//
// DDK API
//

/// A function which provides a DDK operation.
///
/// An `Op<Context, Args, Return>` is the DDK's representation of a function
/// which implements an operation, takes a `Context`, extra arguments `Args`,
/// and returns a `Return`value. The `#[ddk_op]` attribute generates `Op` values
/// for functions automatically, so a driver author should never need to
/// construct an `Op`.
///
/// For example, the following function has an op type of
/// `Op<Context, (usize, usize), usize>`:
///
/// ```rust,ignore
/// #[ddk_op]
/// fn multiply(ctx: &mut Context, a: usize, b: usize) -> usize { ... }
/// ```
pub struct Op<Context, Args, Return> {
    #[doc(hidden)]
    pub ptr: *const c_void,
    #[doc(hidden)]
    pub _marker: PhantomData<(Context, Args, Return)>,
}

/// A collection of operations that implement a protocol.
///
/// A `ProtocolDevice` is a collection of operations that implement a protocol.
/// All operations take the context type `C`. There is a single static instance
/// of `ProtocolDevice` for each driver. For example, for a protocol with the
/// `foo` and `bar` operations:
///
/// ```rust,ignore
/// static DEVICE_OPS: ProtocolDevice<Context> =
///     ProtocolDevice::default().foo(foo).bar(bar);
/// ```
///
struct ProtocolDevice<C> { ... }

impl<C> ProtocolDevice<C> {
    /// A default `ProtocolDevice` with all operations defaulted.
    ///
    /// `default` creates a `ProtocolDevice` in which every operation is set
    /// to the default, which returns `ZX_STATUS_ERR`.
    const fn default() -> ProtocolDevice<C> { ... }

    /// Add a `get_protocol` operation.
    ///
    /// `get_protocol` overrides the default `get_protocol` operation.
    const fn get_protocol(self, get_protocol: Op<C, (), ()>) -> ProtocolDevice { ... }
}

//
// What they write
//

static DEVICE_OPS: ProtocolDevice = ProtocolDevice::default().get_protocol(get_protocol);

struct Context;

impl Context {
    #[ddk_op]
    fn get_protocol(&self) {}
}

//
// What it desugars to
//

static DEVICE_OPS: ProtocolDevice = ProtocolDevice::default().get_protocol(get_protocol);

struct Context;

// TODO: can this be const instead of static?
static get_protocol: Op<Context, (), ()> = Op { ptr: __get_protocol as *const c_void, _marker: PhantomData };

impl Context {
    fn __get_protocol(&self) {}
}