// 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 (
	"context"
	"sync"
)

// TODO: recycle *pollDesc
func newPollDesc(fd int) *pollDesc {
	pd, op := &pollDesc{}, &FDOperator{}
	op.FD = fd
	pd.operator = op
	return pd
}

type pollDesc struct {
	once     sync.Once
	operator *FDOperator

	// The write event is OneShot, then mark the writable to skip duplicate calling.
	writeTrigger chan struct{}
	closeTrigger chan struct{}
}

// WaitWrite .
// TODO: implement - poll support timeout hung up.
func (pd *pollDesc) WaitWrite(ctx context.Context) error {
	var err error
	pd.once.Do(func() {
		pd.writeTrigger = make(chan struct{})
		pd.closeTrigger = make(chan struct{})
		pd.operator.OnWrite = func(p Poll) error {
			select {
			case <-pd.writeTrigger:
			default:
				close(pd.writeTrigger)
			}
			return nil
		}
		pd.operator.OnHup = func(p Poll) error {
			close(pd.closeTrigger)
			return nil
		}
		// add ET|Write|Hup
		pd.operator.poll = pollmanager.Pick()
		err = pd.operator.Control(PollWritable)
		if err != nil {
			pd.operator.Control(PollDetach)
		}
	})
	if err != nil {
		return err
	}

	select {
	case <-ctx.Done():
		pd.operator.Control(PollDetach)
		return mapErr(ctx.Err())
	case <-pd.closeTrigger:
		return Exception(ErrConnClosed, "by peer")
	case <-pd.writeTrigger:
		// if writable, check hup by select
		select {
		case <-pd.closeTrigger:
			return Exception(ErrConnClosed, "by peer")
		default:
			return nil
		}
	}
}