func fetchPackageReleaseInfo()

in Sources/PackageRegistryExample/Controllers/PackageReleasesController.swift [58:111]
42 lines of code
7 McCabe index (conditional complexity)

    func fetchPackageReleaseInfo(request: Request) async throws -> Response {
        let package = try request.getPackageParam(validating: true)
        // Client may append .json extension to the URI (4.2)
        let version = try request.getVersionParam(removingExtension: ".json")

        let release = try await self.packageReleases.get(package: package, version: version)
        guard release.status != .deleted else {
            throw PackageRegistry.APIError.resourceGone("\(package)@\(version) has been removed")
        }

        let allReleases = try await self.packageReleases.list(for: package)
        guard !allReleases.isEmpty else {
            throw PackageRegistry.APIError.serverError("\(package) should have at least one release")
        }

        let sourceArchive: PackageRegistryModel.PackageResource?
        do {
            sourceArchive = try await self.packageResources.get(package: package, version: version, type: .sourceArchive)
        } catch DataAccessError.notFound {
            sourceArchive = nil
        } catch {
            throw error
        }

        let sortedReleases = allReleases.sorted { $0.version > $1.version }
        // The requested version is not found
        guard let releaseIndex = sortedReleases.firstIndex(where: { $0.version == version }) else {
            throw PackageRegistry.APIError.serverError("\(package)'s releases should include \(version)")
        }

        var links = [String]()
        // Link to the latest published release - `list` is already sorted with most recent first
        let latest = allReleases.first! // !-safe since list is not empty at this point
        links.append("<\(self.configuration.api.baseURL)/\(package.scope)/\(package.name)/\(latest.version)>; rel=\"latest-version\"")
        // Link to the next published release, if one exists
        if let successor = releaseIndex == 0 ? nil : sortedReleases[releaseIndex - 1] {
            links.append("<\(self.configuration.api.baseURL)/\(package.scope)/\(package.name)/\(successor.version)>; rel=\"successor-version\"")
        }
        // Link to the previously published release, if one exists
        if let predecessor = releaseIndex == (sortedReleases.count - 1) ? nil : sortedReleases[releaseIndex + 1] {
            links.append("<\(self.configuration.api.baseURL)/\(package.scope)/\(package.name)/\(predecessor.version)>; rel=\"predecessor-version\"")
        }

        var headers = HTTPHeaders()
        headers.setLinkHeader(links)

        let response = PackageReleaseInfo(
            id: package.description,
            version: version.description,
            resource: sourceArchive.map { PackageReleaseInfo.ReleaseResource.sourceArchive(checksum: $0.checksum) },
            metadata: PackageReleaseMetadata(repositoryURL: release.repositoryURL, commitHash: release.commitHash)
        )
        return Response.json(status: .ok, body: response, headers: headers)
    }