passgen/

parser.rs

use super::pattern::*;
use pest::{
    iterators::{Pair, Pairs},
    Parser,
};
use pest_derive::Parser;

type Pattern = crate::pattern::Pattern<Parsed>;
type Group = crate::pattern::Group<Parsed>;
type Segment = crate::pattern::Segment<Parsed>;
type Item = crate::pattern::Item<Parsed>;

#[derive(Parser)]
#[grammar = "grammar.pest"]
pub struct PatternParser;

#[derive(thiserror::Error, Debug)]
pub enum Error {
    #[error("syntax error")]
    Syntax(#[from] pest::error::Error<Rule>),
}

type Result<T, E = Error> = std::result::Result<T, E>;

impl Pattern {
    pub fn parse(input: &str) -> Result<Self> {
        let pairs = PatternParser::parse(Rule::pattern, input)?;
        Ok(Self::Group(Group::parse_pairs(pairs)?))
    }

    fn parse_pair(input: Pair<'_, Rule>) -> Result<Self> {
        let pattern = match input.as_rule() {
            Rule::literal => Literal::parse_pairs(input.into_inner())?.into(),
            Rule::group => Group::parse_pairs(input.into_inner())?.into(),
            Rule::set => Set::parse_pairs(input.into_inner())?.into(),
            Rule::special => Special::parse_pairs(input.into_inner())?.into(),
            _ => unreachable!(),
        };
        Ok(pattern)
    }
}

impl Special {
    fn parse_pairs(mut input: Pairs<'_, Rule>) -> Result<Self> {
        let pair = input.next().unwrap();
        let result = match pair.as_rule() {
            Rule::wordlist => {
                let name = pair.into_inner().next().unwrap();
                Self::Wordlist(name.as_str().to_string())
            }
            Rule::markov => {
                let name = pair.into_inner().next().unwrap();
                Self::Markov(name.as_str().to_string())
            }
            _ => unreachable!(),
        };
        Ok(result)
    }
}

impl Literal {
    fn parse_pairs(mut input: Pairs<'_, Rule>) -> Result<Self> {
        let pair = input.next().unwrap();
        Self::parse_pair(pair)
    }

    fn parse_pair(pair: Pair<'_, Rule>) -> Result<Self> {
        let value = match pair.as_rule() {
            Rule::unicode => pair.as_str().chars().next().unwrap(),
            Rule::escaped => pair.as_str().chars().nth(1).unwrap(),
            _ => unreachable!(),
        };
        Ok(Literal { value })
    }
}

impl Item {
    fn parse_pairs(mut input: Pairs<'_, Rule>) -> Result<Self> {
        let pattern = input.next().unwrap();

        let mut item = Item::new(Pattern::parse_pair(pattern)?);

        for pair in input {
            match pair.as_rule() {
                Rule::repeat => {
                    let mut amount = pair.into_inner();
                    let min = amount.next().unwrap().as_str().parse().unwrap();
                    item.repeat = min..=min;
                    if let Some(pair) = amount.next() {
                        let max = pair.as_str().parse().unwrap();
                        item.repeat = min..=max;
                    }
                }
                Rule::optional => item.optional = true,
                _ => unreachable!(),
            }
        }

        Ok(item)
    }
}

impl Segment {
    fn parse_pairs(input: Pairs<'_, Rule>) -> Result<Self> {
        let mut segment = Self::default();
        for pair in input {
            match pair.as_rule() {
                Rule::item => {
                    segment.items.push(Item::parse_pairs(pair.into_inner())?);
                }
                _ => unreachable!(),
            }
        }
        Ok(segment)
    }
}

impl Group {
    fn parse_pairs(input: Pairs<'_, Rule>) -> Result<Self> {
        let mut group = Self::default();
        for pair in input {
            match pair.as_rule() {
                Rule::segment => {
                    group
                        .segments
                        .push(Segment::parse_pairs(pair.into_inner())?);
                }
                Rule::EOI => {}
                _ => unreachable!("unexpected rule {:?}", pair.as_rule()),
            }
        }
        Ok(group)
    }
}

fn get_char(pair: Pair<'_, Rule>) -> Result<char> {
    match pair.as_rule() {
        Rule::literal => Literal::parse_pairs(pair.into_inner()).map(|literal| literal.value),
        _ => unreachable!(),
    }
}

impl Set {
    fn parse_pairs(input: Pairs<'_, Rule>) -> Result<Self> {
        let mut set = Self::default();
        for range in input {
            match range.as_rule() {
                Rule::range => {
                    let mut inner = range.into_inner();
                    let min = get_char(inner.next().unwrap()).unwrap();
                    let mut range = min..=min;
                    if let Some(pair) = inner.next() {
                        let max = get_char(pair).unwrap();
                        // fixup range min-max
                        range = min.min(max)..=max.max(min);
                    }

                    set.insert(range, 1);
                }
                _ => unreachable!(),
            }
        }
        Ok(set)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use test_strategy::*;

    macro_rules! group {
        ($($segments:tt)*) => {
            Pattern::Group(Group {
                segments: vec![$($segments)*],
            })
        };
    }

    macro_rules! segment {
        ($($items:tt)*) => {
            Segment {
                items: vec![$($items)*],
            }
        };
    }

    macro_rules! set {
        ($($range:expr),*) => {
            {
                let mut set = Set::default();
                $(set.insert($range, 1);)*
                set
            }
        };
    }

    #[test]
    fn parse_literal() {
        assert_eq!(
            Pattern::parse("a").unwrap(),
            group![segment![Item::new(Literal::new('a'))]]
        );
    }

    #[test]
    fn parse_literal_optional() {
        assert_eq!(
            Pattern::parse("a?").unwrap(),
            group![segment![Item::new(Literal::new('a')).optional(true)]]
        );
    }

    #[test]
    fn parse_literal_repeat() {
        assert_eq!(
            Pattern::parse("a{1,3}").unwrap(),
            group![segment![Item::new(Literal::new('a')).repeat(1..=3)]]
        );
    }

    #[test]
    fn parse_group() {
        assert_eq!(
            Pattern::parse("()").unwrap(),
            group![segment![Item::new(group![segment![]])]],
        );
    }

    #[test]
    fn parse_group_segments() {
        assert_eq!(
            Pattern::parse("(a|b|c)").unwrap(),
            group![segment![Item::new(group![
                segment![Item::new(Literal::new('a'))],
                segment![Item::new(Literal::new('b'))],
                segment![Item::new(Literal::new('c'))],
            ])]],
        );
    }

    #[test]
    fn parse_group_optional() {
        assert_eq!(
            Pattern::parse("()?").unwrap(),
            group![segment![Item::new(group![segment![]]).optional(true)]],
        );
    }

    #[test]
    fn parse_group_repeat() {
        assert_eq!(
            Pattern::parse("(){1,3}").unwrap(),
            group![segment![Item::new(group![segment![]]).repeat(1..=3)]],
        );
    }

    #[test]
    fn parse_set() {
        assert_eq!(
            Pattern::parse("[abc]").unwrap(),
            group![segment![Item::new(set!['a'..='c'])]],
        );
    }

    #[test]
    fn parse_set_optional() {
        assert_eq!(
            Pattern::parse("[abc]?").unwrap(),
            group![segment![Item::new(set!['a'..='c']).optional(true)]],
        );
    }

    #[test]
    fn parse_set_repeat() {
        assert_eq!(
            Pattern::parse("[abc]{1,3}").unwrap(),
            group![segment![Item::new(set!['a'..='c']).repeat(1..=3)]],
        );
    }

    #[proptest]
    fn parse_repeat_exact(amount: usize) {
        assert_eq!(
            Pattern::parse(&format!("x{{{amount}}}")).unwrap(),
            group![segment![
                Item::new(Literal::new('x')).repeat(amount..=amount)
            ]],
        );
    }

    #[proptest]
    fn parse_repeat_minmax(min: usize, max: usize) {
        assert_eq!(
            Pattern::parse(&format!("x{{{min},{max}}}")).unwrap(),
            group![segment![Item::new(Literal::new('x')).repeat(min..=max)]],
        );
    }

    #[proptest]
    fn parse_optional(optional: bool) {
        let optional_str = match optional {
            true => "?",
            false => "",
        };
        assert_eq!(
            Pattern::parse(&format!("x{optional_str}")).unwrap(),
            group![segment![Item::new(Literal::new('x')).optional(optional)]],
        );
    }

    #[proptest]
    fn parse_arbitrary(input: String) {
        let result = Pattern::parse(&input);
        let _ = std::hint::black_box(result);
    }
}