use std::collections::VecDeque;

static DAY: u8 = 9;

fn main() {
    let input = advent::read_file(DAY);
    println!("{DAY}a: {}", fs_checksum(&input));
    println!("{DAY}b: {}", 0);
}

fn fs_checksum(map: &str) -> usize {
    let counts = map.trim_end().chars().map(|x| x.to_digit(10).unwrap() as u8).collect::<Vec<_>>();

    let mut file_ids = VecDeque::new();
    let mut block_sizes = VecDeque::new();
    let mut holes = VecDeque::new();
    for (id, c) in counts.chunks(2).enumerate() {
        let file = c[0];
        for _ in 0 .. file {
            file_ids.push_back(id);
        }
        block_sizes.push_back(file);
        if c.len() == 2 {
            let free = c[1];
            holes.push_back(free);
        }
    }

    let mut disk = Vec::new();
    disk.reserve(map.len() * 10);
    while !holes.is_empty() && !file_ids.is_empty() {
        let blocks_front = block_sizes.pop_front().unwrap() as usize;
        for _ in 0 .. blocks_front.min(file_ids.len()) {
            let front = file_ids.pop_front().unwrap();
            disk.push(front);
        }
        let holes_front = holes.pop_front().unwrap() as usize;
        for _ in 0 .. holes_front.min(file_ids.len()) {
            let back = file_ids.pop_back().unwrap();
            disk.push(back);
        }
    }

    disk.iter()
        .enumerate()
        .map(|(i, block)| i * block)
        .sum()
}

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

    #[test]
    fn test() {
        let input = "2333133121414131402";
        assert_eq!(fs_checksum(input), 1928);
    }
}