fix: og image generation

lib/text-highlight.ts

@@ -1,5 +1,9 @@
 // ---------------------------------------------------------------------------
 // Text Fragment Highlight — compact URL encoding for selected text
+//
+// These utilities work in both browser and server environments.
+// The DOM-based findAndHighlightText() is browser-only.
+// The string-based extractMatchedText() is server-safe (for OG image generation).
 // ---------------------------------------------------------------------------
 
 /**
@@ -52,6 +56,67 @@ export function decodeTextFragment(
   return { prefix, suffix, length };
 }
 
+/**
+ * Server-side: extract the full matched text from an array of paragraph strings
+ * using a decoded text fragment (prefix, suffix, length).
+ *
+ * This is the server equivalent of findAndHighlightText() — instead of
+ * walking the DOM, it searches a flat array of HTML paragraph strings.
+ * HTML tags are stripped before matching.
+ *
+ * Returns the matched text string, or null if not found.
+ */
+export function extractMatchedText(
+  fragment: { prefix: string; suffix: string; length: number },
+  paragraphs: string[],
+): string | null {
+  // Strip HTML tags to get plain text
+  const plainParagraphs = paragraphs.map((p) =>
+    p.replace(/<[^>]*>/g, "").replace(/&[^;]+;/g, " "),
+  );
+
+  // Build a single string with paragraph breaks
+  const fullText = plainParagraphs.join(" ");
+  const normalized = fullText.replace(/\s+/g, " ");
+
+  const normalizedPrefix = fragment.prefix.replace(/\s+/g, " ");
+  let searchFrom = 0;
+  let matchStart = -1;
+
+  while (searchFrom < normalized.length) {
+    const idx = normalized.indexOf(normalizedPrefix, searchFrom);
+    if (idx === -1) break;
+
+    if (fragment.suffix) {
+      const normalizedSuffix = fragment.suffix.replace(/\s+/g, " ");
+      const expectedEnd = idx + fragment.length;
+      const suffixSearchStart = Math.max(
+        idx,
+        expectedEnd - normalizedSuffix.length - 20,
+      );
+      const suffixSearchEnd = Math.min(normalized.length, expectedEnd + 20);
+      const searchWindow = normalized.slice(suffixSearchStart, suffixSearchEnd);
+      if (searchWindow.includes(normalizedSuffix)) {
+        matchStart = idx;
+        break;
+      }
+    } else {
+      matchStart = idx;
+      break;
+    }
+    searchFrom = idx + 1;
+  }
+
+  if (matchStart === -1) return null;
+
+  const matchEnd = Math.min(matchStart + fragment.length, normalized.length);
+  const matched = normalized.slice(matchStart, matchEnd).trim();
+
+  if (matched.length === 0) return null;
+
+  return matched;
+}
+
 /**
  * Build the full URL with highlight fragment for the selected text.
  */