use nom::{
    Err,
    branch::alt,
    bytes::complete::tag,
    character::complete::{char, one_of, space0, space1, multispace0, line_ending},
    combinator::{peek, not, value, map},
    error::{context, VerboseError, ParseError},
    multi::{fold_many1, many1, many0, separated_list1},
    sequence::{tuple, preceded},
    IResult, Parser,
};

type ParseResult<'a, O> = IResult<&'a str, O, VerboseError<&'a str>>;

use crate::ast::*;

/*
fn block(input: &str) -> ParseResult<Block> {
    context("block",
    map(
    tuple((
        char('{'),
        value((), context("TOP", many0(alt((line_separator, ws))))),
        block_items,
        value((), many0(alt((line_separator, ws)))),
        char('}'),
    )), |(_, _, items, _, _)| items.into()))(input)
}
*/


fn tok<'a, O>(input_parser: impl Parser<&'a str, O, VerboseError<&'a str>>) -> impl FnMut(&'a str) -> IResult<&'a str, O, VerboseError<&'a str>> {
    map(tuple((ws0, input_parser)), |(_, output)| output)
}

// whitespace does consume at least one piece of whitespace - use ws0 for maybe none
fn whitespace(input: &str) -> ParseResult<()> {
    context("whitespace",
    alt((
    value((), space1),
    line_comment,
    block_comment,
    )))(input)
}

fn ws0(input: &str) -> ParseResult<()> {
    context("WS0",
    value((), many0(whitespace)))(input)
}

fn line_comment(input: &str) -> ParseResult<()> {
    value((),
    tuple((tag("//"), many0(not(line_ending)), peek(line_ending)))
    )(input)
}

fn block_comment(input: &str) -> ParseResult<()> {
    value((),
    tuple((
        tag("/*"), 
        many0(alt((
            block_comment,
            not(tag("*/"))
        ))),
        tag("*/")
    )))(input)
}

fn line_separator(input: &str) -> ParseResult<()> {
    alt((value((), line_ending), value((), char(';'))))(input)
}

fn block_items(input: &str) -> ParseResult<Vec<Statement>> {
    context("Block-item",
    separated_list1(
        preceded(context("LLLL", ws0), many1(line_separator)),
        statement,
    ))(input)
}

fn statement(input: &str) -> ParseResult<Statement> {
    context("Parsing-statement",
    map(
        tuple((
            ws0,
            expression_kind,
            ws0
        )),|(_, kind, _)| Statement {
        id: Default::default(),
        location: Default::default(),
        kind: StatementKind::Expression(Expression::new(Default::default(), kind)),
    }))(input)
}

pub fn expression_kind(input: &str) -> ParseResult<ExpressionKind> {
    context("expression-kind",
    alt((
        number_literal,
        bool_literal,
    )))(input)
}

fn bool_literal(input: &str) -> ParseResult<ExpressionKind> {
    alt((
        map(tok(tag("true")), |_| ExpressionKind::BoolLiteral(true)),
        map(tok(tag("false")), |_| ExpressionKind::BoolLiteral(false)),
    ))(input)
}

fn number_literal(input: &str) -> ParseResult<ExpressionKind> {
    map(alt((tok(hex_literal), tok(bin_literal), tok(dec_literal))), ExpressionKind::NatLiteral)(input)
}

fn dec_literal(input: &str) -> ParseResult<u64> {
    map(digits(digit_group_dec), |chars: Vec<char>| {
        let s: String = chars.into_iter().collect();
        s.parse().unwrap()
    })(input)
}

fn hex_literal(input: &str) -> ParseResult<u64> {
    map(preceded(alt((tag("0x"), tag("0X"))), digits(digit_group_hex)), |chars: Vec<char>| {
        let s: String = chars.into_iter().collect();
        parse_hex(&s).unwrap()
    })(input)
}

fn bin_literal(input: &str) -> ParseResult<u64> {
    map(preceded(alt((tag("0b"), tag("0B"))), digits(digit_group_bin)), |chars: Vec<char>| {
        let s: String = chars.into_iter().collect();
        parse_binary(&s).unwrap()
    })(input)
}

fn digits<'a, E: ParseError<&'a str>>(
    digit_type: impl Parser<&'a str, Vec<char>, E>,
) -> impl FnMut(&'a str) -> IResult<&'a str, Vec<char>, E> {
    map(separated_list1(many1(char('_')), digit_type), |items: Vec<Vec<char>>| {
        items.into_iter().flatten().collect()
    })
}

fn digit_group_dec(input: &str) -> ParseResult<Vec<char>> {
    many1(one_of("0123456789"))(input)
}

fn digit_group_hex(input: &str) -> ParseResult<Vec<char>> {
    many1(one_of("0123456789abcdefABCDEF"))(input)
}

fn digit_group_bin(input: &str) -> ParseResult<Vec<char>> {
    many1(one_of("01"))(input)
}

fn parse_binary(digits: &str) -> Result<u64, &'static str> {
    let mut result: u64 = 0;
    let mut multiplier = 1;
    for d in digits.chars().rev() {
        match d {
            '1' => result += multiplier,
            '0' => (),
            '_' => continue,
            _ => unreachable!(),
        }
        multiplier = match multiplier.checked_mul(2) {
            Some(m) => m,
            None => return Err("Binary expression will overflow"),
        }
    }
    Ok(result)
}

fn parse_hex(digits: &str) -> Result<u64, &'static str> {
    let mut result: u64 = 0;
    let mut multiplier: u64 = 1;
    for d in digits.chars().rev() {
        if d == '_' {
            continue;
        }
        match d.to_digit(16) {
            Some(n) => result += n as u64 * multiplier,
            None => return Err("Internal parser error: invalid hex digit"),
        }
        multiplier = match multiplier.checked_mul(16) {
            Some(m) => m,
            None => return Err("Hexadecimal expression will overflow"),
        }
    }
    Ok(result)
}

#[cfg(test)]
mod test {
    use pretty_assertions::assert_eq;

    use super::*;

    #[test]
    fn combinator_test1() {
        assert_eq!(digits(digit_group_dec)("342").unwrap().1, vec!['3', '4', '2']);
        assert_eq!(bin_literal("0b1111qsdf"), Ok(("qsdf", 15)));
    }

    #[test]
    fn combinator_test2() {
        for s in ["15", "0b1111", "1_5_", "0XF__", "0Xf"].iter() {
            assert_eq!(expression_kind(s).unwrap().1, ExpressionKind::NatLiteral(15));
        }
    }

    /*
    #[test]
    fn combinator_test3() {
        let source = r#"{

            4_5
            11; 0xf
            }"#;
        let parsed = block(source).map_err(|err| match err {
            Err::Error(err) | Err::Failure(err) => nom::error::convert_error(source, err),
            _ => panic!()
        });
        //let parsed = block(source);

        if let Err(err) = parsed {
            println!("{}", err);
            panic!("parse error desu!");
        }

        assert_eq!(parsed.unwrap().1, vec![
            Statement { id: Default::default(), location:
            Default::default(), kind: StatementKind::Expression(Expression::new(Default::default(),
            ExpressionKind::NatLiteral(45))) },
            Statement { id: Default::default(), location:
            Default::default(), kind: StatementKind::Expression(Expression::new(Default::default(),
            ExpressionKind::NatLiteral(11))) },
            Statement { id: Default::default(), location:
            Default::default(), kind: StatementKind::Expression(Expression::new(Default::default(),
            ExpressionKind::NatLiteral(15))) },
        ].into());
    }
    */
}