use std::collections::HashSet;

fn main() {
    let input = "hxbxwxba";
    println!("11a: {}", next_password(input));
    println!("11b: {}", next_password(&next_password(input)));
}

fn has_straight(password: &str) -> bool {
    let mut prevprev = password.chars().next().unwrap().to_digit(36).unwrap();
    let mut prev = password.chars().nth(1).unwrap().to_digit(36).unwrap();

    for c in password.chars().skip(2) {
        let digit = c.to_digit(36).unwrap();
        if prevprev + 1 == prev && prev + 1 == digit {
            return true;
        }
        prevprev = prev;
        prev = digit;
    }
    false
}

fn has_forbidden_letters(password: &str) -> bool {
    password.contains('i') || password.contains('o') || password.contains('l')
}

fn has_two_pairs(password: &str) -> bool {
    let mut pairs = HashSet::new();
    let mut prev = password.chars().next().unwrap();

    for c in password.chars().skip(1) {
        if prev == c {
            pairs.insert(c);
        }
        prev = c;
    }
    pairs.len() > 1
}

fn valid_password(password: &str) -> bool {
    has_straight(password) && !has_forbidden_letters(password) && has_two_pairs(password)
}

fn inc_password_at_position(password: &str, pos: usize) -> String {
    let mut bytes = password.to_string().into_bytes();
    bytes.reverse();
    bytes[pos] += 1;
    if bytes[pos] > b'z' {
        bytes[pos] = b'a';
        bytes.reverse();
        let new_password = String::from_utf8(bytes.to_vec()).unwrap();
        inc_password_at_position(&new_password, pos + 1)
    } else {
        bytes.reverse();
        String::from_utf8(bytes.to_vec()).unwrap()
    }
}

fn next_password(password: &str) -> String {
    let mut password = inc_password_at_position(password, 0);
    while !valid_password(&password) {
        password = inc_password_at_position(&password, 0)
    }
    password
}

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

    #[test]
    fn test() {
        assert!(!valid_password("hijklmmn"));
        assert!(!valid_password("abbceffg"));
        assert!(!valid_password("abbcegjk"));
        assert_eq!(next_password("abcdefgh"), "abcdffaa");
        assert_eq!(next_password("ghijklmn"), "ghjaabcc");
    }
}