Allow deleting small groups for everyone.

Telegram/SourceFiles/apiwrap.cpp

@@ -2350,14 +2350,14 @@ void ApiWrap::deleteHistory(
 		deleteTillId = history->lastMessage()->id;
 	}
 	if (const auto channel = peer->asChannel()) {
-		if (!justClear) {
+		if (!justClear && !revoke) {
 			channel->ptsWaitingForShortPoll(-1);
 			leaveChannel(channel);
 		} else {
 			if (const auto migrated = peer->migrateFrom()) {
 				deleteHistory(migrated, justClear, revoke);
 			}
-			if (IsServerMsgId(deleteTillId)) {
+			if (IsServerMsgId(deleteTillId) || (!justClear && revoke)) {
 				history->owner().histories().deleteAllMessages(
 					history,
 					deleteTillId,

Telegram/SourceFiles/boxes/confirm_box.cpp

@@ -578,7 +578,8 @@ void DeleteMessagesBox::prepare() {
 	const auto appendDetails = [&](TextWithEntities &&text) {
 		details.append(qstr("\n\n")).append(std::move(text));
 	};
-	auto deleteText = tr::lng_box_delete();
+	auto deleteText = lifetime().make_state<rpl::variable<QString>>();
+	*deleteText = tr::lng_box_delete();
 	auto deleteStyle = &st::defaultBoxButton;
 	if (const auto peer = _wipeHistoryPeer) {
 		if (_wipeHistoryJustClear) {
@@ -598,14 +599,22 @@ void DeleteMessagesBox::prepare() {
 				: peer->isMegagroup()
 				? tr::lng_sure_leave_group(tr::now)
 				: tr::lng_sure_leave_channel(tr::now);
-			deleteText = _wipeHistoryPeer->isUser()
-				? tr::lng_box_delete()
-				: tr::lng_box_leave();
+			if (!peer->isUser()) {
+				*deleteText = tr::lng_box_leave();
+			}
 			deleteStyle = &st::attentionBoxButton;
 		}
 		if (auto revoke = revokeText(peer)) {
 			_revoke.create(this, revoke->checkbox, false, st::defaultBoxCheckbox);
 			appendDetails(std::move(revoke->description));
+			if (!peer->isUser() && !_wipeHistoryJustClear) {
+				_revoke->checkedValue(
+				) | rpl::start_with_next([=](bool revokeForAll) {
+					*deleteText = revokeForAll
+						? tr::lng_box_delete()
+						: tr::lng_box_leave();
+				}, _revoke->lifetime());
+			}
 		}
 	} else if (_moderateFrom) {
 		Assert(_moderateInChannel != nullptr);
@@ -642,7 +651,7 @@ void DeleteMessagesBox::prepare() {
 	_text.create(this, rpl::single(std::move(details)), st::boxLabel);
 
 	addButton(
-		std::move(deleteText),
+		deleteText->value(),
 		[=] { deleteAndClear(); },
 		*deleteStyle);
 	addButton(tr::lng_cancel(), [=] { closeBox(); });

Telegram/SourceFiles/data/data_histories.cpp

@@ -593,19 +593,49 @@ void Histories::deleteAllMessages(
 		const auto fail = [=](const RPCError &error) {
 			finish();
 		};
-		if (const auto channel = peer->asChannel()) {
+		const auto chat = peer->asChat();
+		const auto channel = peer->asChannel();
+		if (revoke && channel && channel->canDelete()) {
+			return session().api().request(MTPchannels_DeleteChannel(
+				channel->inputChannel
+			)).done([=](const MTPUpdates &result) {
+				session().api().applyUpdates(result);
+			//}).fail([=](const RPCError &error) {
+			//	if (error.type() == qstr("CHANNEL_TOO_LARGE")) {
+			//		Ui::show(Box<InformBox>(tr::lng_cant_delete_channel(tr::now)));
+			//	}
+			}).send();
+		} else if (channel) {
 			return session().api().request(MTPchannels_DeleteHistory(
 				channel->inputChannel,
 				MTP_int(deleteTillId)
 			)).done([=](const MTPBool &result) {
 				finish();
 			}).fail(fail).send();
-		} else if (revoke && peer->isChat() && peer->asChat()->amCreator()) {
+		} else if (revoke && chat && chat->amCreator()) {
 			return session().api().request(MTPmessages_DeleteChat(
-				peer->asChat()->inputChat
+				chat->inputChat
 			)).done([=](const MTPBool &result) {
 				finish();
-			}).fail(fail).send();
+			}).fail([=](const RPCError &error) {
+				if (error.type() == "PEER_ID_INVALID") {
+					// Try to join and delete,
+					// while delete fails for non-joined.
+					session().api().request(MTPmessages_AddChatUser(
+						chat->inputChat,
+						MTP_inputUserSelf(),
+						MTP_int(0)
+					)).done([=](const MTPUpdates &updates) {
+						session().api().applyUpdates(updates);
+						deleteAllMessages(
+							history,
+							deleteTillId,
+							justClear,
+							revoke);
+					}).send();
+				}
+				finish();
+			}).send();
 		} else {
 			using Flag = MTPmessages_DeleteHistory::Flag;
 			const auto flags = Flag(0)

Telegram/SourceFiles/data/data_peer.cpp

@@ -836,6 +836,10 @@ bool PeerData::canRevokeFullHistory() const {
 			&& (session().serverConfig().revokePrivateTimeLimit == 0x7FFFFFFF);
 	} else if (const auto chat = asChat()) {
 		return chat->amCreator();
+	} else if (const auto megagroup = asMegagroup()) {
+		return megagroup->amCreator()
+			&& megagroup->membersCountKnown()
+			&& megagroup->canDelete();
 	}
 	return false;
 }