package zioutil

// Inspired by transport implementation of buptczq/gotun.
// Some code was copied from buptczq/gotun.

import (
	"context"
	"io"
	"strings"
	"sync"
	"time"
)

type BatchTransporterGlobal struct {
	bufferPool sync.Pool
}

func NewBatchTransporterGlobal(bufsize int) *BatchTransporterGlobal {
	return &BatchTransporterGlobal{
		bufferPool: sync.Pool{New: func() interface{} {
			return make([]byte, bufsize)
		}},
	}
}

type BatchTransporter struct {
	btg                    *BatchTransporterGlobal
	rwc1, rwc2             io.ReadWriteCloser
	ReadTime12, ReadTime21 time.Time
	Error12, Error21       error
	Bytes12, Bytes21       int64
	Start, Stop            time.Time
}

func NewBatchTrasporter(global *BatchTransporterGlobal, start time.Time, rwc1, rwc2 io.ReadWriteCloser) *BatchTransporter {
	return &BatchTransporter{
		btg:        global,
		rwc1:       rwc1,
		rwc2:       rwc2,
		ReadTime12: time.Now(),
		ReadTime21: time.Now(),
		Start:      start,
	}
}

func (bt *BatchTransporter) copyBuffer(ctx context.Context, dst io.Writer, src io.Reader, buf []byte, is12 bool) (cnt int64, err error) {
	nftc := false
	for {
		select {
		case <-ctx.Done():
			return
		default:
		}
		nr, errr := src.Read(buf)
		if !nftc {
			nftc = true
			if is12 {
				bt.ReadTime12 = time.Now()
			} else {
				bt.ReadTime21 = time.Now()
			}
		}
		if nr > 0 {
			nw, errw := dst.Write(buf[0:nr])
			if nw > 0 {
				cnt += int64(nw)
			}
			if errw != nil {
				err = errw
				break
			}
			if nr != nw {
				err = io.ErrShortWrite
				break
			}
		}
		if errr != nil {
			if errr != io.EOF {
				err = errr
			}
			break
		}
	}
	return cnt, err
}

func (bt *BatchTransporter) Copy() {
	ctx, cancel := context.WithCancel(context.Background())
	wg := &sync.WaitGroup{}
	wg.Add(2)
	go func() {
		defer wg.Done()
		buf := bt.btg.bufferPool.Get().([]byte)
		defer bt.btg.bufferPool.Put(buf)
		bt.Bytes12, bt.Error12 = bt.copyBuffer(ctx, bt.rwc2, bt.rwc1, buf, true)
		cancel()
		bt.rwc2.Close()
	}()
	go func() {
		defer wg.Done()
		buf := bt.btg.bufferPool.Get().([]byte)
		defer bt.btg.bufferPool.Put(buf)
		bt.Bytes21, bt.Error21 = bt.copyBuffer(ctx, bt.rwc1, bt.rwc2, buf, false)
		cancel()
		bt.rwc1.Close()
	}()
	wg.Wait()
	bt.Stop = time.Now()
}

func filterNetworkConnClosedError(err error) error {
	if err == nil {
		return nil
	}
	if strings.Contains(err.Error(), "use of closed network connection") {
		return nil
	}
	return err
}

func (bt *BatchTransporter) NoNetworkConnClosedError() error {
	err12 := filterNetworkConnClosedError(bt.Error12)
	err21 := filterNetworkConnClosedError(bt.Error21)
	if err12 == nil {
		err12 = err21
	}
	return err12
}

func (bt *BatchTransporter) PickError() error {
	err12 := bt.Error12
	err21 := bt.Error21
	if err12 == nil {
		err12 = err21
	}
	return err12
}

func (bt *BatchTransporter) GetError12() error {
	return bt.Error12
}

func (bt *BatchTransporter) GetError21() error {
	return bt.Error21
}