fix(threading): ZMSA-5: if referencing a deleted thread then recreate it (#893)

* if referencing a deleted thread then recreate it

* fix comment

Author: NickOvt

lib/message-handler.js

@@ -600,16 +600,9 @@ class MessageHandler {
 
         let thread;
 
-        try {
-            thread = await this.getThreadIdAsync(mailboxData.user, subject, mimeTree);
-        } catch (err) {
-            return rollback(err);
-        }
-
-        // If referencing a message then use referenced message's thread
+        // If referencing a message then use referenced message's thread (applies to any action)
         if (
             options?.referencedMessage?.thread &&
-            ['reply', 'replyAll'].includes(options?.meta?.reference?.action) &&
             this.normalizeSubject(subject, {
                 removePrefix: true
             }) ===
@@ -621,6 +614,12 @@ class MessageHandler {
             thread = options.referencedMessage.thread;
         }
 
+        try {
+            thread = await this.getThreadIdAsync(mailboxData.user, subject, mimeTree, thread);
+        } catch (err) {
+            return rollback(err);
+        }
+
         messageData.thread = thread;
 
         let insertRes;
@@ -1654,7 +1653,7 @@ class MessageHandler {
     }
 
     // resolves or generates new thread id for a message
-    async getThreadIdAsync(userId, subject, mimeTree) {
+    async getThreadIdAsync(userId, subject, mimeTree, referencedThreadId) {
         let referenceIds = new Set(
             [
                 [].concat(mimeTree.parsedHeader['message-id'] || []).pop() || '',
@@ -1698,13 +1697,20 @@ class MessageHandler {
             return existingThread.value._id;
         }
 
-        // otherwise if no existing thread
-        const newThread = await this.database.collection('threads').insertOne({
+        const newThreadData = {
             user: userId,
             subject,
             ids: referenceIds,
             updated: new Date()
-        });
+        };
+
+        // Thread does not exist, but the message is referencing a thread that existed before, recreate thread
+        if (referencedThreadId) {
+            newThreadData._id = new ObjectId(referencedThreadId);
+        }
+
+        // otherwise if no existing thread
+        const newThread = await this.database.collection('threads').insertOne(newThreadData);
 
         return newThread.insertedId;
     }