Reset cache on breaking changes

fixes #154

include/Cache.h

@@ -39,6 +39,9 @@ public:
         void removeRoom(const QString &roomid);
         void setup();
 
+        bool isFormatValid();
+        void setCurrentFormat();
+
 private:
         void setNextBatchToken(lmdb::txn &txn, const QString &token);
         void insertRoomState(lmdb::txn &txn, const QString &roomid, const RoomState &state);

src/Cache.cc

@@ -24,8 +24,10 @@
 #include "Cache.h"
 #include "RoomState.h"
 
+static const std::string CURRENT_CACHE_FORMAT_VERSION("2017.12.10");
+
 static const lmdb::val NEXT_BATCH_KEY("next_batch");
-static const lmdb::val transactionID("transaction_id");
+static const lmdb::val CACHE_FORMAT_VERSION_KEY("cache_format_version");
 
 Cache::Cache(const QString &userId)
   : env_{nullptr}
@@ -270,3 +272,41 @@ Cache::deleteData()
         if (!cacheDirectory_.isEmpty())
                 QDir(cacheDirectory_).removeRecursively();
 }
+
+bool
+Cache::isFormatValid()
+{
+        auto txn = lmdb::txn::begin(env_, nullptr, MDB_RDONLY);
+
+        lmdb::val current_version;
+        bool res = lmdb::dbi_get(txn, stateDb_, CACHE_FORMAT_VERSION_KEY, current_version);
+
+        txn.commit();
+
+        if (!res)
+                return false;
+
+        std::string stored_version(current_version.data(), current_version.size());
+
+        if (stored_version != CURRENT_CACHE_FORMAT_VERSION) {
+                qWarning() << "Stored format version" << QString::fromStdString(stored_version);
+                qWarning() << "There are breaking changes in the cache format.";
+                return false;
+        }
+
+        return true;
+}
+
+void
+Cache::setCurrentFormat()
+{
+        auto txn = lmdb::txn::begin(env_);
+
+        lmdb::dbi_put(
+          txn,
+          stateDb_,
+          CACHE_FORMAT_VERSION_KEY,
+          lmdb::val(CURRENT_CACHE_FORMAT_VERSION.data(), CURRENT_CACHE_FORMAT_VERSION.size()));
+
+        txn.commit();
+}

src/ChatPage.cc

@@ -334,6 +334,12 @@ ChatPage::bootstrap(QString userid, QString homeserver, QString token)
         try {
                 cache_->setup();
 
+                if (!cache_->isFormatValid()) {
+                        cache_->deleteData();
+                        cache_->setup();
+                        cache_->setCurrentFormat();
+                }
+
                 if (cache_->isInitialized()) {
                         loadStateFromCache();
                         return;