public async Task SearchAsync()

in src/Microsoft.Health.Fhir.Shared.Core/Features/Operations/Everything/PatientEverythingService.cs [89:202]
85 lines of code
26 McCabe index (conditional complexity)

        public async Task<SearchResult> SearchAsync(
            string resourceId,
            PartialDateTime start,
            PartialDateTime end,
            PartialDateTime since,
            string type,
            string continuationToken,
            CancellationToken cancellationToken)
        {
            EverythingOperationContinuationToken token = string.IsNullOrEmpty(continuationToken)
                ? new EverythingOperationContinuationToken()
                : EverythingOperationContinuationToken.FromJson(ContinuationTokenConverter.Decode(continuationToken));

            if (token == null || token.Phase < 0 || token.Phase > 3)
            {
                throw new BadRequestException(Core.Resources.InvalidContinuationToken);
            }

            SearchResult searchResult;
            string encodedInternalContinuationToken = string.IsNullOrEmpty(token.InternalContinuationToken)
                ? null
                : ContinuationTokenConverter.Encode(token.InternalContinuationToken);
            IReadOnlyList<string> types = string.IsNullOrEmpty(type) ? new List<string>() : type.SplitByOrSeparator();

            // We will need to store the id of the patient that links to this one if we are processing a "seealso" link
            var parentPatientId = resourceId;

            // If we are currently processing a "seealso" link, set the resource id to the id of the link.
            resourceId = token.IsProcessingSeeAlsoLink ? token.CurrentSeeAlsoLinkId : resourceId;

            var phase = token.Phase;
            switch (phase)
            {
                // Phase 0 gets the patient and any resources it references directly.
                case 0:
                    searchResult = await SearchIncludes(resourceId, parentPatientId, since, types, token, cancellationToken);

                    if (!searchResult.Results.Any())
                    {
                        phase = 1;
                        goto case 1;
                    }

                    break;

                // Phase 1 gets the resources in the patient's compartment that have date/time values.
                case 1:
                    // If both start and end are null, we can just perform a regular compartment search in Phase 2.
                    if (start == null && end == null)
                    {
                        phase = 2;
                        goto case 2;
                    }

                    searchResult = await SearchCompartmentWithDate(resourceId, start, end, since, types, encodedInternalContinuationToken, cancellationToken);
                    if (!searchResult.Results.Any())
                    {
                        phase = 2;
                        goto case 2;
                    }

                    break;

                // Phase 2 gets the resources in the patient's compartment that do not have date/time values.
                case 2:
                    searchResult = start == null && end == null
                        ? await SearchCompartment(resourceId, parentPatientId, since, types, encodedInternalContinuationToken, token, cancellationToken)
                        : await SearchCompartmentWithoutDate(resourceId, parentPatientId, since, types, encodedInternalContinuationToken, token, cancellationToken);

                    if (!searchResult.Results.Any())
                    {
                        phase = 3;
                        goto case 3;
                    }

                    break;

                // Phase 3 gets the patient's devices.
                case 3:
                    searchResult = await SearchRevinclude(resourceId, since, types, encodedInternalContinuationToken, cancellationToken);
                    break;
                default:
                    throw new EverythingOperationException(string.Format(Core.Resources.InvalidEverythingOperationPhase, phase), HttpStatusCode.BadRequest);
            }

            string nextContinuationToken;
            if (searchResult.ContinuationToken != null)
            {
                // Keep processing the remaining results for the current phase.
                token.InternalContinuationToken = searchResult.ContinuationToken;

                nextContinuationToken = token.ToJson();
            }
            else if (phase < 3)
            {
                token.Phase = phase + 1;
                token.InternalContinuationToken = null;

                nextContinuationToken = token.ToJson();
            }
            else
            {
                nextContinuationToken = await CheckForNextSeeAlsoLinkAndSetToken(parentPatientId, token, cancellationToken);

                // If the last phase returned no results and there are links to process
                if (!searchResult.Results.Any() && nextContinuationToken != null)
                {
                    // Run patient $everything on links.
                    return await SearchAsync(parentPatientId, start, end, since, type, ContinuationTokenConverter.Encode(nextContinuationToken), cancellationToken);
                }
            }

            return new SearchResult(searchResult.Results, nextContinuationToken, searchResult.SortOrder, searchResult.UnsupportedSearchParameters);
        }