//go:build windows

package nbconn

import (
	"errors"
	"fmt"
	"golang.org/x/sys/windows"
	"io"
	"syscall"
	"time"
	"unsafe"
)

var dll = syscall.MustLoadDLL("ws2_32.dll")

// int ioctlsocket(
//
//	[in]      SOCKET s,
//	[in]      long   cmd,
//	[in, out] u_long *argp
//
// );
var ioctlsocket = dll.MustFindProc("ioctlsocket")

var deadlineExpErr = errors.New("i/o timeout")

type sockMode int

const (
	FIONBIO             uint32   = 0x8004667e
	sockModeBlocking    sockMode = 0
	sockModeNonBlocking sockMode = 1
)

func setSockMode(fd uintptr, mode sockMode) error {
	res, _, err := ioctlsocket.Call(fd, uintptr(FIONBIO), uintptr(unsafe.Pointer(&mode)))
	// Upon successful completion, the ioctlsocket returns zero.
	if res != 0 && err != nil {
		return err
	}

	return nil
}

func (c *NetConn) isDeadlineSet(dl time.Time) bool {
	return !dl.IsZero() && !dl.Equal(NonBlockingDeadline) && !dl.Equal(disableSetDeadlineDeadline)
}

func (c *NetConn) isWriteDeadlineExpired() bool {
	c.writeDeadlineLock.Lock()
	defer c.writeDeadlineLock.Unlock()

	return c.isDeadlineSet(c.writeDeadline) && !time.Now().Before(c.writeDeadline)
}

func (c *NetConn) isReadDeadlineExpired() bool {
	c.readDeadlineLock.Lock()
	defer c.readDeadlineLock.Unlock()

	return c.isDeadlineSet(c.readDeadline) && !time.Now().Before(c.readDeadline)
}

// realNonblockingWrite does a non-blocking write. readFlushLock must already be held.
func (c *NetConn) realNonblockingWrite(b []byte) (n int, err error) {
	if c.nonblockWriteFunc == nil {
		c.nonblockWriteFunc = func(fd uintptr) (done bool) {
			var written uint32
			var buf syscall.WSABuf
			buf.Buf = &c.nonblockWriteBuf[0]
			buf.Len = uint32(len(c.nonblockWriteBuf))
			c.nonblockWriteErr = syscall.WSASend(syscall.Handle(fd), &buf, 1, &written, 0, nil, nil)
			c.nonblockWriteN = int(written)

			return true
		}
	}
	c.nonblockWriteBuf = b
	c.nonblockWriteN = 0
	c.nonblockWriteErr = nil

	if c.isWriteDeadlineExpired() {
		c.nonblockWriteErr = deadlineExpErr

		return 0, c.nonblockWriteErr
	}

	err = c.rawConn.Write(c.nonblockWriteFunc)
	n = c.nonblockWriteN
	c.nonblockWriteBuf = nil // ensure that no reference to b is kept.
	if err == nil && c.nonblockWriteErr != nil {
		if errors.Is(c.nonblockWriteErr, windows.WSAEWOULDBLOCK) {
			err = ErrWouldBlock
		} else {
			err = c.nonblockWriteErr
		}
	}
	if err != nil {
		// n may be -1 when an error occurs.
		if n < 0 {
			n = 0
		}

		return n, err
	}

	return n, nil
}

func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
	if c.nonblockReadFunc == nil {
		c.nonblockReadFunc = func(fd uintptr) (done bool) {
			var read uint32
			var flags uint32
			var buf syscall.WSABuf
			buf.Buf = &c.nonblockReadBuf[0]
			buf.Len = uint32(len(c.nonblockReadBuf))
			c.nonblockReadErr = syscall.WSARecv(syscall.Handle(fd), &buf, 1, &read, &flags, nil, nil)
			c.nonblockReadN = int(read)

			return true
		}
	}
	c.nonblockReadBuf = b
	c.nonblockReadN = 0
	c.nonblockReadErr = nil

	if c.isReadDeadlineExpired() {
		c.nonblockReadErr = deadlineExpErr

		return 0, c.nonblockReadErr
	}

	err = c.rawConn.Read(c.nonblockReadFunc)
	n = c.nonblockReadN
	c.nonblockReadBuf = nil // ensure that no reference to b is kept.
	if err == nil && c.nonblockReadErr != nil {
		if errors.Is(c.nonblockReadErr, windows.WSAEWOULDBLOCK) {
			err = ErrWouldBlock
		} else {
			err = c.nonblockReadErr
		}
	}
	if err != nil {
		// n may be -1 when an error occurs.
		if n < 0 {
			n = 0
		}

		return n, err
	}

	// syscall read did not return an error and 0 bytes were read means EOF.
	if n == 0 {
		return 0, io.EOF
	}

	return n, nil
}

func (c *NetConn) SetBlockingMode(blocking bool) error {
	// Fake non-blocking I/O is ignored
	if c.rawConn == nil {
		return nil
	}

	// Prevent concurrent SetBlockingMode calls
	c.nbOperMu.Lock()
	defer c.nbOperMu.Unlock()

	// Guard against negative value (which should never happen in practice)
	if c.nbOperCnt < 0 {
		c.nbOperCnt = 0
	}

	if blocking {
		// Socket is already in blocking mode
		if c.nbOperCnt == 0 {
			return nil
		}

		c.nbOperCnt--

		// Not ready to exit from non-blocking mode, there is pending non-blocking operations
		if c.nbOperCnt > 0 {
			return nil
		}
	} else {
		c.nbOperCnt++

		// Socket is already in non-blocking mode
		if c.nbOperCnt > 1 {
			return nil
		}
	}

	mode := sockModeNonBlocking
	if blocking {
		mode = sockModeBlocking
	}

	var ctrlErr, err error

	ctrlErr = c.rawConn.Control(func(fd uintptr) {
		err = setSockMode(fd, mode)
	})

	if ctrlErr != nil || err != nil {
		retErr := ctrlErr
		if retErr == nil {
			retErr = err
		}

		// Revert counters inc/dec in case of error
		if blocking {
			c.nbOperCnt++

			return fmt.Errorf("cannot set socket to blocking mode: %w", retErr)
		} else {
			c.nbOperCnt--

			return fmt.Errorf("cannot set socket to non-blocking mode: %w", retErr)
		}
	}

	return nil
}