From c15fd3fc8274f7b14969fe21e8de00e86b9b5792 Mon Sep 17 00:00:00 2001
From: Skip R <tinyslices@gmail.com>
Date: Mon, 24 Nov 2025 15:07:21 -0800
Subject: [PATCH] implement naive, incomplete backfill

---
 pkg/connector/backfill.go | 129 ++++++++++++++++++++++++++++++++++++++
 pkg/connector/events.go   |   9 +++
 2 files changed, 138 insertions(+)
 create mode 100644 pkg/connector/backfill.go

diff --git a/pkg/connector/backfill.go b/pkg/connector/backfill.go
new file mode 100644
index 0000000..28bfafa
--- /dev/null
+++ b/pkg/connector/backfill.go
@@ -0,0 +1,129 @@
+// mautrix-discord - A Matrix-Discord puppeting bridge.
+// Copyright (C) 2024 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package connector
+
+import (
+	"context"
+	"slices"
+	"strconv"
+
+	"github.com/bwmarrin/discordgo"
+	"github.com/rs/zerolog"
+	"maunium.net/go/mautrix/bridgev2"
+	"maunium.net/go/mautrix/event"
+)
+
+var (
+	_ bridgev2.BackfillingNetworkAPI = (*DiscordClient)(nil)
+)
+
+func (dc *DiscordClient) FetchMessages(ctx context.Context, fetchParams bridgev2.FetchMessagesParams) (*bridgev2.FetchMessagesResponse, error) {
+	if !dc.IsLoggedIn() {
+		return nil, bridgev2.ErrNotLoggedIn
+	}
+
+	channelID := string(fetchParams.Portal.ID)
+	log := zerolog.Ctx(ctx).With().
+		Str("channel_id", channelID).
+		Int("desired_count", fetchParams.Count).
+		Bool("forward", fetchParams.Forward).Logger()
+
+	var beforeID string
+	var afterID string
+
+	if fetchParams.AnchorMessage != nil {
+		anchorID := string(fetchParams.AnchorMessage.ID)
+
+		if fetchParams.Forward {
+			afterID = anchorID
+		} else {
+			beforeID = anchorID
+		}
+	}
+
+	// ChannelMessages returns messages ordered from newest to oldest.
+	count := min(fetchParams.Count, 100)
+	log.Debug().Msg("Fetching channel history for backfill")
+	msgs, err := dc.Session.ChannelMessages(channelID, count, beforeID, afterID, "")
+	if err != nil {
+		return nil, err
+	}
+
+	converted := make([]*bridgev2.BackfillMessage, 0, len(msgs))
+	for _, msg := range msgs {
+		streamOrder, _ := strconv.ParseInt(msg.ID, 10, 64)
+		ts, _ := discordgo.SnowflakeTimestamp(msg.ID)
+
+		// FIXME(skip): Backfill reactions.
+
+		converted = append(converted, &bridgev2.BackfillMessage{
+			ConvertedMessage: dc.convertMessage(msg),
+			Sender:           dc.makeEventSender(msg.Author),
+			Timestamp:        ts,
+			StreamOrder:      streamOrder,
+		})
+	}
+	// FetchMessagesResponse expects messages to always be ordered from oldest to newest.
+	slices.Reverse(converted)
+
+	log.Debug().Int("converted_count", len(converted)).Msg("Finished fetching and converting, returning backfill response")
+
+	return &bridgev2.FetchMessagesResponse{
+		Messages: converted,
+		Forward:  fetchParams.Forward,
+		// This might not actually be true if the channel's total number of messages is itself a multiple
+		// of `count`, but that's probably okay.
+		HasMore: len(msgs) == count,
+	}, nil
+}
+
+func (dc *DiscordClient) convertMessage(msg *discordgo.Message) *bridgev2.ConvertedMessage {
+	// FIXME(skip): This isn't bridging a lot of things (replies, forwards, voice messages, attachments, webhooks, embeds, etc.). Copy from main branch.
+
+	var parts []*bridgev2.ConvertedMessagePart
+	switch msg.Type {
+	case discordgo.MessageTypeCall:
+		parts = append(parts, &bridgev2.ConvertedMessagePart{
+			Content: &event.MessageEventContent{
+				MsgType: event.MsgEmote,
+				Body:    "started a call",
+			},
+		})
+	case discordgo.MessageTypeGuildMemberJoin:
+		parts = append(parts, &bridgev2.ConvertedMessagePart{
+			Content: &event.MessageEventContent{
+				MsgType: event.MsgEmote,
+				Body:    "joined the server",
+			},
+		})
+	}
+
+	if msg.Content != "" {
+		// FIXME(skip): This needs to render into HTML.
+		parts = append(parts, &bridgev2.ConvertedMessagePart{
+			Content: &event.MessageEventContent{
+				MsgType: event.MsgText,
+				Body:    msg.Content,
+			},
+		})
+	}
+
+	return &bridgev2.ConvertedMessage{
+		// TODO(skip): Replies.
+		Parts: parts,
+	}
+}
diff --git a/pkg/connector/events.go b/pkg/connector/events.go
index ad4cca9..631bb06 100644
--- a/pkg/connector/events.go
+++ b/pkg/connector/events.go
@@ -22,6 +22,7 @@ import (
 	"github.com/bwmarrin/discordgo"
 	"github.com/rs/zerolog"
 	"maunium.net/go/mautrix/bridgev2"
+	"maunium.net/go/mautrix/bridgev2/database"
 	"maunium.net/go/mautrix/bridgev2/networkid"
 )
 
@@ -33,6 +34,7 @@ type DiscordChatResync struct {
 
 var (
 	_ bridgev2.RemoteChatResyncWithInfo       = (*DiscordChatResync)(nil)
+	_ bridgev2.RemoteChatResyncBackfill       = (*DiscordChatResync)(nil)
 	_ bridgev2.RemoteEventThatMayCreatePortal = (*DiscordChatResync)(nil)
 )
 
@@ -63,3 +65,10 @@ func (d *DiscordChatResync) GetChatInfo(ctx context.Context, portal *bridgev2.Po
 func (d *DiscordChatResync) ShouldCreatePortal() bool {
 	return true
 }
+
+func (d *DiscordChatResync) CheckNeedsBackfill(ctx context.Context, latestBridged *database.Message) (bool, error) {
+	if latestBridged == nil {
+		return true, nil
+	}
+	return latestBridged.ID < networkid.MessageID(d.channel.LastMessageID), nil
+}