/**
 * Kotlin Fundamentals — Practical Exercises
 * Mobile Application Development | SUZA | Semester II 2025/2026
 *
 * Run each exercise from main(). Uncomment the line you want to test.
 * You can run individual files at https://play.kotlinlang.org
 */

fun main() {
    // ex01_variables()
    // ex02_gradeCalculator()
    // ex03_fizzBuzz()
    // ex04_listOperations()
    // ex05_studentClass()
    // ex06_nullSafety()
    // ex07_dataClassAndCopy()
    // ex08_higherOrderFunctions()
    // ex09_whenExpression()
    // ex10_extensionFunction()
}

// 1. Variables — declare, print, and swap two values without a temp variable.
fun ex01_variables() {
    var a = 5
    var b = 10
    // TODO: swap a and b using one line (hint: destructuring)
    a = b.also { b = a }
    println("a=$a, b=$b")
}

// 2. Grade Calculator using "when"
fun grade(score: Int): String = when {
    score >= 80 -> "A"
    score >= 70 -> "B"
    score >= 60 -> "C"
    score >= 50 -> "D"
    else        -> "F"
}
fun ex02_gradeCalculator() {
    listOf(95, 72, 58, 33).forEach { println("$it -> ${grade(it)}") }
}

// 3. FizzBuzz 1..30
fun ex03_fizzBuzz() {
    for (i in 1..30) {
        println(when {
            i % 15 == 0 -> "FizzBuzz"
            i % 3 == 0  -> "Fizz"
            i % 5 == 0  -> "Buzz"
            else        -> i.toString()
        })
    }
}

// 4. List Operations
fun ex04_listOperations() {
    val nums = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    println("Sum = ${nums.sum()}")
    println("Evens = ${nums.filter { it % 2 == 0 }}")
    println("Doubled = ${nums.map { it * 2 }}")
    println("Sum of squares = ${nums.sumOf { it * it }}")
    println("Max = ${nums.maxOrNull()}")
}

// 5. Student class with method
class Student(val name: String, var gpa: Double) {
    fun standing(): String = when {
        gpa >= 3.5 -> "Dean's List"
        gpa >= 2.0 -> "Good Standing"
        else       -> "Probation"
    }
    override fun toString() = "$name (GPA=$gpa, ${standing()})"
}
fun ex05_studentClass() {
    val students = listOf(Student("Amina", 3.8), Student("Juma", 2.1), Student("Zahra", 1.7))
    students.forEach(::println)
}

// 6. Null Safety
fun ex06_nullSafety() {
    val name: String? = null
    println("Length: ${name?.length ?: 0}")      // Elvis operator
    val upper = name?.uppercase() ?: "UNKNOWN"    // default
    println("Upper: $upper")
    // val boom = name!!.length                   // would throw NPE — avoid
}

// 7. Data class, copy(), destructuring
data class Book(val title: String, val author: String, val pages: Int)
fun ex07_dataClassAndCopy() {
    val b1 = Book("Clean Code", "Robert Martin", 464)
    val b2 = b1.copy(pages = 500)
    val (t, a, p) = b2
    println("$t by $a, $p pages")
    println("b1 == b2? ${b1 == b2}")              // data class equality
}

// 8. Higher-order functions
fun <T, R> transform(list: List<T>, f: (T) -> R): List<R> = list.map(f)
fun ex08_higherOrderFunctions() {
    val words = listOf("suza", "mobile", "compose")
    println(transform(words) { it.uppercase() })
    println(transform(words, String::length))
}

// 9. "when" with ranges, types, predicates
fun describe(obj: Any): String = when (obj) {
    is Int -> "Int $obj"
    is String -> "String of length ${obj.length}"
    in 1.0..10.0 -> "Double in 1..10"
    null -> "null"
    else -> "Something else"
}
fun ex09_whenExpression() {
    listOf(5, "hello", 3.14, null, listOf(1)).forEach { println(describe(it ?: "null")) }
}

// 10. Extension function
fun String.reverseWords(): String = split(" ").reversed().joinToString(" ")
fun ex10_extensionFunction() {
    println("hello world from suza".reverseWords())
}