/**
 * 第 10 章 · 实战项目 — 命令模型 + 解析器
 *
 * 用 sealed class 表示"命令是这几种之一"，配合 when 表达式，编译器
 * 强制覆盖所有分支，新增命令时不会漏。
 */

sealed class Command {
    data class Add(val title: String, val priority: Priority, val due: String?) : Command()
    data class Done(val id: Int) : Command()
    data class Remove(val id: Int) : Command()
    data class List(val filter: Filter) : Command()
    object Stats : Command()
    object Help : Command()

    enum class Filter { ALL, ACTIVE, DONE }
}

object CommandParser {
    fun parse(args: Array<String>): Command {
        if (args.isEmpty()) return Command.Help
        return when (val cmd = args[0].lowercase()) {
            "add" -> parseAdd(args.drop(1))
            "done" -> Command.Done(args.getOrNull(1)?.toIntOrNull()
                ?: error("done 需要数字 id"))
            "rm", "remove" -> Command.Remove(args.getOrNull(1)?.toIntOrNull()
                ?: error("rm 需要数字 id"))
            "list", "ls" -> Command.List(parseFilter(args.getOrNull(1)))
            "stats" -> Command.Stats
            "help", "-h", "--help" -> Command.Help
            else -> error("未知命令: $cmd（用 todo help 查看用法）")
        }
    }

    private fun parseFilter(s: String?): Command.Filter = when (s) {
        "active" -> Command.Filter.ACTIVE
        "done" -> Command.Filter.DONE
        null, "all" -> Command.Filter.ALL
        else -> error("未知 filter: $s（可选 active / done / all）")
    }

    private fun parseAdd(args: kotlin.collections.List<String>): Command.Add {
        require(args.isNotEmpty()) { "add 需要标题" }
        val title = args[0]
        var priority = Priority.MID
        var due: String? = null

        var i = 1
        while (i < args.size) {
            when (args[i]) {
                "--priority", "-p" -> {
                    val v = args.getOrNull(++i) ?: error("--priority 需要值")
                    priority = runCatching { Priority.valueOf(v.uppercase()) }
                        .getOrElse { error("无效优先级: $v（可选 LOW / MID / HIGH）") }
                }
                "--due", "-d" -> {
                    due = args.getOrNull(++i) ?: error("--due 需要值")
                }
                else -> error("未知参数: ${args[i]}")
            }
            i++
        }
        return Command.Add(title, priority, due)
    }
}