Refactor InnerFAT into Savegame and Extdata

And derive TitleDB from it too.

src/core/extdata.h

@@ -0,0 +1,49 @@
+// Copyright 2021 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "core/inner_fat.hpp"
+
+namespace Core {
+
+class SDMCDecryptor;
+
+class Extdata final : public Archive<Extdata> {
+public:
+    /**
+     * Loads an SD extdata folder.
+     * @param data_path Path to the ENCRYPTED SD extdata folder, relative to decryptor root
+     * @param decryptor Const reference to the SDMCDecryptor.
+     */
+    explicit Extdata(std::string data_path, const SDMCDecryptor& decryptor);
+
+    /**
+     * Loads an Extdata folder without encryption.
+     * @param data_path Path to the DECRYPTED extdata folder
+     */
+    explicit Extdata(std::string data_path);
+
+    ~Extdata();
+
+    bool IsGood() const;
+    bool Extract(std::string path) const;
+
+private:
+    bool Init();
+    bool CheckMagic() const;
+    std::vector<u8> ReadFile(const std::string& path) const;
+    bool ExtractFile(const std::string& path, std::size_t index) const;
+    ArchiveFormatInfo GetFormatInfo() const;
+
+    bool is_good = false;
+    std::string data_path;
+    const SDMCDecryptor* decryptor = nullptr;
+    bool use_decryptor = true;
+
+    friend class Archive<Extdata>;
+    friend class InnerFAT<Extdata>;
+};
+
+} // namespace Core