/**
 * 第 7 章 · 集合 & 函数式操作 — 综合示例
 *
 * 涵盖：map/filter/reduce/groupBy/partition/zip/chunked/windowed/Sequence
 */

data class Order(
    val id: String,
    val userId: String,
    val amount: Double,
    val items: List<String>,
    val status: String,
)

fun main() {
    println("=== 1. 创建集合 ===")
    val list = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    val mset = mutableSetOf("a", "b", "c")
    val map = mapOf("x" to 1, "y" to 2)
    println("list = $list")
    println("set = $mset")
    println("map = $map")

    println("\n=== 2. 转换 ===")
    println("map { it * 2 } = ${list.map { it * 2 }}")
    println("mapIndexed = ${list.mapIndexed { i, v -> "[${i}]=${v}" }}")
    println("flatMap = ${list.take(3).flatMap { listOf(it, it * 10) }}")

    println("\n=== 3. 筛选 ===")
    println("偶数: ${list.filter { it % 2 == 0 }}")
    val (even, odd) = list.partition { it % 2 == 0 }
    println("partition: even=$even, odd=$odd")
    println("take(3) = ${list.take(3)}")
    println("drop(7) = ${list.drop(7)}")
    println("takeWhile{<5} = ${list.takeWhile { it < 5 }}")

    println("\n=== 4. 聚合 ===")
    println("sum = ${list.sum()}")
    println("average = ${list.average()}")
    println("count{>5} = ${list.count { it > 5 }}")
    println("reduce: 1+2+...+10 = ${list.reduce { acc, x -> acc + x }}")
    println("fold(100): 100 + 1+2+...+10 = ${list.fold(100) { acc, x -> acc + x }}")

    println("\n=== 5. 排序 ===")
    val users = listOf(
        "Charlie" to 25,
        "Alice" to 30,
        "Bob" to 20,
    )
    println("按年龄: ${users.sortedBy { it.second }}")
    println("按名字倒序: ${users.sortedByDescending { it.first }}")

    println("\n=== 6. 分组 ===")
    val words = listOf("apple", "banana", "apricot", "blueberry", "cherry")
    println("groupBy 首字母:")
    words.groupBy { it.first() }.forEach { (k, v) -> println("  $k -> $v") }

    println("associateBy 首字母（重复 key 后者覆盖）:")
    println("  ${words.associateBy { it.first() }}")

    println("associateWith 长度:")
    println("  ${words.associateWith { it.length }}")

    println("\n=== 7. zip / unzip / chunked / windowed ===")
    val names = listOf("a", "b", "c")
    val ages = listOf(1, 2, 3)
    println("zip: ${names.zip(ages)}")
    println("zip + transform: ${names.zip(ages) { n, a -> "$n=$a" }}")
    println("chunked(3): ${list.chunked(3)}")
    println("windowed(3): ${list.windowed(3).take(3)}")

    println("\n=== 8. Sequence vs List ===")
    println("--- List 急性 ---")
    listOf(1, 2, 3, 4, 5)
        .filter { print("F$it "); it % 2 == 0 }
        .map { print("M$it "); it * 2 }
        .first()
    println()

    println("--- Sequence 惰性 ---")
    listOf(1, 2, 3, 4, 5).asSequence()
        .filter { print("F$it "); it % 2 == 0 }
        .map { print("M$it "); it * 2 }
        .first()
    println()
    println("👆 Sequence 在找到第一个就停了！")

    println("\n=== 9. 实战：电商订单分析 ===")
    val orders = listOf(
        Order("o001", "u1", 100.0, listOf("apple"), "PAID"),
        Order("o002", "u1", 50.0, listOf("banana", "cherry"), "PAID"),
        Order("o003", "u2", 200.0, listOf("apple", "banana"), "REFUND"),
        Order("o004", "u2", 80.0, listOf("apple"), "PAID"),
        Order("o005", "u3", 30.0, listOf("cherry"), "CANCEL"),
        Order("o006", "u3", 150.0, listOf("banana"), "PAID"),
    )

    val revenue = orders.filter { it.status == "PAID" }.sumOf { it.amount }
    println("总收入: ¥$revenue")

    println("\n按用户统计已付金额:")
    orders
        .filter { it.status == "PAID" }
        .groupBy { it.userId }
        .mapValues { (_, list) -> list.sumOf { it.amount } }
        .toList()
        .sortedByDescending { it.second }
        .forEach { (uid, total) -> println("  $uid: ¥$total") }

    println("\n商品销量 Top 3:")
    orders
        .flatMap { it.items }
        .groupingBy { it }
        .eachCount()
        .toList()
        .sortedByDescending { it.second }
        .take(3)
        .forEach { (item, cnt) -> println("  $item: $cnt 单") }

    val (paid, others) = orders.partition { it.status == "PAID" }
    println("\n已付订单数: ${paid.size} / 其他: ${others.size}")
}