use crate::input::Input;

fn make_ascii_titlecase(s: &mut str) -> &str {
    if let Some(r) = s.get_mut(0..1) {
        r.make_ascii_uppercase();
    }
    s
}

fn sum_required_fuel(input_string: &str, fuel_calculator: fn(u32) -> u32) -> Result<u32, String> {
    let parts = input_string
        .lines()
        .enumerate()
        .map(|(line_index, line)| {
            let module_mass = line.parse::<u32>().map_err(|error| {
                format!(
                    "Line {}: {}",
                    line_index + 1,
                    make_ascii_titlecase(&mut error.to_string())
                )
            })?;
            if module_mass < 6 {
                return Err(format!(
                    "Line {}: Too small module mass (less than 6)",
                    line_index + 1
                ));
            }
            Ok(fuel_calculator(module_mass))
        })
        .collect::<Result<Vec<u32>, String>>()?;
    Ok(parts.iter().sum())
}

pub fn solve(input: &mut Input) -> Result<u32, String> {
    if input.is_part_one() {
        sum_required_fuel(input.text, |mass| mass / 3 - 2)
    } else {
        fn required_fuel(mass: u32) -> u32 {
            match (mass / 3).checked_sub(2) {
                Some(fuel) => fuel + required_fuel(fuel),
                None => 0,
            }
        }
        sum_required_fuel(input.text, required_fuel)
    }
}

#[test]
pub fn tests() {
    use crate::input::{test_part_one, test_part_one_error, test_part_two};

    test_part_one!("12" => 2);
    test_part_one!("14" => 2);
    test_part_one!("1969" => 654);
    test_part_one!("100756" => 33583);

    let input = include_str!("day01_input.txt");
    test_part_one!(input => 3_262_358);
    test_part_one_error!(
        "\n" => "Line 1: Cannot parse integer from empty string"
    );

    test_part_two!("14" => 2);
    test_part_two!("1969" => 966);
    test_part_two!("100756" => 50346);

    test_part_two!(input => 4_890_696);
}