use std::marker::PhantomData;

use unique_type_id::UniqueTypeId;
use wasmer::FromToNativeWasmType;

use crate::script_implementations::wasm::script_resolver::{WebAssemblyEnv, WebAssemblyScriptResolver};

pub(crate) struct ExternRef<T: UniqueTypeId<u64>> {
    index: u32,
    _phantom: PhantomData<T>,
}

impl<T: UniqueTypeId<u64>> ExternRef<T> {
    pub fn new(env: &WebAssemblyEnv, value: &T) -> Self {
        Self {
            index: env.resolver().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<'a, 'b>(&'a self, env: &'b WebAssemblyEnv) -> Option<&'b T> {
        let ptr = env.resolver().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
    }
}