/**
 * 第 6 章 · 类与对象 — 综合示例
 *
 * 涵盖：data class / 主构造 + init / 计算属性 / lazy /
 *      继承 + override / object 单例 / companion object /
 *      sealed class / 解构声明
 */

// ========== 1. data class ==========
data class User(val id: String, val name: String, val age: Int)

// ========== 2. 普通 class + 主构造 + init + 计算属性 ==========
class Rectangle(val width: Double, val height: Double) {
    init {
        require(width > 0 && height > 0) { "宽高必须为正数" }
    }
    val area: Double get() = width * height
    val perimeter: Double get() = 2 * (width + height)
    override fun toString() = "Rect(${width}x${height}, area=$area)"
}

// ========== 3. lateinit + by lazy ==========
class Service {
    lateinit var dependency: String
    val database: String by lazy {
        println("  ⏳ 第一次访问，初始化数据库...")
        "DB-Connection-${System.currentTimeMillis()}"
    }
}

// ========== 4. 继承 ==========
open class Animal(val name: String) {
    open fun sound() = "..."
    fun introduce() = "我是 $name，${sound()}"
}
class Dog(name: String) : Animal(name) {
    override fun sound() = "汪汪!"
}
class Cat(name: String) : Animal(name) {
    override fun sound() = "喵~"
}

// ========== 5. 接口 + 多实现 ==========
interface Drawable { fun draw(): String }
interface Named { val name: String }

class Circle(override val name: String, val r: Double) : Drawable, Named {
    override fun draw() = "画一个圆 $name (r=$r)"
}

// ========== 6. object 单例 ==========
object DatabaseManager {
    private var connectionCount = 0
    fun connect(): String {
        connectionCount++
        return "Connection #$connectionCount"
    }
    fun stats() = "总连接数: $connectionCount"
}

// ========== 7. companion object ==========
class HttpClient private constructor(val baseUrl: String) {
    companion object {
        const val DEFAULT_TIMEOUT = 5000
        fun create(baseUrl: String) = HttpClient(baseUrl)
    }
}

// ========== 8. sealed class ==========
sealed class Result<out T> {
    data class Success<T>(val data: T) : Result<T>()
    data class Failure(val error: String) : Result<Nothing>()
    object Loading : Result<Nothing>()
}

fun handle(r: Result<String>): String = when (r) {
    is Result.Success -> "✅ 成功: ${r.data}"
    is Result.Failure -> "❌ 失败: ${r.error}"
    Result.Loading -> "⏳ 加载中..."
}

fun main() {
    println("=== 1. data class ===")
    val u1 = User("u001", "Alice", 25)
    val u2 = User("u001", "Alice", 25)
    val u3 = u1.copy(age = 26)
    println("u1 = $u1")
    println("u1 == u2 ? ${u1 == u2}")    // true
    println("u1 === u2 ? ${u1 === u2}")  // false
    println("u3 = $u3")
    val (id, name, age) = u1
    println("解构: id=$id, name=$name, age=$age")

    println("\n=== 2. 普通类 + 计算属性 ===")
    val rect = Rectangle(3.0, 4.0)
    println(rect)
    println("周长 = ${rect.perimeter}")
    try {
        Rectangle(-1.0, 2.0)
    } catch (e: IllegalArgumentException) {
        println("⚠️ 校验失败: ${e.message}")
    }

    println("\n=== 3. lateinit 和 lazy ===")
    val s = Service()
    s.dependency = "MyDep"
    println("dependency = ${s.dependency}")
    println("准备访问 database... (会触发懒初始化)")
    println("database = ${s.database}")
    println("再次访问 database (用缓存)")
    println("database = ${s.database}")

    println("\n=== 4. 继承 ===")
    val animals: List<Animal> = listOf(Dog("旺财"), Cat("咪咪"), Animal("X"))
    animals.forEach { println(it.introduce()) }

    println("\n=== 5. 接口 + 多实现 ===")
    val c = Circle("c1", 5.0)
    println(c.draw())
    println("name (from Named) = ${c.name}")

    println("\n=== 6. object 单例 ===")
    DatabaseManager.connect()
    DatabaseManager.connect()
    DatabaseManager.connect()
    println(DatabaseManager.stats())

    println("\n=== 7. companion object ===")
    val client = HttpClient.create("https://api.example.com")
    println("客户端: ${client.baseUrl}")
    println("默认超时: ${HttpClient.DEFAULT_TIMEOUT}ms")

    println("\n=== 8. sealed class + when ===")
    listOf<Result<String>>(
        Result.Success("OK"),
        Result.Failure("网络错误"),
        Result.Loading,
    ).forEach { println(handle(it)) }
}