use std::fmt;
use std::str::{from_utf8, from_utf8_unchecked};

#[derive(Copy,Clone,Debug,Eq,PartialEq,Ord,PartialOrd)]
pub enum IrcCommand<'a> {
    Stringy(Stringy<'a>),
    Numeric(Numeric<'a>)
}

#[derive(Copy,Clone,Debug,Eq,PartialEq,Ord,PartialOrd)]
pub struct Stringy<'a>(&'a [u8]);

#[derive(Copy,Clone,Debug,Eq,PartialEq,Ord,PartialOrd)]
pub struct Numeric<'a>(u16, &'a [u8; 3]);

impl<'a> Numeric<'a> {
    // not unsafe, but may produce unexpected results
    // keep this private
    fn new(cmd: &'a [u8; 3]) -> Numeric<'a> {
        Numeric(cmd.iter().map(|x| (x-b'0') as u16).fold(0, |x,y| x*10+y), cmd)
    }
}

pub trait IrcCommandCall {
    fn get_command<'a>(&'a self) -> IrcCommand<'a>;
}

impl<'a> fmt::Display for Stringy<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut i = 0;
        let l = self.0.len();
        let v = self.0;
        while i < l {
            let st = from_utf8(&v[i..]);
            if let Ok(s) = st {
                write!(f, "{}", s)?;
            } else {
                let err = st.err().unwrap();
                write!(f, "{}", unsafe { from_utf8_unchecked(&v[i..][..err.valid_up_to()])})?;
                write!(f, "\u{FFFD}")?;
                match err.error_len() {
                    None => i = l,
                    Some(len) => i = i + err.valid_up_to() + len
                }
            }
        }
        Ok(())
    }
}

impl<'a> fmt::Display for Numeric<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", unsafe { from_utf8_unchecked(self.1) })
    }
}

impl<'a> IrcCommand<'a> {
    pub fn new(cmd: &'a [u8]) -> IrcCommand<'a> {
        if cmd.len() == 3 && matches!((cmd[0], cmd[1], cmd[2]), (b'0'...b'9', b'0'...b'9', b'0'...b'9')) {
            // TODO switch to TryFrom/TryInto once those are stable. (rust-lang/rust#33417)
            IrcCommand::Numeric(Numeric::new(array_ref![cmd,0,3]))
        } else {
            IrcCommand::Stringy(Stringy(cmd))
        }
    }
}
 