#include "sqlite3.h"
#include <switch.h>

// Important points:
// - There is no file truncation
//   -> journal_mode=truncate won't work
// - There is no file locking
//   -> as far as I know Horizon doesn't support it?
// - Doesn't support temp files
// - Doesn't support dynamic libraries (not my fault)

// FsFileSystem used to interact with files on SD Card
static FsFileSystem fs;

// Size of write buffer (in bytes)
#define SQLITE_NXVFS_BUFFERSZ 8192

// sqlite3_file * actually points to this structure
typedef struct nxFile nxFile;
struct nxFile {
	sqlite3_file base;          // Base class
	FsFile file;                // NX (Horizon) file object
	char * buf;                 // Buffer for writes
	int bufSize;                // Number of bytes in buffer
	sqlite3_int64 bufOffset;    // Offset of bytes in buffer from buf[0]
};

// Close a file
static int nxClose(sqlite3_file * pFile) {
	nxFile * file = (nxFile *) pFile;
	fsFileClose(&file->file);
	return SQLITE_OK;
}

// Read data from a file
static int nxRead(sqlite3_file * pFile, void * buf, int bytes, sqlite_int64 offset) {
	// Bytes read and result code
	u64 read = 0;
	Result rc;

	// Read from file
	nxFile * file = (nxFile *) pFile;
	rc = fsFileRead(&file->file, offset, buf, bytes, FsReadOption_None, &read);

	// Return IO error if result isn't good
	if (R_FAILED(rc)) {
		return SQLITE_IOERR_READ;
	}

	// Check if we read the right amount of bytes
	if (read == bytes) {
		return SQLITE_OK;

		// Zero-pad the remaining buffer if not enough bytes were read
	} else if (read >= 0) {
		if (read < bytes) {
			memset(&((char *) buf)[read], 0, bytes-read);
		}
		return SQLITE_IOERR_SHORT_READ;
	}

	// Don't think this should be reached?
	return SQLITE_IOERR_READ;
}

// Write to a file (and flush immediately)
static int nxDirectWrite(nxFile * file, const void * buf, int bytes, sqlite_int64 offset) {
	Result rc = fsFileWrite(&file->file, offset, buf, bytes, FsWriteOption_Flush);

	// Return IO error if result is not good
	if (R_FAILED(rc)) {
		return SQLITE_IOERR_WRITE;
	}

	return SQLITE_OK;
}

// Flush file's buffer to disk (no-op if buffer is empty)
static int nxFlushBuffer(nxFile * file) {
	int rc = SQLITE_OK;
	if (file->buf) {
		rc = nxDirectWrite(file, file->buf, file->bufSize, file->bufOffset);
		file->buf = NULL;
	}
	return rc;
}

// Write to a file (without flushing)
static int nxWrite(sqlite3_file * pFile, const void * buf, int bytes, sqlite_int64 offset) {
	nxFile * file = (nxFile *) pFile;

	// If the buffer exists
	if (file->buf) {
		char * buf2 = (char *) buf;         // Pointer to remaining data in write buffer
		int bytes2 = bytes;                 // Remaining number of bytes in write buffer
		sqlite3_int64 offset2 = offset;     // File offset to write to

		// While there's still bytes to write
		while (bytes2 > 0) {
			int copy;       // Number of bytes to copy into file buffer

			// If the buffer is full or not being used - flush the buffer
			if (file->bufSize == SQLITE_NXVFS_BUFFERSZ || file->bufOffset + file->bufSize != offset2) {
				int rc = nxFlushBuffer(file);
				if (rc != SQLITE_OK) {
					return rc;
				}
			}
			file->bufOffset = offset2 - file->bufSize;

			// Copy as much data as possible into the buffer
			copy = SQLITE_NXVFS_BUFFERSZ - file->bufSize;
			if (copy > bytes2) {
				copy = bytes2;
			}
			memcpy(&file->buf[file->bufSize], buf2, copy);
			file->bufSize += copy;

			// Update variables
			bytes2 -= copy;
			offset2 += copy;
			buf2 += copy;
		}

		// Otherwise if there's no buffer just write to file
	} else {
		return nxDirectWrite(file, buf, bytes, offset);
	}

	return SQLITE_OK;
}

// This is meant to truncate a file (maybe I'll get to it later)
// This means that journal_mode=truncate is not supported
static int nxTruncate(sqlite3_file * pFile, sqlite_int64 size) {
	return SQLITE_OK;
}

// Sync contents of file to the disk
static int nxSync(sqlite3_file * pFile, int flags) {
	nxFile * file = (nxFile *) pFile;

	// Flush buffer to disk
	int tmp = nxFlushBuffer(file);
	if (tmp != SQLITE_OK) {
		return tmp;
	}

	// Call system to flush it's cache
	Result rc = fsFileFlush(&file->file);
	return (R_SUCCEEDED(rc) ? SQLITE_OK : SQLITE_IOERR_FSYNC);
}

// Get the size of the file and write to pointer
static int nxFileSize(sqlite3_file * pFile, sqlite_int64 * size) {
	nxFile * file = (nxFile *) pFile;

	// Flush buffer to disk first
	int tmp = nxFlushBuffer(file);
	if (tmp != SQLITE_OK) {
		return tmp;
	}

	// Query using system call
	s64 sz;
	Result rc = fsFileGetSize(&file->file, &sz);
	if (R_FAILED(rc)) {
		return SQLITE_IOERR_FSTAT;
	}
	*(size) = sz;
	return SQLITE_OK;
}

// All locking functions do nothing
static int nxLock(sqlite3_file * pFile, int lock) {
	return SQLITE_OK;
}
static int nxUnlock(sqlite3_file * pFile, int lock) {
	return SQLITE_OK;
}
static int nxCheckReservedLock(sqlite3_file * pFile, int lock) {
	return SQLITE_OK;
}

// File control also does nothing
static int nxFileControl(sqlite3_file * pFile, int op, void * arg) {
	return SQLITE_NOTFOUND;
}

// Don't return any info about device
static int nxSectorSize(sqlite3_file * pFile) {
	return 0;
}
static int nxDeviceCharacteristics(sqlite3_file * pFile) {
	return 0;
}

// Open a file
static int nxOpen(sqlite3_vfs * vfs, const char * path, sqlite3_file * pFile, int flags, int * outFlags) {
	// Set file's IO methods to the ones above
	static const sqlite3_io_methods nxIO = {
		1,                          // iVersion
		nxClose,                    // xClose
		nxRead,                     // xRead
		nxWrite,                    // xWrite
		nxTruncate,                 // xTruncate
		nxSync,                     // xSync
		nxFileSize,                 // xFileSize
		nxLock,                     // xLock
		nxUnlock,                   // xUnlock
		nxCheckReservedLock,        // xCheckReservedLock
		nxFileControl,              // xFileControl
		nxSectorSize,               // xSectorSize
		nxDeviceCharacteristics     // xDeviceCharacteristics
	};

	nxFile * file = (nxFile *) pFile;
	Result rc;
	char * tmpBuf = NULL;           // Temporary pointer to potential file buffer

	// Don't support temp files
	if (path == NULL) {
		return SQLITE_IOERR;
	}

	// Create file buffer if it's a journal file
	if (flags & SQLITE_OPEN_MAIN_JOURNAL) {
		tmpBuf = (char *) sqlite3_malloc(SQLITE_NXVFS_BUFFERSZ);
		if (!tmpBuf) {
			return SQLITE_NOMEM;
		}
	}

	// Create file if flag is set
	if (flags & SQLITE_OPEN_CREATE) {
		rc = fsFsCreateFile(&fs, path, 0, 0);
	}

	// Choose mode based on flags
	u32 mode = 0;
	if (flags & SQLITE_OPEN_READONLY) {
		mode |= FsOpenMode_Read;
	} else if (flags & SQLITE_OPEN_READWRITE) {
		mode |= FsOpenMode_Read;
		mode |= FsOpenMode_Write;
	}

	// Allocate memory for file object and open
	memset(pFile, 0, sizeof(nxFile));
	rc = fsFsOpenFile(&fs, path, mode, &file->file);
	printf("%s: %i %i\n", path, R_MODULE(rc), R_DESCRIPTION(rc));
	if (R_FAILED(rc)) {
		file->base.pMethods = NULL;     // Prevents nxClose being called
		sqlite3_free(tmpBuf);
		return SQLITE_CANTOPEN;
	}
	file->buf = tmpBuf;

	// Set output flags
	if (outFlags) {
		*(outFlags) = flags;
	}
	file->base.pMethods = &nxIO;
	return SQLITE_OK;
}

// Delete the given file
static int nxDelete(sqlite3_vfs * vfs, const char * path, int sync) {
	Result rc = fsFsDeleteFile(&fs, path);

	// Commit changes if flag set
	if (R_SUCCEEDED(rc) && sync) {
		fsFsCommit(&fs);
	}

	return (R_SUCCEEDED(rc) ? SQLITE_OK : SQLITE_IOERR_DELETE);
}

// Check if the file exists
static int nxAccess(sqlite3_vfs * vfs, const char * path, int flags, int * out) {
	// Only check exists flag, fake the other ones
	if (flags & SQLITE_ACCESS_EXISTS) {
		FsDirEntryType type = FsDirEntryType_Dir;
		Result rc = fsFsGetEntryType(&fs, path, &type);
		if (R_FAILED(rc) || type != FsDirEntryType_File) {
			return SQLITE_IOERR_ACCESS;
		}
	}

	return SQLITE_OK;
}

// Simply returns the given path (should return full path though)
static int nxFullPathname(sqlite3_vfs * vfs, const char * path, int outBytes, char * outPath) {
	int num = strlen(path);
	if (outBytes > num) {
		num = outBytes;
	}
	memcpy(outPath, path, num);

	return SQLITE_OK;
}

// All dynamic library related functions do nothing due to no support
static void * nxDlOpen(sqlite3_vfs * vfs, const char * path){
	return NULL;
}
static void nxDlError(sqlite3_vfs * vfs, int bytes, char * err){
	sqlite3_snprintf(bytes, err, "Loadable extensions are not supported");
	err[bytes-1] = '\0';
}
static void (*nxDlSym(sqlite3_vfs * vfs, void * handle, const char * z))(void){
	return NULL;
}
static void nxDlClose(sqlite3_vfs * vfs, void * handle){
	return;
}

// Fill the provided buffer with pseudo-random bytes
static int nxRandomness(sqlite3_vfs * vfs, int bytes, char * buf) {
	randomGet((void *) buf, bytes);
	return SQLITE_OK;
}

// Sleep for the given number of microseconds
static int nxSleep(sqlite3_vfs * vfs, int mSecs) {
	svcSleepThread(mSecs * 1000);
	return mSecs;
}

// Returns the current time as UTC in Julian days
static int nxCurrentTime(sqlite3_vfs * vfs, double * time) {
	u64 ts;
	Result rc = timeGetCurrentTime(TimeType_Default, &ts);
	if (R_FAILED(rc)) {
		return SQLITE_ERROR;
	}

	*(time) = ts/86400.0 + 2440587.5;
	return SQLITE_OK;
}

// Returns a pointer to this VFS so it can be used
sqlite3_vfs * sqlite3_nxvfs() {
	static sqlite3_vfs nxvfs = {
		1,                            // iVersion
		sizeof(nxFile),               // szOsFile
		FS_MAX_PATH,                  // mxPathname
		0,                            // pNext
		"nx",                         // zName
		0,                            // pAppData
		nxOpen,                       // xOpen
		nxDelete,                     // xDelete
		nxAccess,                     // xAccess
		nxFullPathname,               // xFullPathname
		nxDlOpen,                     // xDlOpen
		nxDlError,                    // xDlError
		nxDlSym,                      // xDlSym
		nxDlClose,                    // xDlClose
		nxRandomness,                 // xRandomness
		nxSleep,                      // xSleep
		nxCurrentTime,                // xCurrentTime
	};
	return &nxvfs;
}

// Opens the FsFileSystem and registers the VFS
SQLITE_API int sqlite3_os_init() {
	Result rc = fsOpenImageDirectoryFileSystem(&fs, FsImageDirectoryId_Sd);
	if (R_FAILED(rc)) {
		return SQLITE_ERROR;
	}
	sqlite3_vfs_register(sqlite3_nxvfs(), 1);
	return SQLITE_OK;
}

// Closes the FsFileSystem
SQLITE_API int sqlite3_os_end() {
	fsFsClose(&fs);
	return SQLITE_OK;
}