//go:build windows
// +build windows

package winio

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"time"
	"unsafe"

	"golang.org/x/sys/windows"

	"github.com/tailscale/go-winio/internal/socket"
	"github.com/tailscale/go-winio/pkg/guid"
)

const afHVSock = 34 // AF_HYPERV

// Well known Service and VM IDs
// https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/user-guide/make-integration-service#vmid-wildcards

// HvsockGUIDWildcard is the wildcard VmId for accepting connections from all partitions.
func HvsockGUIDWildcard() guid.GUID { // 00000000-0000-0000-0000-000000000000
	return guid.GUID{}
}

// HvsockGUIDBroadcast is the wildcard VmId for broadcasting sends to all partitions.
func HvsockGUIDBroadcast() guid.GUID { // ffffffff-ffff-ffff-ffff-ffffffffffff
	return guid.GUID{
		Data1: 0xffffffff,
		Data2: 0xffff,
		Data3: 0xffff,
		Data4: [8]uint8{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff},
	}
}

// HvsockGUIDLoopback is the Loopback VmId for accepting connections to the same partition as the connector.
func HvsockGUIDLoopback() guid.GUID { // e0e16197-dd56-4a10-9195-5ee7a155a838
	return guid.GUID{
		Data1: 0xe0e16197,
		Data2: 0xdd56,
		Data3: 0x4a10,
		Data4: [8]uint8{0x91, 0x95, 0x5e, 0xe7, 0xa1, 0x55, 0xa8, 0x38},
	}
}

// HvsockGUIDSiloHost is the address of a silo's host partition:
//   - The silo host of a hosted silo is the utility VM.
//   - The silo host of a silo on a physical host is the physical host.
func HvsockGUIDSiloHost() guid.GUID { // 36bd0c5c-7276-4223-88ba-7d03b654c568
	return guid.GUID{
		Data1: 0x36bd0c5c,
		Data2: 0x7276,
		Data3: 0x4223,
		Data4: [8]byte{0x88, 0xba, 0x7d, 0x03, 0xb6, 0x54, 0xc5, 0x68},
	}
}

// HvsockGUIDChildren is the wildcard VmId for accepting connections from the connector's child partitions.
func HvsockGUIDChildren() guid.GUID { // 90db8b89-0d35-4f79-8ce9-49ea0ac8b7cd
	return guid.GUID{
		Data1: 0x90db8b89,
		Data2: 0xd35,
		Data3: 0x4f79,
		Data4: [8]uint8{0x8c, 0xe9, 0x49, 0xea, 0xa, 0xc8, 0xb7, 0xcd},
	}
}

// HvsockGUIDParent is the wildcard VmId for accepting connections from the connector's parent partition.
// Listening on this VmId accepts connection from:
//   - Inside silos: silo host partition.
//   - Inside hosted silo: host of the VM.
//   - Inside VM: VM host.
//   - Physical host: Not supported.
func HvsockGUIDParent() guid.GUID { // a42e7cda-d03f-480c-9cc2-a4de20abb878
	return guid.GUID{
		Data1: 0xa42e7cda,
		Data2: 0xd03f,
		Data3: 0x480c,
		Data4: [8]uint8{0x9c, 0xc2, 0xa4, 0xde, 0x20, 0xab, 0xb8, 0x78},
	}
}

// hvsockVsockServiceTemplate is the Service GUID used for the VSOCK protocol.
func hvsockVsockServiceTemplate() guid.GUID { // 00000000-facb-11e6-bd58-64006a7986d3
	return guid.GUID{
		Data2: 0xfacb,
		Data3: 0x11e6,
		Data4: [8]uint8{0xbd, 0x58, 0x64, 0x00, 0x6a, 0x79, 0x86, 0xd3},
	}
}

// An HvsockAddr is an address for a AF_HYPERV socket.
type HvsockAddr struct {
	VMID      guid.GUID
	ServiceID guid.GUID
}

type rawHvsockAddr struct {
	Family    uint16
	_         uint16
	VMID      guid.GUID
	ServiceID guid.GUID
}

var _ socket.RawSockaddr = &rawHvsockAddr{}

// Network returns the address's network name, "hvsock".
func (*HvsockAddr) Network() string {
	return "hvsock"
}

func (addr *HvsockAddr) String() string {
	return fmt.Sprintf("%s:%s", &addr.VMID, &addr.ServiceID)
}

// VsockServiceID returns an hvsock service ID corresponding to the specified AF_VSOCK port.
func VsockServiceID(port uint32) guid.GUID {
	g := hvsockVsockServiceTemplate() // make a copy
	g.Data1 = port
	return g
}

func (addr *HvsockAddr) raw() rawHvsockAddr {
	return rawHvsockAddr{
		Family:    afHVSock,
		VMID:      addr.VMID,
		ServiceID: addr.ServiceID,
	}
}

func (addr *HvsockAddr) fromRaw(raw *rawHvsockAddr) {
	addr.VMID = raw.VMID
	addr.ServiceID = raw.ServiceID
}

// Sockaddr returns a pointer to and the size of this struct.
//
// Implements the [socket.RawSockaddr] interface, and allows use in
// [socket.Bind] and [socket.ConnectEx].
func (r *rawHvsockAddr) Sockaddr() (unsafe.Pointer, int32, error) {
	return unsafe.Pointer(r), int32(unsafe.Sizeof(rawHvsockAddr{})), nil
}

// Sockaddr interface allows use with `sockets.Bind()` and `.ConnectEx()`.
func (r *rawHvsockAddr) FromBytes(b []byte) error {
	n := int(unsafe.Sizeof(rawHvsockAddr{}))

	if len(b) < n {
		return fmt.Errorf("got %d, want %d: %w", len(b), n, socket.ErrBufferSize)
	}

	copy(unsafe.Slice((*byte)(unsafe.Pointer(r)), n), b[:n])
	if r.Family != afHVSock {
		return fmt.Errorf("got %d, want %d: %w", r.Family, afHVSock, socket.ErrAddrFamily)
	}

	return nil
}

// HvsockListener is a socket listener for the AF_HYPERV address family.
type HvsockListener struct {
	sock *win32File
	addr HvsockAddr
}

var _ net.Listener = &HvsockListener{}

// HvsockConn is a connected socket of the AF_HYPERV address family.
type HvsockConn struct {
	sock          *win32File
	local, remote HvsockAddr
}

var _ net.Conn = &HvsockConn{}

func newHVSocket() (*win32File, error) {
	fd, err := windows.Socket(afHVSock, windows.SOCK_STREAM, 1)
	if err != nil {
		return nil, os.NewSyscallError("socket", err)
	}
	f, err := makeWin32File(fd)
	if err != nil {
		windows.Close(fd)
		return nil, err
	}
	f.socket = true
	return f, nil
}

// ListenHvsock listens for connections on the specified hvsock address.
func ListenHvsock(addr *HvsockAddr) (_ *HvsockListener, err error) {
	l := &HvsockListener{addr: *addr}
	sock, err := newHVSocket()
	if err != nil {
		return nil, l.opErr("listen", err)
	}
	sa := addr.raw()
	err = socket.Bind(sock.handle, &sa)
	if err != nil {
		return nil, l.opErr("listen", os.NewSyscallError("socket", err))
	}
	err = windows.Listen(sock.handle, 16)
	if err != nil {
		return nil, l.opErr("listen", os.NewSyscallError("listen", err))
	}
	return &HvsockListener{sock: sock, addr: *addr}, nil
}

func (l *HvsockListener) opErr(op string, err error) error {
	return &net.OpError{Op: op, Net: "hvsock", Addr: &l.addr, Err: err}
}

// Addr returns the listener's network address.
func (l *HvsockListener) Addr() net.Addr {
	return &l.addr
}

// Accept waits for the next connection and returns it.
func (l *HvsockListener) Accept() (_ net.Conn, err error) {
	sock, err := newHVSocket()
	if err != nil {
		return nil, l.opErr("accept", err)
	}
	defer func() {
		if sock != nil {
			sock.Close()
		}
	}()
	c, err := l.sock.prepareIO()
	if err != nil {
		return nil, l.opErr("accept", err)
	}
	defer l.sock.wg.Done()

	// AcceptEx, per documentation, requires an extra 16 bytes per address.
	//
	// https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-acceptex
	const addrlen = uint32(16 + unsafe.Sizeof(rawHvsockAddr{}))
	var addrbuf [addrlen * 2]byte

	var bytes uint32
	err = windows.AcceptEx(l.sock.handle, sock.handle, &addrbuf[0], 0 /* rxdatalen */, addrlen, addrlen, &bytes, &c.o)
	if _, err = l.sock.asyncIO(c, nil, bytes, err); err != nil {
		return nil, l.opErr("accept", os.NewSyscallError("acceptex", err))
	}

	conn := &HvsockConn{
		sock: sock,
	}
	// The local address returned in the AcceptEx buffer is the same as the Listener socket's
	// address. However, the service GUID reported by GetSockName is different from the Listeners
	// socket, and is sometimes the same as the local address of the socket that dialed the
	// address, with the service GUID.Data1 incremented, but othertimes is different.
	// todo: does the local address matter? is the listener's address or the actual address appropriate?
	conn.local.fromRaw((*rawHvsockAddr)(unsafe.Pointer(&addrbuf[0])))
	conn.remote.fromRaw((*rawHvsockAddr)(unsafe.Pointer(&addrbuf[addrlen])))

	// initialize the accepted socket and update its properties with those of the listening socket
	if err = windows.Setsockopt(sock.handle,
		windows.SOL_SOCKET, windows.SO_UPDATE_ACCEPT_CONTEXT,
		(*byte)(unsafe.Pointer(&l.sock.handle)), int32(unsafe.Sizeof(l.sock.handle))); err != nil {
		return nil, conn.opErr("accept", os.NewSyscallError("setsockopt", err))
	}

	sock = nil
	return conn, nil
}

// Close closes the listener, causing any pending Accept calls to fail.
func (l *HvsockListener) Close() error {
	return l.sock.Close()
}

// HvsockDialer configures and dials a Hyper-V Socket (ie, [HvsockConn]).
type HvsockDialer struct {
	// Deadline is the time the Dial operation must connect before erroring.
	Deadline time.Time

	// Retries is the number of additional connects to try if the connection times out, is refused,
	// or the host is unreachable
	Retries uint

	// RetryWait is the time to wait after a connection error to retry
	RetryWait time.Duration

	rt *time.Timer // redial wait timer
}

// Dial the Hyper-V socket at addr.
//
// See [HvsockDialer.Dial] for more information.
func Dial(ctx context.Context, addr *HvsockAddr) (conn *HvsockConn, err error) {
	return (&HvsockDialer{}).Dial(ctx, addr)
}

// Dial attempts to connect to the Hyper-V socket at addr, and returns a connection if successful.
// Will attempt (HvsockDialer).Retries if dialing fails, waiting (HvsockDialer).RetryWait between
// retries.
//
// Dialing can be cancelled either by providing (HvsockDialer).Deadline, or cancelling ctx.
func (d *HvsockDialer) Dial(ctx context.Context, addr *HvsockAddr) (conn *HvsockConn, err error) {
	op := "dial"
	// create the conn early to use opErr()
	conn = &HvsockConn{
		remote: *addr,
	}

	if !d.Deadline.IsZero() {
		var cancel context.CancelFunc
		ctx, cancel = context.WithDeadline(ctx, d.Deadline)
		defer cancel()
	}

	// preemptive timeout/cancellation check
	if err = ctx.Err(); err != nil {
		return nil, conn.opErr(op, err)
	}

	sock, err := newHVSocket()
	if err != nil {
		return nil, conn.opErr(op, err)
	}
	defer func() {
		if sock != nil {
			sock.Close()
		}
	}()

	sa := addr.raw()
	err = socket.Bind(sock.handle, &sa)
	if err != nil {
		return nil, conn.opErr(op, os.NewSyscallError("bind", err))
	}

	c, err := sock.prepareIO()
	if err != nil {
		return nil, conn.opErr(op, err)
	}
	defer sock.wg.Done()
	var bytes uint32
	for i := uint(0); i <= d.Retries; i++ {
		err = socket.ConnectEx(
			sock.handle,
			&sa,
			nil, // sendBuf
			0,   // sendDataLen
			&bytes,
			(*windows.Overlapped)(unsafe.Pointer(&c.o)))
		_, err = sock.asyncIO(c, nil, bytes, err)
		if i < d.Retries && canRedial(err) {
			if err = d.redialWait(ctx); err == nil {
				continue
			}
		}
		break
	}
	if err != nil {
		return nil, conn.opErr(op, os.NewSyscallError("connectex", err))
	}

	// update the connection properties, so shutdown can be used
	if err = windows.Setsockopt(
		sock.handle,
		windows.SOL_SOCKET,
		windows.SO_UPDATE_CONNECT_CONTEXT,
		nil, // optvalue
		0,   // optlen
	); err != nil {
		return nil, conn.opErr(op, os.NewSyscallError("setsockopt", err))
	}

	// get the local name
	var sal rawHvsockAddr
	err = socket.GetSockName(sock.handle, &sal)
	if err != nil {
		return nil, conn.opErr(op, os.NewSyscallError("getsockname", err))
	}
	conn.local.fromRaw(&sal)

	// one last check for timeout, since asyncIO doesn't check the context
	if err = ctx.Err(); err != nil {
		return nil, conn.opErr(op, err)
	}

	conn.sock = sock
	sock = nil

	return conn, nil
}

// redialWait waits before attempting to redial, resetting the timer as appropriate.
func (d *HvsockDialer) redialWait(ctx context.Context) (err error) {
	if d.RetryWait == 0 {
		return nil
	}

	if d.rt == nil {
		d.rt = time.NewTimer(d.RetryWait)
	} else {
		// should already be stopped and drained
		d.rt.Reset(d.RetryWait)
	}

	select {
	case <-ctx.Done():
	case <-d.rt.C:
		return nil
	}

	// stop and drain the timer
	if !d.rt.Stop() {
		<-d.rt.C
	}
	return ctx.Err()
}

// assumes error is a plain, unwrapped windows.Errno provided by direct syscall.
func canRedial(err error) bool {
	//nolint:errorlint // guaranteed to be an Errno
	switch err {
	case windows.WSAECONNREFUSED, windows.WSAENETUNREACH, windows.WSAETIMEDOUT,
		windows.ERROR_CONNECTION_REFUSED, windows.ERROR_CONNECTION_UNAVAIL:
		return true
	default:
		return false
	}
}

func (conn *HvsockConn) opErr(op string, err error) error {
	// translate from "file closed" to "socket closed"
	if errors.Is(err, ErrFileClosed) {
		err = socket.ErrSocketClosed
	}
	return &net.OpError{Op: op, Net: "hvsock", Source: &conn.local, Addr: &conn.remote, Err: err}
}

func (conn *HvsockConn) Read(b []byte) (int, error) {
	c, err := conn.sock.prepareIO()
	if err != nil {
		return 0, conn.opErr("read", err)
	}
	defer conn.sock.wg.Done()
	buf := windows.WSABuf{Buf: &b[0], Len: uint32(len(b))}
	var flags, bytes uint32
	err = windows.WSARecv(conn.sock.handle, &buf, 1, &bytes, &flags, &c.o, nil)
	n, err := conn.sock.asyncIO(c, &conn.sock.readDeadline, bytes, err)
	if err != nil {
		var eno windows.Errno
		if errors.As(err, &eno) {
			err = os.NewSyscallError("wsarecv", eno)
		}
		return 0, conn.opErr("read", err)
	} else if n == 0 {
		err = io.EOF
	}
	return n, err
}

func (conn *HvsockConn) Write(b []byte) (int, error) {
	t := 0
	for len(b) != 0 {
		n, err := conn.write(b)
		if err != nil {
			return t + n, err
		}
		t += n
		b = b[n:]
	}
	return t, nil
}

func (conn *HvsockConn) write(b []byte) (int, error) {
	c, err := conn.sock.prepareIO()
	if err != nil {
		return 0, conn.opErr("write", err)
	}
	defer conn.sock.wg.Done()
	buf := windows.WSABuf{Buf: &b[0], Len: uint32(len(b))}
	var bytes uint32
	err = windows.WSASend(conn.sock.handle, &buf, 1, &bytes, 0, &c.o, nil)
	n, err := conn.sock.asyncIO(c, &conn.sock.writeDeadline, bytes, err)
	if err != nil {
		var eno windows.Errno
		if errors.As(err, &eno) {
			err = os.NewSyscallError("wsasend", eno)
		}
		return 0, conn.opErr("write", err)
	}
	return n, err
}

// Close closes the socket connection, failing any pending read or write calls.
func (conn *HvsockConn) Close() error {
	return conn.sock.Close()
}

func (conn *HvsockConn) IsClosed() bool {
	return conn.sock.IsClosed()
}

// shutdown disables sending or receiving on a socket.
func (conn *HvsockConn) shutdown(how int) error {
	if conn.IsClosed() {
		return socket.ErrSocketClosed
	}

	err := windows.Shutdown(conn.sock.handle, how)
	if err != nil {
		// If the connection was closed, shutdowns fail with "not connected"
		if errors.Is(err, windows.WSAENOTCONN) ||
			errors.Is(err, windows.WSAESHUTDOWN) {
			err = socket.ErrSocketClosed
		}
		return os.NewSyscallError("shutdown", err)
	}
	return nil
}

// CloseRead shuts down the read end of the socket, preventing future read operations.
func (conn *HvsockConn) CloseRead() error {
	err := conn.shutdown(windows.SHUT_RD)
	if err != nil {
		return conn.opErr("closeread", err)
	}
	return nil
}

// CloseWrite shuts down the write end of the socket, preventing future write operations and
// notifying the other endpoint that no more data will be written.
func (conn *HvsockConn) CloseWrite() error {
	err := conn.shutdown(windows.SHUT_WR)
	if err != nil {
		return conn.opErr("closewrite", err)
	}
	return nil
}

// LocalAddr returns the local address of the connection.
func (conn *HvsockConn) LocalAddr() net.Addr {
	return &conn.local
}

// RemoteAddr returns the remote address of the connection.
func (conn *HvsockConn) RemoteAddr() net.Addr {
	return &conn.remote
}

// SetDeadline implements the net.Conn SetDeadline method.
func (conn *HvsockConn) SetDeadline(t time.Time) error {
	// todo: implement `SetDeadline` for `win32File`
	if err := conn.SetReadDeadline(t); err != nil {
		return fmt.Errorf("set read deadline: %w", err)
	}
	if err := conn.SetWriteDeadline(t); err != nil {
		return fmt.Errorf("set write deadline: %w", err)
	}
	return nil
}

// SetReadDeadline implements the net.Conn SetReadDeadline method.
func (conn *HvsockConn) SetReadDeadline(t time.Time) error {
	return conn.sock.SetReadDeadline(t)
}

// SetWriteDeadline implements the net.Conn SetWriteDeadline method.
func (conn *HvsockConn) SetWriteDeadline(t time.Time) error {
	return conn.sock.SetWriteDeadline(t)
}
