gistfile1.txt

use nom::is_alphabetic;
use std::str;

#[derive(Debug, PartialEq, Eq)]
pub enum Keyword {
    Unknown,
    Help,
    Echo,
}

#[derive(Debug, PartialEq, Eq)]
pub enum Command {
    Unknown,
    Help,
    Echo(String),
}

fn to_keyword(s: &[u8]) -> Keyword {
    if compare_no_case(&s, b"help") {
        return Keyword::Help;
    } else if compare_no_case(&s, b"echo") {
        return Keyword::Echo;
    }

    Keyword::Unknown
}

fn is_argument_char(i: u8) -> bool {
    !b"\r\n".contains(&i)
}

pub fn to_command(keyword: Keyword, argument: &[u8]) -> Command {
    match keyword {
        Keyword::Unknown => Command::Unknown,
        Keyword::Help => Command::Help,
        Keyword::Echo => Command::Echo(str::from_utf8(argument).unwrap().into()),
    }
}

fn is_token_char(i: u8) -> bool {
    is_alphabetic(i) || b"_-".contains(&i)
}

pub fn compare_no_case(left: &[u8], right: &[u8]) -> bool {
    if left.len() != right.len() {
        return false;
    }

    left.iter().zip(right).all(|(a, b)| match (*a, *b) {
        (0...64, 0...64) | (91...96, 91...96) | (123...255, 123...255) => a == b,
        (65...90, 65...90) | (97...122, 97...122) | (65...90, 97...122) | (97...122, 65...90) => {
            *a | 0b00_10_00_00 == *b | 0b00_10_00_00
        }
        _ => false,
    })
}

named!(eoc, alt!(tag!("\n") | tag!("\r\n")));
named!(space, alt!(tag!(" ") | tag!("\t")));
named!(keyword<&[u8], Keyword>, map!(take_while!(is_token_char), to_keyword));
named!(argument, take_while!(is_argument_char));

named!(command<&[u8], Command>,
       do_parse!(
           tag!("!") >>
           keyword: keyword >>
           opt!(space) >>
           argument: argument >>
           eoc >>
           (to_command(keyword, argument))
       )
);

pub fn parse(input: &str) -> Result<Command, nom::Err<&[u8]>> {
    let result = command(input.as_bytes())?;
    Ok(result.1)
}

#[cfg(test)]
mod tests {
    use crate::parser::*;

    #[test]
    fn parse_command_with_crlf() {
        assert_eq!(parse("!help\r\n"), Ok(Command::Help));
    }

    #[test]
    fn parse_command_with_lf() {
        assert_eq!(parse("!help\n"), Ok(Command::Help));
    }

    #[test]
    fn parse_unknown_command() {
        assert_eq!(parse("!omg\n"), Ok(Command::Unknown));
    }

    #[test]
    fn parse_command_with_argument() {
        assert_eq!(parse("!echo omg\n"), Ok(Command::Echo("omg".into())));
    }
}