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/// Traits for signature schemes
use crate::Result;

/// A public key for a signature scheme
pub trait PublicKey {
    fn as_bytes(&self) -> &[u8];
    fn from_bytes(bytes: &[u8]) -> Result<Self>
    where
        Self: Sized;
}

/// A secret key for a signature scheme
pub trait SecretKey {
    fn as_bytes(&self) -> &[u8];
    fn from_bytes(bytes: &[u8]) -> Result<Self>
    where
        Self: Sized;
}

/// A signed message.
///
/// This object contains both the signed message and the signature on it.
/// If you use this struct, you no longer should send the plain text along
/// with it. The [`open`] methods make sure that you will not
/// process invalid ciphertexts by not returning the plain text if the signature
/// is invalid.
///
/// [`open`]: https://docs.rs/pqcrypto/0.7.0/pqcrypto/sign/sphincsshake256128ssimple/fn.open.html
pub trait SignedMessage {
    fn as_bytes(&self) -> &[u8];
    fn from_bytes(bytes: &[u8]) -> Result<Self>
    where
        Self: Sized;
}

/// A detached signature
///
/// This signature does not include the message it certifies; this means that to verify it you also
/// need the message.
///
/// If you can get away with it, use the [`SignedMessage`] API, which ensures you won't use the message
/// before having authenticated it.
pub trait DetachedSignature {
    fn as_bytes(&self) -> &[u8];
    fn from_bytes(bytes: &[u8]) -> Result<Self>
    where
        Self: Sized;
}

/// Errors that may arise when verifying a signature
#[derive(Clone, Copy, Debug)]
#[non_exhaustive]
pub enum VerificationError {
    InvalidSignature,
    UnknownVerificationError,
}

impl core::fmt::Display for VerificationError {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error> {
        match self {
            VerificationError::InvalidSignature => write!(f, "error: verification failed"),
            VerificationError::UnknownVerificationError => write!(f, "unknown error"),
        }
    }
}

#[cfg(feature = "std")]
impl std::error::Error for VerificationError {}