Revert "Delete the ability to load file handler plugins from extracted game folders"

This reverts commit e806192154.

Core/FileSystems/VirtualDiscFileSystem.h

@@ -66,6 +66,73 @@ private:
 	int getFileListIndex(u32 accessBlock, u32 accessSize, bool blockMode = false) const;
 	Path GetLocalPath(std::string_view localpath) const;
 
+	typedef void *HandlerLibrary;
+	typedef int HandlerHandle;
+	typedef s64 HandlerOffset;
+	typedef void (*HandlerLogFunc)(void *arg, HandlerHandle handle, LogLevel level, const char *msg);
+
+	static void HandlerLogger(void *arg, HandlerHandle handle, LogLevel level, const char *msg);
+
+	// The primary purpose of handlers is to make it easier to work with large archives.
+	// However, they have other uses as well, such as patching individual files.
+	struct Handler {
+		Handler(const char *filename, VirtualDiscFileSystem *const sys);
+		~Handler();
+
+		typedef bool (*InitFunc)(HandlerLogFunc logger, void *loggerArg);
+		typedef void (*ShutdownFunc)();
+		typedef void (*ShutdownV2Func)(void *loggerArg);
+		typedef HandlerHandle (*OpenFunc)(const char *basePath, const char *filename);
+		typedef HandlerOffset (*SeekFunc)(HandlerHandle handle, HandlerOffset offset, FileMove origin);
+		typedef HandlerOffset (*ReadFunc)(HandlerHandle handle, void *data, HandlerOffset size);
+		typedef void (*CloseFunc)(HandlerHandle handle);
+		typedef int (*VersionFunc)();
+
+		HandlerLibrary library;
+		VirtualDiscFileSystem *const sys_;
+		InitFunc Init;
+		ShutdownFunc Shutdown;
+		ShutdownV2Func ShutdownV2;
+		OpenFunc Open;
+		SeekFunc Seek;
+		ReadFunc Read;
+		CloseFunc Close;
+
+		bool IsValid() const { return library != nullptr; }
+	};
+
+	struct HandlerFileHandle {
+		Handler *handler;
+		HandlerHandle handle;
+
+		HandlerFileHandle() : handler(nullptr), handle(0) {}
+		HandlerFileHandle(Handler *handler_) : handler(handler_), handle(-1) {}
+
+		bool Open(const std::string& basePath, const std::string& fileName, FileAccess access) {
+			// Ignore access, read only.
+			handle = handler->Open(basePath.c_str(), fileName.c_str());
+			return handle > 0;
+		}
+		size_t Read(u8 *data, s64 size) {
+			return (size_t)handler->Read(handle, data, size);
+		}
+		size_t Seek(s32 position, FileMove type) {
+			return (size_t)handler->Seek(handle, position, type);
+		}
+		void Close() {
+			handler->Close(handle);
+		}
+
+		bool IsValid() {
+			return handler != nullptr && handler->IsValid();
+		}
+
+		HandlerFileHandle &operator =(Handler *_handler) {
+			handler = _handler;
+			return *this;
+		}
+	};
+
 	typedef enum { VFILETYPE_NORMAL, VFILETYPE_LBN, VFILETYPE_ISO } VirtualFileType;
 
 	struct OpenFileEntry {
@@ -75,6 +142,7 @@ private:
 		}
 
 		DirectoryFileHandle hFile;
+		HandlerFileHandle handler;
 		VirtualFileType type = VFILETYPE_NORMAL;
 		u32 fileIndex = 0;
 		u64 curOffset = 0;
@@ -84,16 +152,32 @@ private:
 		bool Open(const Path &basePath, std::string& fileName, FileAccess access) {
 			// Ignored, we're read only.
 			u32 err;
-			return hFile.Open(basePath, fileName, access, err);
+			if (handler.IsValid()) {
+				return handler.Open(basePath.ToString(), fileName, access);
+			} else {
+				return hFile.Open(basePath, fileName, access, err);
+			}
 		}
 		size_t Read(u8 *data, s64 size) {
-			return hFile.Read(data, size);
+			if (handler.IsValid()) {
+				return handler.Read(data, size);
+			} else {
+				return hFile.Read(data, size);
+			}
 		}
 		size_t Seek(s32 position, FileMove type) {
-			return hFile.Seek(position, type);
+			if (handler.IsValid()) {
+				return handler.Seek(position, type);
+			} else {
+				return hFile.Seek(position, type);
+			}
 		}
 		void Close() {
-			return hFile.Close();
+			if (handler.IsValid()) {
+				return handler.Close();
+			} else {
+				return hFile.Close();
+			}
 		}
 	};
 
@@ -107,9 +191,12 @@ private:
 		std::string fileName;
 		u32 firstBlock;
 		u32 totalSize;
+		Handler *handler;
 	};
 
 	std::vector<FileListEntry> fileList;
 	u32 currentBlockIndex;
 	u32 lastReadBlock_;
+
+	std::map<std::string, Handler *> handlers;
 };