#![allow(dead_code)]

struct Parser<'a> {
    chars: std::str::Chars<'a>,
}

impl<'a> Parser<'a> {
    fn new(chars: std::str::Chars<'a>) -> Self {
        Parser { chars }
    }
}

impl<'a> Iterator for Parser<'a> {
    type Item = bool;

    fn next(&mut self) -> Option<Self::Item> {
        self.chars.next().and_then(|ch| match ch {
            't' => Some(true),
            'f' => Some(false),
            '!' => {
                assert_eq!(self.chars.next(), Some('('));
                let r = self.next().map(|r| !r);
                assert_eq!(self.chars.next(), Some(')'));
                r
            }
            '&' => {
                assert_eq!(self.chars.next(), Some('('));
                Some(self.fold(true, |r, v| r && v))
            }
            '|' => {
                assert_eq!(self.chars.next(), Some('('));
                Some(self.fold(false, |r, v| r || v))
            }
            ',' => self.next(),
            ')' => None,
            _ => panic!("Unexpected char {}", ch),
        })
    }
}

struct Solution;

impl Solution {
    pub fn parse_bool_expr(expression: String) -> bool {
        Parser::new(expression.chars()).next().unwrap()
    }
}

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

    #[test]
    fn test_simple() {
        assert_eq!(Solution::parse_bool_expr("f".into()), false);
        assert_eq!(Solution::parse_bool_expr("t".into()), true);
    }

    #[test]
    fn test_not() {
        assert_eq!(Solution::parse_bool_expr("!(f)".into()), true);
        assert_eq!(Solution::parse_bool_expr("!(t)".into()), false);
    }

    #[test]
    fn test_and() {
        assert_eq!(Solution::parse_bool_expr("&(f,t)".into()), false);
        assert_eq!(Solution::parse_bool_expr("&(t,t)".into()), true);
    }

    #[test]
    fn test_or() {
        assert_eq!(Solution::parse_bool_expr("|(f,t)".into()), true);
        assert_eq!(Solution::parse_bool_expr("|(t,t)".into()), true);
        assert_eq!(Solution::parse_bool_expr("|(f,f)".into()), false);
    }

    #[test]
    fn test_subexpressions() {
        assert_eq!(Solution::parse_bool_expr("|(f,!(f))".into()), true);
        assert_eq!(Solution::parse_bool_expr("&(!(f),f)".into()), false);
        assert_eq!(
            Solution::parse_bool_expr("!(&(&(!(&(f)),&(t),|(f,f,t)),&(t),&(t,t,f)))".into()),
            true
        );
    }
}