use combine::{
    attempt, between, choice, many1,
    parser::char::{alpha_num, digit, hex_digit, space, spaces, string},
    skip_many1,
    stream::position,
    token, EasyParser, ParseError, Parser, Stream,
};

use crate::ast::{Constant, Program, Term};

pub fn program(src: &str) -> anyhow::Result<Program> {
    let mut parser = program_();

    let result = parser.easy_parse(position::Stream::new(src));

    match result {
        Ok((program, _)) => Ok(program),
        Err(err) => Err(anyhow::anyhow!("{}", err)),
    }
}

fn program_<Input>() -> impl Parser<Input, Output = Program>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    let prog = string("program").with(skip_many1(space())).with(
        (version(), skip_many1(space()), term().skip(spaces()))
            .map(|(version, _, term)| Program { version, term }),
    );

    between(token('('), token(')'), prog).skip(spaces())
}

fn version<Input>() -> impl Parser<Input, Output = String>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    (
        many1(digit()),
        token('.'),
        many1(digit()),
        token('.'),
        many1(digit()),
    )
        .map(
            |(major, _, minor, _, patch): (String, char, String, char, String)| {
                format!("{}.{}.{}", major, minor, patch)
            },
        )
}

fn term<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    choice((
        attempt(delay()),
        attempt(lambda()),
        attempt(apply()),
        attempt(constant()),
        attempt(force()),
    ))
}

parser! {
    fn term_[I]()(I) -> Term
    where [I: Stream<Token = char>]
    {
        term()
    }
}

fn delay<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    between(
        token('('),
        token(')'),
        string("delay")
            .with(skip_many1(space()))
            .with(term_())
            .map(|term| Term::Delay(Box::new(term))),
    )
}

fn force<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    between(
        token('('),
        token(')'),
        string("force")
            .with(skip_many1(space()))
            .with(term_())
            .map(|term| Term::Force(Box::new(term))),
    )
}

fn lambda<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    between(
        token('('),
        token(')'),
        string("lam")
            .with(skip_many1(space()))
            .with((many1(alpha_num()), skip_many1(space()), term_()))
            .map(|(parameter_name, _, term)| Term::Lambda {
                parameter_name,
                body: Box::new(term),
            }),
    )
}

fn apply<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    between(
        token('['),
        token(']'),
        (term_().skip(skip_many1(space())), term_()).map(|(function, argument)| Term::Apply {
            function: Box::new(function),
            argument: Box::new(argument),
        }),
    )
}

fn constant<Input>() -> impl Parser<Input, Output = Term>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    between(
        token('('),
        token(')'),
        string("con")
            .with(skip_many1(space()))
            .with(choice((
                attempt(constant_integer()),
                attempt(constant_bytestring()),
                attempt(constant_string()),
                attempt(constant_unit()),
                attempt(constant_bool()),
            )))
            .map(Term::Constant),
    )
}

fn constant_integer<Input>() -> impl Parser<Input, Output = Constant>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    string("integer")
        .with(skip_many1(space()))
        .with(many1(digit()))
        .map(|d: String| Constant::Integer(d.parse::<i64>().unwrap()))
}

fn constant_bytestring<Input>() -> impl Parser<Input, Output = Constant>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    string("bytestring")
        .with(skip_many1(space()))
        .with(token('#'))
        .with(many1(hex_digit()))
        .map(|b: String| Constant::ByteString(hex::decode(b).unwrap()))
}

fn constant_string<Input>() -> impl Parser<Input, Output = Constant>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    string("string")
        .with(skip_many1(space()))
        .with(between(token('"'), token('"'), many1(alpha_num())))
        .map(Constant::String)
}

fn constant_unit<Input>() -> impl Parser<Input, Output = Constant>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    string("unit")
        .with(skip_many1(space()))
        .with(string("()"))
        .map(|_| Constant::Unit)
}

fn constant_bool<Input>() -> impl Parser<Input, Output = Constant>
where
    Input: Stream<Token = char>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
{
    string("bool")
        .with(skip_many1(space()))
        .with(string("True").or(string("False")))
        .map(|b| Constant::Bool(b == "True"))
}

#[cfg(test)]
mod test {
    use combine::Parser;

    const CODE: &str = include_str!("../example/plutus-core");

    #[test]
    fn parse_program() {
        let result = super::program_().parse(CODE);

        assert!(result.is_ok());

        let program = result.unwrap().0;

        assert_eq!(program.version, "1.0.0");
    }
}