use std::string::FromUtf8Error;
use base32::{self, Alphabet};

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SecretParseError {
    ParseBase32,
    Utf8Error(FromUtf8Error),
}

/// Representation of a secret either a "raw" \[u8\] or "base 32" encoded String
///
/// # Examples
///
/// - Create a TOTP from a "raw" secret
/// ```
/// use totp_rs::{Secret, TOTP, Algorithm};
///
/// let secret = [
///     0x70, 0x6c, 0x61, 0x69, 0x6e, 0x2d, 0x73, 0x74, 0x72, 0x69, 0x6e, 0x67, 0x2d, 0x73, 0x65,
///     0x63, 0x72, 0x65, 0x74, 0x2d, 0x31, 0x32, 0x33,
/// ];
/// let secret_raw = Secret::Raw(secret.to_vec());
/// let totp_raw = TOTP::new(
///     Algorithm::SHA1,
///     6,
///     1,
///     30,
///     secret_raw.to_bytes().unwrap(),
///     None,
///     "account".to_string(),
/// ).unwrap();
///
/// println!("code from raw secret:\t{}", totp_raw.generate_current().unwrap());
/// ```
///
/// - Create a TOTP from a base32 encoded secret
/// ```
/// use totp_rs::{Secret, TOTP, Algorithm};
///
/// let secret_b32 = Secret::Encoded(String::from("OBWGC2LOFVZXI4TJNZTS243FMNZGK5BNGEZDG"));
/// let totp_b32 = TOTP::new(
///     Algorithm::SHA1,
///     6,
///     1,
///     30,
///     secret_b32.to_bytes().unwrap(),
///     None,
///     "account".to_string(),
/// ).unwrap();
///
/// println!("code from base32:\t{}", totp_b32.generate_current().unwrap());
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Secret {
    /// represent a non-encoded "raw" secret
    Raw(Vec<u8>),
    /// represent a base32 encoded secret
    Encoded(String),
}

impl Secret {

    /// Get the inner String value as a Vec of bytes
    pub fn to_bytes(&self) -> Result<Vec<u8>, SecretParseError> {
        match self {
            Secret::Raw(s) => Ok(s.to_vec()),
            Secret::Encoded(s) => match base32::decode(Alphabet::RFC4648 { padding: false }, s) {
                Some(bytes) => Ok(bytes),
                None => Err(SecretParseError::ParseBase32),
            },
        }
    }

    /// Try to transform a `Secret::Encoded` into a `Secret::Raw`
    pub fn to_raw(&self) -> Result<Self, SecretParseError> {
        match self {
            Secret::Raw(_) => Ok(self.clone()),
            Secret::Encoded(s) => match base32::decode(Alphabet::RFC4648 { padding: false }, s) {
                Some(buf) => Ok(Secret::Raw(buf)),
                None => Err(SecretParseError::ParseBase32),
            },
        }
    }

    /// Try to transforms a `Secret::Raw` into a `Secret::Encoded`
    pub fn to_encoded(&self) -> Self {
        match self {
            Secret::Raw(s) => Secret::Encoded(base32::encode(
                Alphabet::RFC4648 { padding: false },
                &s,
            )),
            Secret::Encoded(_) => self.clone(),
        }
    }

    /// ⚠️ requires feature `gen_secret`
    ///
    /// Generate a CSPRNG binary value of 160 bits,
    /// the recomended size from [rfc-4226](https://www.rfc-editor.org/rfc/rfc4226#section-4)
    ///
    /// > The length of the shared secret MUST be at least 128 bits.
    /// > This document RECOMMENDs a shared secret length of 160 bits.
    ///
    /// ⚠️ The generated secret is not guaranteed to be a valid UTF-8 sequence
    #[cfg(feature = "gen_secret")]
    pub fn generate_secret() -> Secret {
        use rand::Rng;

        let mut rng = rand::thread_rng();
        let mut secret: [u8; 20] = Default::default();
        rng.fill(&mut secret);
        Secret::Raw(secret.to_vec())
    }
}

impl std::fmt::Display for Secret {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Secret::Raw(bytes) => {
                let mut s: String = String::new();
                for b in bytes {
                    s = format!("{}{:02x}", &s, &b);
                }
                write!(f, "{}", s)
            },
            Secret::Encoded(s) => write!(f, "{}", s),
        }
    }
}

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

    const BASE32: &str = "OBWGC2LOFVZXI4TJNZTS243FMNZGK5BNGEZDG";
    const BYTES: [u8; 23] = [
        0x70, 0x6c, 0x61, 0x69, 0x6e, 0x2d, 0x73, 0x74, 0x72, 0x69, 0x6e, 0x67, 0x2d, 0x73, 0x65,
        0x63, 0x72, 0x65, 0x74, 0x2d, 0x31, 0x32, 0x33,
    ];
    const BYTES_DISPLAY: &str = "706c61696e2d737472696e672d7365637265742d313233";

    #[test]
    fn secret_display() {
        let base32_str = String::from(BASE32);
        let secret_raw = Secret::Raw(BYTES.to_vec());
        let secret_base32 = Secret::Encoded(base32_str.clone());
        println!("{}", secret_raw);
        assert_eq!(secret_raw.to_string(), BYTES_DISPLAY.to_string());
        assert_eq!(secret_base32.to_string(), BASE32.to_string());
    }

    #[test]
    fn secret_convert_base32_raw() {
        let base32_str = String::from(BASE32);
        let secret_raw = Secret::Raw(BYTES.to_vec());
        let secret_base32 = Secret::Encoded(base32_str.clone());

        assert_eq!(&secret_raw.to_encoded(), &secret_base32);
        assert_eq!(&secret_raw.to_raw().unwrap(), &secret_raw);

        assert_eq!(&secret_base32.to_raw().unwrap(), &secret_raw);
        assert_eq!(&secret_base32.to_encoded(), &secret_base32);
    }

    #[test]
    fn secret_as_bytes() {
        let base32_str = String::from(BASE32);
        assert_eq!(Secret::Raw(BYTES.to_vec()).to_bytes().unwrap(), BYTES.to_vec());
        assert_eq!(Secret::Encoded(base32_str).to_bytes().unwrap(), BYTES.to_vec());
    }

    #[test]
    #[cfg(feature = "gen_secret")]
    fn secret_gen_secret() {
        match Secret::generate_secret() {
            Secret::Raw(secret) => assert_eq!(secret.len(), 20),
            Secret::Encoded(_) => panic!("should be raw"),
        }
    }
}