use structopt::StructOpt;

#[derive(Debug, StructOpt)]
#[structopt(name = "Day 4: Secure Container")]
/// Calculates how many possible lock values there are
///
/// See https://adventofcode.com/2019/day/4 for details.
struct Opt {
    /// Repeated digits must be exactly 2 long
    #[structopt(long = "larger-range-rule")]
    larger_range_rule: bool,
    min: u32,
    max: u32,
}

fn main() {
    let opt = Opt::from_args();

    println!(
        "{}",
        valid_combinations(opt.min, opt.max, opt.larger_range_rule)
    )
}

fn valid_combinations(min: u32, max: u32, larger_range_rule: bool) -> u32 {
    (min..max)
        .filter(|x| {
            two_adjacent_identical_digits(*x, larger_range_rule) && digits_never_decrease(*x)
        })
        .count() as u32
}

fn two_adjacent_identical_digits(x: u32, larger_range_rule: bool) -> bool {
    if larger_range_rule {
        (0..5).any(|d| {
            digit(x, d) == digit(x, d + 1)
                && digit(x, d) != digit(x, d + 2)
                && digit(x, d) != digit(x, d - 1)
        })
    } else {
        (0..5).any(|d| digit(x, d) == digit(x, d + 1))
    }
}

fn digits_never_decrease(x: u32) -> bool {
    (0..5).all(|d| digit(x, d) >= digit(x, d + 1))
}

fn digit(x: u32, digit: i32) -> u32 {
    if digit < 0 {
        0
    } else {
        (x / 10u32.pow(digit as u32)) % 10
    }
}