/**
* A ridiculously complex example of tail recursion in Kotlin
* This goes deep into function programming in addition to doing
* simple tail recursion
*@author gtowell
* Created Aug 2021
 */
import java.time.LocalDateTime 
import java.time.Duration

@Suppress("UNUSED_PARAMETER")
fun main(args: Array<String>) {
    looper(3);
}

// Do everything idx times
fun looper(idx: Int) {
    if (idx<0) {  return; }
    println("NOT TR")
    // the thing in {} is an anonymous function that is passed to the timer function
    timer( { println(sum(10000)) } );
    println("TR")
    timer( { println(sumTR(10000)) } );
    looper(idx-1);
}

//When passing / returning functions as arguements, I like to define types
// This one is weird as functional programing goes, because it does
// not return value!!
typealias WKLambda = ()->Unit;

/*
* Time how long the passed in function takes to complete.
* @param funcc -- the function to be timed
* @return the time required to complete the passed in function.  
 */
fun timer (funcc: WKLambda) : Duration {
    val nw = LocalDateTime.now()
    funcc()
    val dur = Duration.between(nw, LocalDateTime.now())
    println("The operation took ${dur} ms")
    return dur
}

// add up numbers from 1 to N
// Not tagged as tail recursive
fun sum(max:Long, sss:Long=0) : Long {
    if (max<=0) return sss;
    return sum(max-1, sss+max);
}

// add up numbers from 1 to N
// Tagged as tail recursive
// Otherwise identical to summ
tailrec fun sumTR(max:Long, sss:Long=0) : Long {
    if (max<=0) return sss;
    return sumTR(max-1, sss+max);
}