tenebrous-dicebot/src/parser.rs

use nom::{
    alt,
    tag,
    complete,
    named,
    many0,
    IResult,
    bytes::complete::{tag, take_while},
    character::complete::digit1,
    sequence::tuple
};

#[derive(Debug, PartialEq, Eq)]
struct Dice {
    count: u32,
    sides: u32,
}

impl Dice {
    fn new(count: u32, sides: u32) -> Dice {
        Dice {
            count,
            sides,
        }
    }
}

#[derive(Debug, PartialEq, Eq)]
enum Element {
    Dice(Dice),
    Bonus(u32),
}

#[derive(Debug, PartialEq, Eq)]
enum Sign {
    Plus,
    Minus,
}

#[derive(Debug, PartialEq, Eq)]
enum SignedElement {
    Positive(Element),
    Negative(Element),
}

#[derive(Debug, PartialEq, Eq)]
struct ElementExpression(Vec<SignedElement>);

fn is_whitespace(input: char) -> bool {
    input == ' ' || input == '\n' || input == '\t' || input == '\r'
}

fn eat_whitespace(input: &str) -> IResult<&str, ()> {
    let (input, _) = take_while(is_whitespace)(input)?;
    Ok((input, ()))
}

// Parse a dice expression.  Does not eat whitespace
fn parse_dice(input: &str) -> IResult<&str, Dice> {
    let (input, (count, _, sides)) = tuple((digit1, tag("d"), digit1))(input)?;
    Ok((input, Dice::new(count.parse().unwrap(), sides.parse().unwrap())))
}

// Parse a single digit expression.  Does not eat whitespace
fn parse_bonus(input: &str) -> IResult<&str, u32> {
    let (input, bonus) = digit1(input)?;
    Ok((input, bonus.parse().unwrap()))
}

// Parse a sign expression.  Eats whitespace.
fn parse_sign(input: &str) -> IResult<&str, Sign> {
    let (input, _) = eat_whitespace(input)?;
    named!(sign(&str) -> Sign, alt!(
            tag!("+") => { |_| Sign::Plus } |
            tag!("-") => { |_| Sign::Minus }
    ));

    let (input, sign) = sign(input)?;
    Ok((input, sign))
}

// Parse an element expression.  Eats whitespace.
fn parse_element(input: &str) -> IResult<&str, Element> {
    let (input, _) = eat_whitespace(input)?;
    named!(element(&str) -> Element, alt!(
            parse_dice => { |d| Element::Dice(d) } |
            parse_bonus => { |b| Element::Bonus(b) }
    ));

    let (input, element) = element(input)?;
    Ok((input, element))
}

// Parse a signed element expression.  Eats whitespace.
fn parse_signed_element(input: &str) -> IResult<&str, SignedElement> {
    let (input, _) = eat_whitespace(input)?;
    let (input, sign) = parse_sign(input)?;
    let (input, _) = eat_whitespace(input)?;

    let (input, element) = parse_element(input)?;
    let element = match sign {
        Sign::Plus => SignedElement::Positive(element),
        Sign::Minus => SignedElement::Negative(element),
    };
    Ok((input, element))
}

// Parse a full element expression.  Eats whitespace.
fn parse_element_expression(input: &str) -> IResult<&str, ElementExpression> {
    named!(first_element(&str) -> SignedElement, alt!(
            parse_signed_element => { |e| e } |
            parse_element => { |e| SignedElement::Positive(e) }
    ));
    let (input, first) = first_element(input)?;
    let (input, rest) = if input.trim().is_empty() {
        (input, vec![first])
    } else {
        named!(rest_elements(&str) -> Vec<SignedElement>, many0!(complete!(parse_signed_element)));
        let (input, mut rest) = rest_elements(input)?;
        rest.insert(0, first);
        (input, rest)
    };

    Ok((input, ElementExpression(rest)))
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn dice_test() {
        assert_eq!(parse_dice("2d4"), Ok(("", Dice::new(2, 4))));
        assert_eq!(parse_dice("20d40"), Ok(("", Dice::new(20, 40))));
        assert_eq!(parse_dice("8d7"), Ok(("", Dice::new(8, 7))));
    }

    #[test]
    fn element_test() {
        assert_eq!(parse_element("  \t\n\r\n 8d7 \n"), Ok((" \n", Element::Dice(Dice::new(8, 7)))));
        assert_eq!(parse_element("  \t\n\r\n 8 \n"), Ok((" \n", Element::Bonus(8))));
    }

    #[test]
    fn signed_element_test() {
        assert_eq!(parse_signed_element("+ 7"), Ok(("", SignedElement::Positive(Element::Bonus(7)))));
        assert_eq!(parse_signed_element("  \t\n\r\n- 8 \n"), Ok((" \n", SignedElement::Negative(Element::Bonus(8)))));
        assert_eq!(parse_signed_element("  \t\n\r\n- 8d4 \n"), Ok((" \n", SignedElement::Negative(Element::Dice(Dice::new(8, 4))))));
        assert_eq!(parse_signed_element("  \t\n\r\n+ 8d4 \n"), Ok((" \n", SignedElement::Positive(Element::Dice(Dice::new(8, 4))))));
    }

    #[test]
    fn element_expression_test() {
        assert_eq!(parse_element_expression("8d4"), Ok(("", ElementExpression(vec![SignedElement::Positive(Element::Dice(Dice::new(8, 4)))]))));
        assert_eq!(parse_element_expression(" -  8d4 \n "), Ok((" \n ", ElementExpression(vec![SignedElement::Negative(Element::Dice(Dice::new(8, 4)))]))));
        assert_eq!(parse_element_expression("\t3d4 + 7 - 5 - 6d12 + 1d1 + 53 1d5 "), Ok((" 1d5 ", ElementExpression(vec![
            SignedElement::Positive(Element::Dice(Dice::new(3, 4))),
            SignedElement::Positive(Element::Bonus(7)),
            SignedElement::Negative(Element::Bonus(5)),
            SignedElement::Negative(Element::Dice(Dice::new(6, 12))),
            SignedElement::Positive(Element::Dice(Dice::new(1, 1))),
            SignedElement::Positive(Element::Bonus(53)),
        ]))));
    }
}