// 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 (
	"context"
	"internal/itoa"
	"io"
	"net/netip"
	"os"
	"syscall"
	"time"
)

// BUG(mikio): On JS and Windows, the File method of TCPConn and
// TCPListener is not implemented.

// 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, itoa.Itoa(a.Port))
	}
	return JoinHostPort(ip, itoa.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", "tcp6":
	case "": // a hint wildcard for Go 1.0 undocumented behavior
		network = "tcp"
	default:
		return nil, UnknownNetworkError(network)
	}
	addrs, err := DefaultResolver.internetAddrList(context.Background(), network, address)
	if err != nil {
		return nil, err
	}
	return addrs.forResolve(network, address).(*TCPAddr), 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 {
	conn
}

// KeepAliveConfig contains TCP keep-alive options.
//
// If the Idle, Interval, or Count fields are zero, a default value is chosen.
// If a field is negative, the corresponding socket-level option will be left unchanged.
//
// Note that prior to Windows 10 version 1709, neither setting Idle and Interval
// separately nor changing Count (which is usually 10) is supported.
// Therefore, it's recommended to set both Idle and Interval to non-negative values
// in conjunction with a -1 for Count on those old Windows if you intend to customize
// the TCP keep-alive settings.
// By contrast, if only one of Idle and Interval is set to a non-negative value,
// the other will be set to the system default value, and ultimately,
// set both Idle and Interval to negative values if you want to leave them unchanged.
type KeepAliveConfig struct {
	// If Enable is true, keep-alive probes are enabled.
	Enable bool

	// Idle is the time that the connection must be idle before
	// the first keep-alive probe is sent.
	// If zero, a default value of 15 seconds is used.
	Idle time.Duration

	// Interval is the time between keep-alive probes.
	// If zero, a default value of 15 seconds is used.
	Interval time.Duration

	// Count is the maximum number of keep-alive probes that
	// can go unanswered before dropping a connection.
	// If zero, a default value of 9 is used.
	Count int
}

// SyscallConn returns a raw network connection.
// This implements the [syscall.Conn] interface.
func (c *TCPConn) SyscallConn() (syscall.RawConn, error) {
	if !c.ok() {
		return nil, syscall.EINVAL
	}
	return newRawConn(c.fd), nil
}

// ReadFrom implements the [io.ReaderFrom] ReadFrom method.
func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
	if !c.ok() {
		return 0, syscall.EINVAL
	}
	n, err := c.readFrom(r)
	if err != nil && err != io.EOF {
		err = &OpError{Op: "readfrom", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return n, err
}

// WriteTo implements the io.WriterTo WriteTo method.
func (c *TCPConn) WriteTo(w io.Writer) (int64, error) {
	if !c.ok() {
		return 0, syscall.EINVAL
	}
	n, err := c.writeTo(w)
	if err != nil && err != io.EOF {
		err = &OpError{Op: "writeto", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return n, err
}

// CloseRead shuts down the reading side of the TCP connection.
// Most callers should just use Close.
func (c *TCPConn) CloseRead() error {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := c.fd.closeRead(); err != nil {
		return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
}

// CloseWrite shuts down the writing side of the TCP connection.
// Most callers should just use Close.
func (c *TCPConn) CloseWrite() error {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := c.fd.closeWrite(); err != nil {
		return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	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 {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := setLinger(c.fd, sec); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
}

// SetKeepAlive sets whether the operating system should send
// keep-alive messages on the connection.
func (c *TCPConn) SetKeepAlive(keepalive bool) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := setKeepAlive(c.fd, keepalive); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
}

// SetKeepAlivePeriod sets the duration the connection needs to
// remain idle before TCP starts sending keepalive probes.
//
// Note that calling this method on Windows will reset the KeepAliveInterval
// to the default system value, which is normally 1 second.
func (c *TCPConn) SetKeepAlivePeriod(d time.Duration) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := setKeepAliveIdle(c.fd, d); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	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.
func (c *TCPConn) SetNoDelay(noDelay bool) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	if err := setNoDelay(c.fd, noDelay); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
}

// MultipathTCP reports whether the ongoing connection is using MPTCP.
//
// If Multipath TCP is not supported by the host, by the other peer or
// intentionally / accidentally filtered out by a device in between, a
// fallback to TCP will be done. This method does its best to check if
// MPTCP is still being used or not.
//
// On Linux, more conditions are verified on kernels >= v5.16, improving
// the results.
func (c *TCPConn) MultipathTCP() (bool, error) {
	if !c.ok() {
		return false, syscall.EINVAL
	}
	return isUsingMultipathTCP(c.fd), nil
}

func newTCPConn(fd *netFD, keepAliveIdle time.Duration, keepAliveCfg KeepAliveConfig, preKeepAliveHook func(*netFD), keepAliveHook func(KeepAliveConfig)) *TCPConn {
	setNoDelay(fd, true)
	if !keepAliveCfg.Enable && keepAliveIdle >= 0 {
		keepAliveCfg = KeepAliveConfig{
			Enable: true,
			Idle:   keepAliveIdle,
		}
	}
	c := &TCPConn{conn{fd}}
	if keepAliveCfg.Enable {
		if preKeepAliveHook != nil {
			preKeepAliveHook(fd)
		}
		c.SetKeepAliveConfig(keepAliveCfg)
		if keepAliveHook != nil {
			keepAliveHook(keepAliveCfg)
		}
	}
	return c
}

// 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", "tcp6":
	default:
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if raddr == nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialTCP(context.Background(), laddr, raddr)
	if err != nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
}

// TCPListener is a TCP network listener. Clients should typically
// use variables of type [Listener] instead of assuming TCP.
type TCPListener struct {
	fd *netFD
	lc ListenConfig
}

// SyscallConn returns a raw network connection.
// This implements the [syscall.Conn] interface.
//
// The returned RawConn only supports calling Control. Read and
// Write return an error.
func (l *TCPListener) SyscallConn() (syscall.RawConn, error) {
	if !l.ok() {
		return nil, syscall.EINVAL
	}
	return newRawListener(l.fd), nil
}

// AcceptTCP accepts the next incoming call and returns the new
// connection.
func (l *TCPListener) AcceptTCP() (*TCPConn, error) {
	if !l.ok() {
		return nil, syscall.EINVAL
	}
	c, err := l.accept()
	if err != nil {
		return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return c, nil
}

// Accept implements the Accept method in the [Listener] interface; it
// waits for the next call and returns a generic [Conn].
func (l *TCPListener) Accept() (Conn, error) {
	if !l.ok() {
		return nil, syscall.EINVAL
	}
	c, err := l.accept()
	if err != nil {
		return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return c, nil
}

// Close stops listening on the TCP address.
// Already Accepted connections are not closed.
func (l *TCPListener) Close() error {
	if !l.ok() {
		return syscall.EINVAL
	}
	if err := l.close(); err != nil {
		return &OpError{Op: "close", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return nil
}

// Addr returns the listener's network address, a [*TCPAddr].
// The Addr returned is shared by all invocations of Addr, so
// do not modify it.
func (l *TCPListener) Addr() Addr { return l.fd.laddr }

// SetDeadline sets the deadline associated with the listener.
// A zero time value disables the deadline.
func (l *TCPListener) SetDeadline(t time.Time) error {
	if !l.ok() {
		return syscall.EINVAL
	}
	return l.fd.SetDeadline(t)
}

// File returns a copy of the underlying [os.File].
// It is the caller's responsibility to close f when finished.
// Closing l does not affect f, and closing f does not affect l.
//
// The returned os.File's file descriptor is different from the
// connection's. Attempting to change properties of the original
// using this duplicate may or may not have the desired effect.
func (l *TCPListener) File() (f *os.File, err error) {
	if !l.ok() {
		return nil, syscall.EINVAL
	}
	f, err = l.file()
	if err != nil {
		return nil, &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return
}

// 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", "tcp6":
	default:
		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if laddr == nil {
		laddr = &TCPAddr{}
	}
	sl := &sysListener{network: network, address: laddr.String()}
	ln, err := sl.listenTCP(context.Background(), laddr)
	if err != nil {
		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: err}
	}
	return ln, nil
}

// roundDurationUp rounds d to the next multiple of to.
func roundDurationUp(d time.Duration, to time.Duration) time.Duration {
	return (d + to - 1) / to
}