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//! 🎁 Applet module

/// Applet creation & update trait
pub trait Applet {
    /// Creation of a new module
    ///
    /// This is called once on startup of the module
    fn new() -> Self;

    /// Implement the update of the applet module here
    fn update(&mut self) {}
}

/// Persistable applet state accessor
#[cfg(feature = "with_serde")]
pub trait AppletPersist<T>
where
    T: serde::de::DeserializeOwned + serde::Serialize,
{
    /// Accessor to Serde-serializable structure for serializing and deserializing state
    fn persistable_state(&mut self) -> &mut T;

    /// Optional callback just before state is persisted
    fn pre_persist(&mut self) {}

    /// Optional callback after state has een restored
    fn post_restore(&mut self) {}
}

/// Implement an applet module
#[macro_export]
macro_rules! impl_applet {
    ($module: ty) => {
        use $crate::applet::Applet as _;

        static mut MODULE: Option<$module> = None;

        #[no_mangle]
        pub fn ark_initialize() {
            $crate::init();
            // SAFETY: Sound to access static as we do not use threads in Wasm and this is guaranteed to be called first in the module
            unsafe {
                MODULE = Some(<$module as $crate::applet::Applet>::new());
            }
        }

        #[no_mangle]
        pub fn ark_applet_update() {
            // SAFETY: Sound to access static as we do not use threads in Wasm and this is guaranteed to be initialized on startup with `ark_initialize` first
            unsafe {
                let module = MODULE.as_mut().unwrap();
                <$module as $crate::applet::Applet>::update(module);
            }
        }
    };
}

/// Implement an applet module that can have persistent state
#[macro_export]
#[cfg(feature = "with_serde")]
macro_rules! impl_applet_persist {
    ($module: ty) => {
        $crate::impl_applet!($module);

        use $crate::applet::AppletPersist as _;
        use $crate::ErrorCode;

        #[no_mangle]
        pub unsafe fn ark_state_persist() -> ErrorCode {
            if let Some(module) = MODULE.as_mut() {
                module.pre_persist();
                match $crate::applet::serialize_state(module.persistable_state()) {
                    Ok(state) => {
                        ark::core::return_slice(&state);
                        ErrorCode::Success
                    }
                    Err(err) => {
                        $crate::error!("Couldn't save state, err: {:?}", &err);
                        ErrorCode::InternalError
                    }
                }
            } else {
                ErrorCode::InternalError
            }
        }

        #[no_mangle]
        pub unsafe fn ark_state_restore(state_ptr: *const u8, state_size: u32) -> ErrorCode {
            let state_slice = std::slice::from_raw_parts(state_ptr, state_size as usize);

            if let Some(module) = MODULE.as_mut() {
                let module_state = module.persistable_state();

                match $crate::applet::deserialize_state(state_slice) {
                    Ok(new_state) => {
                        *module_state = new_state;
                        module.post_restore();
                        ErrorCode::Success
                    }
                    Err(err) => {
                        $crate::error!("Couldn't load state, err: {:?}", &err);
                        ErrorCode::InternalError
                    }
                }
            } else {
                ErrorCode::InternalError
            }
        }
    };
}

/// Serialize applet state to binary blob
///
/// This is an internal function used by the `impl_applet_persist` macro
#[doc(hidden)]
#[cfg(feature = "with_serde")]
pub fn serialize_state<T: ?Sized>(value: &T) -> Result<Vec<u8>, flexbuffers::SerializationError>
where
    T: serde::Serialize,
{
    let mut serializer = flexbuffers::FlexbufferSerializer::new();
    value.serialize(&mut serializer)?;
    let vec = serializer.take_buffer();
    Ok(vec)
}

/// Deserialize applet from binary blob
///
/// This is an internal function used by the `impl_applet_persist` macro
#[doc(hidden)]
#[cfg(feature = "with_serde")]
pub fn deserialize_state<'a, T>(bytes: &'a [u8]) -> Result<T, flexbuffers::DeserializationError>
where
    T: serde::Deserialize<'a>,
{
    let reader = flexbuffers::Reader::get_root(bytes)?;
    let v = T::deserialize(reader)?;
    Ok(v)
}