RUST: CAS number validation checker

use regex::Regex;
use std::io;

fn is_valid_cas_number(cas: &str) -> bool {
    // Check if the CAS number matches the format
    let cas_pattern = Regex::new(r"^\d{2,7}-\d{2}-\d$").unwrap();
    if !cas_pattern.is_match(cas) {
        return false;
    }

    // Remove hyphens and convert to a vector of digits
    let digits: Vec<u32> = cas
        .replace("-", "")
        .chars()
        .filter_map(|c| c.to_digit(10))
        .collect();

    // Ensure there are at least 3 digits (2 for the number, 1 for the checksum)
    if digits.len() < 3 {
        return false;
    }

    // Separate the checksum from the rest of the digits
    let checksum = digits[digits.len() - 1];
    let number_digits = &digits[..digits.len() - 1];

    // Calculate the weighted sum
    let sum: u32 = number_digits
        .iter()
        .rev() // Start multiplying from the right
        .enumerate()
        .map(|(i, &digit)| digit * (i as u32 + 1))
        .sum();

    // Compare the last digit of the sum to the checksum
    sum % 10 == checksum
}

fn main() {
    // Prompt the user for input
    println!("Enter a CAS number to validate:");

    let mut input = String::new();
    io::stdin()
        .read_line(&mut input)
        .expect("Failed to read input");

    // Trim whitespace from the input
    let cas_number = input.trim();

    // Validate the CAS number
    if is_valid_cas_number(cas_number) {
        println!("'{}' is a valid CAS number.", cas_number);
    } else {
        println!("'{}' is NOT a valid CAS number.", cas_number);
    }
}