use base64::{engine::general_purpose, Engine as _};
use hmac::{Mac, SimpleHmac};
use sha2::Sha256;

use crate::{LibraryResult, LibraryError};

pub struct RegToken {
    token: Vec<u8>,
}

impl RegToken {
    pub fn parse_from_qrcode_uri(uri: &str) -> LibraryResult<RegToken> {
        if uri.len() <= 23 {
            return Err(LibraryError::DecodeError("RegTokenUri too short".to_string()));
        }
        if !uri.starts_with("urn:dhl.de:regtoken:v1:") {
            return Err(LibraryError::DecodeError("RegTokenUri has invalid magic".to_string()));
        }

        let token = &uri[23..];
        let token = general_purpose::STANDARD.decode(token);

        let Ok(mut token) = token else {
            return Err(LibraryError::DecodeError("RegTokenUri not decodeable (base64)".to_string()));
        };

        if token.len() > 64 {
            return Err(LibraryError::DecodeError("RegToken longer than expected".to_string()));
        }

        if token.len() < 32 {
            token.extend(vec![0; 32 - token.len()].iter())
        }

        Ok(RegToken { token })
    }

    pub fn customer_password(&self) -> String {
        general_purpose::STANDARD.encode(&self.token[32..])
    }

    pub fn hmac(&self) -> SimpleHmac<Sha256> {
        let mac = SimpleHmac::<Sha256>::new_from_slice(&self.token[0..32])
            .expect("HMAC can take key of any size");

        mac
    }
}