[api] additional function to reset to the last snapshot position

Also QML plugin is switched to use this function instead of resetMaster(),
otherwise if previous backup was interrupted, intermediate commits will be
included into next backup

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>

include/vault/vault.hpp

@@ -94,9 +94,10 @@ class Vault
 
     Lock lock() const;
 
+    void resetLastSnapshot();
+
     std::tuple<QString, bool, QString> backupUnit(const QString &, const QString &);
     QString tagSnapshot(const QString &message);
-    void resetMaster();
 
     std::tuple<QString, bool, QString> restoreUnit
     (const QString &, const QString &, const QString &);
@@ -106,6 +107,7 @@ class Vault
     bool backupUnit(const QString &home, const QString &unit, const ProgressCallback &callback);
     bool restoreUnit(const QString &home, const QString &unit, const ProgressCallback &callback);
     void checkout(const QString &);
+    void resetMaster();
 
     void setup(const QVariantMap *config);
     QString absolutePath(QString const &) const;

qml/Vault/vault.cpp

@@ -66,8 +66,8 @@ class Worker : public QObject
 
     Q_INVOKABLE void reset()
     {
-        debug::debug("Reset storage");
-        m_vault->resetMaster();
+        debug::debug("Reset storage master to the last snapshot");
+        m_vault->resetLastSnapshot();
         emit done(Vault::Maintenance, {{"operation", "reset"}});
     }
 

src/vault.cpp

@@ -430,7 +430,7 @@ Vault::Result Vault::backup(const QString &home, const QStringList &units, const
         qDebug() << "Progress" << name << status;
     };
 
-    resetMaster();
+    resetLastSnapshot();
     Gittin::Commit head = Gittin::Branch(&m_vcs, "master").head();
 
     QStringList usedUnits = units;
@@ -535,6 +535,25 @@ void Vault::resetMaster()
     m_vcs.checkout("master", CheckoutOptions::Force);
 }
 
+/**
+ * Reset master branch to the last snapshot commit
+ *
+ * This action should be done before doing backup to avoid inclusion
+ * of any traces/remnants of previous backup tryouts
+ */
+void Vault::resetLastSnapshot()
+{
+    auto l = lock();
+    resetMaster();
+
+    QString lastSnapshot = "anchor";
+    auto snaps = snapshots();
+    if (!snaps.isEmpty())
+        lastSnapshot = snaps.back().tag().name();
+
+    m_vcs.reset(ResetOptions::Hard, lastSnapshot);
+}
+
 Vault::Result Vault::restore(const QString &snapshot, const QString &home, const QStringList &units, const ProgressCallback &callback)
 {
     auto l = lock();