Improve Nostr link handling

Fixes a bunch of problems with how Nostr links are created and replaced
in Markdown content

nostr/links.ts

@@ -0,0 +1,129 @@
+import { lookupUsernameByPubkey } from "../directory.ts";
+import { nip19 } from "@nostr/tools";
+import config from "../config.ts";
+
+const nostrUriRegex = /(nostr:|@)(nprofile|naddr|nevent|npub)[a-z0-9]+/g;
+
+export async function nostrUriToUrl(uri: string): Promise<string> {
+  const bech32 = uri.replace(/^(nostr:|@)/, "");
+
+  if (bech32.match(/^(naddr|nprofile|npub)/)) {
+    try {
+      const r = nip19.decode(bech32);
+      let username;
+
+      switch (r.type) {
+        case "naddr":
+          username = await lookupUsernameByPubkey(r.data.pubkey);
+          if (username) return `/${bech32}`;
+          break;
+        case "nprofile":
+          username = await lookupUsernameByPubkey(r.data.pubkey);
+          if (username) return `/@${username}`;
+          break;
+        case "npub":
+          username = await lookupUsernameByPubkey(r.data);
+          if (username) return `/@${username}`;
+          break;
+      }
+    } catch (e) {
+      console.error(e);
+    }
+  }
+
+  return `${config.njump_url}/${bech32}`;
+}
+
+export async function replaceNostrUris(markdown: string): Promise<string> {
+  const protectedRegex = /(`{3,}[\s\S]*?`{3,})|(`[^`]*`)|(<pre>[\s\S]*?<\/pre>)|(https?:\/\/[^\s<>"']+)/gi;
+
+  // Split text into segments: unprotected text and protected areas (code blocks, URLs)
+  const segments: string[] = [];
+  let lastIndex = 0;
+
+  markdown.replace(protectedRegex, (match, _fencedCode, _inlineCode, _preTag, _url, index) => {
+    segments.push(markdown.slice(lastIndex, index));
+    segments.push(match);
+    lastIndex = index + match.length;
+    return match;
+  });
+  segments.push(markdown.slice(lastIndex));
+
+  // Process each segment
+  let result = '';
+  for (let i = 0; i < segments.length; i++) {
+    if (i % 2 === 1 || protectedRegex.test(segments[i])) {
+      // Protected segment (code block or URL), leave unchanged
+      result += segments[i];
+    } else {
+      // Unprotected text, replace URIs and handle markdown links
+      result += await processUnprotectedText(segments[i]);
+    }
+  }
+
+  return result;
+}
+
+async function processUnprotectedText(text: string): Promise<string> {
+  const markdownLinkRegex = /\[([^\]]+)\]\(([^)]+)\)/g;
+  let lastIndex = 0;
+  const parts: string[] = [];
+
+  // Process markdown links first
+  let match;
+  while ((match = markdownLinkRegex.exec(text)) !== null) {
+    const [fullMatch, linkText, target] = match;
+
+    // Add text before the link
+    parts.push(await replaceUrisInText(text.slice(lastIndex, match.index)));
+
+    // Process the link target
+    if (nostrUriRegex.test(target) && target.match(nostrUriRegex)![0] === target) {
+      // Target is a Nostr URI, replace with resolved URL
+      const resolvedUrl = await nostrUriToUrl(target);
+      parts.push(`[${linkText}](${resolvedUrl})`);
+    } else {
+      // Not a Nostr URI, keep the original link
+      parts.push(fullMatch);
+    }
+
+    lastIndex = match.index + fullMatch.length;
+  }
+
+  // Add any remaining text after the last link
+  parts.push(await replaceUrisInText(text.slice(lastIndex)));
+
+  return parts.join('');
+}
+
+async function replaceUrisInText(text: string): Promise<string> {
+  let modifiedText = text;
+  const replacements: { start: number; end: number; replacement: string }[] = [];
+
+  // Collect all replacements for bare Nostr URIs
+  let match;
+  while ((match = nostrUriRegex.exec(modifiedText)) !== null) {
+    const fullUri = match[0];
+    const url = await nostrUriToUrl(fullUri);
+    const linkTitle = cleanUriForTitle(fullUri);
+    const markdownLink = `[${linkTitle}](${url})`;
+    replacements.push({
+      start: match.index,
+      end: match.index + fullUri.length,
+      replacement: markdownLink,
+    });
+  }
+
+  // Apply replacements from right to left to avoid index shifting
+  for (let i = replacements.length - 1; i >= 0; i--) {
+    const { start, end, replacement } = replacements[i];
+    modifiedText = modifiedText.slice(0, start) + replacement + modifiedText.slice(end);
+  }
+
+  return modifiedText;
+}
+
+function cleanUriForTitle(uri: string): string {
+  // Remove "nostr:" prefix, keep "@" for the title
+  return uri.startsWith('nostr:') ? uri.replace(/^nostr:/, '') : uri;
+}