try to avoid showing duplicate topics

2 files changed, 97 insertions, 9 deletions

diff --git a/fetchtopicsaction.cpp b/fetchtopicsaction.cpp
index 9e42723..d8ea173 100644
--- a/fetchtopicsaction.cpp
+++ b/fetchtopicsaction.cpp
@@ -62,12 +62,23 @@ void FetchTopicsAction::handleFinishedCall()
 		QSqlDatabase db = _board->database();
 		db.transaction();
 
+		const int total_topic_num = map["total_topic_num"].toInt();
+		int expected_end = _end == FetchAllTopics ? _start + MAX_FORUM_PAGE_SIZE : _end;
+		QList<int> current_topics = getCurrentDbTopics(_start, expected_end);
+		QList<int> unchanged_topics = current_topics;
+
+		if (_start >= total_topic_num) {
+			// Workaround an issue where the service always returns one post.
+			topics.clear();
+		}
+
+		Q_ASSERT(_start >= 0);
+		int position = _start;
+
 		QSqlQuery query(db);
 		query.prepare("INSERT OR REPLACE INTO topics (forum_id, topic_id, topic_title, topic_author_id, topic_author_name, is_subscribed, is_closed, icon_url, last_reply_time, reply_number, new_post, position, last_update_time) "
 		              "VALUES (:forum_id, :topic_id, :topic_title, :topic_author_id, :topic_author_name, :is_subscribed, :is_closed, :icon_url, :last_reply_time, :reply_number, :new_post, :position, :last_update_time)");
 
-		Q_ASSERT(_start >= 0);
-		int position = _start;
 
 		foreach (const QVariant& topic_v, topics) {
 			QVariantMap topic = topic_v.toMap();
@@ -80,7 +91,9 @@ void FetchTopicsAction::handleFinishedCall()
 			int topic_id = topic["topic_id"].toInt(&ok);
 			if (!ok) {
 				qWarning() << "No topic_id in" << topic;
-				continue;
+				// This is now a fatal error.
+				db.rollback();
+				goto finish;
 			}
 
 			query.bindValue(":forum_id", forum_id);
@@ -102,21 +115,73 @@ void FetchTopicsAction::handleFinishedCall()
 			if (!query.exec()) {
 				qWarning() << "Failed to store topic info for:" << topic_id;
 				handleDatabaseError("storing topic info", query);
-				continue;
+				db.rollback();
+				goto finish;
+			}
+
+			unchanged_topics.removeOne(topic_id);
+		}
+
+		// "position" would now point to "_end + 1", if we had gotten as
+		// many topics as we requested.
+
+		int fetched_end = position - 1;
+		bool eof = fetched_end < expected_end;
+		if (eof) {
+			// Service did not return as many topics as we expected, thus we
+			// can safely delete any topics after the current position.
+			query.prepare("DELETE FROM topics WHERE forum_id = :forum_id AND position >= :position");
+			query.bindValue(":forum_id", _forumId);
+			query.bindValue(":position", position);
+			if (query.exec()) {
+				position += query.numRowsAffected(); // Advance the position counter
+			} else {
+				handleDatabaseError("deleting topics", query);
+				db.rollback();
+				goto finish;
+			}
+
+			if (!unchanged_topics.empty()) {
+				// The topics that were in the begin..end range but were not updated
+				// need to be removed.
+				query.prepare("DELETE FROM topics WHERE topic_id = :topic_id");
+				foreach (int topic_id, unchanged_topics) {
+					query.bindValue(":topic_id", topic_id);
+					if (!query.exec()) {
+						handleDatabaseError("deleting topics", query);
+						db.rollback();
+						goto finish;
+					}
+					position++;
+				}
+			}
+		} else if (!unchanged_topics.empty()) {
+			// The topics that were in the begin..end range but were not updated
+			// need to be renumbered.
+			query.prepare("UPDATE topics SET position = :position WHERE topic_id = :topic_id");
+			foreach (int topic_id, unchanged_topics) {
+				query.bindValue(":position", position);
+				query.bindValue(":topic_id", topic_id);
+				if (!query.exec()) {
+					handleDatabaseError("updating topic position", query);
+					db.rollback();
+					goto finish;
+				}
+				position++;
 			}
+
+			Q_ASSERT(position >= expected_end + 1);
 		}
 
 		db.commit();
-		if (!topics.isEmpty()) {
-			Q_ASSERT(_start >= 0);
-			Q_ASSERT(position - 1 >= _start);
+		if (position > _start) {
 			_board->notifyForumTopicsChanged(_forumId,
 			                                 _start, position - 1);
 		}
-		if (_end == FetchAllTopics && topics.size() == MAX_FORUM_PAGE_SIZE) {
+		if (_end == FetchAllTopics && !eof) {
 			// Ok, let's prepare to fetch the next block of topics because
 			// there are probably more of them
-			int next_start = _start + MAX_FORUM_PAGE_SIZE;
+			int next_start = fetched_end + 1;
 			_board->enqueueAction(new FetchTopicsAction(_forumId,
 			                                            next_start,
 			                                            FetchAllTopics,
@@ -126,6 +191,7 @@ void FetchTopicsAction::handleFinishedCall()
 		qWarning() << "Could not fetch topics";
 		// TODO emit error ...
 	}
+finish:
 	emit finished(this);
 	_call->deleteLater();
 }
@@ -135,3 +201,24 @@ QString FetchTopicsAction::decodeTopicText(const QVariant &v)
 	QByteArray ba = v.toByteArray();
 	return QString::fromUtf8(ba.constData(), ba.length());
 }
+
+QList<int> FetchTopicsAction::getCurrentDbTopics(int start, int end)
+{
+	QSqlQuery query(_board->database());
+	query.prepare("SELECT topic_id FROM topics "
+	              "WHERE forum_id = :forum_id AND position BETWEEN :start AND :end "
+	              "ORDER by position ASC");
+	query.bindValue(":forum_id", _forumId);
+	query.bindValue(":start", start);
+	query.bindValue(":end", end);
+	if (query.exec()) {
+		QList<int> list;
+		while (query.next()) {
+			list << query.value(0).toInt();
+		}
+		return list;
+	} else {
+		qWarning() << "Could not get current topics list:" << query.lastError().text();
+		return QList<int>();
+	}
+}
diff --git a/fetchtopicsaction.h b/fetchtopicsaction.h
index 87b756f..307e528 100644
--- a/fetchtopicsaction.h
+++ b/fetchtopicsaction.h
@@ -26,6 +26,7 @@ private slots:
 
 private:
 	static QString decodeTopicText(const QVariant& v);
+	QList<int> getCurrentDbTopics(int start, int end);
 
 private:
 	XmlRpcPendingCall *_call;