Enum Class trong Kotlin

enum class Color {
    RED, GREEN, BLUE
}
 
fun main() {
    val color = Color.RED
    println(color)       // RED
    println(color.name)  // RED
    println(color.ordinal)  // 0
}

enum class Color(val rgb: Int) {
    RED(0xFF0000),
    GREEN(0x00FF00),
    BLUE(0x0000FF)
}
 
fun main() {
    println(Color.RED.rgb)        // 16711680
    println(Color.RED.rgb.toString(16))  // ff0000
}

enum class Planet(
    val mass: Double,      // kg
    val radius: Double     // m
) {
    MERCURY(3.303e23, 2.4397e6),
    VENUS(4.869e24, 6.0518e6),
    EARTH(5.976e24, 6.37814e6),
    MARS(6.421e23, 3.3972e6);
    
    val surfaceGravity: Double
        get() = 6.67300E-11 * mass / (radius * radius)
}

enum class Operation {
    ADD {
        override fun apply(a: Int, b: Int) = a + b
    },
    SUBTRACT {
        override fun apply(a: Int, b: Int) = a - b
    },
    MULTIPLY {
        override fun apply(a: Int, b: Int) = a * b
    };
    
    abstract fun apply(a: Int, b: Int): Int
}
 
fun main() {
    println(Operation.ADD.apply(5, 3))      // 8
    println(Operation.MULTIPLY.apply(5, 3)) // 15
}

enum class Direction {
    NORTH, SOUTH, EAST, WEST
}
 
fun describe(dir: Direction) = when (dir) {
    Direction.NORTH -> "Going up"
    Direction.SOUTH -> "Going down"
    Direction.EAST -> "Going right"
    Direction.WEST -> "Going left"
}

enum class Color {
    RED, GREEN, BLUE
}
 
fun main() {
    // Lấy tất cả values
    val colors = Color.values()
    colors.forEach { println(it) }
    
    // Parse từ string
    val color = Color.valueOf("RED")
    println(color)  // RED
    
    // entries (Kotlin 1.9+)
    Color.entries.forEach { println(it) }
}

interface Printable {
    fun print()
}
 
enum class Status : Printable {
    PENDING {
        override fun print() = println("⏳ Pending...")
    },
    APPROVED {
        override fun print() = println("✅ Approved!")
    },
    REJECTED {
        override fun print() = println("❌ Rejected!")
    }
}
 
fun main() {
    Status.APPROVED.print()
}

enum class HttpStatus(val code: Int, val description: String) {
    OK(200, "Success"),
    CREATED(201, "Created"),
    BAD_REQUEST(400, "Bad Request"),
    UNAUTHORIZED(401, "Unauthorized"),
    NOT_FOUND(404, "Not Found"),
    SERVER_ERROR(500, "Internal Server Error");
    
    companion object {
        fun fromCode(code: Int): HttpStatus? {
            return entries.find { it.code == code }
        }
    }
}
 
fun main() {
    val status = HttpStatus.fromCode(404)
    println(status?.description)  // Not Found
}

// Enum - instances cố định, giống nhau
enum class Simple { A, B, C }
 
// Sealed - có thể có data khác nhau
sealed class Rich {
    data class WithData(val x: Int) : Rich()
    object NoData : Rich()
}