gRPC Swift with Build Plugin

import SwiftUI
import GRPCCore
import GRPCNIOTransportHTTP2
import GRPCProtobuf

// MARK: - Shared Client Manager

@MainActor
final class GRPCClientManager: ObservableObject {
    private var _client: GRPCClient?

    func client() throws -> GRPCClient {
        if let existing = _client { return existing }
        let transport = try HTTP2ClientTransport.Posix(
            target: .ipv4(host: "127.0.0.1", port: 1234),
            transportSecurity: .plaintext
        )
        let client = GRPCClient(transport: transport)
        _client = client
        // Run the client in a detached task so it stays alive
        Task.detached { try await client.run() }
        return client
    }

    func disconnect() {
        _client?.beginGracefulShutdown()
        _client = nil
    }
}

// MARK: - Race model (mirrors generated Protobuf message fields)

struct Race: Identifiable {
    let id = UUID()
    let name: String
    let location: String
    let laps: Int
}

// MARK: - Race Schedule View
// NOTE: SwiftKart_SwiftKartClient and SwiftKart_ListRacesRequest are
// generated by the GRPCProtobufGenerator build plugin from a .proto file.

struct RaceScheduleView: View {
    @EnvironmentObject var clientManager: GRPCClientManager
    @State private var races: [Race] = []
    @State private var errorMessage: String?

    var body: some View {
        NavigationStack {
            List(races) { race in
                VStack(alignment: .leading, spacing: 4) {
                    Text(race.name).font(.headline)
                    Text(race.location).font(.subheadline).foregroundStyle(.secondary)
                    Text("\(race.laps) laps").font(.caption).foregroundStyle(.tertiary)
                }
            }
            .navigationTitle("Upcoming Races")
            .overlay {
                if let error = errorMessage {
                    ContentUnavailableView(error, systemImage: "wifi.exclamationmark")
                }
            }
        }
        .task { await fetchSchedule() }
    }

    private func fetchSchedule() async {
        do {
            let grpcClient = try clientManager.client()
            // SwiftKart_SwiftKartClient is auto-generated by the build plugin
            let swiftKartClient = SwiftKart_SwiftKartClient(wrapping: grpcClient)
            var request = SwiftKart_ListRacesRequest()
            request.limit = 20
            let response = try await swiftKartClient.listRaces(request)
            races = response.races.map {
                Race(name: $0.name, location: $0.location, laps: Int($0.laps))
            }
        } catch {
            errorMessage = error.localizedDescription
        }
    }
}

// MARK: - App Entry Point

@main
struct SwiftKartApp: App {
    @StateObject private var clientManager = GRPCClientManager()
    @Environment(\.scenePhase) private var scenePhase

    var body: some Scene {
        WindowGroup {
            RaceScheduleView()
                .environmentObject(clientManager)
        }
        .onChange(of: scenePhase) { _, newPhase in
            if newPhase == .background {
                clientManager.disconnect()
            }
        }
    }
}