Discord: add PluralKit sender identity resolver (#5838)

* Discord: add PluralKit sender identity resolver

* fix: resolve PluralKit sender identities (#5838) (thanks @thewilloftheshadow)

src/discord/monitor/sender-identity.ts

@@ -0,0 +1,82 @@
+import type { User } from "@buape/carbon";
+
+import { formatDiscordUserTag } from "./format.js";
+import type { DiscordMessageEvent } from "./listeners.js";
+import type { PluralKitMessageInfo } from "../pluralkit.js";
+
+export type DiscordSenderIdentity = {
+  id: string;
+  name?: string;
+  tag?: string;
+  label: string;
+  isPluralKit: boolean;
+  pluralkit?: {
+    memberId: string;
+    memberName?: string;
+    systemId?: string;
+    systemName?: string;
+  };
+};
+
+type DiscordWebhookMessageLike = {
+  webhookId?: string | null;
+  webhook_id?: string | null;
+};
+
+export function resolveDiscordWebhookId(message: DiscordWebhookMessageLike): string | null {
+  const candidate = message.webhookId ?? message.webhook_id;
+  return typeof candidate === "string" && candidate.trim() ? candidate.trim() : null;
+}
+
+export function resolveDiscordSenderIdentity(params: {
+  author: User;
+  member?: DiscordMessageEvent["member"] | null;
+  pluralkitInfo?: PluralKitMessageInfo | null;
+}): DiscordSenderIdentity {
+  const pkInfo = params.pluralkitInfo ?? null;
+  const pkMember = pkInfo?.member ?? undefined;
+  const pkSystem = pkInfo?.system ?? undefined;
+  const memberId = pkMember?.id?.trim();
+  const memberNameRaw = pkMember?.display_name ?? pkMember?.name ?? "";
+  const memberName = memberNameRaw?.trim();
+  if (memberId && memberName) {
+    const systemName = pkSystem?.name?.trim();
+    const label = systemName ? `${memberName} (PK:${systemName})` : `${memberName} (PK)`;
+    return {
+      id: memberId,
+      name: memberName,
+      tag: pkMember?.name?.trim() || undefined,
+      label,
+      isPluralKit: true,
+      pluralkit: {
+        memberId,
+        memberName,
+        systemId: pkSystem?.id?.trim() || undefined,
+        systemName,
+      },
+    };
+  }
+
+  const senderTag = formatDiscordUserTag(params.author);
+  const senderDisplay =
+    params.member?.nickname ?? params.author.globalName ?? params.author.username;
+  const senderLabel =
+    senderDisplay && senderTag && senderDisplay !== senderTag
+      ? `${senderDisplay} (${senderTag})`
+      : (senderDisplay ?? senderTag ?? params.author.id);
+  return {
+    id: params.author.id,
+    name: params.author.username ?? undefined,
+    tag: senderTag,
+    label: senderLabel,
+    isPluralKit: false,
+  };
+}
+
+export function resolveDiscordSenderLabel(params: {
+  author: User;
+  member?: DiscordMessageEvent["member"] | null;
+  pluralkitInfo?: PluralKitMessageInfo | null;
+}): string {
+  return resolveDiscordSenderIdentity(params).label;
+}