use arrayvec::ArrayString;
use rand::{rngs::OsRng, seq::SliceRandom};
use std::array;

const CHARS: &[u8] = br##"!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_abcdefghijklmnopqrstuvwxyz{|}~"##;

bitflags::bitflags! {
    struct PasswordFlags: u8 {
        const LOWERCASE = 0b0001;
        const UPPERCASE = 0b0010;
        const NUMBER = 0b0100;
        const SPECIAL_CHARACTER = 0b1000;
    }
}

/// Returns true if the generated master password is valid.
/// It checks that it has at least one lowercase, one uppercase, one number and one punctuation char
#[inline]
fn check_generated_password(password: &[u8; 32]) -> bool {
    let mut flags = PasswordFlags::empty();
    for &byte in password {
        match byte {
            b'a'..=b'z' => flags |= PasswordFlags::LOWERCASE,
            b'A'..=b'Z' => flags |= PasswordFlags::UPPERCASE,
            b'0'..=b'9' => flags |= PasswordFlags::NUMBER,
            b'!'..=b'/' | b':'..=b'@' | b'['..=b'`' | b'{'..=b'~' => {
                flags |= PasswordFlags::SPECIAL_CHARACTER
            }
            _ => (),
        }
        if flags.is_all() {
            return true;
        }
    }
    false
}

#[inline]
fn generate_password() -> ArrayString<32> {
    loop {
        let password: [u8; 32] = array::from_fn(|_| *CHARS.choose(&mut OsRng).unwrap());
        if check_generated_password(&password) {
            return ArrayString::from_byte_string(&password).unwrap();
        }
    }
}

/// Continuously generates the password until it passes the checks
#[inline]
pub fn generate_passwords() -> [ArrayString<32>; 10] {
    array::from_fn(|_| generate_password())
}