//! Zero-sized types .

use std::{cell::Cell, marker::PhantomData, rc::Rc};

use crate::{
    abi_stability::PrefixStableAbi,
    derive_macro_reexports::*,
    type_layout::{GenericTLData, MonoTLData, MonoTypeLayout, ReprAttr, TypeLayout},
};

#[macro_use]
mod stable_abi_impls;

/////////////////

/// Marker type used to mark a type as being `Send + Sync`.
#[repr(C)]
#[derive(StableAbi)]
pub struct SyncSend;

const _: () = zst_assert! {SyncSend};

/////////////////

/// Marker type used to mark a type as being `!Send + !Sync`.
pub struct UnsyncUnsend {
    _marker: UnsafeIgnoredType<Rc<()>>,
}

monomorphic_marker_type! {UnsyncUnsend, UnsafeIgnoredType<Rc<()>>}

impl UnsyncUnsend {
    /// Constructs a `UnsyncUnsend`
    pub const NEW: Self = Self {
        _marker: UnsafeIgnoredType::NEW,
    };
}

/////////////////

/// Marker type used to mark a type as being `Send + !Sync`.
pub struct UnsyncSend {
    _marker: UnsafeIgnoredType<Cell<()>>,
}

monomorphic_marker_type! {UnsyncSend, UnsafeIgnoredType<Cell<()>>}

impl UnsyncSend {
    /// Constructs a `UnsyncSend`
    pub const NEW: Self = Self {
        _marker: UnsafeIgnoredType::NEW,
    };
}

/////////////////

/// Marker type used to mark a type as being `!Send + Sync`.
// #[sabi(debug_print)]
pub struct SyncUnsend {
    _marker: UnsyncUnsend,
}

monomorphic_marker_type! {SyncUnsend, UnsyncUnsend}

impl SyncUnsend {
    /// Constructs a `SyncUnsend`
    pub const NEW: Self = Self {
        _marker: UnsyncUnsend::NEW,
    };
}

unsafe impl Sync for SyncUnsend {}

/////////////////

/// Zero-sized marker type used to signal that even though a type
/// could implement `Copy` and `Clone`,
/// it is semantically an error to do so.
#[repr(C)]
#[derive(StableAbi)]
// #[sabi(debug_print)]
pub struct NotCopyNotClone;

const _: () = zst_assert! {NotCopyNotClone};

//////////////////////////////////////////////////////////////

/// Used by vtables/pointers to signal that the type has been erased.
///
#[repr(C)]
#[derive(StableAbi)]
pub struct ErasedObject<T = ()> {
    _marker: NonOwningPhantom<T>,
}

const _: () = zst_assert! {ErasedObject};

//////////////////////////////////////////////////////////////

/// Used by pointers to vtables/modules to signal that the type has been erased.
///
pub struct ErasedPrefix {
    _priv: PhantomData<u8>,
}

const _: () = zst_assert!(ErasedPrefix);

unsafe impl GetStaticEquivalent_ for ErasedPrefix {
    type StaticEquivalent = ErasedPrefix;
}

unsafe impl PrefixStableAbi for ErasedPrefix {
    type IsNonZeroType = False;
    const LAYOUT: &'static TypeLayout = <ErasedObject as StableAbi>::LAYOUT;
}

//////////////////////////////////////////////////////////////

/// MarkerType which ignores its type parameter in its [`StableAbi`] implementation.
///
/// # Safety
///
/// `Unsafe` is part of its name,
/// because users can violate memory safety
/// if they depend on the value of the type parameter passed to `UnsafeIgnoredType` for safety,
/// since the type parameter is ignored when type checking dynamic libraries.
///
///
/// [`StableAbi`]: ../trait.StableAbi.html
///
pub struct UnsafeIgnoredType<T: ?Sized> {
    /// This field must be public to promise (for semver) that a repr change would be a breaking
    /// change (see <https://github.com/rust-lang/rust/issues/78586>), which is important as this is
    /// used as a zero-sized type in `repr(transparent)` structs.
    pub _inner: PhantomData<T>,
}

impl<T: ?Sized> UnsafeIgnoredType<T> {
    /// Constructs an `UnsafeIgnoredType`.
    pub const DEFAULT: Self = Self {
        _inner: PhantomData,
    };

    /// Constructs an `UnsafeIgnoredType`.
    pub const NEW: Self = Self {
        _inner: PhantomData,
    };
}

impl<T: ?Sized> Copy for UnsafeIgnoredType<T> {}

impl<T: ?Sized> Default for UnsafeIgnoredType<T> {
    fn default() -> Self {
        Self::DEFAULT
    }
}

impl<T: ?Sized> Clone for UnsafeIgnoredType<T> {
    fn clone(&self) -> Self {
        *self
    }
}

unsafe impl<T> GetStaticEquivalent_ for UnsafeIgnoredType<T> {
    type StaticEquivalent = ();
}
unsafe impl<T> StableAbi for UnsafeIgnoredType<T> {
    type IsNonZeroType = False;

    const LAYOUT: &'static TypeLayout = {
        const MONO_TYPE_LAYOUT: &MonoTypeLayout = &MonoTypeLayout::new(
            *mono_shared_vars,
            rstr!("UnsafeIgnoredType"),
            make_item_info!(),
            MonoTLData::struct_(rslice![]),
            tl_genparams!(;;),
            ReprAttr::C,
            ModReflMode::Module,
            rslice![],
        );

        make_shared_vars! {
            impl[T] UnsafeIgnoredType<T>;

            let (mono_shared_vars,shared_vars)={};
        }

        zst_assert!(Self);

        &TypeLayout::from_std::<Self>(
            shared_vars,
            MONO_TYPE_LAYOUT,
            Self::ABI_CONSTS,
            GenericTLData::Struct,
        )
    };
}

//////////////////////////////////////////////////////////////

/// An ffi-safe equivalent of a `PhantomData<fn()->T>`
pub struct NonOwningPhantom<T: ?Sized> {
    // The StableAbi layout for a `NonOwningPhantom<T>` is the same as `PhantomData<T>`,
    // the type of this field is purely for variance.
    _marker: PhantomData<extern "C" fn() -> T>,
}

impl<T: ?Sized> NonOwningPhantom<T> {
    /// Constructs a `NonOwningPhantom`
    pub const DEFAULT: Self = Self {
        _marker: PhantomData,
    };

    /// Constructs a `NonOwningPhantom`
    pub const NEW: Self = Self {
        _marker: PhantomData,
    };
}

impl<T: ?Sized> Copy for NonOwningPhantom<T> {}

impl<T: ?Sized> Default for NonOwningPhantom<T> {
    #[inline(always)]
    fn default() -> Self {
        Self::DEFAULT
    }
}

impl<T: ?Sized> Clone for NonOwningPhantom<T> {
    #[inline(always)]
    fn clone(&self) -> Self {
        *self
    }
}

unsafe impl<T: ?Sized> GetStaticEquivalent_ for NonOwningPhantom<T>
where
    PhantomData<T>: GetStaticEquivalent_,
{
    type StaticEquivalent = GetStaticEquivalent<PhantomData<T>>;
}

unsafe impl<T: ?Sized> StableAbi for NonOwningPhantom<T>
where
    PhantomData<T>: StableAbi,
{
    type IsNonZeroType = False;

    const LAYOUT: &'static TypeLayout = {
        zst_assert!(Self);
        <PhantomData<T> as StableAbi>::LAYOUT
    };
}