fix: discord mention handling (#33224) (thanks @thewilloftheshadow) (#33224)

src/discord/mentions.ts

@@ -0,0 +1,83 @@
+import { resolveDiscordDirectoryUserId } from "./directory-cache.js";
+
+const MARKDOWN_CODE_SEGMENT_PATTERN = /```[\s\S]*?```|`[^`\n]*`/g;
+const MENTION_CANDIDATE_PATTERN = /(^|[\s([{"'.,;:!?])@([a-z0-9_.-]{2,32}(?:#[0-9]{4})?)/gi;
+const DISCORD_RESERVED_MENTIONS = new Set(["everyone", "here"]);
+
+function normalizeSnowflake(value: string | number | bigint): string | null {
+  const text = String(value ?? "").trim();
+  if (!/^\d+$/.test(text)) {
+    return null;
+  }
+  return text;
+}
+
+export function formatMention(params: {
+  userId?: string | number | bigint | null;
+  roleId?: string | number | bigint | null;
+  channelId?: string | number | bigint | null;
+}): string {
+  const userId = params.userId == null ? null : normalizeSnowflake(params.userId);
+  const roleId = params.roleId == null ? null : normalizeSnowflake(params.roleId);
+  const channelId = params.channelId == null ? null : normalizeSnowflake(params.channelId);
+  const values = [
+    userId ? { kind: "user" as const, id: userId } : null,
+    roleId ? { kind: "role" as const, id: roleId } : null,
+    channelId ? { kind: "channel" as const, id: channelId } : null,
+  ].filter((entry): entry is { kind: "user" | "role" | "channel"; id: string } => Boolean(entry));
+  if (values.length !== 1) {
+    throw new Error("formatMention requires exactly one of userId, roleId, or channelId");
+  }
+  const target = values[0];
+  if (target.kind === "user") {
+    return `<@${target.id}>`;
+  }
+  if (target.kind === "role") {
+    return `<@&${target.id}>`;
+  }
+  return `<#${target.id}>`;
+}
+
+function rewritePlainTextMentions(text: string, accountId?: string | null): string {
+  if (!text.includes("@")) {
+    return text;
+  }
+  return text.replace(MENTION_CANDIDATE_PATTERN, (match, prefix, rawHandle) => {
+    const handle = String(rawHandle ?? "").trim();
+    if (!handle) {
+      return match;
+    }
+    const lookup = handle.toLowerCase();
+    if (DISCORD_RESERVED_MENTIONS.has(lookup)) {
+      return match;
+    }
+    const userId = resolveDiscordDirectoryUserId({
+      accountId,
+      handle,
+    });
+    if (!userId) {
+      return match;
+    }
+    return `${String(prefix ?? "")}${formatMention({ userId })}`;
+  });
+}
+
+export function rewriteDiscordKnownMentions(
+  text: string,
+  params: { accountId?: string | null },
+): string {
+  if (!text.includes("@")) {
+    return text;
+  }
+  let rewritten = "";
+  let offset = 0;
+  MARKDOWN_CODE_SEGMENT_PATTERN.lastIndex = 0;
+  for (const match of text.matchAll(MARKDOWN_CODE_SEGMENT_PATTERN)) {
+    const matchIndex = match.index ?? 0;
+    rewritten += rewritePlainTextMentions(text.slice(offset, matchIndex), params.accountId);
+    rewritten += match[0];
+    offset = matchIndex + match[0].length;
+  }
+  rewritten += rewritePlainTextMentions(text.slice(offset), params.accountId);
+  return rewritten;
+}