)($rightLines[$op['bi']] ?? '');
269            $side[]=['lno'=>'','rno'=>$ri,'lclass'=>'empty','rclass'=>'add','lhtml'=>'','rhtml'=>$R,'l_intra'=>false,'r_intra'=>false];
270            $uni[] =['lno'=>'','rno'=>$ri,'class'=>'add','html'=>$R,'intra'=>false];
271            $ri++;
272        }
273    }
274    return [$side,$uni];
275}
276
277// Apply inline word/char diff across adjacent del/add in side-by-side rows.
278function apply_inline_sxs(array &$sideRows): void {
279    for ($i=0; $i<count($sideRows)-1; $i++) {
280        $a=$sideRows[$i]; $b=$sideRows[$i+1];
281        if ($a['lclass']==='del' && $b['rclass']==='add') {
282            [$L,$R] = inline_diff((string)$a['lhtml'], (string)$b['rhtml']);
283            $sideRows[$i]['lhtml']=$L; $sideRows[$i]['l_intra']=true;
284            $sideRows[$i+1]['rhtml']=$R; $sideRows[$i+1]['r_intra']=true;
285            $i++;
286        }
287    }
288}
289
290// Proper unified .diff (xdiff if present; else POSIX-ish fallback)
291function unified_diff_download(string $left, string $right, string $nameA='a', string $nameB='b', int $ctx=3): string {
292    if (function_exists('xdiff_string_diff')) {
293        // Use non-minimal for speed; we rewrite headers below
294        $ud = xdiff_string_diff($left, $right, $ctx, false);
295        if ($ud !== false) {
296            $ts = gmdate('Y-m-d H:i:s O');
297            $hdr = "--- {$nameA}\t{$ts}\n+++ {$nameB}\t{$ts}\n";
298            $ud = preg_replace('~^--- .*\R\+\+\+ .*\R~', $hdr, $ud, 1);
299            return $ud;
300        }
301    }
302
303    // Manual fallback
304    $aOrig = preg_split("/\R/u", $left);
305    $bOrig = preg_split("/\R/u", $right);
306    if ($aOrig === false) $aOrig = [$left];
307    if ($bOrig === false) $bOrig = [$right];
308
309    $ops = diff_lines_idx($aOrig, $bOrig, null);
310
311    $hunks = [];
312    $flush = static function (&$hunks, &$buf) {
313        if (empty($buf['lines'])) return;
314        $oldLen = max(0, $buf['oldLen']);
315        $newLen = max(0, $buf['newLen']);
316        $h = "@@ -{$buf['oldStart']}" . ($oldLen===1?'':",$oldLen")
317           . " +{$buf['newStart']}" . ($newLen===1?'':",$newLen") . " @@\n";
318        $h .= implode('', $buf['lines']);
319        $hunks[] = $h;
320        $buf = ['oldStart'=>0,'newStart'=>0,'oldLen'=>0,'newLen'=>0,'lines'=>[],'open'=>false];
321    };
322
323    $buf = ['oldStart'=>0,'newStart'=>0,'oldLen'=>0,'newLen'=>0,'lines'=>[],'open'=>false];
324    $ctxAhead = 0;
325    $ai=1; $bi=1;
326
327    $grab_context = static function($aOrig, $bOrig, $ai, $bi, $ctx) use (&$buf) {
328        $startA = max(1, $ai - $ctx);
329        $startB = max(1, $bi - $ctx);
330        $buf['oldStart'] = $startA;
331        $buf['newStart'] = $startB;
332        for ($k=0; $k<($ai-$startA); $k++) {
333            $buf['lines'][] = ' ' . rtrim((string)$aOrig[$startA-1+$k], "\r") . "\n";
334        }
335        $buf['oldLen'] += ($ai-$startA);
336        $buf['newLen'] += ($bi-$startB);
337    };
338
339    foreach ($ops as $op) {
340        if ($op['op'] === 'eq') {
341            if ($buf['open']) {
342                if ($ctxAhead < 3) {
343                    $line = rtrim((string)$aOrig[$op['ai']], "\r");
344                    $buf['lines'][] = ' ' . $line . "\n";
345                    $buf['oldLen']++; $buf['newLen']++; $ctxAhead++;
346                } else {
347                    $flush($hunks, $buf);
348                    $ctxAhead = 0;
349                }
350            }
351            $ai++; $bi++;
352        } elseif ($op['op'] === 'del') {
353            if (!$buf['open']) { $buf['open']=true; $ctxAhead=0; $grab_context($aOrig, $bOrig, $ai, $bi, 3); }
354            $line = rtrim((string)$aOrig[$op['ai']], "\r");
355            $buf['lines'][] = '-' . $line . "\n";
356            $buf['oldLen']++; $ai++;
357        } else { // add
358            if (!$buf['open']) { $buf['open']=true; $ctxAhead=0; $grab_context($aOrig, $bOrig, $ai, $bi, 3); }
359            $line = rtrim((string)$bOrig[$op['bi']], "\r");
360            $buf['lines'][] = '+' . $line . "\n";
361            $buf['newLen']++; $bi++;
362        }
363    }
364    if ($buf['open']) $flush($hunks, $buf);
365
366    $ts = gmdate('Y-m-d H:i:s O');
367    $out  = "--- {$nameA}\t{$ts}\n+++ {$nameB}\t{$ts}\n";
368    $out .= implode('', $hunks);
369    return $out;
370}
371
372// Render a single line with highlight.php if available (else plain-escaped).
373function hl_render_line(string $text, string $lang='text'): string {
374    global $highlighter;
375    static $hl = null;
376
377    $esc = static fn($s)=>htmlspecialchars($s, ENT_QUOTES|ENT_SUBSTITUTE, 'UTF-8');
378
379    if (($highlighter ?? 'geshi') === 'highlight') {
380        if ($hl === null) $hl = make_highlighter();
381        if ($hl) {
382            try {
383                if ($lang && !in_array(strtolower($lang), ['autodetect','text','plaintext'], true)) {
384                    $res = $hl->highlight($lang, $text);
385                    return '<span class="hljs">'.$res->value.'</span>';
386                }
387                $res = $hl->highlightAuto($text);
388                return '<span class="hljs">'.$res->value.'</span>';
389            } catch (Throwable $e) { /* fall through */ }
390        }
391    }
392    return $esc($text);
393}
394
395/* =========================================================
396 * Page inputs
397 * =======================================================*/
398
399$left  = '';
400$right = '';
401$leftLabel  = 'Old';
402$rightLabel = 'New';
403
404/* ---------- Minimal site/bootstrap so header/footer look right ---------- */
405$mod_rewrite = $mod_rewrite ?? '0';
406$baseurl     = $baseurl     ?? '/';
407$site_name   = $site_name   ?? '';
408$title       = 'Diff';
409$ges_style   = '';          // keep themes CSS-only
410$ads_1 = $ads_2 = $text_ads = ''; // optional ad slots
411
412try {
413    // site_info
414    $stmt = $pdo->query("SELECT * FROM site_info WHERE id='1'");
415    if ($stmt) {
416        $si = $stmt->fetch() ?: [];
417        $title     = trim($si['title'] ?? $title);
418        $des       = trim($si['des'] ?? '');
419        $baseurl   = rtrim(trim($si['baseurl'] ?? $baseurl), '/') . '/';
420        $keyword   = trim($si['keyword'] ?? '');
421        $site_name = trim($si['site_name'] ?? $site_name);
422        $email     = trim($si['email'] ?? '');
423        $twit      = trim($si['twit'] ?? '');
424        $face      = trim($si['face'] ?? '');
425        $gplus     = trim($si['gplus'] ?? '');
426        $ga        = trim($si['ga'] ?? '');
427        $additional_scripts = trim($si['additional_scripts'] ?? '');
428        if (isset($si['mod_rewrite']) && $si['mod_rewrite'] !== '') {
429            $mod_rewrite = (string)$si['mod_rewrite'];
430        }
431    }
432
433    // interface
434    $stmt = $pdo->query("SELECT * FROM interface WHERE id='1'");
435    if ($stmt) {
436        $iface = $stmt->fetch() ?: [];
437        $default_lang  = trim($iface['lang']  ?? 'en.php');
438        $default_theme = trim($iface['theme'] ?? 'default');
439        if (is_file(__DIR__ . "/langs/$default_lang")) {
440            require_once __DIR__ . "/langs/$default_lang";
441        }
442    } else {
443        $default_theme = $default_theme ?? 'default';
444    }
445
446    // permissions
447    $stmt = $pdo->query("SELECT * FROM site_permissions WHERE id='1'");
448    if ($stmt) {
449        $perm = $stmt->fetch() ?: [];
450        $disableguest = trim($perm['disableguest'] ?? 'off');
451        $siteprivate  = trim($perm['siteprivate']  ?? 'off');
452    }
453
454    // ads (optional)
455    $stmt = $pdo->query("SELECT * FROM ads WHERE id='1'");
456    if ($stmt) {
457        $ads  = $stmt->fetch() ?: [];
458        $text_ads = trim($ads['text_ads'] ?? '');
459        $ads_1    = trim($ads['ads_1'] ?? '');
460        $ads_2    = trim($ads['ads_2'] ?? '');
461    }
462} catch (Throwable $e) {
463    // keep sane defaults, but don't break the page
464    error_log('diff.php bootstrap: ' . $e->getMessage());
465    $default_theme = $default_theme ?? 'default';
466}
467
468/* ---------- Paste IDs from query (supports ?a & ?b) ---------- */
469$lid = isset($_GET['a']) ? (int)$_GET['a'] : (isset($_GET['left_id']) ? (int)$_GET['left_id'] : 0);
470$rid = isset($_GET['b']) ? (int)$_GET['b'] : (isset($_GET['right_id']) ? (int)$_GET['right_id'] : 0);
471
472if ($lid) { $p = load_paste($pdo, $lid); if ($p){ $left=$p['content'];  $leftLabel='Paste #'.$lid; } }
473if ($rid) { $p = load_paste($pdo, $rid); if ($p){ $right=$p['content']; $rightLabel='Paste #'.$rid; } }
474
475/* ---------- POST inputs (compare / download keeps buffers) ---------- */
476if ($_SERVER['REQUEST_METHOD']==='POST') {
477    $left       = (string)($_POST['left_text']  ?? $left);
478    $right      = (string)($_POST['right_text'] ?? $right);
479    $leftLabel  = trim((string)($_POST['left_label']  ?? $leftLabel))  ?: $leftLabel;
480    $rightLabel = trim((string)($_POST['right_label'] ?? $rightLabel)) ?: $rightLabel;
481}
482
483/* ---------- Language engine + maps ---------- */
484$engine = function_exists('paste_current_engine') ? paste_current_engine() : ($highlighter ?? 'geshi');
485
486if ($engine === 'highlight') {
487    $langs         = highlight_supported_languages();
488    $language_map  = highlight_language_map($langs);
489    $alias_map     = highlight_alias_map($langs);
490    $popular_langs = paste_popular_formats_highlight();
491} else {
492    $language_map  = geshi_language_map();
493    $alias_map     = geshi_alias_map($language_map);
494    $popular_langs = paste_popular_formats_geshi();
495}
496
497/* ---------- Picked languages ---------- */
498$lang_left  = strtolower((string)($_POST['left_lang']  ?? $_GET['left_lang']  ?? 'autodetect'));
499$lang_right = strtolower((string)($_POST['right_lang'] ?? $_GET['right_lang'] ?? 'autodetect'));
500$lang_left  = $alias_map[$lang_left]  ?? 'autodetect';
501$lang_right = $alias_map[$lang_right] ?? 'autodetect';
502
503$lang_left_label  = $language_map[$lang_left]  ?? ucfirst($lang_left);
504$lang_right_label = $language_map[$lang_right] ?? ucfirst($lang_right);
505
506/* ---------- highlight.php default style (no picker) ---------- */
507if (($highlighter ?? 'geshi') === 'highlight') {
508    $hl_style = $hl_style ?? 'hybrid.css'; // header.php reads this
509}
510
511/* ---------- View options ---------- */
512$view_mode = ($_GET['view'] ?? 'side') === 'unified' ? 'unified' : 'side';
513$wrap      = isset($_GET['wrap'])      ? (int)$_GET['wrap']      : 0;
514$lineno    = isset($_GET['lineno'])    ? (int)$_GET['lineno']    : 1;
515
516/* ---------- Ignore trailing whitespace (toggle via ?ignore_ws=1) ---------- */
517$ignore_ws = isset($_GET['ignore_ws']) ? (int)$_GET['ignore_ws'] : 0;
518$normalizer = $ignore_ws ? static fn($s) => rtrim($s, " \t") : null;
519
520/* ---------- Persisted split percentage ---------- */
521$split_pct = 50.0;
522if (isset($_POST['split_pct'])) {
523    $split_pct = (float)$_POST['split_pct'];
524} elseif (isset($_COOKIE['diffSplitPct'])) {
525    $split_pct = (float)$_COOKIE['diffSplitPct'];
526}
527$split_pct = max(20.0, min(80.0, (float)$split_pct));
528setcookie('diffSplitPct', (string)$split_pct, [
529    'expires'  => time() + 60*60*24*30,
530    'path'     => '/',
531    'secure'   => !empty($_SERVER['HTTPS']),
532    'httponly' => false,
533    'samesite' => 'Lax',
534]);
535
536/* ---------- Download unified diff ---------- */
537if (isset($_GET['download']) && $_GET['download'] === '1') {
538    $nameA = $leftLabel  ?: 'Old';
539    $nameB = $rightLabel ?: 'New';
540    $ud = unified_diff_download($left, $right, $nameA, $nameB, 3);
541    // Surface engine in headers for debug
542    header('X-Diff-Engine: '.(function_exists('xdiff_string_diff') ? 'xdiff' : 'myers'));
543    header('X-Diff-Ignore-WS: '.($ignore_ws ? '1':'0'));
544    header('Content-Type: text/x-diff; charset=utf-8');
545    header('Content-Disposition: attachment; filename="paste.diff"');
546    echo $ud;
547    exit;
548}
549
550/* ---------- Compute opcodes ---------- */
551$leftLines  = preg_split("/\R/u", $left);
552$rightLines = preg_split("/\R/u", $right);
553if ($leftLines === false)  $leftLines  = [$left];
554if ($rightLines === false) $rightLines = [$right];
555
556$ops = diff_lines_idx($leftLines, $rightLines, $normalizer);
557
558/* ---------- change counts & exposure ----------
559 * Treat an adjacent del-run followed by an add-run (or vice-versa) as "mods".
560 * Each paired line counts as 1 change in the total.
561 * Returns: [$adds, $dels, $mods, $total, $no_changes]
562 */
563function compute_change_counts(array $ops): array {
564    $adds = 0; $dels = 0; $mods = 0;
565    $n = count($ops);
566    for ($i = 0; $i < $n; ) {
567        $op = $ops[$i]['op'] ?? 'eq';
568        if ($op !== 'add' && $op !== 'del') { $i++; continue; }
569
570        // First run (all adds or all dels)
571        $t1 = $op;
572        $c1 = 0;
573        $j  = $i;
574        while ($j < $n && ($ops[$j]['op'] ?? 'eq') === $t1) { $c1++; $j++; }
575
576        // Optional immediately-adjacent opposite run
577        $t2 = ($t1 === 'add') ? 'del' : 'add';
578        $c2 = 0;
579        $k  = $j;
580        while ($k < $n && ($ops[$k]['op'] ?? 'eq') === $t2) { $c2++; $k++; }
581
582        // Pair min(c1,c2) as modifications
583        $pair = min($c1, $c2);
584        $mods += $pair;
585
586        if ($t1 === 'add') {
587            $adds += $c1 - $pair;
588            $dels += $c2 - $pair;
589        } else {
590            $dels += $c1 - $pair;
591            $adds += $c2 - $pair;
592        }
593
594        // Advance past both runs
595        $i = ($c2 > 0) ? $k : $j;
596    }
597
598    $total = $adds + $dels + $mods;   // modified lines count as 1
599    $no_changes = ($total === 0);
600    return [$adds, $dels, $mods, $total, $no_changes];
601}
602
603/* ---------- change counts (mods collapse -/+ into 1) ---------- */
604[$adds, $dels, $mods, $changed_total, $no_changes] = compute_change_counts($ops);
605
606header('X-Diff-No-Changes: ' . ($no_changes ? '1' : '0'));
607header('X-Diff-Change-Add: ' . $adds);
608header('X-Diff-Change-Del: ' . $dels);
609header('X-Diff-Change-Mod: ' . $mods);
610header('X-Diff-Change-Total: ' . $changed_total);
611
612$GLOBALS['diff_no_changes']     = $no_changes;
613$GLOBALS['diff_changes_add']    = $adds;
614$GLOBALS['diff_changes_del']    = $dels;
615$GLOBALS['diff_changes_mod']    = $mods;         // available if you want a separate badge
616$GLOBALS['diff_changes_total']  = $changed_total; // theme uses this for ±T
617
618/* ---------- Build tables server-side ---------- */
619[$sideRows, $uniRows] = build_tables_idx($ops, $leftLines, $rightLines);
620
621/* ---------- Limit expensive inline diff pass for very large diffs ---------- */
622$perform_inline = true;
623$totalBytes = strlen($left) + strlen($right);
624if (count($sideRows) > 4000 || $totalBytes > 4*1024*1024) {
625    $perform_inline = false;
626}
627if ($perform_inline) {
628    apply_inline_sxs($sideRows);
629}
630
631/* ---------- Expose engine + toggle info to theme and headers ---------- */
632$engine_is_xdiff = function_exists('xdiff_string_diff');
633$engine_label    = $engine_is_xdiff ? 'xdiff' : 'myers';
634header('X-Diff-Engine: '.$engine_label);
635header('X-Diff-Ignore-WS: '.($ignore_ws ? '1':'0'));
636
637// Convenience strings the theme can show in the toolbar:
638$diff_engine_badge = '<span class="badge bg-secondary" title="Diff engine">'.$engine_label.'</span>';
639$ignore_ws_on      = (bool)$ignore_ws;
640
641// Build toggle URL for ignore_ws (preserve other query params)
642$qs = $_GET;
643$qs['ignore_ws'] = $ignore_ws ? 0 : 1;
644$ignore_ws_toggle_url = strtok($_SERVER['REQUEST_URI'], '?') . '?' . http_build_query($qs);
645
646/* ---------- Render theme ---------- */
647$themeDir = 'theme/' . htmlspecialchars($default_theme ?? 'default', ENT_QUOTES, 'UTF-8');
648
649// expose split pct to the view if needed by JS
650$GLOBALS['split_pct'] = $split_pct;
651
652// badges/toggle url for the theme
653$GLOBALS['diff_engine_badge']  = $diff_engine_badge;
654$GLOBALS['ignore_ws_on']       = $ignore_ws_on;
655$GLOBALS['ignore_ws_toggle']   = $ignore_ws_toggle_url;
656
657require_once $themeDir . '/header.php';
658require_once $themeDir . '/diff.php';
659require_once $themeDir . '/footer.php';