use std::fs;

#[derive(Clone, Debug)]
struct Disc {
    pos: usize,
    period: usize,
}

fn parse(lines: Vec<&str>) -> Vec<Disc> {
    let mut result = Vec::new();
    // Add a dummy 0th disc for slightly cleaner code later
    result.push(Disc { pos: 0, period: 1 });

    for line in lines {
        let words: Vec<&str> = line.split_ascii_whitespace().collect();
        result.push(Disc {
            pos: words[11].trim_end_matches('.').parse().unwrap(),
            period: words[3].parse().unwrap(),
        });
    }

    result
}

fn solve_puzzle(discs: &Vec<Disc>) -> usize {
    let mut t_start = 0;

    'outer: loop {
        let mut dt = 1;
        while dt < discs.len() {
            // Calculate the disc's current position. If 0, the capsule
            // can continue, otherwise this `t_start' must be rejected.
            if (discs[dt].pos + t_start + dt) % discs[dt].period != 0 {
                t_start += 1;
                continue 'outer;
            }
            dt += 1;
        }

        return t_start;
    }
}

fn main() {
    // Read disc stats from input text file
    let input = fs::read_to_string("input.txt").unwrap();
    let lines = input.lines().collect();
    let mut discs = parse(lines);

    // Part 1 gives 203660 for me
    println!("Part 1 solution: {}", solve_puzzle(&discs));

    discs.push(Disc { pos: 0, period: 11 });
    // Part 2 gives 2408135 for me
    println!("Part 2 solution: {}", solve_puzzle(&discs));
}

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

    #[test]
    fn part1_example1() {
        let lines = vec![
            "Disc #1 has 5 positions; at time=0, it is at position 4.",
            "Disc #2 has 2 positions; at time=0, it is at position 1.",
        ];
        let discs = parse(lines);
        assert_eq!(solve_puzzle(&discs), 5);
    }
}