use std::collections::{HashMap, HashSet};

fn main() {
    let input = advent::read_lines(19);
    println!("19a: {}", distinct_molecules(&input));
    println!("19b: {}", 0);
}

fn distinct_molecules(input: &[String]) -> usize {
    let mut input = input.to_owned();
    let molecule = input.pop().unwrap();
    input.pop(); // drop empty line

    let mut replacements = HashMap::new();
    for line in input {
        let replacement : Vec<_> = line.split(" => ").collect();
        let (left, right) = (replacement[0].to_string(), replacement[1].to_string());
        replacements.entry(left).or_insert(Vec::new()).push(right);
    }

    let mut result = HashSet::new();

    for (left, rights) in replacements {
        for right in rights {
            for i in 0 .. molecule.len() {
                let check_pos = std::cmp::min(i + left.len(), molecule.len());
                if molecule[i..check_pos].contains(&left) {
                    let new_molecule = molecule[0..i].to_string()
                                     + &right
                                     + &molecule[(i + left.len())..];
                    result.insert(new_molecule);
                }
            }
        }
    }

    result.len()
}

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

    #[test]
    fn test() {
        let mut input = Vec::from([
            "H => HO".to_string(),
            "H => OH".to_string(),
            "O => HH".to_string(),
            "".to_string(),
            "HOH".to_string(),
        ]);
        assert_eq!(distinct_molecules(&input), 4);
        input.pop();
        input.push("HOHOHO".to_string());
        assert_eq!(distinct_molecules(&input), 7);
    }
}