package sqlite

/*
#include <string.h>

#define SKIP_SQLITE_VERSION
#include "sqlite3.h"
*/
import "C"

import (
	"io"
	"os"
	"sync"
	"time"
	"unsafe"
)

// Our map of fake fds to our internal *os.File. These aren't
// actual fd numbers, since those don't exist on Windows.
// Instead we just make some identifiers up.
var fmu sync.Mutex
var fileMap = make(map[int]*os.File) // fake_fd -> *os.File
var lastFakeFd = 99000               // start high to catch bugs of people using these like real fds

func GetFile(fd int) (file *os.File) {
	fmu.Lock()
	defer fmu.Unlock()
	return fileMap[fd]
}

//export GoFileClose
// Returns 0 on success and -1 on error.
func GoFileClose(fd C.int) int {
	file := GetFile(int(fd))
	fmu.Lock()
	fileMap[int(fd)] = nil, false
	fmu.Unlock()
	if file.Close() != nil {
		return -1
	}
	return 0
}

//export GoFileRead
// Returns SQLite error code to be returned by xRead:
//   SQLITE_OK: read n bytes
//   SQLITE_IOERR_READ: got error while reading
//   SQLITE_IOERR_SHORT_READ: read fewer than n bytes; rest will be zeroed
func GoFileRead(fd C.int, dst *C.char, n C.int, offset C.long) (rv int) {
	println("reading", n, "bytes at offset", offset, "from fd", fd)
	defer func() {
		println("read returning", rv)
	}()

	file := GetFile(int(fd))
	if file == nil {
		return C.SQLITE_IOERR_READ
	}

	buf := make([]byte, n)
	curbuf := buf
	for n > 0 {
		read, err := file.ReadAt(curbuf, int64(offset))
		curbuf = curbuf[read:]
		n -= C.int(read)
		if err == io.EOF {
			break
		}
		if err != nil {
			return C.SQLITE_IOERR_READ
		}
	}

	C.memcpy(unsafe.Pointer(dst), unsafe.Pointer(&buf[0]), C.size_t(len(buf)))

	if n != 0 {
		return C.SQLITE_IOERR_SHORT_READ
	}
	return C.SQLITE_OK
}

//export GoFileWrite
// Returns SQLite error code to be returned by xWrite:
//   SQLITE_OK: wrote n bytes
//   SQLITE_IOERR_WRITE: got error while writing
//   SQLITE_FULL: partial write
func GoFileWrite(fd C.int, src *C.char, n C.int, offset C.long) (rv int) {
	println("writing", n, "bytes at offset", offset, "to fd", fd)
	defer func() {
		println("write returning", rv)
	}()

	file := GetFile(int(fd))
	if file == nil {
		return C.SQLITE_IOERR_WRITE
	}

	// TODO: avoid this copy
	buf := make([]byte, n)
	C.memcpy(unsafe.Pointer(&buf[0]), unsafe.Pointer(src), C.size_t(len(buf)))

	nwritten, err := file.WriteAt(buf, int64(offset))
	if err != nil {
		if err == os.ENOSPC {
			return C.SQLITE_FULL
		}
		return C.SQLITE_IOERR_WRITE
	}
	if nwritten != int(n) {
		return C.SQLITE_IOERR_WRITE
	}

	return C.SQLITE_OK
}

//export GoFileFileSize
// return[0]: 0 on success and -1 on error.
// return[1]: size
func GoFileFileSize(fd C.int) (rv int, size C.long) {
	println("getting file size for fd", fd)
	defer func() {
		println("returning", rv, "with size", size)
	}()

	file := GetFile(int(fd))
	if file == nil {
		return -1, 0
	}

	info, err := file.Stat()
	if err != nil {
		return -1, 0
	}
	return 0, C.long(info.Size)
}

//export GoVFSOpen
// fd is -1 on error.
func GoVFSOpen(filename *C.char, flags C.int) (fd int) {
	println("opening", C.GoString(filename), "with flags", int(flags))

	goflags := 0
	if flags&C.SQLITE_OPEN_READONLY != 0 {
		goflags |= os.O_RDONLY
	}
	if flags&C.SQLITE_OPEN_READWRITE != 0 {
		goflags |= os.O_RDWR
	}
	if flags&C.SQLITE_OPEN_CREATE != 0 {
		goflags |= os.O_RDWR | os.O_CREATE
	}
	if flags&C.SQLITE_OPEN_DELETEONCLOSE != 0 {
		// TODO: Do something.
	}
	if flags&C.SQLITE_OPEN_EXCLUSIVE != 0 {
		goflags |= os.O_EXCL
	}

	file, err := os.OpenFile(C.GoString(filename), goflags, 0666)
	defer func() {
		if err != nil {
			println("got error:", err.String())
		}
		println("returning fd", fd)
	}()
	if err != nil {
		return -1
	}

	fmu.Lock()
	defer fmu.Unlock()
	fakeFd := lastFakeFd
	lastFakeFd++
	fileMap[fakeFd] = file
	return fakeFd
}

//export GoVFSDelete
// Returns SQLite error code to be returned by xWrite:
//   SQLITE_OK: deleted the file
//   SQLITE_IOERR_DELETE: failed to delete
//   SQLITE_IOERR_DIR_FSYNC: failed to fsync dir after deleting
func GoVFSDelete(filename *C.char, syncDir C.int) (rv int) {
	println("deleting", C.GoString(filename), "with syncdir", syncDir)
	if err := os.Remove(C.GoString(filename)); err != nil {
		if os.IsNotExist(err) {
			return C.SQLITE_OK
		}
		println("delete of", C.GoString(filename), "failed:", err.String())
		return C.SQLITE_IOERR_DELETE
	}
	// TODO: Support syncDir.
	return C.SQLITE_OK
}

//export GoVFSAccess
func GoVFSAccess(filename *C.char, flags C.int) (rv int) {
	fi, err := os.Stat(C.GoString(filename))
	if err != nil {
		return 0
	}
	switch flags {
	case C.SQLITE_ACCESS_EXISTS:
		if fi.Size != 0 {
			return 1
		} else {
			return 0
		}
	case C.SQLITE_ACCESS_READWRITE:
		// TODO: compute read/writeability in a manner similar to access()
		return 1
	case C.SQLITE_ACCESS_READ:
		return 1
	}
	return 0
}

//export GoVFSCurrentTimeInt64
func GoVFSCurrentTimeInt64() (now int64) {
	// Unix epoch as a Julian Day number times 86_400_000.
	const unixEpoch = 24405875 * 8640000
	return unixEpoch + (time.Nanoseconds() / 1000000)
}