Panduan Backend

// panduan_backend.kt
// Tour singkat Panduan Backend Kotlin:
// - Ktor: https://ktor.io/docs/
// - Spring Boot: https://spring.io
//
// File ini mendemokan konsep server HTTP sederhana dan pola MVC
// tanpa dependency eksternal — dijalankan di JVM biasa.

import java.util.concurrent.ConcurrentHashMap

// 1. Routing — simulasi router Ktor/Spring
data class Route(val method: String, val path: String, val handler: (Map<String, String>) -> String)

class Router {
    private val routes = mutableListOf<Route>()

    fun get(path: String, handler: (Map<String, String>) -> String) {
        routes.add(Route("GET", path, handler))
    }

    fun post(path: String, handler: (Map<String, String>) -> String) {
        routes.add(Route("POST", path, handler))
    }

    fun dispatch(method: String, path: String, params: Map<String, String> = emptyMap()): String {
        val route = routes.find { it.method == method && it.path == path }
            ?: return "404 Not Found: $method $path"
        return route.handler(params)
    }
}

// 2. Service layer — bisnis logika
class PenggunaService {
    private val storage = ConcurrentHashMap<Int, String>()

    fun simpan(id: Int, nama: String) { storage[id] = nama }
    fun ambil(id: Int): String? = storage[id]
    fun hapus(id: Int): Boolean = storage.remove(id) != null
    fun daftar(): List<Pair<Int, String>> = storage.entries.map { it.key to it.value }.sortedBy { it.first }
}

// 3. Request / Response model
data class PenggunaRequest(val id: Int, val nama: String)
data class PenggunaResponse(val id: Int, val nama: String, val sukses: Boolean)

fun main() {
    println("=== Panduan Backend Kotlin ===")
    println("Ktor: https://ktor.io/docs/   |   Spring Boot: https://spring.io")
    println()

    val service = PenggunaService()
    val router = Router()

    // Definisi route
    router.get("/users") { _ ->
        val users = service.daftar()
        if (users.isEmpty()) "[]"
        else users.joinToString(prefix = "[", postfix = "]") { "{\"id\":${it.first},\"nama\":\"${it.second}\"}" }
    }
    router.post("/users") { params ->
        val id = params["id"]?.toIntOrNull() ?: -1
        val nama = params["nama"] ?: ""
        if (id < 0 || nama.isEmpty()) {
            "400 Bad Request"
        } else {
            service.simpan(id, nama)
            "201 Created: {\"id\":$id,\"nama\":\"$nama\"}"
        }
    }
    router.get("/users/{id}") { params ->
        val id = params["id"]?.toIntOrNull() ?: -1
        service.ambil(id)?.let { "200 OK: {\"id\":$id,\"nama\":\"$it\"}" }
            ?: "404 Not Found"
    }

    println("--- 1. POST /users ---")
    println(router.dispatch("POST", "/users", mapOf("id" to "1", "nama" to "Budi")))
    println(router.dispatch("POST", "/users", mapOf("id" to "2", "nama" to "Siti")))
    println(router.dispatch("POST", "/users", mapOf("id" to "3", "nama" to "Dewi")))

    println()
    println("--- 2. GET /users ---")
    println(router.dispatch("GET", "/users"))

    println()
    println("--- 3. GET /users/{id} ---")
    println(router.dispatch("GET", "/users/{id}", mapOf("id" to "2")))
    println(router.dispatch("GET", "/users/{id}", mapOf("id" to "999")))

    println()
    println("--- 4. GET /unknown ---")
    println(router.dispatch("GET", "/unknown"))

    println()
    println("--- 5. Framework backend populer ---")
    val frameworks = listOf(
        Triple("Ktor", "JetBrains", "Lightweight, coroutine-native, DSL routing"),
        Triple("Spring Boot", "VMware/Pivotal", "Mature, dependency injection, annotation-based"),
        Triple("http4k", "Community", "Functional HTTP, serverless-ready"),
        Triple("Javalin", "Community", "Simple, Express.js-like untuk Kotlin/Java"),
        Triple("Quarkus", "Red Hat", "Cloud-native, low memory, hot reload"),
        Triple("Micronaut", "OCI", "Compile-time DI, fast startup, low overhead")
    )
    frameworks.forEach { (nama, pembuat, desk) ->
        println("  ${nama.padEnd(14)} ($pembuat): $desk")
    }

    println()
    println("--- 6. Perbandingan Ktor vs Spring Boot ---")
    val perbandingan = listOf(
        "Startup:    Ktor <1s, Spring Boot 2-5s",
        "Memory:     Ktor ~50MB, Spring Boot ~200MB",
        "Learning:   Ktor mudah, Spring Boot kompleks (banyak konsep)",
        "Ecosystem:  Ktor kecil, Spring Boot masif (Spring Security, Data, Batch)",
        "Coroutine:  Ktor native, Spring Boot 5+ mendukung",
        "Skala:      Ktor microservice, Spring Boot enterprise monolith"
    )
    perbandingan.forEach { println("  $it") }

    println()
    println("--- 7. Panduan belajar backend Kotlin ---")
    val panduan = listOf(
        "1. Mulai dengan Ktor 'Hello World' (2 menit jalan)",
        "2. Pelajari routing DSL: get(), post(), dll",
        "3. Tambahkan persistence (Exposed, JOOQ, atau Hibernate)",
        "4. Tambahkan JSON serialization (kotlinx.serialization)",
        "5. Tambahkan autentikasi (JWT, OAuth2)",
        "6. Deploy ke container (Docker, Kubernetes)",
        "7. Untuk enterprise: migrasi ke Spring Boot bila butuh ekosistem"
    )
    panduan.forEach { println("  $it") }
}

=== Panduan Backend Kotlin ===
Ktor: https://ktor.io/docs/   |   Spring Boot: https://spring.io

--- 1. POST /users ---
201 Created: {"id":1,"nama":"Budi"}
201 Created: {"id":2,"nama":"Siti"}
201 Created: {"id":3,"nama":"Dewi"}

--- 2. GET /users ---
[{"id":1,"nama":"Budi"}, {"id":2,"nama":"Siti"}, {"id":3,"nama":"Dewi"}]

--- 3. GET /users/{id} ---
200 OK: {"id":2,"nama":"Siti"}
404 Not Found

--- 4. GET /unknown ---
404 Not Found: GET /unknown

--- 5. Framework backend populer ---
  Ktor           (JetBrains): Lightweight, coroutine-native, DSL routing
  Spring Boot    (VMware/Pivotal): Mature, dependency injection, annotation-based
  http4k         (Community): Functional HTTP, serverless-ready
  Javalin        (Community): Simple, Express.js-like untuk Kotlin/Java
  Quarkus        (Red Hat): Cloud-native, low memory, hot reload
  Micronaut      (OCI): Compile-time DI, fast startup, low overhead

--- 6. Perbandingan Ktor vs Spring Boot ---
  Startup:    Ktor <1s, Spring Boot 2-5s
  Memory:     Ktor ~50MB, Spring Boot ~200MB
  Learning:   Ktor mudah, Spring Boot kompleks (banyak konsep)
  Ecosystem:  Ktor kecil, Spring Boot masif (Spring Security, Data, Batch)
  Coroutine:  Ktor native, Spring Boot 5+ mendukung
  Skala:      Ktor microservice, Spring Boot enterprise monolith

--- 7. Panduan belajar backend Kotlin ---
  1. Mulai dengan Ktor 'Hello World' (2 menit jalan)
  2. Pelajari routing DSL: get(), post(), dll
  3. Tambahkan persistence (Exposed, JOOQ, atau Hibernate)
  4. Tambahkan JSON serialization (kotlinx.serialization)
  5. Tambahkan autentikasi (JWT, OAuth2)
  6. Deploy ke container (Docker, Kubernetes)
  7. Untuk enterprise: migrasi ke Spring Boot bila butuh ekosistem