core, frontend: Better progress reporter

A new "quick" decryptor is implemented. This is not really much faster (not slower either) but provides the benefit of being able to report progress on a single file. The frontend is updated accordingly to support this feature.

src/core/quick_decryptor.h

@@ -0,0 +1,62 @@
+// Copyright 2019 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <atomic>
+#include <memory>
+#include <string>
+#include "common/common_types.h"
+#include "common/thread.h"
+
+namespace Core {
+
+class QuickDecryptor {
+public:
+    /// (current_size, total_size)
+    using ProgressCallback = std::function<void(std::size_t, std::size_t)>;
+
+    /**
+     * Initializes the decryptor.
+     * @param root_folder Path to the "Nintendo 3DS/<ID0>/<ID1>" folder.
+     */
+    explicit QuickDecryptor(const std::string& root_folder);
+
+    ~QuickDecryptor();
+
+    bool DecryptAndWriteFile(const std::string& source, const std::string& destination,
+                             const ProgressCallback& callback = [](std::size_t, std::size_t) {});
+
+    void DataReadLoop();
+    void DataDecryptLoop();
+    void DataWriteLoop();
+
+    void Abort();
+
+private:
+    static constexpr std::size_t BufferSize = 16 * 1024; // 16 KB
+
+    std::string root_folder;
+    std::string source;
+    std::string destination;
+    std::size_t total_size{};
+
+    std::array<std::array<u8, BufferSize>, 3> buffers;
+    std::array<Common::Event, 3> data_read_event;
+    std::array<Common::Event, 3> data_decrypted_event;
+    std::array<Common::Event, 3> data_written_event;
+
+    std::unique_ptr<std::thread> read_thread;
+    std::unique_ptr<std::thread> decrypt_thread;
+    std::unique_ptr<std::thread> write_thread;
+
+    ProgressCallback callback;
+
+    Common::Event completion_event;
+    bool is_good{true};
+    std::atomic_bool is_running{false};
+};
+
+} // namespace Core