/**
 * 第 3 章 · 实战案例 — 学生成绩等级判定器
 *
 * 综合演示了：
 *   - when 表达式
 *   - 范围 (in 0..100)
 *   - 字符串模板
 *   - for + withIndex
 *   - 函数定义
 *
 * 业务场景：教务系统给一批学生算成绩等级。
 */

data class Student(val name: String, val score: Int)

fun grade(score: Int): String = when {
    score !in 0..100 -> "无效分数"
    score >= 90 -> "A"
    score >= 80 -> "B"
    score >= 70 -> "C"
    score >= 60 -> "D"
    else -> "F"
}

fun comment(score: Int): String = when (score) {
    in 90..100 -> "优秀！继续保持 🎉"
    in 80..89 -> "良好，下次冲一冲 💪"
    in 70..79 -> "中等，还有提升空间"
    in 60..69 -> "刚及格，要加把劲！"
    in 0..59 -> "不及格，需要补课 😢"
    else -> "分数无效，请检查输入"
}

fun main() {
    val students = listOf(
        Student("Alice", 95),
        Student("Bob", 82),
        Student("Charlie", 73),
        Student("David", 60),
        Student("Eve", 45),
        Student("Frank", 105),
    )

    println("=== 学生成绩单 ===")
    println("%-10s %-6s %-6s %s".format("姓名", "分数", "等级", "评语"))
    println("-".repeat(50))
    for (s in students) {
        val g = grade(s.score)
        val c = comment(s.score)
        println("%-10s %-6d %-6s %s".format(s.name, s.score, g, c))
    }

    println("\n=== 班级统计 ===")
    val valid = students.filter { it.score in 0..100 }
    val avg = valid.map { it.score }.average()
    val max = valid.maxByOrNull { it.score }
    val min = valid.minByOrNull { it.score }
    val passed = valid.count { it.score >= 60 }
    println("有效人数: ${valid.size}")
    println("平均分:   ${"%.1f".format(avg)}")
    println("最高分:   ${max?.name} ${max?.score}")
    println("最低分:   ${min?.name} ${min?.score}")
    println("及格率:   ${"%.0f%%".format(passed * 100.0 / valid.size)}")
}