AwesomeKotlin.kt

package io.jadu

import java.io.File

data class User(
    val name: String?,
    val email: String?,
    val role: String,
    val age: Int
)

class Repository {
    fun getUser(id: Int): User? {
        return when(id) {
            1 -> User("Alice", "[email protected]", "admin", 30)
            2 -> User("Bob", null, "user", 25)
            3 -> User(null, "[email protected]", "guest", 15)
            else -> null
        }
    }

    fun getAllUsers(): List<User> {
        return listOf(
            User("Alice", "[email protected]", "admin", 30),
            User("Bob", null, "user", 25),
            User("Charlie", "[email protected]", "admin", 35),
            User("Dave", "[email protected]", "guest", 12)
        )
    }
}

fun sendMessage(email: String) {
    println(">> Sent email to $email")
}

fun logError(message: String) {
    println(">> ERROR: $message")
}

fun executeNullCheckOld(id: Int) {
    val repo = Repository()
    val user = repo.getUser(id)

    if (user != null) {
        val email = user.email
        if (email != null) {
            sendMessage(email)
        } else {
            logError("Email is missing")
        }
    } else {
        logError("User not found")
    }
}

fun executeNullCheckNew(id: Int) {
    val repo = Repository()

    repo.getUser(id)?.email?.let {
        sendMessage(it)
    } ?: logError("User or Email missing")
}








fun getRoleDescriptionOld(user: User): String {
    if (user.role == "admin") {
        return "Has full access"
    } else if (user.role == "user") {
        return "Has limited access"
    } else {
        return "Read only"
    }
}

fun getRoleDescriptionNew(user: User) = when (user.role) {
    "admin" -> "Has full access"
    "user" -> "Has limited access"
    else -> "Read only"
}



fun processAdminsOld() {
    val repo = Repository()
    val users = repo.getAllUsers()
    val adminNames = ArrayList<String>()

    for (u in users) {
        if (u.role == "admin" && u.age > 20) {
            val name = u.name
            if (name != null) {
                adminNames.add(name.uppercase())
            }
        }
    }

    for (name in adminNames) {
        println(name)
    }
}

fun processAdminsNew() {
    val repo = Repository()

    repo.getAllUsers()
        .filter { it.role == "admin" && it.age > 20 }
        .mapNotNull { it.name?.uppercase() }  // A, null, b -> A, B
        .forEach { println(it) }
}




fun configureFileOld() {
    val file = File("test.txt")
    file.setReadable(true)
    file.setWritable(true)
    file.setExecutable(false)
    println("File config done: ${file.name}")
}

fun configureFileNew() {
    val file = File("test.txt").apply {
        setReadable(true)
        setWritable(true)
        setExecutable(false)
    }
    println("File config done: ${file.name}")
}