feat(chat ls): support channel that has more than 101 topics (#556)

* feat(chat ls): support channel that has more than 101 topics

* fix repeat after 100th topic issue

* Adapt iyear’s refactor

* fix(ls): do not re-query last topic message via rpc

---------

Co-authored-by: iyear <[email protected]>

app/chat/ls.go

@@ -8,6 +8,7 @@ import (
  "strings"
 
  "github.com/expr-lang/expr"
+ "github.com/go-faster/errors"
  "github.com/gotd/td/telegram"
  "github.com/gotd/td/telegram/message/peer"
  "github.com/gotd/td/telegram/peers"
@@ -226,28 +227,63 @@ func processChannel(ctx context.Context, api *tg.Client, id int64, entities peer
  }
 
  if c.Forum {
+ topics, err := fetchTopics(ctx, api, c.AsInput())
+ if err != nil {
+ logctx.From(ctx).Error("failed to fetch topics",
+ zap.Int64("channel_id", c.ID),
+ zap.String("channel_username", c.Username),
+ zap.Error(err))
+ return nil
+ }
+
+ d.Topics = topics
+ }
+
+ return d
+}
+
+// fetchTopics https:/telegramdesktop/tdesktop/blob/4047f1733decd5edf96d125589f128758b68d922/Telegram/SourceFiles/data/data_forum.cpp#L135
+func fetchTopics(ctx context.Context, api *tg.Client, c tg.InputChannelClass) ([]Topic, error) {
+ res := make([]Topic, 0)
+ limit := 100 // why can't we use 500 like tdesktop?
+ offsetTopic, offsetID, offsetDate := 0, 0, 0
+
+ for {
  req := &tg.ChannelsGetForumTopicsRequest{
- Channel: c.AsInput(),
- Limit: 100,
+ Channel: c,
+ Limit: limit,
+ OffsetTopic: offsetTopic,
+ OffsetID: offsetID,
+ OffsetDate: offsetDate,
  }
 
  topics, err := api.ChannelsGetForumTopics(ctx, req)
  if err != nil {
- return nil
+ return nil, errors.Wrap(err, "get forum topics")
  }
 
- d.Topics = make([]Topic, 0, len(topics.Topics))
  for _, tp := range topics.Topics {
  if t, ok := tp.(*tg.ForumTopic); ok {
- d.Topics = append(d.Topics, Topic{
+ res = append(res, Topic{
  ID: t.ID,
  Title: t.Title,
  })
+
+ offsetTopic = t.ID
  }
  }
+
+ // last page
+ if len(topics.Topics) < limit {
+ break
+ }
+
+ if lastMsg, ok := topics.Messages[len(topics.Messages)-1].AsNotEmpty(); ok {
+ offsetID, offsetDate = lastMsg.GetID(), lastMsg.GetDate()
+ }
  }
 
- return d
+ return res, nil
 }
 
 func processChat(id int64, entities peer.Entities) *Dialog {