AutoMappingJavelinPaths.kt

import infrastructure.Json
import io.javalin.Javalin
import io.javalin.http.Context
import io.javalin.http.HandlerType
import io.javalin.plugin.json.FromJsonMapper
import io.javalin.plugin.json.JavalinJson
import io.javalin.plugin.json.ToJsonMapper

fun main() {
    val app: Javalin = Javalin.create().start(7000)

    JavalinJson.toJsonMapper = object : ToJsonMapper {
        override fun map(obj: Any): String = Json.toJson(obj)
    }
    JavalinJson.fromJsonMapper = object : FromJsonMapper {
        override fun <T> map(json: String, targetClass: Class<T>): T = Json.fromJsonWithClass(json, targetClass)
    }
    app.get("/") { ctx ->
        ctx.result("Hello, World!")
    }
    app.exception(Exception::class.java) { e, ctx ->
        e.printStackTrace()
    }
    app.register(EmployeeController())
}

fun String.makeHandlerPath() : String = this.replace("//","/").trim().removeSuffix("/")

fun <T : Any> Javalin.register(controller:T) {
    val kClass = controller.javaClass
    val controllerPath = (kClass.annotations.first { it is Root } as Root).value
    //lets get actions
    kClass.declaredMethods.forEach {
        when (val annotation = it.annotations.firstOrNull()) {
            is Get -> {
                val x = annotation.value
                val handlerPath = "$controllerPath/$x".makeHandlerPath()
                println("Registering path = $handlerPath")
                this.addHandler(HandlerType.GET,
                        handlerPath) { ctx -> it.invoke(controller,ctx)}
            }
            is Post -> this.addHandler(HandlerType.POST,
                    "$controllerPath/$annotation.value".makeHandlerPath()) { ctx -> it.invoke(ctx)}
        }
    }
}

annotation class Get(val value: String="")
annotation class Post(val value: String)
annotation class Root(val value: String)

@Root("/employee")
class EmployeeController {

    sealed class Device {
        data class Laptop(val model: String) : Device()
        data class Phone(val model: String, val carrier: String) : Device()
    }

    class Employee(val id: Int, val device: List<Device>)

    private val employees = listOf(
            Employee(1, listOf(Device.Laptop("Macbook Pro"), Device.Phone("IPhone", "T-Mobile"))),
            Employee(2, listOf(Device.Laptop("Macbook Pro"), Device.Phone("IPhone", "T-Mobile")))
    )
    @Get()
    fun allEmployees(ctx : Context) {
        ctx.json(employees)
    }

    @Get("/:id")
    fun byId(ctx:Context) {
        val result = when(ctx.pathParam("id").toInt()){
            1 -> employees[0]
            2 -> employees[1]
            else -> throw Exception("Invalid id")
        }
        ctx.json(result)
    }

}