package grpcapi

import (
	"context"
	"errors"

	"galaxy/gateway/internal/session"
	gatewayv1 "galaxy/gateway/proto/galaxy/gateway/v1"

	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

// resolvedSessionFromContext returns the session record previously attached to
// ctx by the session-lookup gateway wrapper.
func resolvedSessionFromContext(ctx context.Context) (session.Record, bool) {
	if ctx == nil {
		return session.Record{}, false
	}

	record, ok := ctx.Value(resolvedSessionContextKey{}).(session.Record)
	if !ok {
		return session.Record{}, false
	}

	return cloneSessionRecord(record), true
}

// sessionLookupService resolves the authenticated session from SessionCache
// after envelope parsing succeeds and before later auth steps run.
type sessionLookupService struct {
	gatewayv1.UnimplementedEdgeGatewayServer

	delegate gatewayv1.EdgeGatewayServer
	cache    session.Cache
}

// ExecuteCommand resolves the cached session for req and only then forwards it
// to the configured delegate with the resolved session attached to ctx.
func (s sessionLookupService) ExecuteCommand(ctx context.Context, req *gatewayv1.ExecuteCommandRequest) (*gatewayv1.ExecuteCommandResponse, error) {
	record, err := s.lookupSession(ctx)
	if err != nil {
		return nil, err
	}

	return s.delegate.ExecuteCommand(context.WithValue(ctx, resolvedSessionContextKey{}, cloneSessionRecord(record)), req)
}

// SubscribeEvents resolves the cached session for req and only then forwards it
// to the configured delegate with the resolved session attached to the stream
// context.
func (s sessionLookupService) SubscribeEvents(req *gatewayv1.SubscribeEventsRequest, stream grpc.ServerStreamingServer[gatewayv1.GatewayEvent]) error {
	record, err := s.lookupSession(stream.Context())
	if err != nil {
		return err
	}

	return s.delegate.SubscribeEvents(req, resolvedSessionContextStream{
		ServerStreamingServer: stream,
		ctx:                   context.WithValue(stream.Context(), resolvedSessionContextKey{}, cloneSessionRecord(record)),
	})
}

// newSessionLookupService wraps delegate with the session-cache lookup gate.
func newSessionLookupService(delegate gatewayv1.EdgeGatewayServer, cache session.Cache) gatewayv1.EdgeGatewayServer {
	return sessionLookupService{
		delegate: delegate,
		cache:    cache,
	}
}

func (s sessionLookupService) lookupSession(ctx context.Context) (session.Record, error) {
	envelope, ok := parsedEnvelopeFromContext(ctx)
	if !ok {
		return session.Record{}, status.Error(codes.Internal, "authenticated request context is incomplete")
	}

	record, err := s.cache.Lookup(ctx, envelope.DeviceSessionID)
	switch {
	case err == nil:
	case errors.Is(err, session.ErrNotFound):
		return session.Record{}, status.Error(codes.Unauthenticated, "unknown device session")
	default:
		return session.Record{}, status.Error(codes.Unavailable, "session cache is unavailable")
	}

	if record.Status == session.StatusRevoked {
		return session.Record{}, status.Error(codes.FailedPrecondition, "device session is revoked")
	}

	return cloneSessionRecord(record), nil
}

func cloneSessionRecord(record session.Record) session.Record {
	cloned := record
	if record.RevokedAtMS != nil {
		value := *record.RevokedAtMS
		cloned.RevokedAtMS = &value
	}

	return cloned
}

type resolvedSessionContextKey struct{}

type resolvedSessionContextStream struct {
	grpc.ServerStreamingServer[gatewayv1.GatewayEvent]
	ctx context.Context
}

func (s resolvedSessionContextStream) Context() context.Context {
	if s.ctx == nil {
		return context.Background()
	}

	return s.ctx
}

type unavailableSessionCache struct{}

func (unavailableSessionCache) Lookup(context.Context, string) (session.Record, error) {
	return session.Record{}, errors.New("session cache is unavailable")
}

var _ gatewayv1.EdgeGatewayServer = sessionLookupService{}