Day 3：CLI 參數解析（clap）

use clap::{Parser, Subcommand};

#[derive(Parser)]
#[command(name = "todo", about = "CLI 任務管理工具")]
struct Cli {
    #[command(subcommand)]
    command: Command,
}

#[derive(Subcommand)]
enum Command {
    /// 新增任務
    Add {
        /// 任務內容
        title: String,
    },
    /// 列出所有任務
    List,
    /// 標記任務完成
    Done { id: u64 },
    /// 刪除任務
    Remove { id: u64 },
}

fn main() {
    let cli = Cli::parse();   // 從命令列解析

    match cli.command {
        Command::Add { title } => println!("Add: {}", title),
        Command::List => println!("List all"),
        Command::Done { id } => println!("Done: {}", id),
        Command::Remove { id } => println!("Remove: {}", id),
    }
}

cargo run -- add "學習 Rust"
cargo run -- list
cargo run -- done 1
cargo run -- remove 2
cargo run -- --help   # clap 自動產生說明