use std::convert::From;


#[derive(Copy, Clone, Debug)]
enum Keypress {
    Left,
    Right,
    Down,
    Up,
    Enter,
}


macro_rules! enum_from_bytes{
    (@enumerate $type:ident, $bytes:ident, $index:expr, (($current_variant:ident)); $($arms:tt)+) => ({
        const $current_variant: u8 = $index;
        match $bytes[0] {
            $($arms)*
            $current_variant => $current_expression,
            _ => panic!(concat!("No valid enum of type ", stringify!($type), " could be constructed from {} (max index is {})"), $bytes[0], $current_variant),
        }
    });
    (@enumerate $type:ident, $bytes:ident, $index:expr, (($current_variant:ident), $($variant:tt)+); $($arms:tt)*) => ({
        const $current_variant: u8 = $index;
        enum_from_bytes!(@enumerate $type, $bytes, $index + 1, ($($variant),+); $($arms)* $current_variant => $current_expression,)
    });
    ($type:ident => {$($variant:tt)+}) => ({
        impl<'a> From<&'a [u8]> for $type {
            #[allow(non_upper_case_globals)]
            fn from(bytes: &'a [u8]) -> Self {
                enum_from_bytes!(@enumerate $type, bytes, 0, ($($variant)+) ;)
            }
    }
    });
    ($type:ident => [$($variant:ident),+]) => ({
        impl<'a> From<&'a [u8]> for $type {
            fn from(bytes: &'a [u8]) -> Self {
                [$($type::$variant),+][bytes[0] as usize]
            }
        }
    })
}

fn main() {
    enum_from_bytes!(Keypress => {
        (Left)
        (Right)
        (Down)
        (Up)
        (Enter)
    });

    println!("{:?}", Keypress::from(&[1, 4][..]));
}