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use core::ffi::c_void;

use crate::Encoding;

/// Types that have an Objective-C type-encoding.
///
/// # Safety
///
/// Objective-C will make assumptions about the type (like its size and
/// alignment) from its encoding, so the implementer must verify that the
/// encoding is accurate.
pub unsafe trait Encode {
    /// The Objective-C type-encoding for this type.
    const ENCODING: Encoding<'static>;
}

macro_rules! encode_impls {
    ($($t:ty : $e:ident,)*) => ($(
        unsafe impl Encode for $t {
            const ENCODING: Encoding<'static> = Encoding::$e;
        }
    )*);
}

encode_impls!(
    i8: Char,
    i16: Short,
    i32: Int,
    i64: LongLong,
    u8: UChar,
    u16: UShort,
    u32: UInt,
    u64: ULongLong,
    f32: Float,
    f64: Double,
    bool: Bool,
    (): Void,
    *mut i8: String,
    *const i8: String,
    *mut u8: String,
    *const u8: String,
);

unsafe impl Encode for isize {
    #[cfg(target_pointer_width = "16")]
    const ENCODING: Encoding<'static> = i16::ENCODING;

    #[cfg(target_pointer_width = "32")]
    const ENCODING: Encoding<'static> = i32::ENCODING;

    #[cfg(target_pointer_width = "64")]
    const ENCODING: Encoding<'static> = i64::ENCODING;
}

unsafe impl Encode for usize {
    #[cfg(target_pointer_width = "16")]
    const ENCODING: Encoding<'static> = u16::ENCODING;

    #[cfg(target_pointer_width = "32")]
    const ENCODING: Encoding<'static> = u32::ENCODING;

    #[cfg(target_pointer_width = "64")]
    const ENCODING: Encoding<'static> = u64::ENCODING;
}

unsafe impl Encode for *mut c_void {
    const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Void);
}

unsafe impl Encode for *const c_void {
    const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Void);
}

unsafe impl<T: Encode, const LENGTH: usize> Encode for [T; LENGTH] {
    const ENCODING: Encoding<'static> = Encoding::Array(LENGTH, &<T as Encode>::ENCODING);
}

// External crates cannot implement Encode for pointers or [`Option`], but
// they *can* implement it for references. See
// [rust-lang/rust#25126](https://github.com/rust-lang/rust/issues/25126)
//
// So, as a workaround, we provide implementations for these types that return
// the same encoding as references.
//
// Using `?Sized` is safe here because we delegate to other implementations
// (which will verify that the implementation is safe for the unsized type).

unsafe impl<T: ?Sized> Encode for *const T
where
    for<'b> &'b T: Encode,
{
    const ENCODING: Encoding<'static> = <&T>::ENCODING;
}

unsafe impl<T: ?Sized> Encode for *mut T
where
    for<'b> &'b mut T: Encode,
{
    const ENCODING: Encoding<'static> = <&mut T>::ENCODING;
}

unsafe impl<'a, T: ?Sized> Encode for Option<&'a T>
where
    for<'b> &'b T: Encode,
{
    const ENCODING: Encoding<'static> = <&T>::ENCODING;
}

unsafe impl<'a, T: ?Sized> Encode for Option<&'a mut T>
where
    for<'b> &'b mut T: Encode,
{
    const ENCODING: Encoding<'static> = <&mut T>::ENCODING;
}