package rmq

import (
	"github.com/cockroachdb/errors"

	"github.com/milvus-io/milvus/pkg/mq/mqimpl/rocksmq/client"
	"github.com/milvus-io/milvus/pkg/mq/mqimpl/rocksmq/server"
	"github.com/milvus-io/milvus/pkg/streaming/util/message"
	"github.com/milvus-io/milvus/pkg/streaming/walimpls"
	"github.com/milvus-io/milvus/pkg/streaming/walimpls/helper"
)

var _ walimpls.ScannerImpls = (*scannerImpl)(nil)

// newScanner creates a new scanner.
func newScanner(
	scannerName string,
	exclude *rmqID,
	consumer client.Consumer,
) *scannerImpl {
	s := &scannerImpl{
		ScannerHelper: helper.NewScannerHelper(scannerName),
		exclude:       exclude,
		consumer:      consumer,
		msgChannel:    make(chan message.ImmutableMessage),
	}
	go s.executeConsume()
	return s
}

// scannerImpl is the implementation of ScannerImpls for rmq.
type scannerImpl struct {
	*helper.ScannerHelper
	exclude    *rmqID
	consumer   client.Consumer
	msgChannel chan message.ImmutableMessage
}

// Chan returns the channel of message.
func (s *scannerImpl) Chan() <-chan message.ImmutableMessage {
	return s.msgChannel
}

// Close the scanner, release the underlying resources.
// Return the error same with `Error`
func (s *scannerImpl) Close() error {
	err := s.ScannerHelper.Close()
	s.consumer.Close()
	return err
}

// executeConsume consumes the message from the consumer.
func (s *scannerImpl) executeConsume() (err error) {
	defer func() {
		s.Finish(err)
		close(s.msgChannel)
	}()

	for {
		select {
		case <-s.Context().Done():
			return nil
		case msg, ok := <-s.consumer.Chan():
			if !ok {
				return errors.New("mq consumer unexpected channel closed")
			}
			msgID := rmqID(msg.ID().(*server.RmqID).MessageID)
			// record the last message id to avoid repeated consume message.
			// and exclude message id should be filterred.
			if s.exclude == nil || !s.exclude.EQ(msgID) {
				msg := message.NewImmutableMesasge(msgID, msg.Payload(), msg.Properties())
				select {
				case <-s.Context().Done():
					return nil
				case s.msgChannel <- msg:
				}
			}
		}
	}
}