// TINYGO: The following is copied and modified from Go 1.26.2 official implementation.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package net

import (
	"errors"
	"fmt"
	"io"
	"net/netip"
	"strconv"
	"syscall"
	"time"
)

// KeepAliveConfig specifies the keep-alive probe configuration
// for an active network connection, when supported by the
// protocol and operating system.
// TINYGO: Stub definition for compatibility; not used on embedded devices.
type KeepAliveConfig struct {
	Enable   bool
	Idle     time.Duration
	Interval time.Duration
	Count    int
}

// TCPAddr represents the address of a TCP end point.
type TCPAddr struct {
	IP   IP
	Port int
	Zone string // IPv6 scoped addressing zone
}

// AddrPort returns the [TCPAddr] a as a [netip.AddrPort].
//
// If a.Port does not fit in a uint16, it's silently truncated.
//
// If a is nil, a zero value is returned.
func (a *TCPAddr) AddrPort() netip.AddrPort {
	if a == nil {
		return netip.AddrPort{}
	}
	na, _ := netip.AddrFromSlice(a.IP)
	na = na.WithZone(a.Zone)
	return netip.AddrPortFrom(na, uint16(a.Port))
}

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

func (a *TCPAddr) String() string {
	if a == nil {
		return "<nil>"
	}
	ip := ipEmptyString(a.IP)
	if a.Zone != "" {
		return JoinHostPort(ip+"%"+a.Zone, strconv.Itoa(a.Port))
	}
	return JoinHostPort(ip, strconv.Itoa(a.Port))
}

func (a *TCPAddr) isWildcard() bool {
	if a == nil || a.IP == nil {
		return true
	}
	return a.IP.IsUnspecified()
}

func (a *TCPAddr) opAddr() Addr {
	if a == nil {
		return nil
	}
	return a
}

// ResolveTCPAddr returns an address of TCP end point.
//
// The network must be a TCP network name.
//
// If the host in the address parameter is not a literal IP address or
// the port is not a literal port number, ResolveTCPAddr resolves the
// address to an address of TCP end point.
// Otherwise, it parses the address as a pair of literal IP address
// and port number.
// The address parameter can use a host name, but this is not
// recommended, because it will return at most one of the host name's
// IP addresses.
//
// See func [Dial] for a description of the network and address
// parameters.
func ResolveTCPAddr(network, address string) (*TCPAddr, error) {

	switch network {
	case "tcp", "tcp4":
	default:
		return nil, fmt.Errorf("Network '%s' not supported", network)
	}

	switch address {
	case ":http":
		address = ":80"
	}

	// TINYGO: Use netdev resolver

	host, sport, err := SplitHostPort(address)
	if err != nil {
		return nil, err
	}

	port, err := strconv.Atoi(sport)
	if err != nil {
		return nil, fmt.Errorf("Error parsing port '%s' in address: %s",
			sport, err)
	}

	if host == "" {
		return &TCPAddr{Port: port}, nil
	}

	ip, err := netdev.GetHostByName(host)
	if err != nil {
		return nil, fmt.Errorf("Lookup of host name '%s' failed: %s", host, err)
	}

	return &TCPAddr{IP: ip.AsSlice(), Port: port}, nil
}

// TCPAddrFromAddrPort returns addr as a [TCPAddr]. If addr.IsValid() is false,
// then the returned TCPAddr will contain a nil IP field, indicating an
// address family-agnostic unspecified address.
func TCPAddrFromAddrPort(addr netip.AddrPort) *TCPAddr {
	return &TCPAddr{
		IP:   addr.Addr().AsSlice(),
		Zone: addr.Addr().Zone(),
		Port: int(addr.Port()),
	}
}

// TCPConn is an implementation of the [Conn] interface for TCP network
// connections.
type TCPConn struct {
	fd            int
	net           string
	laddr         *TCPAddr
	raddr         *TCPAddr
	readDeadline  time.Time
	writeDeadline time.Time
}

// DialTCP acts like Dial for TCP networks.
//
// The network must be a TCP network name; see func Dial for details.
//
// If laddr is nil, a local address is automatically chosen.
// If the IP field of raddr is nil or an unspecified IP address, the
// local system is assumed.
func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error) {

	switch network {
	case "tcp", "tcp4":
	default:
		return nil, errors.New("Network not supported: '" + network + "'")
	}

	// TINYGO: Use netdev to create TCP socket and connect

	if raddr == nil {
		raddr = &TCPAddr{}
	}

	if raddr.IP.IsUnspecified() {
		return nil, errors.New("Sorry, localhost isn't available on Tinygo")
	} else if len(raddr.IP) != 4 {
		return nil, errors.New("only ipv4 supported")
	}

	fd, err := netdev.Socket(_AF_INET, _SOCK_STREAM, _IPPROTO_TCP)
	if err != nil {
		return nil, err
	}

	rip, _ := netip.AddrFromSlice(raddr.IP)
	raddrport := netip.AddrPortFrom(rip, uint16(raddr.Port))
	if err = netdev.Connect(fd, "", raddrport); err != nil {
		netdev.Close(fd)
		return nil, err
	}

	return &TCPConn{
		fd:    fd,
		net:   network,
		laddr: laddr,
		raddr: raddr,
	}, nil
}

// TINYGO: Use netdev for Conn methods: Read = Recv, Write = Send, etc.

// SyscallConn returns a raw network connection.
// This implements the [syscall.Conn] interface.
func (c *TCPConn) SyscallConn() (syscall.RawConn, error) {
	return nil, errors.New("SyscallConn not implemented")
}

func (c *TCPConn) Read(b []byte) (int, error) {
	n, err := netdev.Recv(c.fd, b, 0, c.readDeadline)
	// Turn the -1 socket error into 0 and let err speak for error
	if n < 0 {
		n = 0
	}
	if err != nil && err != io.EOF {
		err = &OpError{Op: "read", Net: c.net, Source: c.laddr, Addr: c.raddr, Err: err}
	}
	return n, err
}

func (c *TCPConn) Write(b []byte) (int, error) {
	n, err := netdev.Send(c.fd, b, 0, c.writeDeadline)
	// Turn the -1 socket error into 0 and let err speak for error
	if n < 0 {
		n = 0
	}
	if err != nil {
		err = &OpError{Op: "write", Net: c.net, Source: c.laddr, Addr: c.raddr, Err: err}
	}
	return n, err
}

func (c *TCPConn) Close() error {
	return netdev.Close(c.fd)
}

func (c *TCPConn) LocalAddr() Addr {
	return c.laddr
}

func (c *TCPConn) RemoteAddr() Addr {
	return c.raddr
}

func (c *TCPConn) SetDeadline(t time.Time) error {
	c.readDeadline = t
	c.writeDeadline = t
	return nil
}

// SetLinger sets the behavior of Close on a connection which still
// has data waiting to be sent or to be acknowledged.
//
// If sec < 0 (the default), the operating system finishes sending the
// data in the background.
//
// If sec == 0, the operating system discards any unsent or
// unacknowledged data.
//
// If sec > 0, the data is sent in the background as with sec < 0.
// On some operating systems including Linux, this may cause Close to block
// until all data has been sent or discarded.
// On some operating systems after sec seconds have elapsed any remaining
// unsent data may be discarded.
func (c *TCPConn) SetLinger(sec int) error {
	return netdev.SetSockOpt(c.fd, _SOL_SOCKET, _SO_LINGER, sec)
}

// SetKeepAlive sets whether the operating system should send
// keep-alive messages on the connection.
func (c *TCPConn) SetKeepAlive(keepalive bool) error {
	return netdev.SetSockOpt(c.fd, _SOL_SOCKET, _SO_KEEPALIVE, keepalive)
}

// SetKeepAlivePeriod sets the duration the connection needs to
// remain idle before TCP starts sending keepalive probes.
//
// Note that calling this method on Windows prior to Windows 10 version 1709
// will reset the KeepAliveInterval to the default system value, which is normally 1 second.
func (c *TCPConn) SetKeepAlivePeriod(d time.Duration) error {
	// Units are 1/2 seconds
	return netdev.SetSockOpt(c.fd, _SOL_TCP, _TCP_KEEPINTVL, 2*d.Seconds())
}

func (c *TCPConn) SetReadDeadline(t time.Time) error {
	c.readDeadline = t
	return nil
}

func (c *TCPConn) SetWriteDeadline(t time.Time) error {
	c.writeDeadline = t
	return nil
}

func (c *TCPConn) CloseWrite() error {
	return fmt.Errorf("CloseWrite not implemented")
}

// CloseRead shuts down the reading side of the TCP connection.
// Most callers should just use Close.
//
// TINYGO: no-op; netdev has no half-close, reads simply stop when Close
// is called.
func (c *TCPConn) CloseRead() error {
	return nil
}

// SetNoDelay controls whether the operating system should delay
// packet transmission in hopes of sending fewer packets (Nagle's
// algorithm). The default is true (no delay), meaning that data is
// sent as soon as possible after a Write.
//
// TINYGO: no-op; Nagle behavior is managed by the netdev driver.
func (c *TCPConn) SetNoDelay(noDelay bool) error {
	return nil
}

// SetReadBuffer sets the size of the operating system's receive buffer
// associated with the connection.
//
// TINYGO: no-op; buffer sizing is managed by the netdev driver.
func (c *TCPConn) SetReadBuffer(bytes int) error {
	return nil
}

// SetWriteBuffer sets the size of the operating system's transmit buffer
// associated with the connection.
//
// TINYGO: no-op; buffer sizing is managed by the netdev driver.
func (c *TCPConn) SetWriteBuffer(bytes int) error {
	return nil
}

// ReadFrom implements the io.ReaderFrom ReadFrom method.
//
// TINYGO: generic copy loop over Write; no zero-copy sendfile path.
func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
	return genericReadFrom(c, r)
}

// genericReadFrom copies from r into w until EOF, returning the number
// of bytes copied.
func genericReadFrom(w io.Writer, r io.Reader) (int64, error) {
	// Wrap w to hide its ReadFrom method, so io.Copy uses the generic
	// read/write loop instead of recursing back into TCPConn.ReadFrom.
	return io.Copy(onlyWriter{w}, r)
}

// onlyWriter hides w's ReadFrom method from io.Copy.
type onlyWriter struct {
	io.Writer
}

type listener struct {
	fd    int
	laddr *TCPAddr
}

func (l *listener) Accept() (Conn, error) {
	fd, raddr, err := netdev.Accept(l.fd)
	if err != nil {
		return nil, err
	}

	return &TCPConn{
		fd:    fd,
		net:   "tcp",
		laddr: l.laddr,
		raddr: TCPAddrFromAddrPort(raddr),
	}, nil
}

func (l *listener) Close() error {
	return netdev.Close(l.fd)
}

func (l *listener) Addr() Addr {
	return l.laddr
}

func listenTCP(laddr *TCPAddr) (Listener, error) {
	fd, err := netdev.Socket(_AF_INET, _SOCK_STREAM, _IPPROTO_TCP)
	if err != nil {
		return nil, err
	}

	laddrport := laddr.AddrPort()
	err = netdev.Bind(fd, laddrport)
	if err != nil {
		return nil, err
	}

	err = netdev.Listen(fd, 5)
	if err != nil {
		return nil, err
	}

	return &listener{fd: fd, laddr: laddr}, nil
}

// TCPListener is a TCP network listener. Clients should typically
// use variables of type Listener instead of assuming TCP.
type TCPListener struct {
	listener
}

// ListenTCP acts like [Listen] for TCP networks.
//
// The network must be a TCP network name; see func [Dial] for details.
// If the IP field of laddr is nil or an unspecified IP address,
// ListenTCP listens on all available unicast and anycast IP addresses
// of the local system. If the Port field of laddr is 0, a port number
// is automatically chosen.
func ListenTCP(network string, laddr *TCPAddr) (*TCPListener, error) {
	switch network {
	case "tcp", "tcp4":
	default:
		return nil, fmt.Errorf("Network '%s' not supported", network)
	}

	if laddr == nil {
		laddr = &TCPAddr{}
	}

	fd, err := netdev.Socket(_AF_INET, _SOCK_STREAM, _IPPROTO_TCP)
	if err != nil {
		return nil, err
	}

	if err = netdev.Bind(fd, laddr.AddrPort()); err != nil {
		netdev.Close(fd)
		return nil, err
	}

	if err = netdev.Listen(fd, 5); err != nil {
		netdev.Close(fd)
		return nil, err
	}

	return &TCPListener{listener{fd: fd, laddr: laddr}}, nil
}

// AcceptTCP accepts the next incoming call and returns the new
// connection.
func (l *TCPListener) AcceptTCP() (*TCPConn, error) {
	fd, raddr, err := netdev.Accept(l.fd)
	if err != nil {
		return nil, err
	}

	return &TCPConn{
		fd:    fd,
		net:   "tcp",
		laddr: l.laddr,
		raddr: TCPAddrFromAddrPort(raddr),
	}, nil
}

// SetDeadline sets the deadline associated with the listener.
// A zero time value disables the deadline.
//
// TINYGO: no-op; netdev.Accept has no deadline support.
func (l *TCPListener) SetDeadline(t time.Time) error {
	return nil
}