package v1

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"sync"

	remotev1 "code.icb4dc0.de/buildr/api/generated/remote/v1"

	"github.com/google/uuid"
)

var (
	ErrNoReplyMsgID      = errors.New("no repliesTo set - cannot handle message")
	ErrNoMatchingRequest = errors.New("no matching request for given message id")
)

func NewRequestResponseClient(logger *slog.Logger, sender StreamSender[*remotev1.ExecutionServerMessage]) *RequestResponseClient {
	return &RequestResponseClient{
		logger:   logger,
		sender:   sender,
		requests: make(map[uuid.UUID]chan *remotev1.ExecutionClientMessage),
	}
}

type RequestResponseClient struct {
	sender   StreamSender[*remotev1.ExecutionServerMessage]
	logger   *slog.Logger
	requests map[uuid.UUID]chan *remotev1.ExecutionClientMessage
	lock     sync.Mutex
}

func (rrc *RequestResponseClient) DispatchMessages(receiver StreamReceiver[*remotev1.ExecutionClientMessage]) (errs chan error) {
	errs = make(chan error)

	go func() {
		for {
			msg, err := receiver.Receive()
			if err != nil {
				if errors.Is(err, io.EOF) {
					slog.Default().Info("Closing request response client")
					return
				}
				errs <- err
				return
			}

			rrc.logger.Debug("Dispatching message")
			repliesTo, ok := msg.Meta.(*remotev1.ExecutionClientMessage_RepliesTo)
			if !ok {
				errs <- ErrNoReplyMsgID
				continue
			}

			msgID, err := uuid.FromBytes(repliesTo.RepliesTo)
			if err != nil {
				errs <- err
				continue
			}

			rrc.logger.Debug("Checking for pending request", slog.String("msgId", msgID.String()))
			rrc.lock.Lock()
			waitingChan, ok := rrc.requests[msgID]
			if !ok {
				rrc.lock.Unlock()
				errs <- fmt.Errorf("%w: %s", ErrNoMatchingRequest, msgID)
				continue
			}

			delete(rrc.requests, msgID)
			rrc.lock.Unlock()

			rrc.logger.Debug("Replying to pending request", slog.String("msgId", msgID.String()))
			waitingChan <- msg
		}
	}()

	return errs
}

func (rrc *RequestResponseClient) Send(
	ctx context.Context,
	req *remotev1.ExecutionServerMessage,
) (resp *remotev1.ExecutionClientMessage, err error) {
	var (
		msgID    = uuid.New()
		respChan = make(chan *remotev1.ExecutionClientMessage)
	)

	req.Meta = &remotev1.ExecutionServerMessage_MessageId{
		MessageId: uuidBytes(msgID),
	}
	rrc.lock.Lock()
	rrc.requests[msgID] = respChan
	rrc.lock.Unlock()

	defer rrc.cleanRequest(msgID)

	if err := rrc.sender.Send(req); err != nil {
		return nil, err
	}

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case resp := <-respChan:
		switch unwrap := resp.Envelope.(type) {
		case *remotev1.ExecutionClientMessage_Error:
			if errMsg := unwrap.Error.Error; errMsg != "" {
				return nil, errors.New(unwrap.Error.Error)
			}
			//nolint:nilnil // fine here
			return nil, nil
		default:
			return resp, nil
		}
	}
}

func (rrc *RequestResponseClient) cleanRequest(id uuid.UUID) {
	rrc.lock.Lock()
	defer rrc.lock.Unlock()

	c, ok := rrc.requests[id]
	if ok {
		close(c)
		delete(rrc.requests, id)
	}
}

func uuidBytes(uid uuid.UUID) []byte {
	b, _ := uid.MarshalBinary()
	return b
}