functionnal_example.scala

case class User(firstName: String,
                nickName: Option[String] = None,
                lastName: String,
                happiness: Option[Boolean] = None,
                age : Int)

val allUsers: List[User] = List(
  User("Calvin", Some("Murican"), "Ference", happiness = Some(false), age = 78),
  User("Max", Some("Mad"), "Millette-Coulombe", happiness = Some(true), age = 12),
  User("Johann", lastName = "David", age = 26),
  User("Dom", Some("Pink Scarf"), "Caron", Some(true), age = 32)
)

/**
  * Check on user age.
  */
val isOldEnough: User => Boolean = { _.age >= 18 }

/**
  * Return full name for a user
  */
val getFullName: User => String = {user =>
  s"${user.firstName}" +
    s"${user.nickName.fold("")(nick => s" $nick")}" +
    s" ${user.lastName}"
}

/**
  * Get hello message according to user's mood
  */
val getHelloMessage: Option[Boolean] => String = {
  case Some(happy) =>
    if(happy) "We are happy too! have a good day."
    else      "Have a bad day ! you suck !"
  case _ =>   "We have no clue if you are happy or not but have a good day !"
}

/**
  * print hello message for specific user.
  *
  * @param authz authorization filter. True is not provided.
  */
def printHelloMessage(authz: User => Boolean = User => true): List[User] => Unit = {
  users =>
    users.filter(authz)
      .map(user => (user.happiness, getFullName(user)))
      .map { case (hapiness, name) => s"Hi $name ! ${getHelloMessage(hapiness)}" }
      .foreach(println)
}

//call with filter on age
printHelloMessage(isOldEnough){ allUsers }
//call without filter
printHelloMessage(){ allUsers }