line links

static/js/line-links.js

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2026 Mateusz Gruszczyński @linuxiarz.pl
+ * Source-Available Code / Dual-Licensed.
+ *
+ * Free for non-commercial and evaluation use under terms of BSL/GPLv3.
+ * Commercial or production use requires a valid paid license.
+ * See LICENSE file in repository root for details.
+ */
+
+const LINE_HASH = /^#L([1-9]\d*)$/i;
+
+export function lineFromHash(hash, lineCount = Number.POSITIVE_INFINITY) {
+  const match = LINE_HASH.exec(String(hash || ""));
+  if (!match) return null;
+  const line = Number(match[1]);
+  if (!Number.isSafeInteger(line) || line > lineCount) return null;
+  return line;
+}
+
+export function lineStartOffset(text, line) {
+  const target = Number(line);
+  if (!Number.isSafeInteger(target) || target < 1) return null;
+  if (target === 1) return 0;
+
+  let currentLine = 1;
+  for (let index = 0; index < text.length; index += 1) {
+    if (text.charCodeAt(index) !== 10) continue;
+    currentLine += 1;
+    if (currentLine === target) return index + 1;
+  }
+  return null;
+}
+
+export function lineLink(href, line) {
+  const target = Number(line);
+  if (!Number.isSafeInteger(target) || target < 1) throw new TypeError("Invalid line number");
+  const url = new URL(href);
+  url.hash = `L${target}`;
+  return url.href;
+}