Backfill threads when found and from server thread list sync

thread.go

@@ -1,10 +1,13 @@
 package main
 
 import (
+	"context"
 	"sync"
 	"time"
 
 	"github.com/bwmarrin/discordgo"
+	"github.com/rs/zerolog"
+	"golang.org/x/exp/slices"
 	"maunium.net/go/mautrix/id"
 
 	"go.mau.fi/mautrix-discord/database"
@@ -14,7 +17,8 @@ type Thread struct {
 	*database.Thread
 	Parent *Portal
 
-	creationNoticeLock sync.Mutex
+	creationNoticeLock       sync.Mutex
+	initialBackfillAttempted bool
 }
 
 func (br *DiscordBridge) GetThreadByID(id string, root *database.Message) *Thread {
@@ -74,12 +78,63 @@ func (br *DiscordBridge) loadThread(dbThread *database.Thread, id string, root *
 	return thread
 }
 
+func (br *DiscordBridge) threadFound(ctx context.Context, source *User, rootMessage *database.Message, id string, metadata *discordgo.Channel) {
+	thread := br.GetThreadByID(id, rootMessage)
+	log := zerolog.Ctx(ctx)
+	log.Debug().Msg("Marked message as thread root")
+	if thread.CreationNoticeMXID == "" {
+		thread.Parent.sendThreadCreationNotice(ctx, thread)
+	}
+	// TODO member_ids_preview is probably not guaranteed to contain the source user
+	if source != nil && metadata != nil && slices.Contains(metadata.MemberIDsPreview, source.DiscordID) && !source.IsInPortal(thread.ID) {
+		source.MarkInPortal(database.UserPortal{
+			DiscordID: thread.ID,
+			Type:      database.UserPortalTypeThread,
+			Timestamp: time.Now(),
+		})
+		if metadata.MessageCount > 0 {
+			go thread.maybeInitialBackfill(source)
+		} else {
+			thread.initialBackfillAttempted = true
+		}
+	}
+}
+
+func (thread *Thread) maybeInitialBackfill(source *User) {
+	if thread.initialBackfillAttempted || thread.Parent.bridge.Config.Bridge.Backfill.Limits.Initial.Thread == 0 {
+		return
+	}
+	thread.Parent.forwardBackfillLock.Lock()
+	if thread.Parent.bridge.DB.Message.GetLastInThread(thread.Parent.Key, thread.ID) != nil {
+		thread.Parent.forwardBackfillLock.Unlock()
+		return
+	}
+	thread.Parent.forwardBackfillInitial(source, thread)
+}
+
 func (thread *Thread) Join(user *User) {
 	if user.IsInPortal(thread.ID) {
 		return
 	}
 	log := user.log.With().Str("thread_id", thread.ID).Str("channel_id", thread.ParentID).Logger()
 	log.Debug().Msg("Joining thread")
+
+	var doBackfill, backfillStarted bool
+	if !thread.initialBackfillAttempted && thread.Parent.bridge.Config.Bridge.Backfill.Limits.Initial.Thread > 0 {
+		thread.Parent.forwardBackfillLock.Lock()
+		lastMessage := thread.Parent.bridge.DB.Message.GetLastInThread(thread.Parent.Key, thread.ID)
+		if lastMessage != nil {
+			thread.Parent.forwardBackfillLock.Unlock()
+		} else {
+			doBackfill = true
+			defer func() {
+				if !backfillStarted {
+					thread.Parent.forwardBackfillLock.Unlock()
+				}
+			}()
+		}
+	}
+
 	var err error
 	if user.Session.IsUser {
 		err = user.Session.ThreadJoinWithLocation(thread.ID, discordgo.ThreadJoinLocationContextMenu)
@@ -94,5 +149,9 @@ func (thread *Thread) Join(user *User) {
 			Type:      database.UserPortalTypeThread,
 			Timestamp: time.Now(),
 		})
+		if doBackfill {
+			go thread.Parent.forwardBackfillInitial(user, thread)
+			backfillStarted = true
+		}
 	}
 }