case class Person(name: String, age: Int)


def searchForJohn(personList:List[Person]):List[Person] = {

  personList match {
    case Nil => Nil
    case p :: ps if(p.name.map(_.toLower).startsWith("john") ) => p :: searchForJohn(ps)
    case _ :: ps => searchForJohn(ps)
  }
}

val people = List(Person("Jon Stewart", 56), Person("Zorro", 100), Person("John Stuart Mill", 66), Person("David Hume", 65), Person("David Bowie", 69))
searchForJohn(people)

//if we look at the majority of this function it documents
//how to traverse the structure of a list
//not about what we're deciding to return
//what if we could encapsulate that into a function and pass it
//to our function

//functions in scala are first order, they can be
// treated as values and passed around into functions
// and returned from functions

def searchFor(predicate: Person => Boolean)(personList:List[Person]):List[Person] = {
  personList match {
    case Nil => Nil
    case p :: ps if(predicate(p)) => p :: searchFor(predicate)(ps)
    case _ :: ps => searchFor(predicate)(ps)
  }
}

val searchForJohn2: List[Person] => List[Person] = searchFor((p:Person) => p.name.map(_.toLower).startsWith("john"))(_)
searchForJohn2(people)

//We've curried the function above, we've partially applied it
// in order to create a new function we can use as many times as we want

val searchForDavid: List[Person] => List[Person] = searchFor((p:Person) => p.name.map(_.toLower).startsWith("david"))(_)
searchForDavid(people)

//HOF lets us concentrate on each concern in the right place
//SearchFor deals with walking the data structure
//The predicate we pass in is the logic for deciding if we
// want to keep it