simplify_truths/src/parsing/expression_parser.rs

use nom::branch::alt;
use nom::bytes::complete::{tag, take_while, take_while1};
use nom::character::complete::char;
use nom::combinator::opt;
use nom::error::Error;
use nom::IResult;
use nom::sequence::{pair, preceded};

use crate::{and, atomic, implies, not, or};
use crate::expressions::expression::Expression;
use crate::parsing::utils::{exhausted, IntoResult, parenthesized, trim};

pub fn parse_expression(input: &str) -> Result<Expression, nom::Err<Error<&str>>> {
    exhausted(_parse_expression)(input).into_result()
}

fn _parse_expression(input: &str) -> IResult<&str, Expression> {
    let (remaining, atomic_expression) = left_hand_side(input)?;
    if let (remaining, Some(complex_expression)) = opt(expression(atomic_expression.clone()))(remaining)? {
        Ok((remaining, complex_expression))
    } else {
        Ok((remaining, atomic_expression))
    }
}

fn left_hand_side(input: &str) -> IResult<&str, Expression> {
    alt((
        value,
        not,
        parenthesized(complete_expression)
    ))(input)
}

fn expression<'a>(previous: Expression) -> impl Fn(&'a str) -> IResult<&'a str, Expression> {
    move |input: &'a str| {
        let (remaining, new) = operator_combinators(previous.clone())(input)?;
        if !remaining.is_empty() {
            expression(new.clone())(remaining)
        } else {
            Ok((remaining, new))
        }
    }
}

fn operator_combinators(expression: Expression) -> impl Fn(&str) -> IResult<&str, Expression> {
    move |input: &str| {
        alt((
            implies(expression.clone()),
            or(expression.clone()),
            and(expression.clone()),
            not,
        ))(input)
    }
}

fn complete_expression(input: &str) -> IResult<&str, Expression> {
    let (remaining, atomic) = left_hand_side(input)?;
    operator_combinators(atomic.clone())(remaining)
}

fn and<'a>(previous: Expression) -> impl Fn(&'a str) -> IResult<&'a str, Expression> {
    move |input: &'a str| {
        preceded(
            trim(char('&')),
            left_hand_side,
        )(input).map(|(remaining, right)| {
            (remaining, and!(previous.clone(), right))
        })
    }
}

fn complete_and(input: &str) -> IResult<&str, Expression> {
    let (remaining, atomic) = value(input)?;
    and(atomic.clone())(remaining)
}

fn or<'a>(previous: Expression) -> impl Fn(&'a str) -> IResult<&'a str, Expression> {
    move |input: &'a str| {
        preceded(
            trim(char('|')),
            alt((
                complete_and,
                left_hand_side,
            )),
        )(input).map(|(remaining, right)| {
            (remaining, or!(previous.clone(), right))
        })
    }
}

fn complete_or(input: &str) -> IResult<&str, Expression> {
    let (remaining, atomic) = value(input)?;
    or(atomic.clone())(remaining)
}

fn implies<'a>(previous: Expression) -> impl Fn(&'a str) -> IResult<&'a str, Expression> {
    move |input: &'a str| {
        preceded(
            trim(tag("=>")),
            alt((
                complete_and,
                complete_or,
                left_hand_side,
            )),
        )(input).map(|(remaining, right)| {
            (remaining, implies!(previous.clone(), right))
        })
    }
}

fn not(input: &str) -> IResult<&str, Expression> {
    preceded(
        char('!'),
        left_hand_side,
    )(input).map(|(remaining, right)| {
        (remaining, not!(right))
    })
}

fn value(input: &str) -> IResult<&str, Expression> {
    pair(
        take_while1(|c: char| c.is_ascii_alphabetic()),
        take_while(|c: char| c.is_ascii_alphanumeric() || c == '_'),
    )(input)
        .map(|(remaining, (first, rest))| {
            let value = format!("{first}{rest}");
            (remaining, atomic!(value))
        })
}

#[cfg(test)]
mod tests {
    use crate::{and, atomic, implies, not, or};

    #[test]
    fn test_parse() {
        let input = "a & b => c";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(implies!(and!(atomic!("a"), atomic!("b")), atomic!("c"))));
    }

    #[test]
    fn test_parse_complex() {
        let input = "a => b | !(!c | d & e) => b";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(implies!(
            implies!(
                atomic!("a"),
                or!(
                    atomic!("b"),
                    not!(
                        or!(
                            not!(atomic!("c")),
                            and!(atomic!("d"), atomic!("e"))
                        )
                    )
                )
            ),
            atomic!("b")
        )));
    }

    #[test]
    fn test_operator_weight() {
        let input = "A & B | C => D | E & F";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(implies!(or!(and!(atomic!("A"), atomic!("B")), atomic!("C")), or!(atomic!("D"), and!(atomic!("E"), atomic!("F"))))));
    }

    #[test]
    fn test_implies_chain() {
        let input = "a => b => c";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(implies!(implies!(atomic!("a"), atomic!("b")), atomic!("c"))));
    }

    #[test]
    fn test_parse_parentheses() {
        let input = "a & (b => c)";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(and!(atomic!("a"), implies!(atomic!("b"), atomic!("c")))));
    }

    #[test]
    fn test_parse_not() {
        let input = "!a";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(not!(atomic!("a"))));
    }

    #[test]
    fn test_parse_not_parentheses() {
        let input = "!(a & b)";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(not!(and!(atomic!("a"), atomic!("b")))));
    }

    #[test]
    fn test_expression_with_not_inside_and() {
        let input = "a & !b";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(and!(atomic!("a"), not!(atomic!("b")))));
    }

    #[test]
    fn test_expression_with_not_inside_or() {
        let input = "a | !b";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(or!(atomic!("a"), not!(atomic!("b")))));
    }

    #[test]
    fn test_expression_with_not_inside_implies() {
        let input = "a => !b";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(implies!(atomic!("a"), not!(atomic!("b")))));
    }

    #[test]
    fn test_expression_with_not_inside_parentheses() {
        let input = "a & !(b | c)";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(and!(atomic!("a"), not!(or!(atomic!("b"), atomic!("c"))))));
    }

    #[test]
    fn test_even_not() {
        let input = "!!!!a";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(not!(not!(not!(not!(atomic!("a")))))));
    }

    #[test]
    fn test_odd_not() {
        let input = "!!!!!a";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(not!(not!(not!(not!(not!(atomic!("a"))))))));
    }

    #[test]
    fn test_atomic() {
        let input = "a";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(atomic!("a")));
    }

    #[test]
    fn test_atomic_with_underscore() {
        let input = "a_b";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(atomic!("a_b")));
    }

    #[test]
    fn test_atomic_with_digits() {
        let input = "a1";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(atomic!("a1")));
    }

    #[test]
    fn test_empty() {
        let input = "";
        let result = super::parse_expression(input);
        assert!(result.is_err());
    }

    #[test]
    fn test_or_chain() {
        let input = "a | b | c | d | e | f | g";
        let result = super::parse_expression(input);
        assert_eq!(result, Ok(or!(or!(or!(or!(or!(or!(atomic!("a"), atomic!("b")), atomic!("c")), atomic!("d")), atomic!("e")), atomic!("f")), atomic!("g"))));
    }

    #[test]
    fn test_expression() {
        let input = "a";
        let result = super::_parse_expression(input);
        assert_eq!(result, Ok(("", atomic!("a"))));
    }

    #[test]
    fn test_expression_and() {
        let expression = atomic!("a");
        let input = " & b";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", and!(atomic!("a"), atomic!("b")))));
    }

    #[test]
    fn test_expression_and_or() {
        let expression = atomic!("a");
        let input = " & b | c";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", or!(and!(atomic!("a"), atomic!("b")), atomic!("c")))));
    }

    #[test]
    fn test_expression_and_or_implies() {
        let expression = atomic!("a");
        let input = " & b | c => d";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", implies!(or!(and!(atomic!("a"), atomic!("b")), atomic!("c")), atomic!("d")))));
    }

    #[test]
    fn test_expression_parentheses_or() {
        let expression = atomic!("a");
        let input = " & (b | c) => d";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", implies!(and!(atomic!("a"), or!(atomic!("b"), atomic!("c"))), atomic!("d")))));
    }

    #[test]
    fn test_expression_parentheses_and() {
        let input = "(a & b) | (c & d)";
        let result = super::_parse_expression(input);
        assert_eq!(result, Ok(("", or!(and!(atomic!("a"), atomic!("b")), and!(atomic!("c"), atomic!("d"))))));
    }

    #[test]
    fn test_expression_parentheses_implies() {
        let expression = atomic!("a");
        let input = " & b | (c => d)";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", or!(and!(atomic!("a"), atomic!("b")), implies!(atomic!("c"), atomic!("d"))))));
    }

    #[test]
    fn test_expression_nested_parentheses() {
        let expression = atomic!("a");
        let input = " & (b | (c => d))";
        let result = super::expression(expression)(input);
        assert_eq!(result, Ok(("", and!(atomic!("a"), or!(atomic!("b"), implies!(atomic!("c"), atomic!("d")))))));
    }

    #[test]
    fn test_parse_or() {
        let expression = atomic!("a");
        let input = " | b";
        let result = super::or(expression)(input);
        assert_eq!(result, Ok(("", or!(atomic!("a"), atomic!("b")))));
    }

    #[test]
    fn test_parse_or_parentheses() {
        let input = "(a | b)";
        let result = super::_parse_expression(input);
        assert_eq!(result, Ok(("", or!(atomic!("a"), atomic!("b")))));
    }
}