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//! # OpenMLS Key Store Trait

/// Sealed list of struct openmls manages (create/read/delete) through [OpenMlsKeyStore]
pub enum MlsEntityId {
    SignatureKeyPair,
    HpkePrivateKey,
    KeyPackage,
    PskBundle,
    EncryptionKeyPair,
    GroupState,
}

/// To implement by any struct owned by openmls aiming to be persisted in [OpenMlsKeyStore]
pub trait MlsEntity: serde::Serialize + serde::de::DeserializeOwned {
    /// Identifier used to downcast the actual entity within an [OpenMlsKeyStore] method.
    /// In case for example you need to select a SQL table depending on the entity type
    const ID: MlsEntityId;
}

/// Blanket impl for when you have to lookup a list of entities from the keystore
impl<T> MlsEntity for Vec<T>
where
    T: MlsEntity + std::fmt::Debug,
{
    const ID: MlsEntityId = T::ID;
}

/// The Key Store trait
pub trait OpenMlsKeyStore: Send + Sync {
    /// The error type returned by the [`OpenMlsKeyStore`].
    type Error: std::error::Error + std::fmt::Debug + PartialEq;

    /// Store a value `v` that implements the [`MlsEntity`] trait for
    /// serialization for ID `k`.
    ///
    /// Returns an error if storing fails.
    fn store<V: MlsEntity>(&self, k: &[u8], v: &V) -> Result<(), Self::Error>
    where
        Self: Sized;

    /// Read and return a value stored for ID `k` that implements the
    /// [`MlsEntity`] trait for deserialization.
    ///
    /// Returns [`None`] if no value is stored for `k` or reading fails.
    fn read<V: MlsEntity>(&self, k: &[u8]) -> Option<V>
    where
        Self: Sized;

    /// Delete a value stored for ID `k`.
    ///
    /// Returns an error if storing fails.
    fn delete<V: MlsEntity>(&self, k: &[u8]) -> Result<(), Self::Error>;
}