PkmnLib_rs/src/script_implementations/wasm/extern_ref.rs

use std::marker::PhantomData;
use std::mem::transmute;
use std::sync::Arc;

use crate::script_implementations::wasm::script_resolver::{
    WebAssemblyEnv, WebAssemblyEnvironmentData, WebAssemblyScriptResolver,
};
use unique_type_id::UniqueTypeId;
use wasmer::FromToNativeWasmType;
use wasmer::FunctionEnvMut;

/// An Extern Ref allows us to pass objects to WASM without actually passing raw memory, or
/// requiring us to make copies. Instead, we pass a simple increment index, that we can then use
/// to find the relevant data.
#[derive(Copy, Clone)]
pub(crate) struct ExternRef<T: UniqueTypeId<u64>> {
    /// The lookup index we can use to find the data.
    index: u32,
    /// Phantom data so we can get a type generic.
    _phantom: PhantomData<T>,
}

impl<T: UniqueTypeId<u64>> ExternRef<T> {
    /// Instantiates a new ExternRef for a bit of data. If we already have made an Extern Ref for
    /// this data and type, we use that instead.
    pub fn new(env: &WebAssemblyEnvironmentData, value: &T) -> Self {
        Self {
            index: env.get_extern_ref_index(value),
            _phantom: Default::default(),
        }
    }

    /// Instantiates a new ExternRef for a bit of data using the function environment. If we already
    /// have made an Extern Ref for this data and type, we use that instead.
    pub fn func_new(env: &FunctionEnvMut<WebAssemblyEnv>, value: &T) -> Self {
        Self {
            index: env.data().data().get_extern_ref_index(value),
            _phantom: Default::default(),
        }
    }

    /// Creates an ExternRef with a given resolver. This can be used in cases where we do not have an environment variable.
    pub(crate) fn new_with_resolver(resolver: &WebAssemblyScriptResolver, value: &T) -> Self {
        Self {
            index: resolver.environment_data().get_extern_ref_index(value),
            _phantom: Default::default(),
        }
    }

    /// An empty value ExternRef.
    pub fn null() -> Self {
        Self {
            index: 0,
            _phantom: Default::default(),
        }
    }

    /// Returns the real value for a given ExternRef. Note that the requested type must be the same as the type of the
    /// value when it was passed before. If these types do not match, this will panic.
    pub fn value_func<'a, 'b>(&'a self, env: &'b FunctionEnvMut<WebAssemblyEnv>) -> Option<&'b T> {
        self.value(&env.data().data())
    }

    /// Returns the real value for a given ExternRef. Note that the requested type must be the same as the type of the
    /// value when it was passed before. If these types do not match, this will panic.
    pub fn value<'a, 'b, 'c>(&'a self, env: &'b Arc<WebAssemblyEnvironmentData>) -> Option<&'c T> {
        let ptr = env.get_extern_ref_value(self.index) as *const T;
        unsafe { ptr.as_ref() }
    }
}

unsafe impl<T: UniqueTypeId<u64>> FromToNativeWasmType for ExternRef<T> {
    type Native = i32;

    fn from_native(native: Self::Native) -> Self {
        Self {
            index: native as u32,
            _phantom: Default::default(),
        }
    }

    fn to_native(self) -> Self::Native {
        self.index as i32
    }
}

/// A VecExternRef is an Extern Ref for vector types. This allows us to pass Vecs to WASM without
/// actually passing raw memory, or requiring us to make copies.
pub(crate) struct VecExternRef<T> {
    /// The lookup index we can use to find the data.
    index: u32,
    /// The number of items in the vec.
    size: u32,
    /// Phantom data so we can get a type generic.
    _phantom: PhantomData<T>,
}

impl<T: UniqueTypeId<u64>> VecExternRef<T> {
    /// Instantiates a new VecExternRef for a given slice.
    pub fn new(env: &WebAssemblyEnvironmentData, value: &[T]) -> Self {
        Self {
            index: env.get_extern_vec_ref_index(value),
            size: value.len() as u32,
            _phantom: Default::default(),
        }
    }
}

unsafe impl<T: UniqueTypeId<u64>> FromToNativeWasmType for VecExternRef<T> {
    type Native = i64;

    fn from_native(native: Self::Native) -> Self {
        let split: (u32, u32) = unsafe { transmute(native) };
        Self {
            index: split.0,
            size: split.1,
            _phantom: Default::default(),
        }
    }

    fn to_native(self) -> Self::Native {
        let v: i64 = unsafe { transmute((self.index, self.size)) };
        v
    }
}