// Copyright 2021 CloudWeGo Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package netpoll

import (
	"sync"
	"sync/atomic"
	"syscall"
	"time"
)

const (
	defaultZeroCopyTimeoutSec = 60
)

// connection is the implement of Connection
type connection struct {
	netFD
	onEvent
	locker
	operator        *FDOperator
	readTimeout     time.Duration
	readTimer       *time.Timer
	readTrigger     chan struct{}
	waitReadSize    int32
	writeTrigger    chan error
	inputBuffer     *LinkBuffer
	outputBuffer    *LinkBuffer
	inputBarrier    *barrier
	outputBarrier   *barrier
	supportZeroCopy bool
	maxSize         int // The maximum size of data between two Release().
	bookSize        int // The size of data that can be read at once.
}

var _ Connection = &connection{}
var _ Reader = &connection{}
var _ Writer = &connection{}

// Reader implements Connection.
func (c *connection) Reader() Reader {
	return c
}

// Writer implements Connection.
func (c *connection) Writer() Writer {
	return c
}

// IsActive implements Connection.
func (c *connection) IsActive() bool {
	return c.isCloseBy(none)
}

// SetIdleTimeout implements Connection.
func (c *connection) SetIdleTimeout(timeout time.Duration) error {
	if timeout > 0 {
		return c.SetKeepAlive(int(timeout.Seconds()))
	}
	return nil
}

// SetReadTimeout implements Connection.
func (c *connection) SetReadTimeout(timeout time.Duration) error {
	if timeout >= 0 {
		c.readTimeout = timeout
	}
	return nil
}

// ------------------------------------------ implement zero-copy reader ------------------------------------------

// Next implements Connection.
func (c *connection) Next(n int) (p []byte, err error) {
	if err = c.waitRead(n); err != nil {
		return p, err
	}
	return c.inputBuffer.Next(n)
}

// Peek implements Connection.
func (c *connection) Peek(n int) (buf []byte, err error) {
	if err = c.waitRead(n); err != nil {
		return buf, err
	}
	return c.inputBuffer.Peek(n)
}

// Skip implements Connection.
func (c *connection) Skip(n int) (err error) {
	if err = c.waitRead(n); err != nil {
		return err
	}
	return c.inputBuffer.Skip(n)
}

// Release implements Connection.
func (c *connection) Release() (err error) {
	// Check inputBuffer length first to reduce contention in mux situation.
	// c.operator.do competes with c.inputs/c.inputAck
	if c.inputBuffer.Len() == 0 && c.operator.do() {
		maxSize := c.inputBuffer.calcMaxSize()
		// Set the maximum value of maxsize equal to mallocMax to prevent GC pressure.
		if maxSize > mallocMax {
			maxSize = mallocMax
		}

		if maxSize > c.maxSize {
			c.maxSize = maxSize
		}
		// Double check length to reset tail node
		if c.inputBuffer.Len() == 0 {
			c.inputBuffer.resetTail(c.maxSize)
		}
		c.operator.done()
	}
	return c.inputBuffer.Release()
}

// Slice implements Connection.
func (c *connection) Slice(n int) (r Reader, err error) {
	if err = c.waitRead(n); err != nil {
		return nil, err
	}
	return c.inputBuffer.Slice(n)
}

// Len implements Connection.
func (c *connection) Len() (length int) {
	return c.inputBuffer.Len()
}

// Until implements Connection.
func (c *connection) Until(delim byte) (line []byte, err error) {
	var n, l int
	for {
		if err = c.waitRead(n + 1); err != nil {
			// return all the data in the buffer
			line, _ = c.inputBuffer.Next(c.inputBuffer.Len())
			return
		}

		l = c.inputBuffer.Len()
		i := c.inputBuffer.indexByte(delim, n)
		if i < 0 {
			n = l //skip all exists bytes
			continue
		}
		return c.Next(i + 1)
	}
}

// ReadString implements Connection.
func (c *connection) ReadString(n int) (s string, err error) {
	if err = c.waitRead(n); err != nil {
		return s, err
	}
	return c.inputBuffer.ReadString(n)
}

// ReadBinary implements Connection.
func (c *connection) ReadBinary(n int) (p []byte, err error) {
	if err = c.waitRead(n); err != nil {
		return p, err
	}
	return c.inputBuffer.ReadBinary(n)
}

// ReadByte implements Connection.
func (c *connection) ReadByte() (b byte, err error) {
	if err = c.waitRead(1); err != nil {
		return b, err
	}
	return c.inputBuffer.ReadByte()
}

// ------------------------------------------ implement zero-copy writer ------------------------------------------

// Malloc implements Connection.
func (c *connection) Malloc(n int) (buf []byte, err error) {
	return c.outputBuffer.Malloc(n)
}

// MallocLen implements Connection.
func (c *connection) MallocLen() (length int) {
	return c.outputBuffer.MallocLen()
}

// Flush will send all malloc data to the peer,
// so must confirm that the allocated bytes have been correctly assigned.
//
// Flush first checks whether the out buffer is empty.
// If empty, it will call syscall.Write to send data directly,
// otherwise the buffer will be sent asynchronously by the epoll trigger.
func (c *connection) Flush() error {
	if !c.IsActive() || !c.lock(flushing) {
		return Exception(ErrConnClosed, "when flush")
	}
	defer c.unlock(flushing)
	c.outputBuffer.Flush()
	return c.flush()
}

// MallocAck implements Connection.
func (c *connection) MallocAck(n int) (err error) {
	return c.outputBuffer.MallocAck(n)
}

// Append implements Connection.
func (c *connection) Append(w Writer) (err error) {
	return c.outputBuffer.Append(w)
}

// WriteString implements Connection.
func (c *connection) WriteString(s string) (n int, err error) {
	return c.outputBuffer.WriteString(s)
}

// WriteBinary implements Connection.
func (c *connection) WriteBinary(b []byte) (n int, err error) {
	return c.outputBuffer.WriteBinary(b)
}

// WriteDirect implements Connection.
func (c *connection) WriteDirect(p []byte, remainCap int) (err error) {
	return c.outputBuffer.WriteDirect(p, remainCap)
}

// WriteByte implements Connection.
func (c *connection) WriteByte(b byte) (err error) {
	return c.outputBuffer.WriteByte(b)
}

// ------------------------------------------ implement net.Conn ------------------------------------------

// Read behavior is the same as net.Conn, it will return io.EOF if buffer is empty.
func (c *connection) Read(p []byte) (n int, err error) {
	l := len(p)
	if l == 0 {
		return 0, nil
	}
	if err = c.waitRead(1); err != nil {
		return 0, err
	}
	if has := c.inputBuffer.Len(); has < l {
		l = has
	}
	src, err := c.inputBuffer.Next(l)
	n = copy(p, src)
	if err == nil {
		err = c.inputBuffer.Release()
	}
	return n, err
}

// Write will Flush soon.
func (c *connection) Write(p []byte) (n int, err error) {
	if !c.IsActive() || !c.lock(flushing) {
		return 0, Exception(ErrConnClosed, "when write")
	}
	defer c.unlock(flushing)

	dst, _ := c.outputBuffer.Malloc(len(p))
	n = copy(dst, p)
	c.outputBuffer.Flush()
	err = c.flush()
	return n, err
}

// Close implements Connection.
func (c *connection) Close() error {
	return c.onClose()
}

// ------------------------------------------ private ------------------------------------------

var barrierPool = sync.Pool{
	New: func() interface{} {
		return &barrier{
			bs:  make([][]byte, barriercap),
			ivs: make([]syscall.Iovec, barriercap),
		}
	},
}

// init initialize the connection with options
func (c *connection) init(conn Conn, opts *options) (err error) {
	// init buffer, barrier, finalizer
	c.readTrigger = make(chan struct{}, 1)
	c.writeTrigger = make(chan error, 1)
	c.bookSize, c.maxSize = block1k/2, pagesize
	c.inputBuffer, c.outputBuffer = NewLinkBuffer(pagesize), NewLinkBuffer()
	c.inputBarrier, c.outputBarrier = barrierPool.Get().(*barrier), barrierPool.Get().(*barrier)

	c.initNetFD(conn) // conn must be *netFD{}
	c.initFDOperator()
	c.initFinalizer()

	syscall.SetNonblock(c.fd, true)
	// enable TCP_NODELAY by default
	switch c.network {
	case "tcp", "tcp4", "tcp6":
		setTCPNoDelay(c.fd, true)
	}
	// check zero-copy
	if setZeroCopy(c.fd) == nil && setBlockZeroCopySend(c.fd, defaultZeroCopyTimeoutSec, 0) == nil {
		c.supportZeroCopy = true
	}

	// connection initialized and prepare options
	return c.onPrepare(opts)
}

func (c *connection) initNetFD(conn Conn) {
	if nfd, ok := conn.(*netFD); ok {
		c.netFD = *nfd
		return
	}
	c.netFD = netFD{
		fd:         conn.Fd(),
		localAddr:  conn.LocalAddr(),
		remoteAddr: conn.RemoteAddr(),
	}
}

func (c *connection) initFDOperator() {
	op := allocop()
	op.FD = c.fd
	op.OnRead, op.OnWrite, op.OnHup = nil, nil, c.onHup
	op.Inputs, op.InputAck = c.inputs, c.inputAck
	op.Outputs, op.OutputAck = c.outputs, c.outputAck

	// if connection has been registered, must reuse poll here.
	if c.pd != nil && c.pd.operator != nil {
		op.poll = c.pd.operator.poll
	}
	c.operator = op
}

func (c *connection) initFinalizer() {
	c.AddCloseCallback(func(connection Connection) error {
		c.stop(flushing)
		// stop the finalizing state to prevent conn.fill function to be performed
		c.stop(finalizing)
		freeop(c.operator)
		c.netFD.Close()
		c.closeBuffer()
		return nil
	})
}

func (c *connection) triggerRead() {
	select {
	case c.readTrigger <- struct{}{}:
	default:
	}
}

func (c *connection) triggerWrite(err error) {
	select {
	case c.writeTrigger <- err:
	default:
	}
}

// waitRead will wait full n bytes.
func (c *connection) waitRead(n int) (err error) {
	if n <= c.inputBuffer.Len() {
		return nil
	}
	atomic.StoreInt32(&c.waitReadSize, int32(n))
	defer atomic.StoreInt32(&c.waitReadSize, 0)
	if c.readTimeout > 0 {
		return c.waitReadWithTimeout(n)
	}
	// wait full n
	for c.inputBuffer.Len() < n {
		if c.IsActive() {
			<-c.readTrigger
			continue
		}
		// confirm that fd is still valid.
		if atomic.LoadUint32(&c.netFD.closed) == 0 {
			return c.fill(n)
		}
		return Exception(ErrConnClosed, "wait read")
	}
	return nil
}

// waitReadWithTimeout will wait full n bytes or until timeout.
func (c *connection) waitReadWithTimeout(n int) (err error) {
	// set read timeout
	if c.readTimer == nil {
		c.readTimer = time.NewTimer(c.readTimeout)
	} else {
		c.readTimer.Reset(c.readTimeout)
	}

	for c.inputBuffer.Len() < n {
		if !c.IsActive() {
			// cannot return directly, stop timer before !
			// confirm that fd is still valid.
			if atomic.LoadUint32(&c.netFD.closed) == 0 {
				err = c.fill(n)
			} else {
				err = Exception(ErrConnClosed, "wait read")
			}
			break
		}

		select {
		case <-c.readTimer.C:
			// double check if there is enough data to be read
			if c.inputBuffer.Len() >= n {
				return nil
			}
			return Exception(ErrReadTimeout, c.remoteAddr.String())
		case <-c.readTrigger:
			continue
		}
	}

	// clean timer.C
	if !c.readTimer.Stop() {
		<-c.readTimer.C
	}
	return err
}

// fill data after connection is closed.
func (c *connection) fill(need int) (err error) {
	if !c.lock(finalizing) {
		return ErrConnClosed
	}
	defer c.unlock(finalizing)

	var n int
	for {
		n, err = readv(c.fd, c.inputs(c.inputBarrier.bs), c.inputBarrier.ivs)
		c.inputAck(n)
		err = c.eofError(n, err)
		if err != nil {
			break
		}
	}
	if c.inputBuffer.Len() >= need {
		return nil
	}
	return err
}

func (c *connection) eofError(n int, err error) error {
	if err == syscall.EINTR {
		return nil
	}
	if n == 0 && err == nil {
		return Exception(ErrEOF, "")
	}
	return err
}