use super::*;
use bindings::IWeakReferenceSource;
/// Provides low-level access to a COM interface.
///
/// This trait is automatically implemented by the generated bindings and should not be
/// implemented manually.
///
/// # Safety
///
/// It is only safe to implement this trait if the implementing type is a valid COM interface pointer meaning
/// the following criteria are met:
/// * its in-memory representation is equal to `NonNull<NonNull<Self::VTable>>`
/// * the vtable is correctly structured beginning with the `IUnknown` function pointers
/// * the vtable must be the correct vtable for the supplied IID
pub unsafe trait Interface: Vtable {
/// A unique identifier representing this interface.
const IID: GUID;
/// Attempts to cast the current interface to another interface using `QueryInterface`.
///
/// The name `cast` is preferred to `query` because there is a WinRT method named query but not one
/// named cast.
fn cast<T: Interface>(&self) -> Result<T> {
let mut result = None;
// SAFETY: `result` is valid for writing an interface pointer and it is safe
// to cast the `result` pointer as `T` on success because we are using the `IID` tied
// to `T` which the implementor of `Interface` has guaranteed is correct
unsafe { self.query(&T::IID, &mut result as *mut _ as _).and_some(result) }
}
/// Attempts to create a [`Weak`] reference to this object.
fn downgrade(&self) -> Result<Weak<Self>> {
self.cast::<IWeakReferenceSource>().and_then(|source| Weak::downgrade(&source))
}
/// Call `QueryInterface` on this interface
///
/// # SAFETY
///
/// `interface` must be a non-null, valid pointer for writing an interface pointer
#[doc(hidden)]
unsafe fn query(&self, iid: &GUID, interface: *mut *const std::ffi::c_void) -> HRESULT {
(self.assume_vtable::<IUnknown>().QueryInterface)(self.as_raw(), iid, interface)
}
}