// Copyright (c) Meta Platforms, Inc. and affiliates.
//
// This source code is dual-licensed under either the MIT license found in the
// LICENSE-MIT file in the root directory of this source tree or the Apache
// License, Version 2.0 found in the LICENSE-APACHE file in the root directory
// of this source tree. You may select, at your option, one of the above-listed
// licenses.

//! HashEdDSA implementation for [`SigmaI`](crate::SigmaI). Currently only
//! supports [`Ed25519`](crate::Ed25519).

use core::marker::PhantomData;

use generic_array::GenericArray;
use rand::{CryptoRng, Rng};
use zeroize::Zeroize;

use self::implementation::HashEddsaImpl;
use super::{Message, MessageBuilder, SignatureProtocol};
use crate::ciphersuite::CipherSuite;
use crate::errors::ProtocolError;
use crate::key_exchange::group::Group;

/// HashEdDSA for [`SigmaI`](crate::SigmaI).
///
/// The ["verification state"](Self::VerifyState) is the pre-hash for the
/// message to be verified.
pub struct HashEddsa<G>(PhantomData<G>);

impl<G: HashEddsaImpl> SignatureProtocol for HashEddsa<G> {
    type Group = G;
    type Signature = G::Signature;
    type SignatureLen = G::SignatureLen;
    type VerifyState<CS: CipherSuite, KE: Group> = G::VerifyState<CS, KE>;

    fn sign<'a, R: CryptoRng + Rng, CS: CipherSuite, KE: Group>(
        sk: &<Self::Group as Group>::Sk,
        _: &mut R,
        message: &Message<CS, KE>,
    ) -> (Self::Signature, Self::VerifyState<CS, KE>) {
        G::sign(sk, message)
    }

    fn verify<CS: CipherSuite, KE: Group>(
        pk: &<Self::Group as Group>::Pk,
        _: MessageBuilder<'_, CS>,
        state: Self::VerifyState<CS, KE>,
        signature: &Self::Signature,
    ) -> Result<(), ProtocolError> {
        G::verify(pk, state, signature)
    }

    fn serialize_signature(signature: &Self::Signature) -> GenericArray<u8, Self::SignatureLen> {
        G::serialize_signature(signature)
    }

    fn deserialize_take_signature(bytes: &mut &[u8]) -> Result<Self::Signature, ProtocolError> {
        G::deserialize_take_signature(bytes)
    }
}

pub(in super::super) mod implementation {
    use generic_array::ArrayLength;

    use super::*;

    pub trait HashEddsaImpl: Group {
        type Signature: Clone + Zeroize;
        type SignatureLen: ArrayLength;
        type VerifyState<CS: CipherSuite, KE: Group>: Clone + Zeroize;

        fn sign<CS: CipherSuite, KE: Group>(
            sk: &Self::Sk,
            message: &Message<CS, KE>,
        ) -> (Self::Signature, Self::VerifyState<CS, KE>);

        fn verify<CS: CipherSuite, KE: Group>(
            pk: &Self::Pk,
            state: Self::VerifyState<CS, KE>,
            signature: &Self::Signature,
        ) -> Result<(), ProtocolError>;

        fn deserialize_take_signature(bytes: &mut &[u8]) -> Result<Self::Signature, ProtocolError>;

        fn serialize_signature(signature: &Self::Signature)
        -> GenericArray<u8, Self::SignatureLen>;
    }
}