use std::collections::HashMap;
use std::fs;

fn solve_puzzle(lines: &Vec<&str>, use_max: bool) -> String {
    let mut freqs = Vec::new();
    for _i in 0..lines[0].len() {
        let hm: HashMap<char, usize> = HashMap::new();
        freqs.push(hm);
    }

    // Count char occurrences at each index in line
    for line in lines {
        for (i, c) in line.chars().enumerate() {
            *freqs[i].entry(c).or_insert(0) += 1;
        }
    }

    let mut result = String::new();
    for hm in freqs {
        let c = if use_max {
            // Part 1: take most common character
            hm.into_iter().max_by_key(|x| x.1).unwrap().0
        } else {
            // Part 2: take least common character
            hm.into_iter().min_by_key(|x| x.1).unwrap().0
        };
        result.push(c);
    }

    result
}

fn main() {
    // Read messages from input text file
    let input = fs::read_to_string("input.txt").unwrap();
    let lines = input.lines().collect();

    // Part 1 gives "mlncjgdg" for me
    println!("Part 1 solution: {}", solve_puzzle(&lines, true));

    // Part 2 gives "bipjaytb" for me
    println!("Part 2 solution: {}", solve_puzzle(&lines, false));
}

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

    const EXAMPLE1_LINES: [&str; 16] = [
        "eedadn", "drvtee", "eandsr", "raavrd", "atevrs", "tsrnev", "sdttsa", "rasrtv",
        "nssdts", "ntnada", "svetve", "tesnvt", "vntsnd", "vrdear", "dvrsen", "enarar",
    ];

    #[test]
    fn part1_example1() {
        assert_eq!(solve_puzzle(&Vec::from(EXAMPLE1_LINES), true), "easter");
    }

    #[test]
    fn part2_example1() {
        assert_eq!(solve_puzzle(&Vec::from(EXAMPLE1_LINES), false), "advent");
    }
}