function references

fun fibonacci(n: Int): Int {
    var a = 1
    var b = 1
    for (i in 2 until n) {
        val temp = a + b
        a = b
        b = temp
    }
    return b
}

fun square(n: Int): Int = n * n

fun cube(n: Int): Int = n * n * n

fun collatzDepth(n: Int): Int {
    var current = n
    var depth = 1
    while (current != 1) {
        depth++
        current = if (current % 2 == 0) {
            current / 2
        } else {
            3 * current + 1
        }
    }
    return depth
}

data class MenuItem(val text: String, val function: (Int) -> Int)

object Menu {
    val items = mutableListOf<MenuItem>()

    init {
        items.add(MenuItem("Square", ::square))
        items.add(MenuItem("Cube", ::cube))
        items.add(MenuItem("Fibonacci", ::fibonacci))
        items.add(MenuItem("Collatz Depth", ::collatzDepth))
    }
}

fun main() {
    do {
        // Print the menu of functions as a numbered list
        Menu.items.forEachIndexed { index, menuItem ->
            println("${index + 1}. ${menuItem.text}")
        }

        println("Enter the number of the function to execute, or 0 to exit:")
        val inputFunction = readLine()?.toIntOrNull() ?: 0

        if (inputFunction == 0) break

        if (inputFunction !in 1..Menu.items.size) {
            println("Invalid selection. Please try again.")
            continue
        }

        println("Enter an integer argument for the function:")
        val inputArgument = readLine()?.toIntOrNull()
        if (inputArgument == null) {
            println("Invalid input. Please enter an integer.")
            continue
        }

        val selectedMenuItem = Menu.items[inputFunction - 1]
        val result = selectedMenuItem.function(inputArgument)
        println("Result: $result")

    } while (true)

    println("Exiting...")
}