refactor: unify threading contexts

src/slack/threading.ts

@@ -1,13 +1,44 @@
 import type { ReplyToMode } from "../config/types.js";
 import type { SlackAppMentionEvent, SlackMessageEvent } from "./types.js";
 
+export type SlackThreadContext = {
+  incomingThreadTs?: string;
+  messageTs?: string;
+  isThreadReply: boolean;
+  replyToId?: string;
+  messageThreadId?: string;
+};
+
+export function resolveSlackThreadContext(params: {
+  message: SlackMessageEvent | SlackAppMentionEvent;
+  replyToMode: ReplyToMode;
+}): SlackThreadContext {
+  const incomingThreadTs = params.message.thread_ts;
+  const eventTs = params.message.event_ts;
+  const messageTs = params.message.ts ?? eventTs;
+  const hasThreadTs = typeof incomingThreadTs === "string" && incomingThreadTs.length > 0;
+  const isThreadReply =
+    hasThreadTs && (incomingThreadTs !== messageTs || Boolean(params.message.parent_user_id));
+  const replyToId = incomingThreadTs ?? messageTs;
+  const messageThreadId = isThreadReply
+    ? incomingThreadTs
+    : params.replyToMode === "all"
+      ? messageTs
+      : undefined;
+  return {
+    incomingThreadTs,
+    messageTs,
+    isThreadReply,
+    replyToId,
+    messageThreadId,
+  };
+}
+
 export function resolveSlackThreadTargets(params: {
   message: SlackMessageEvent | SlackAppMentionEvent;
   replyToMode: ReplyToMode;
 }) {
-  const incomingThreadTs = params.message.thread_ts;
-  const eventTs = params.message.event_ts;
-  const messageTs = params.message.ts ?? eventTs;
+  const { incomingThreadTs, messageTs } = resolveSlackThreadContext(params);
   const replyThreadTs = incomingThreadTs ?? (params.replyToMode === "all" ? messageTs : undefined);
   const statusThreadTs = replyThreadTs ?? messageTs;
   return { replyThreadTs, statusThreadTs };