// This example shows how to implement a command with a "catch all."
//
// This requires writing your own impl for `Decodable` because docopt's
// decoder uses `Option<T>` to mean "T may not be present" rather than
// "T may be present but incorrect."

use std::fmt;

use qsv_docopt::Docopt;
use serde::{
    de::{Deserializer, Error, Visitor},
    Deserialize,
};

// Write the Docopt usage string.
const USAGE: &str = "
Rust's package manager

Usage:
    mycli [<command>]

Options:
    -h, --help       Display this message
";

#[derive(Debug, Deserialize)]
struct Args {
    arg_command: Command,
}

struct CommandVisitor;

impl<'de> Visitor<'de> for CommandVisitor {
    type Value = Command;

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("a string A, B or C")
    }

    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
    where
        E: Error,
    {
        Ok(match s {
            "" => Command::None,
            "A" => Command::A,
            "B" => Command::B,
            "C" => Command::C,
            s => Command::Unknown(s.to_string()),
        })
    }
}

impl<'de> Deserialize<'de> for Command {
    fn deserialize<D>(d: D) -> Result<Command, D::Error>
    where
        D: Deserializer<'de>,
    {
        d.deserialize_str(CommandVisitor)
    }
}

#[derive(Debug)]
enum Command {
    A,
    B,
    C,
    Unknown(String),
    None,
}

fn main() {
    let args: Args = Docopt::new(USAGE)
        .and_then(|d| d.deserialize())
        .unwrap_or_else(|e| e.exit());
    println!("{:?}", args);
}