use std::env;
use std::error::Error;
use std::fs::File;
use std::io::{BufReader, prelude::*};

fn parse_line(line: &str) -> Result<(i64, i64), Box<dyn Error>> {
    // Split line on whitespace
    // Expecting "88789   64926"
    // Should end up with two string, if not something is wrong.
    let split_line: Vec<_> = line
        .splitn(2, char::is_whitespace)
        .map(|elm| elm.trim())
        .collect();

    // Parse and return our two elements
    let first_element = split_line[0].parse::<i64>()?;
    let second_element = split_line[1].parse::<i64>()?;
    return Ok((first_element, second_element));
}

/// Part one of day 1
/// Calculate the difference after sorting each list from smallest to biggest
fn calculate_diff(mut left_list: Vec<i64>, mut right_list: Vec<i64>) -> i64 {
    // sort lists
    left_list.sort();
    right_list.sort();

    let mut accumulator = 0;
    for (index, left_value) in left_list.iter().enumerate() {
        let right_value = right_list[index];
        let absolute_diff = (left_value - right_value).abs();
        accumulator += absolute_diff;
    }

    accumulator
}

fn main() -> Result<(), Box<dyn Error>> {
    // Handle command input
    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        panic!(
            "{} must be run with a single argument of files name!",
            &args[0]
        )
    }
    let input_file_string = &args[1];

    let input_file = File::open(input_file_string)?;
    let input_reader = BufReader::new(input_file);

    let mut left_list: Vec<i64> = Vec::new();
    let mut right_list: Vec<i64> = Vec::new();

    for line in input_reader.lines() {
        let line = line?;
        let parsed_line = parse_line(&line)?;
        //println!("({},{})", parsed_line.0, parsed_line.1);
        left_list.push(parsed_line.0);
        right_list.push(parsed_line.1);
    }

    println!("Result: {}", calculate_diff(left_list, right_list));

    return Ok(());
}