use chumsky::{self, prelude::*, Parser};

/// Parses a text character that is not the specified delimiter
fn text_parser(delim: char) -> impl Parser<char, char, Error = Simple<char>> {
    // Copied directly from Chumsky's JSON example.
    let escape = just('\\').ignore_then(
        just('\\')
            .or(just('/'))
            .or(just('"'))
            .or(just('b').to('\x08'))
            .or(just('f').to('\x0C'))
            .or(just('n').to('\n'))
            .or(just('r').to('\r'))
            .or(just('t').to('\t'))
            .or(just('u').ignore_then(
                filter(|c: &char| c.is_digit(16))
                    .repeated()
                    .exactly(4)
                    .collect::<String>()
                    .validate(|digits, span, emit| {
                        char::from_u32(u32::from_str_radix(&digits, 16).unwrap())
                            .unwrap_or_else(|| {
                                emit(Simple::custom(span, "invalid unicode character"));
                                '\u{FFFD}' // unicode replacement character
                            })
                    }),
            )),
    );
    filter(move |&c| c != '\\' && c != delim).or(escape)
}

/// Parse a character literal between single quotes
pub fn char_parser() -> impl Parser<char, char, Error = Simple<char>> {
    just('\'').ignore_then(text_parser('\'')).then_ignore(just('\''))
}

/// Parse a string between double quotes
pub fn str_parser() -> impl Parser<char, String, Error = Simple<char>> {
    just('"')
    .ignore_then(
        text_parser('"').map(Some)
        .or(just("\\\n").map(|_| None)) // Newlines preceded by backslashes are ignored.
        .repeated()
    ).then_ignore(just('"'))
    .flatten().collect()
}