rwadurian/backend/mpc-system/services/server-party/application/use_cases/participate_keygen.go

package use_cases

import (
	"context"
	"errors"
	"time"

	"github.com/google/uuid"
	"github.com/rwadurian/mpc-system/pkg/crypto"
	"github.com/rwadurian/mpc-system/pkg/logger"
	"github.com/rwadurian/mpc-system/pkg/tss"
	"github.com/rwadurian/mpc-system/services/server-party/domain/entities"
	"github.com/rwadurian/mpc-system/services/server-party/domain/repositories"
	"go.uber.org/zap"
)

var (
	ErrKeygenFailed    = errors.New("keygen failed")
	ErrKeygenTimeout   = errors.New("keygen timeout")
	ErrInvalidSession  = errors.New("invalid session")
	ErrShareSaveFailed = errors.New("failed to save share")
)

// ParticipateKeygenInput contains input for keygen participation
type ParticipateKeygenInput struct {
	SessionID uuid.UUID
	PartyID   string
	JoinToken string
}

// ParticipateKeygenOutput contains output from keygen participation
type ParticipateKeygenOutput struct {
	Success   bool
	KeyShare  *entities.PartyKeyShare
	PublicKey []byte
}

// SessionCoordinatorClient defines the interface for session coordinator communication
type SessionCoordinatorClient interface {
	JoinSession(ctx context.Context, sessionID uuid.UUID, partyID, joinToken string) (*SessionInfo, error)
	ReportCompletion(ctx context.Context, sessionID uuid.UUID, partyID string, publicKey []byte) error
}

// MessageRouterClient defines the interface for message router communication
type MessageRouterClient interface {
	RouteMessage(ctx context.Context, sessionID uuid.UUID, fromParty string, toParties []string, roundNumber int, payload []byte) error
	SubscribeMessages(ctx context.Context, sessionID uuid.UUID, partyID string) (<-chan *MPCMessage, error)
}

// SessionInfo contains session information from coordinator
type SessionInfo struct {
	SessionID    uuid.UUID
	SessionType  string
	ThresholdN   int
	ThresholdT   int
	MessageHash  []byte
	Participants []ParticipantInfo
}

// ParticipantInfo contains participant information
type ParticipantInfo struct {
	PartyID    string
	PartyIndex int
}

// MPCMessage represents an MPC message from the router
type MPCMessage struct {
	FromParty   string
	IsBroadcast bool
	RoundNumber int
	Payload     []byte
}

// ParticipateKeygenUseCase handles keygen participation
type ParticipateKeygenUseCase struct {
	keyShareRepo  repositories.KeyShareRepository
	sessionClient SessionCoordinatorClient
	messageRouter MessageRouterClient
	cryptoService *crypto.CryptoService
}

// NewParticipateKeygenUseCase creates a new participate keygen use case
func NewParticipateKeygenUseCase(
	keyShareRepo repositories.KeyShareRepository,
	sessionClient SessionCoordinatorClient,
	messageRouter MessageRouterClient,
	cryptoService *crypto.CryptoService,
) *ParticipateKeygenUseCase {
	return &ParticipateKeygenUseCase{
		keyShareRepo:  keyShareRepo,
		sessionClient: sessionClient,
		messageRouter: messageRouter,
		cryptoService: cryptoService,
	}
}

// Execute participates in a keygen session using real TSS protocol
func (uc *ParticipateKeygenUseCase) Execute(
	ctx context.Context,
	input ParticipateKeygenInput,
) (*ParticipateKeygenOutput, error) {
	// 1. Join session via coordinator
	sessionInfo, err := uc.sessionClient.JoinSession(ctx, input.SessionID, input.PartyID, input.JoinToken)
	if err != nil {
		return nil, err
	}

	if sessionInfo.SessionType != "keygen" {
		return nil, ErrInvalidSession
	}

	// 2. Find self in participants and build party index map
	var selfIndex int
	partyIndexMap := make(map[string]int)
	for _, p := range sessionInfo.Participants {
		partyIndexMap[p.PartyID] = p.PartyIndex
		if p.PartyID == input.PartyID {
			selfIndex = p.PartyIndex
		}
	}

	// 3. Subscribe to messages
	msgChan, err := uc.messageRouter.SubscribeMessages(ctx, input.SessionID, input.PartyID)
	if err != nil {
		return nil, err
	}

	// 4. Run TSS Keygen protocol
	saveData, publicKey, err := uc.runKeygenProtocol(
		ctx,
		input.SessionID,
		input.PartyID,
		selfIndex,
		sessionInfo.Participants,
		sessionInfo.ThresholdN,
		sessionInfo.ThresholdT,
		msgChan,
		partyIndexMap,
	)
	if err != nil {
		return nil, err
	}

	// 5. Encrypt and save the share
	encryptedShare, err := uc.cryptoService.EncryptShare(saveData, input.PartyID)
	if err != nil {
		return nil, err
	}

	keyShare := entities.NewPartyKeyShare(
		input.PartyID,
		selfIndex,
		input.SessionID,
		sessionInfo.ThresholdN,
		sessionInfo.ThresholdT,
		encryptedShare,
		publicKey,
	)

	if err := uc.keyShareRepo.Save(ctx, keyShare); err != nil {
		return nil, ErrShareSaveFailed
	}

	// 6. Report completion to coordinator
	if err := uc.sessionClient.ReportCompletion(ctx, input.SessionID, input.PartyID, publicKey); err != nil {
		logger.Error("failed to report completion", zap.Error(err))
		// Don't fail - share is saved
	}

	return &ParticipateKeygenOutput{
		Success:   true,
		KeyShare:  keyShare,
		PublicKey: publicKey,
	}, nil
}

// runKeygenProtocol runs the TSS keygen protocol using tss-lib
func (uc *ParticipateKeygenUseCase) runKeygenProtocol(
	ctx context.Context,
	sessionID uuid.UUID,
	partyID string,
	selfIndex int,
	participants []ParticipantInfo,
	n, t int,
	msgChan <-chan *MPCMessage,
	partyIndexMap map[string]int,
) ([]byte, []byte, error) {
	logger.Info("Running keygen protocol",
		zap.String("session_id", sessionID.String()),
		zap.String("party_id", partyID),
		zap.Int("self_index", selfIndex),
		zap.Int("n", n),
		zap.Int("t", t))

	// Create message handler adapter
	msgHandler := &keygenMessageHandler{
		sessionID:     sessionID,
		partyID:       partyID,
		messageRouter: uc.messageRouter,
		msgChan:       make(chan *tss.ReceivedMessage, 100),
		partyIndexMap: partyIndexMap,
	}

	// Start message conversion goroutine
	go msgHandler.convertMessages(ctx, msgChan)

	// Create keygen config
	config := tss.KeygenConfig{
		Threshold:    t,
		TotalParties: n,
		Timeout:      10 * time.Minute,
	}

	// Create party list
	allParties := make([]tss.KeygenParty, len(participants))
	for i, p := range participants {
		allParties[i] = tss.KeygenParty{
			PartyID:    p.PartyID,
			PartyIndex: p.PartyIndex,
		}
	}

	selfParty := tss.KeygenParty{
		PartyID:    partyID,
		PartyIndex: selfIndex,
	}

	// Create keygen session
	session, err := tss.NewKeygenSession(config, selfParty, allParties, msgHandler)
	if err != nil {
		return nil, nil, err
	}

	// Run keygen
	result, err := session.Start(ctx)
	if err != nil {
		return nil, nil, err
	}

	logger.Info("Keygen completed successfully",
		zap.String("session_id", sessionID.String()),
		zap.String("party_id", partyID))

	return result.LocalPartySaveData, result.PublicKeyBytes, nil
}

// keygenMessageHandler adapts MPCMessage channel to tss.MessageHandler
type keygenMessageHandler struct {
	sessionID     uuid.UUID
	partyID       string
	messageRouter MessageRouterClient
	msgChan       chan *tss.ReceivedMessage
	partyIndexMap map[string]int
}

func (h *keygenMessageHandler) SendMessage(ctx context.Context, isBroadcast bool, toParties []string, msgBytes []byte) error {
	return h.messageRouter.RouteMessage(ctx, h.sessionID, h.partyID, toParties, 0, msgBytes)
}

func (h *keygenMessageHandler) ReceiveMessages() <-chan *tss.ReceivedMessage {
	return h.msgChan
}

func (h *keygenMessageHandler) convertMessages(ctx context.Context, inChan <-chan *MPCMessage) {
	for {
		select {
		case <-ctx.Done():
			close(h.msgChan)
			return
		case msg, ok := <-inChan:
			if !ok {
				close(h.msgChan)
				return
			}

			fromIndex, exists := h.partyIndexMap[msg.FromParty]
			if !exists {
				continue
			}

			tssMsg := &tss.ReceivedMessage{
				FromPartyIndex: fromIndex,
				IsBroadcast:    msg.IsBroadcast,
				MsgBytes:       msg.Payload,
			}

			select {
			case h.msgChan <- tssMsg:
			case <-ctx.Done():
				return
			}
		}
	}
}