use nom::{
    branch::alt,
    bytes::complete::{tag, take_until, take_while, take_while1},
    character::is_alphabetic,
    combinator::{all_consuming, opt, recognize},
    error::{context, ContextError, ParseError},
    sequence::{preceded, tuple},
    IResult,
};

use crate::{parse, parse::NL, BStr, ByteSlice, TagRef};

pub fn git_tag<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(i: &'a [u8]) -> IResult<&[u8], TagRef<'a>, E> {
    let (i, target) = context("object <40 lowercase hex char>", |i| {
        parse::header_field(i, b"object", parse::hex_hash)
    })(i)?;

    let (i, kind) = context("type <object kind>", |i| {
        parse::header_field(i, b"type", take_while1(is_alphabetic))
    })(i)?;
    let kind = crate::Kind::from_bytes(kind)
        .map_err(|_| nom::Err::Error(E::from_error_kind(i, nom::error::ErrorKind::MapRes)))?;

    let (i, tag_version) = context("tag <version>", |i| {
        parse::header_field(i, b"tag", take_while1(|b| b != NL[0]))
    })(i)?;

    let (i, signature) = context(
        "tagger <signature>",
        opt(|i| parse::header_field(i, b"tagger", parse::signature)),
    )(i)?;
    let (i, (message, pgp_signature)) = all_consuming(message)(i)?;
    Ok((
        i,
        TagRef {
            target,
            name: tag_version.as_bstr(),
            target_kind: kind,
            message,
            tagger: signature,
            pgp_signature,
        },
    ))
}

pub fn message<'a, E: ParseError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], (&'a BStr, Option<&'a BStr>), E> {
    const PGP_SIGNATURE_BEGIN: &[u8] = b"\n-----BEGIN PGP SIGNATURE-----";
    const PGP_SIGNATURE_END: &[u8] = b"-----END PGP SIGNATURE-----";

    if i.is_empty() {
        return Ok((i, (i.as_bstr(), None)));
    }
    let (i, _) = tag(NL)(i)?;
    fn all_to_end<'a, E: ParseError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], (&'a [u8], &'a [u8]), E> {
        if i.is_empty() {
            return Err(nom::Err::Error(E::from_error_kind(i, nom::error::ErrorKind::Eof)));
        }
        // an empty signature message signals that there is none - the function signature is needed
        // to work with 'alt(…)'. PGP signatures are never empty
        Ok((&[], (i, &[])))
    }
    let (i, (message, signature)) = alt((
        tuple((
            take_until(PGP_SIGNATURE_BEGIN),
            preceded(
                tag(NL),
                recognize(tuple((
                    tag(&PGP_SIGNATURE_BEGIN[1..]),
                    take_until(PGP_SIGNATURE_END),
                    tag(PGP_SIGNATURE_END),
                    take_while(|_| true),
                ))),
            ),
        )),
        all_to_end,
    ))(i)?;
    let (i, _) = opt(tag(NL))(i)?;
    Ok((
        i,
        (
            message.as_bstr(),
            if signature.is_empty() {
                None
            } else {
                Some(signature.as_bstr())
            },
        ),
    ))
}