//! Interface for interfaces.
//!
//! ## Design
//! The design of protocols is based on an idea found in the
//! [`gdbstub`](https://docs.rs/gdbstub/latest/gdbstub/target/ext/index.html) crate.
//! This idea is of so called inlinable dyn extension traits.
//! However, in the form given in `gdbstub` they can't be used for arbitrary interfaces.
//! The main trait still needs to know about all the possible protocols.
//! That is where this module comes in.
//!
//! This module implements a technique we name dynamic inlinable dyn extension traits (DIDETs).
//! DIDETs adds one more layer to IDETs. Instead of a trait that knows all the possible protocols,
//! we have a single trait [`Implementer`] that allows looking up an extension trait
//! using a type ID. This may seem like it defeats the purpose of IDETs, that being to
//! make them inlinable. However, it turns out LLVM (the optimizer) is able to see
//! through this style of runtime reflection. As such, we still gain the benefits of
//! IDETs but with more flexability.
//! Protocols can now be defined in *any* crate and used between arbitrary crates.
//!
//! A protocol is a special trait that can participate as a DIDET. The only thing needed
//! for a protocol is an associated trait object. Because we need to use the
//! [`TypeId`][core::any::TypeId] of a protocol to perform reflection, we can't just use
//! the trait object itself as the protocol type. Instead an uninhabited type is used
//! as a marker for the trait.
//!
//! We then "implement" a protocol for a type by using [`Implementation`]. This provides
//! a mapping from `T` to the protocol's trait object.
//! By itself, [`Implementation`] is not enough for DIDET. A type also needs to implement
//! [`Implementer`] which allows looking up a particular [`Implementation`] trait object
//! from a [`ProtocolId`].
//!
//! The implementation of DIDETs defined by this module allows [`Implementer`] to be object safe.
//! This is done via the help of the [`AnyImpl`] type. This is not required for the core
//! idea of DIDETs.

use core::{
    future::Future,
    marker::PhantomData,
    pin::{pin, Pin},
    ptr,
    task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
};

use crate::any::AnyTrait;
use crate::hkt::{hkt, type_class};

pub mod visitor;
pub mod walker;

#[cfg(all(feature = "alloc", not(feature = "std")))]
use alloc::boxed::Box;

pub type Visitor<'a, 'ctx, Effect> =
    as_obj::T<'a, 'ctx, <Effect as self::EffectAnyTrait<'ctx>>::AnyTrait>;
pub type Walker<'a, 'ctx, Effect> =
    as_obj::T<'a, 'ctx, <Effect as self::EffectAnyTrait<'ctx>>::AnyTrait>;

pub trait AsObj<'a, 'ctx: 'a> {
    fn as_obj(&self) -> &dyn AnyTrait<'ctx>;
    fn as_obj_mut(&mut self) -> &mut dyn AnyTrait<'ctx>;
    fn into_obj(self) -> &'a mut dyn AnyTrait<'ctx>;
}

impl<'a, 'ctx: 'a> AsObj<'a, 'ctx> for &'a mut (dyn AnyTrait<'ctx> + 'a) {
    fn as_obj(&self) -> &dyn AnyTrait<'ctx> {
        *self
    }

    fn as_obj_mut(&mut self) -> &mut dyn AnyTrait<'ctx> {
        *self
    }

    fn into_obj(self) -> &'a mut dyn AnyTrait<'ctx> {
        self
    }
}

impl<'a, 'ctx: 'a> AsObj<'a, 'ctx> for &'a mut (dyn AnyTrait<'ctx> + Send + 'a) {
    fn as_obj(&self) -> &dyn AnyTrait<'ctx> {
        *self
    }

    fn as_obj_mut(&mut self) -> &mut dyn AnyTrait<'ctx> {
        *self
    }

    fn into_obj(self) -> &'a mut dyn AnyTrait<'ctx> {
        self
    }
}

type_class!(for<'lt, 'ctx> pub as_obj: AsObj<'lt, 'ctx>);
type_class!(for<'lt, 'ctx> pub any_t);

pub trait EffectAnyTrait<'ctx>: 'static {
    /// The `dyn AnyTrait<'ctx>` for the effect.
    ///
    /// this allows adding extra bounds to the trait object.
    type AnyTrait: as_obj::Hkt<'ctx>;
}

/// Trait for effects.
pub trait Effect<'ctx, T>: EffectAnyTrait<'ctx> {
    /// The type functions return for this effect.
    ///
    /// This type should resolve into a `T`.
    type Yield: any_t::Hkt<'ctx>;
}

pub type Yield<'a, 'ctx, T, E> = any_t::T<'a, 'ctx, <E as Effect<'ctx, T>>::Yield>;

pub enum SyncEffect {}

hkt!((as_obj): for<'a, 'ctx> pub AnyTraitSendObj => &'a mut (dyn AnyTrait<'ctx> + Send + 'a));
hkt!((as_obj): for<'a, 'ctx> pub AnyTraitObj => &'a mut (dyn AnyTrait<'ctx> + 'a));

hkt!((any_t): for<'a, 'ctx> pub SyncYield[T] => T);

impl<'ctx, T> Effect<'ctx, T> for SyncEffect {
    type Yield = SyncYield<'ctx, T>;
}

impl<'ctx> EffectAnyTrait<'ctx> for SyncEffect {
    type AnyTrait = AnyTraitObj<'ctx>;
}

#[cfg(feature = "alloc")]
hkt!((any_t): for<'a, 'ctx> pub AsyncSendYield[T] =>
    core::pin::Pin<
        Box<dyn core::future::Future<Output = T> + Send + 'a>,
    >
);

#[cfg(feature = "alloc")]
pub enum AsyncSendEffect {}

#[cfg(feature = "alloc")]
impl<'ctx, T> Effect<'ctx, T> for AsyncSendEffect {
    type Yield = AsyncSendYield<'ctx, T>;
}

#[cfg(feature = "alloc")]
impl<'ctx> EffectAnyTrait<'ctx> for AsyncSendEffect {
    type AnyTrait = AnyTraitSendObj<'ctx>;
}

#[cfg(feature = "alloc")]
hkt!((any_t): for<'a, 'ctx> pub AsyncYield[T] =>
    core::pin::Pin<
        Box<dyn core::future::Future<Output = T> + 'a>,
    >
);

#[cfg(feature = "alloc")]
pub enum AsyncEffect {}

#[cfg(feature = "alloc")]
impl<'ctx, T> Effect<'ctx, T> for AsyncEffect {
    type Yield = AsyncYield<'ctx, T>;
}

#[cfg(feature = "alloc")]
impl<'ctx> EffectAnyTrait<'ctx> for AsyncEffect {
    type AnyTrait = AnyTraitObj<'ctx>;
}