use std::borrow::Cow;
use nom::{
    IResult,
    branch::alt,
    character::complete::space0,
    combinator::{into, opt},
    multi::{many0, many1},
    sequence::{pair, tuple},
};

use crate::quoted::quoted_string;
use crate::whitespace::fws;
use crate::words::{atom, vchar_seq};

/// Word
///
/// ```abnf
///    word            =   atom / quoted-string
/// ```
pub fn word(input: &str) -> IResult<&str, Cow<str>> {
    alt((into(quoted_string), into(atom)))(input)
}

/// Phrase
///
/// ```abnf
///    phrase          =   1*word / obs-phrase
/// ```
pub fn phrase(input: &str) -> IResult<&str, String> {
    let (input, words) = many1(word)(input)?;
    let phrase = words.join(" ");
    Ok((input, phrase))
}

/// Unstructured header field body
///
/// ```abnf
/// unstructured    =   (*([FWS] VCHAR_SEQ) *WSP) / obs-unstruct
/// ```
pub fn unstructured(input: &str) -> IResult<&str, String> {
    let (input, r) = many0(tuple((opt(fws), vchar_seq)))(input)?;
    let (input, _) = space0(input)?;

    // Try to optimize for the most common cases
    let body = match r.as_slice() {
        [(None, content)] => content.to_string(),
        [(Some(_), content)] => " ".to_string() + content,
        lines => lines.iter().fold(String::with_capacity(255), |acc, item| {
            let (may_ws, content) = item;
            match may_ws {
                Some(_) => acc + " " + content,
                None => acc + content,
            }
        }),
    };

    Ok((input, body))
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_phrase() {
        assert_eq!(phrase("hello world"), Ok(("", "hello world".into())));
        assert_eq!(phrase("salut \"le\" monde"), Ok(("", "salut le monde".into())));
        assert_eq!(phrase("fin\r\n du\r\nmonde"), Ok(("\r\nmonde", "fin du".into())));
    }
}