use {
    anyhow::{
        anyhow,
        Context,
        Result,
    },
    std::{
        env::args,
        fs::File,
        io::{
            BufRead,
            BufReader,
        },
        path::Path,
    },
};

fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<Vec<usize>>> {
    let reader = BufReader::new(File::open(filename)?);

    let mut elves = vec![vec![]];

    for line in reader.lines() {
        let s = line?;
        if s.is_empty() {
            elves.push(vec![]);
            continue;
        }
        let elf = elves.last_mut().context("Invalid elves vector.")?;
        let n = s.parse().context("Could not parse {s}")?;
        elf.push(n);
    }

    Ok(elves)
}

fn part1<'a, I: IntoIterator<Item = &'a Vec<usize>>>(input: I) -> Result<usize> {
    input.into_iter().map(|foodpacks| foodpacks.iter().sum()).max()
        .context("Iterator chain in first part failed.")
}

fn part2<'a, I: IntoIterator<Item = &'a Vec<usize>>>(input: I) -> Result<usize> {
    let mut calories: Vec<usize> = input.into_iter().map(|foodpacks| foodpacks.iter().sum())
        .collect();
    calories.sort();

    Ok(calories.into_iter().rev().take(3).sum::<usize>())
}

fn main() -> Result<()> {
    let ( do_part_1, do_part_2 ) = aoc::do_parts();

    let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
    let input = read_input(filename).context("Could not read input")?;
    if do_part_1 {
        let solution = part1(&input).context("No solution for part 1")?;
        println!("Part1, solution found to be: {}", solution);
    }
    if do_part_2 {
        let solution = part2(&input).context("No solution for part 2")?;
        println!("Part2, solution found to be: {}", solution);
    }
    Ok(())
}