From 72084f120c1e5a2270c0854540153c35819d0b35 Mon Sep 17 00:00:00 2001
From: Mischa POSLAWSKY <perl@shiar.org>
Date: Fri, 15 Jan 2021 18:41:47 +0100
Subject: [PATCH] login/commits: syntax highlighting of diff lines

Parse chunks returned by git's porcelain word diffing interface,
formatting old/new columns similar to split github commit output.
Ignore strict line numbers in favour of minimal text comparison.
---
 login/commits/index.php | 111 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 105 insertions(+), 6 deletions(-)

diff --git a/login/commits/index.php b/login/commits/index.php
index c53bf39..dbd8cd9 100644
--- a/login/commits/index.php
+++ b/login/commits/index.php
@@ -9,20 +9,119 @@ if (!$hash) {
 	return TRUE;
 }
 
-print "<h2>Wijzigingen in $hash</h2>\n";
+$this->title = "Wijzigingen in ".strtoupper($hash);
+print "<h2>{$this->title}</h2>\n";
 
-$gitcmd = "git show ".$hash;
+$gitcmd = "git show "
+	. "--word-diff=porcelain --no-prefix --pretty='%H%n%at\t%an\t%w(0,0,1)%B' "
+	. escapeshellarg($hash);
 $log = popen($gitcmd, 'r');
-if (!$log or strpos(fgets($log), "commit $hash") !== 0) {
+if (!$log or strpos(fgets($log), $hash) !== 0) {
 	$Page->place['warn'] = "Kon inhoud niet ophalen met <code>$gitcmd</code>";
 	return;
 }
 
-print '<pre>';
+# read metadata and commit message
+list ($atime, $author, $msg) = explode("\t", fgets($log), 3);
 while ( $line = fgets($log) ) {
-	print htmlspecialchars($line);
+	if ($line == "\n") {
+		fgets($log); // assume another empty line
+		break;
+	}
+	$msg .= substr($line, 1);
 }
-print "</pre>\n";
 
+# commit head
+print '<p>';
+printf('<small class="date">%s • %s</small>',
+	htmlspecialchars($author), strftime('%F %H:%M', $atime)
+);
+print "\n".nl2br(htmlspecialchars($msg));
+print "</p>\n";
+
+print '<style>
+.diff {
+	white-space: pre-wrap;
+	white-space: break-spaces;
+	font-family: monospace;
+}
+td:first-of-type.change,
+del {
+	background: #F002;
+	text-decoration: none;
+}
+td:last-of-type.change,
+ins {
+	background: #0F02;
+	text-decoration: none;
+}
+.diff .head {
+	background: #00F2;
+}
+</style>';
+
+# body
+$row = $ln = NULL;
+$col = ['', ''];
+print '<table class="diff">';
+while ( $line = fgets($log) ) {
+	preg_match(isset($ln) ? '/^(\W|\S+ )(.*)/' : '/^(\S+ )(.*)/', $line, $part);
+	$body = htmlspecialchars($part[2]);
+	switch ($part[1]) {
+	case 'diff ':
+		# file start
+		if (preg_match('/^--git (.+) (.*)/', $part[2], $diffhead)) {
+			$row = "$diffhead[1]";
+			if ($diffhead[1] !== $diffhead[2]) {
+				$row .= " → $diffhead[2]";
+			}
+		}
+		else {
+			$row = '?';
+		}
+		$ln = NULL;
+		break;
+	case '@@ ':
+		# chunk start
+		if (preg_match('/^[-](\d+)(?:,\d+)? [+](\d+)(?:,\d+)? @@/', $part[2], $diffstart)) {
+			array_shift($diffstart);
+			$ln = $diffstart;
+		}
+		else {
+			$ln = ['?', '?']; # unrecognised diff header
+		}
+		print '<tr class="head"><td colspan="4">'.$row.'</tr>'."\n";
+		break;
+	case '-':
+		$col[0] .= "<del>$body</del>";
+		break;
+	case '+':
+		$col[1] .= "<ins>$body</ins>";
+		break;
+	case ' ':
+		$col[0] .= $body;
+		$col[1] .= $body;
+		break;
+	case '~':
+		# part end
+		print '<tr>';
+		foreach ($col as $i => $line) {
+			if (empty($line)) {
+				print '<th><td>';
+				continue;
+			}
+			printf('<th>%s</th><td%s>%s</td>',
+				$ln[$i]++,
+				$col[0] == $col[1] ? '' : ' class="change"',
+				$line
+			);
+		}
+		print "</tr>\n";
+		$col = ['', ''];
+		break;
+	}
+}
+print "</table>\n";
 pclose($log);
+
 return;
-- 
2.30.0