get absentees from database for scheduled reminder

cmd/themis-server/main.go

@@ -530,7 +530,20 @@ func main() {
 			case <-ctx.Done():
 				return
 			case <-notifChan:
-				_, err := discord.ChannelMessageSend(channelId, "don't forget we have a session next %s!")
+				absentees, err := store.GetAbsentees(ctx, themis.NextMonday())
+				if err != nil {
+					log.Error().Err(err).Msg("failed to get absentees for next session")
+					return
+				}
+
+				var msg string
+				if len(absentees) == 0 {
+					msg = "Everybody can make it next Monday, see you then!"
+				} else {
+					msg = fmt.Sprintf("%s can't make it next Monday.", strings.Join(absentees, ", "))
+				}
+
+				_, err = discord.ChannelMessageSend(channelId, msg)
 				if err != nil {
 					log.Error().Err(err).Msg("failed to send scheduled notification")
 				}