Dependency Injection

// Demo Dependency Injection: constructor, setter, field injection; manual vs framework.

interface ApiClient {
    fun get(path: String): String
}

class HttpApiClient : ApiClient {
    override fun get(path: String): String = "GET $path -> 200 OK"
}

class MockApiClient : ApiClient {
    override fun get(path: String): String = "MOCK $path -> data"
}

class Service1 {
    // 1. Constructor injection (rekomendasi)
    private val api: ApiClient
    constructor(api: ApiClient) {
        this.api = api
    }
    fun jalankan() = println("Service1: ${api.get("/users")}")
}

class Service2 {
    private lateinit var api: ApiClient
    // 2. Setter injection
    fun setApi(api: ApiClient) { this.api = api }
    fun jalankan() = println("Service2: ${api.get("/orders")}")
}

class Service3 {
    // 3. Field injection (anti-pola; hanya untuk demo)
    var api: ApiClient? = null
    fun jalankan() {
        val a = api ?: throw IllegalStateException("api belum diset")
        println("Service3: ${a.get("/items")}")
    }
}

// === Manual container sederhana ===
class ContainerManual {
    val instances = mutableMapOf<String, Any>()

    inline fun <reified T : Any> register(instance: T) {
        instances[T::class.simpleName ?: "Unknown"] = instance
    }

    @Suppress("UNCHECKED_CAST")
    inline fun <reified T : Any> resolve(): T =
        instances[T::class.simpleName] as T
}

// === Framework-like container (mirip Koin module) ===
object AppContainer {
    lateinit var apiClient: ApiClient
    lateinit var service1: Service1
    lateinit var service2: Service2

    fun init(api: ApiClient) {
        apiClient = api
        service1 = Service1(apiClient)
        service2 = Service2().also { it.setApi(apiClient) }
    }
}

fun main() {
    println("=== Demo Dependency Injection ===")

    println("--- 1. Constructor injection ---")
    val s1 = Service1(HttpApiClient())
    s1.jalankan()

    println()
    println("--- 2. Setter injection ---")
    val s2 = Service2()
    s2.setApi(MockApiClient())
    s2.jalankan()

    println()
    println("--- 3. Field injection (kurang disarankan) ---")
    val s3 = Service3()
    s3.api = HttpApiClient()
    s3.jalankan()

    println()
    println("--- 4. Manual container ---")
    val container = ContainerManual()
    val api = HttpApiClient()
    container.register(api)
    container.register(Service1(api))
    container.resolve<Service1>().jalankan()

    println()
    println("--- 5. Framework-like container ---")
    AppContainer.init(MockApiClient())
    AppContainer.service1.jalankan()
    AppContainer.service2.jalankan()
}

=== Demo Dependency Injection ===
--- 1. Constructor injection ---
Service1: GET /users -> 200 OK

--- 2. Setter injection ---
Service2: MOCK /orders -> data

--- 3. Field injection (kurang disarankan) ---
Service3: GET /items -> 200 OK

--- 4. Manual container ---
Service1: GET /users -> 200 OK

--- 5. Framework-like container ---
Service1: MOCK /users -> data
Service2: MOCK /orders -> data