package internet

import (
	"net"
	"syscall"

	"golang.org/x/sys/unix"
)

const (
	// For incoming connections.
	TCP_FASTOPEN = 23
	// For out-going connections.
	TCP_FASTOPEN_CONNECT = 30
)

func bindAddr(fd uintptr, ip []byte, port uint32) error {
	setReuseAddr(fd)
	setReusePort(fd)

	var sockaddr syscall.Sockaddr

	switch len(ip) {
	case net.IPv4len:
		a4 := &syscall.SockaddrInet4{
			Port: int(port),
		}
		copy(a4.Addr[:], ip)
		sockaddr = a4
	case net.IPv6len:
		a6 := &syscall.SockaddrInet6{
			Port: int(port),
		}
		copy(a6.Addr[:], ip)
		sockaddr = a6
	default:
		return newError("unexpected length of ip")
	}

	return syscall.Bind(int(fd), sockaddr)
}

func applyOutboundSocketOptions(network string, address string, fd uintptr, config *SocketConfig) error {
	if config.Mark != 0 {
		if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_MARK, int(config.Mark)); err != nil {
			return newError("failed to set SO_MARK").Base(err)
		}
	}

	if isTCPSocket(network) {
		tfo := int(config.Tfo)
		if tfo > 0 {
			tfo = 1
		}
		if tfo >= 0 {
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN_CONNECT, tfo); err != nil {
				return newError("failed to set TCP_FASTOPEN_CONNECT=", tfo).Base(err)
			}
		}
	}

	if config.Tproxy.IsEnabled() {
		if err := syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
			return newError("failed to set IP_TRANSPARENT").Base(err)
		}
	}

	return nil
}

func applyInboundSocketOptions(network string, fd uintptr, config *SocketConfig) error {
	if config.Mark != 0 {
		if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_MARK, int(config.Mark)); err != nil {
			return newError("failed to set SO_MARK").Base(err)
		}
	}
	if isTCPSocket(network) {
		if config.Tfo >= 0 {
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN, int(config.Tfo)); err != nil {
				return newError("failed to set TCP_FASTOPEN=", config.Tfo).Base(err)
			}
		}
	}

	if config.Tproxy.IsEnabled() {
		if err := syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
			return newError("failed to set IP_TRANSPARENT").Base(err)
		}
	}

	if config.ReceiveOriginalDestAddress && isUDPSocket(network) {
		err1 := syscall.SetsockoptInt(int(fd), syscall.SOL_IPV6, unix.IPV6_RECVORIGDSTADDR, 1)
		err2 := syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_RECVORIGDSTADDR, 1)
		if err1 != nil && err2 != nil {
			return err1
		}
	}

	return nil
}

func setReuseAddr(fd uintptr) error {
	if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
		return newError("failed to set SO_REUSEADDR").Base(err).AtWarning()
	}
	return nil
}

func setReusePort(fd uintptr) error {
	if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
		return newError("failed to set SO_REUSEPORT").Base(err).AtWarning()
	}
	return nil
}