package notify

import (
	"context"
	"net"
	"sync"
	"sync/atomic"
	"time"
)

const (
	bulkBatchMaxPayloads = 16
)

const (
	bulkBatchRequestQueued int32 = iota
	bulkBatchRequestStarted
	bulkBatchRequestCanceled
)

type bulkBatchRequestState struct {
	value atomic.Int32
}

type bulkBatchRequest struct {
	ctx      context.Context
	payload  []byte
	deadline time.Time
	done     chan error
	state    *bulkBatchRequestState
}

type bulkBatchSender struct {
	binding *transportBinding
	reqCh   chan bulkBatchRequest
	stopCh  chan struct{}
	doneCh  chan struct{}

	stopOnce sync.Once
	errMu    sync.Mutex
	err      error
}

func newBulkBatchSender(binding *transportBinding) *bulkBatchSender {
	sender := &bulkBatchSender{
		binding: binding,
		reqCh:   make(chan bulkBatchRequest, bulkBatchMaxPayloads*4),
		stopCh:  make(chan struct{}),
		doneCh:  make(chan struct{}),
	}
	go sender.run()
	return sender
}

func (s *bulkBatchSender) submit(ctx context.Context, payload []byte) error {
	if s == nil {
		return errTransportDetached
	}
	if ctx == nil {
		ctx = context.Background()
	}
	req := bulkBatchRequest{
		ctx:     ctx,
		payload: payload,
		done:    make(chan error, 1),
		state:   &bulkBatchRequestState{},
	}
	if deadline, ok := ctx.Deadline(); ok {
		req.deadline = deadline
	}
	if err := s.errSnapshot(); err != nil {
		return err
	}
	select {
	case <-ctx.Done():
		return normalizeStreamDeadlineError(ctx.Err())
	case <-s.stopCh:
		return s.stoppedErr()
	case s.reqCh <- req:
	}
	select {
	case err := <-req.done:
		return err
	case <-ctx.Done():
		if req.tryCancel() {
			return normalizeStreamDeadlineError(ctx.Err())
		}
		return <-req.done
	}
}

func (s *bulkBatchSender) run() {
	defer close(s.doneCh)
	for {
		req, ok := s.nextRequest()
		if !ok {
			return
		}
		batch := []bulkBatchRequest{req}
	drain:
		for len(batch) < bulkBatchMaxPayloads {
			select {
			case <-s.stopCh:
				s.failPending(s.stoppedErr())
				return
			case next := <-s.reqCh:
				batch = append(batch, next)
			default:
				break drain
			}
		}
		active, payloads := activeBulkBatchRequests(batch)
		if len(active) == 0 {
			continue
		}
		deadline := bulkBatchRequestsEarliestDeadline(active)
		err := s.flush(payloads, deadline)
		if err != nil {
			s.setErr(err)
			for _, item := range active {
				item.done <- err
			}
			s.failPending(err)
			return
		}
		for _, item := range active {
			item.done <- err
		}
	}
}

func (s *bulkBatchSender) nextRequest() (bulkBatchRequest, bool) {
	select {
	case <-s.stopCh:
		s.failPending(s.stoppedErr())
		return bulkBatchRequest{}, false
	case req := <-s.reqCh:
		return req, true
	}
}

func activeBulkBatchRequests(batch []bulkBatchRequest) ([]bulkBatchRequest, [][]byte) {
	active := make([]bulkBatchRequest, 0, len(batch))
	payloads := make([][]byte, 0, len(batch))
	for _, item := range batch {
		if !item.tryStart() {
			item.done <- item.canceledErr()
			continue
		}
		if err := item.contextErr(); err != nil {
			item.done <- err
			continue
		}
		active = append(active, item)
		payloads = append(payloads, item.payload)
	}
	return active, payloads
}

func bulkBatchRequestsEarliestDeadline(batch []bulkBatchRequest) time.Time {
	var deadline time.Time
	for _, item := range batch {
		if item.deadline.IsZero() {
			continue
		}
		if deadline.IsZero() || item.deadline.Before(deadline) {
			deadline = item.deadline
		}
	}
	return deadline
}

func (r bulkBatchRequest) contextErr() error {
	if r.ctx == nil {
		return nil
	}
	select {
	case <-r.ctx.Done():
		return normalizeStreamDeadlineError(r.ctx.Err())
	default:
		return nil
	}
}

func (r bulkBatchRequest) tryStart() bool {
	if r.state == nil {
		return true
	}
	return r.state.value.CompareAndSwap(bulkBatchRequestQueued, bulkBatchRequestStarted)
}

func (r bulkBatchRequest) tryCancel() bool {
	if r.state == nil {
		return false
	}
	return r.state.value.CompareAndSwap(bulkBatchRequestQueued, bulkBatchRequestCanceled)
}

func (r bulkBatchRequest) canceledErr() error {
	if err := r.contextErr(); err != nil {
		return err
	}
	return context.Canceled
}

func (s *bulkBatchSender) flush(payloads [][]byte, deadline time.Time) error {
	if s == nil || s.binding == nil {
		return errTransportDetached
	}
	queue := s.binding.queueSnapshot()
	if queue == nil {
		return errTransportFrameQueueUnavailable
	}
	return s.binding.withConnWriteLockDeadline(deadline, func(conn net.Conn) error {
		return writeFramedPayloadBatchUnlocked(conn, queue, payloads)
	})
}

func (s *bulkBatchSender) stop() {
	if s == nil {
		return
	}
	s.stopOnce.Do(func() {
		s.setErr(errTransportDetached)
		close(s.stopCh)
	})
	<-s.doneCh
}

func (s *bulkBatchSender) failPending(err error) {
	for {
		select {
		case item := <-s.reqCh:
			item.done <- err
		default:
			return
		}
	}
}

func (s *bulkBatchSender) setErr(err error) {
	if s == nil || err == nil {
		return
	}
	s.errMu.Lock()
	if s.err == nil {
		s.err = err
	}
	s.errMu.Unlock()
}

func (s *bulkBatchSender) errSnapshot() error {
	if s == nil {
		return errTransportDetached
	}
	s.errMu.Lock()
	defer s.errMu.Unlock()
	return s.err
}

func (s *bulkBatchSender) stoppedErr() error {
	if err := s.errSnapshot(); err != nil {
		return err
	}
	return errTransportDetached
}