Optimized thread ID

app/src/main/java/eu/faircode/email/DaoMessage.java

@@ -425,6 +425,11 @@ public interface DaoMessage {
             " AND inreplyto = :inreplyto")
     List<EntityMessage> getMessagesByInReplyTo(long account, String inreplyto);
 
+    @Query("SELECT thread, msgid, hash, inreplyto FROM message" +
+            " WHERE account = :account" +
+            " AND (msgid IN (:msgids) OR inreplyto IN (:msgids))")
+    List<TupleThreadInfo> getThreadInfo(long account, List<String> msgids);
+
     @Query("SELECT * FROM message" +
             " WHERE account = :account" +
             " AND sender = :sender" +

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -1287,7 +1287,10 @@ public class MessageHelper {
 
     String getThreadId(Context context, long account, long folder, long uid) throws MessagingException {
         if (threadId == null)
-            threadId = _getThreadId(context, account, folder, uid);
+            if (BuildConfig.DEBUG)
+                threadId = _getThreadIdAlt(context, account, folder, uid);
+            else
+                threadId = _getThreadId(context, account, folder, uid);
         return threadId;
     }
 
@@ -1370,6 +1373,90 @@ public class MessageHelper {
         return thread;
     }
 
+    private String _getThreadIdAlt(Context context, long account, long folder, long uid) throws MessagingException {
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
+
+        if (imessage instanceof GmailMessage) {
+            // https://developers.google.com/gmail/imap/imap-extensions#access_to_the_gmail_thread_id_x-gm-thrid
+            boolean gmail_thread_id = prefs.getBoolean("gmail_thread_id", false);
+            if (gmail_thread_id) {
+                long thrid = ((GmailMessage) imessage).getThrId();
+                if (thrid > 0)
+                    return "gmail:" + thrid;
+            }
+        }
+
+        String thread = null;
+        String msgid = getMessageID();
+
+        List<String> refs = new ArrayList<>();
+        for (String ref : getReferences())
+            if (!TextUtils.isEmpty(ref) && !refs.contains(ref))
+                refs.add(ref);
+
+        String inreplyto = getInReplyTo();
+        if (!TextUtils.isEmpty(inreplyto) && !refs.contains(inreplyto))
+            refs.add(inreplyto);
+
+        DB db = DB.getInstance(context);
+
+        List<String> all = new ArrayList<>(refs);
+        all.add(msgid);
+        List<TupleThreadInfo> infos = db.message().getThreadInfo(account, all);
+
+        // References, In-Reply-To (before)
+        for (TupleThreadInfo info : infos)
+            if (info.isReference(msgid) && !TextUtils.isEmpty(info.thread)) {
+                thread = info.thread;
+                break;
+            }
+
+        // Similar
+        if (thread == null) {
+            for (TupleThreadInfo info : infos)
+                if (info.isSelf(msgid) &&
+                        !TextUtils.isEmpty(info.thread) && Objects.equals(info.hash, getHash())) {
+                    thread = info.thread;
+                    break;
+                }
+        }
+
+        if (thread == null)
+            thread = getHash() + ":" + uid;
+
+        // Received before
+        for (TupleThreadInfo info : infos)
+            if (info.isReference(msgid) &&
+                    !thread.equals(info.thread)) {
+                Log.w("Updating before thread from " + info.thread + " to " + thread);
+                db.message().updateMessageThread(account, info.thread, thread, null);
+            }
+
+        // Received after
+        for (TupleThreadInfo info : infos)
+            if (info.isInReplyto(msgid) && !thread.equals(info.thread)) {
+                Log.w("Updating after thread from " + info.thread + " to " + thread);
+                db.message().updateMessageThread(account, info.thread, thread, null);
+            }
+
+        boolean subject_threading = prefs.getBoolean("subject_threading", false);
+        if (subject_threading && !isReport()) {
+            String sender = getSortKey(getFrom());
+            String subject = getSubject();
+            long since = new Date().getTime() - MAX_SUBJECT_AGE * 3600 * 1000L;
+            if (!TextUtils.isEmpty(sender) && !TextUtils.isEmpty(subject)) {
+                List<EntityMessage> subjects = db.message().getMessagesBySubject(account, sender, subject, since);
+                for (EntityMessage message : subjects)
+                    if (!thread.equals(message.thread)) {
+                        Log.w("Updating subject thread from " + message.thread + " to " + thread);
+                        db.message().updateMessageThread(message.account, message.thread, thread, since);
+                    }
+            }
+        }
+
+        return thread;
+    }
+
     String[] getLabels() throws MessagingException {
         //ensureMessage(false);
 

app/src/main/java/eu/faircode/email/TupleThreadInfo.java

@@ -0,0 +1,41 @@
+package eu.faircode.email;
+
+/*
+    This file is part of FairEmail.
+
+    FairEmail is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    FairEmail is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with FairEmail.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2018-2022 by Marcel Bokhorst (M66B)
+*/
+
+import java.util.Objects;
+
+public class TupleThreadInfo {
+    public String thread;
+    public String msgid;
+    public String hash;
+    public String inreplyto;
+
+    public boolean isSelf(String msgid) {
+        return Objects.equals(this.msgid, msgid);
+    }
+
+    public boolean isInReplyto(String msgid) {
+        return Objects.equals(this.inreplyto, msgid);
+    }
+
+    public boolean isReference(String msgid) {
+        return !isSelf(msgid) && !isInReplyto(msgid);
+    }
+}