feat(telegram): preserve source media groups (#226)

* feat(telegram): preserve source media groups

* fix(telegram): rewind batch readers before inspection

common/utils/tgutil/message.go

@@ -2,6 +2,7 @@ package tgutil
 
 import (
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 	"unicode"
@@ -359,9 +360,16 @@ func GetGroupedMessages(ctx *ext.Context, chatID int64, msg *tg.Message) ([]*tg.
 			groupedMessages = append(groupedMessages, m)
 		}
 	}
+	sortMessagesByID(groupedMessages)
 	return groupedMessages, nil
 }
 
+func sortMessagesByID(messages []*tg.Message) {
+	sort.Slice(messages, func(i, j int) bool {
+		return messages[i].GetID() < messages[j].GetID()
+	})
+}
+
 func ExtractMessageEntityUrls(msg *tg.Message) []string {
 	if len(msg.Entities) == 0 {
 		return nil

common/utils/tgutil/message_test.go

@@ -0,0 +1,18 @@
+package tgutil
+
+import (
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+func TestSortMessagesByID(t *testing.T) {
+	messages := []*tg.Message{{ID: 9}, {ID: 3}, {ID: 7}}
+	sortMessagesByID(messages)
+	want := []int{3, 7, 9}
+	for i := range messages {
+		if messages[i].GetID() != want[i] {
+			t.Fatalf("message %d has ID %d, want %d", i, messages[i].GetID(), want[i])
+		}
+	}
+}