[Card DB] Split out database loading and querying from main class (#6175)

* Simplify add card.

Took 25 minutes

Took 8 minutes

# Commit time for manual adjustment:
# Took 16 minutes

Took 7 seconds

* Refactor out db loading from card db.

Took 39 minutes

Took 9 minutes

Took 2 minutes


Took 17 seconds

* Refactor out db queries from card db.

Took 42 minutes

* Lint.

Took 3 minutes

* I guess.

Took 7 minutes

* Tests.

Took 15 minutes

* I don't understand this.

Took 9 minutes

* fix linker errors

* Rename to querier and promote to QObject

Took 39 minutes

* Lint.

Took 3 minutes

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
Co-authored-by: ebbit1q <ebbit1q@gmail.com>

cockatrice/src/database/card_database_loader.h

@@ -0,0 +1,57 @@
+#ifndef COCKATRICE_CARD_DATABASE_LOADER_H
+#define COCKATRICE_CARD_DATABASE_LOADER_H
+
+#include <QBasicMutex>
+#include <QList>
+#include <QLoggingCategory>
+#include <QObject>
+
+inline Q_LOGGING_CATEGORY(CardDatabaseLoadingLog, "card_database.loading");
+inline Q_LOGGING_CATEGORY(CardDatabaseLoadingSuccessOrFailureLog, "card_database.loading.success_or_failure");
+
+class CardDatabase;
+class ICardDatabaseParser;
+
+enum LoadStatus
+{
+    Ok,
+    VersionTooOld,
+    Invalid,
+    NotLoaded,
+    FileError,
+    NoCards
+};
+
+class CardDatabaseLoader : public QObject
+{
+    Q_OBJECT
+public:
+    explicit CardDatabaseLoader(QObject *parent, CardDatabase *db);
+    ~CardDatabaseLoader() override;
+
+public slots:
+    LoadStatus loadCardDatabases();                   // discover & load the configured databases
+    LoadStatus loadCardDatabase(const QString &path); // load a single file
+    bool saveCustomTokensToFile();                    // write tokens to custom DB path
+
+signals:
+    void loadingStarted();
+    void loadingFinished();
+    void loadingFailed();
+    void newSetsFound(int numSets, const QStringList &setNames);
+    void allNewSetsEnabled();
+
+private:
+    LoadStatus loadFromFile(const QString &fileName); // internal helper
+    QStringList collectCustomDatabasePaths() const;
+
+    CardDatabase *database; // non-owning pointer to the container
+
+    // parsers
+    QList<ICardDatabaseParser *> availableParsers;
+
+    QBasicMutex *loadFromFileMutex = new QBasicMutex();
+    QBasicMutex *reloadDatabaseMutex = new QBasicMutex();
+};
+
+#endif // COCKATRICE_CARD_DATABASE_LOADER_H