const_shader_layout 0.4.0

use crate::ShaderLayout;

/// Marks the type's uniform-compatible alignment requirement in shader, i.e. with uniform address layout constraints.
///
/// See also <https://www.w3.org/TR/WGSL/#alignment-and-size> and <https://www.w3.org/TR/WGSL/#address-space-layout-constraints>
pub trait ShaderLayoutCompat: ShaderLayout {
    /// The type's alignment constraint in shader if uniform address layout constraints apply when the type is in an array or struct.
    /// If not constrained, this should be [`ShaderLayout::ALIGN`].
    const ALIGN_CONSTRAINT: core::num::NonZero<u64> = Self::ALIGN;
    /// The type's size constraint in shader if uniform address layout constraints apply when the type is in an array or struct.
    /// If not constrained, this should be `size_of::<Self>()`.
    ///
    /// This is used to determined the required offset after this field in struct and is not the actual size of type.
    const SIZE_CONSTRAINT: core::num::NonZero<u64> =
        core::num::NonZero::new(size_of::<Self>() as u64).unwrap();
}

/// Marks the type can be used as array element with uniform address layout constraints.
///
/// There is a blanket implementation of `ShaderLayoutCompat` for `[T; N]` where `T: ShaderLayoutCompatArrayElement`.
pub trait ShaderLayoutCompatArrayElement: crate::ShaderLayoutArrayElement {}

/// Implements [`ShaderLayoutCompat`] (also implements [`ShaderLayout`]) for the types, with the specified alignment.
#[macro_export]
#[doc(hidden)]
macro_rules! impl_shader_layout_compat {
    ($($ty:ty),+$(,)?) => {
        $(
            $crate::impl_shader_layout!($ty);
            impl $crate::ShaderLayoutCompat for $ty {}
        )+
    };
    ($align:expr $(, $ty:ty)+$(,)?) => {
        $(
            $crate::impl_shader_layout!($align, $ty);
            impl $crate::ShaderLayoutCompat for $ty {}
        )+
    };
    ($align:expr, $align_constraint:expr $(, $ty:ty)+$(,)?) => {
        $(
            $crate::impl_shader_layout!($align, $ty);
            impl $crate::ShaderLayoutCompat for $ty {
                const ALIGN_CONSTRAINT: ::core::num::NonZero<u64> = ::core::num::NonZero::new($align_constraint).unwrap();
            }
        )+
    };
    ($align:expr, $align_constraint:expr, $size_constraint:expr $(, $ty:ty)+$(,)?) => {
        const _: () ={
            assert!((($size_constraint) as u64).is_multiple_of(16u64));
        };
        $(
            $crate::impl_shader_layout!($align, $ty);
            impl $crate::ShaderLayoutCompat for $ty {
                const ALIGN_CONSTRAINT: ::core::num::NonZero<u64> = ::core::num::NonZero::new($align_constraint).unwrap();
                const SIZE_CONSTRAINT: ::core::num::NonZero<u64> = ::core::num::NonZero::new($size_constraint).unwrap();
            }
        )+
    };
}

/// Implements [`ShaderLayoutCompat`] (also implements [`ShaderLayout`]) for `[T; N]` for types implemented [`ShaderLayoutCompat`].
///
/// Different from [`ShaderLayout`], the stride of array must be a multiple of 16.
///
/// Checks at compile-time:
/// * Array size must be equal to `N * roundUp(16, roundUp(AlignOf(E), SizeOf(E)))`.
///
/// See also <https://www.w3.org/TR/WGSL/#alignment-and-size> and <https://www.w3.org/TR/WGSL/#address-space-layout-constraints>
#[macro_export]
#[doc(hidden)]
macro_rules! impl_shader_layout_compat_array_element {
    ($($ty:ty),+$(,)?) => {
        $(
            $crate::impl_shader_layout_array_element!($ty);
            impl $crate::ShaderLayoutCompatArrayElement for $ty {}

            // Assert array size is equal to `N * roundUp(16, roundUp(AlignOf(E), SizeOf(E)))`
            const _: () = {
                const ELEMENT_ALIGN: u64 = <$ty as $crate::ShaderLayout>::ALIGN.get().next_multiple_of(16);
                const N: usize = 1;
                const ACTUAL_SIZE: u64 = size_of::<[$ty; N]>() as u64;
                const SIZE: u64 = (size_of::<$ty>() as u64).next_multiple_of(ELEMENT_ALIGN) * N as u64;
                if SIZE != ACTUAL_SIZE {
                    let mut msg = $crate::internal::MsgBuf::<256>::new();
                    msg.write_str("Failed to implement `ShaderLayoutCompatArrayElement`: `[")
                        .write_str(stringify!($ty))
                        .write_str("; N]` size (")
                        .write_usize(size_of::<[$ty; N]>())
                        .write_str(" * N) must be equal to its shader size (")
                        .write_u64(SIZE)
                        .write_str(" * N), i.e. the stride must be rounded up to `ALIGN` (")
                        .write_u64(ELEMENT_ALIGN)
                        .write_str(") and 16");
                    panic!("{}", msg.as_str());
                }
            };
        )+
    };
}

#[macro_export]
macro_rules! impl_shader_layout_compat_struct {
    (
        $(#[$attr:meta])*
        $vis:vis struct $struct_name:ident {
            $(
                $(#[$field_attr:meta])*
                $field_vis:vis $field_name:ident : $field_ty:ty
            ),* $(,)?
        }
   ) => {
       $crate::impl_shader_layout_struct!(
           $(#[$attr])*
           $vis struct $struct_name {
               $(
                   $(#[$field_attr])*
                   $field_vis $field_name: $field_ty
               ),*
           }
       );

        $(
            const _: () = {
                const MEMBER_ALIGN_CONSTRAINT: u64 = <$field_ty as $crate::ShaderLayoutCompat>::ALIGN_CONSTRAINT.get();
                const MEMBER_SIZE_CONSTRAINT: u64 = <$field_ty as $crate::ShaderLayoutCompat>::SIZE_CONSTRAINT.get();
                const MEMBER_SIZE: u64 = size_of::<$field_ty>() as u64;
                const MEMBER_OFFSET: u64 = core::mem::offset_of!($struct_name, $field_name) as u64;

                if MEMBER_SIZE != MEMBER_SIZE_CONSTRAINT {
                    let mut msg = $crate::internal::MsgBuf::<256>::new();
                    msg.write_str("Failed to impl `ShaderLayoutCompat`: field `")
                        .write_str(stringify!($struct_name))
                        .write_str("::")
                        .write_str(stringify!($field_name))
                        .write_str("` (`")
                        .write_str(stringify!($field_ty))
                        .write_str("`) size (")
                        .write_u64(MEMBER_SIZE)
                        .write_str(") must be `SIZE_CONSTRAINT` (")
                        .write_u64(MEMBER_SIZE_CONSTRAINT)
                        .write_str(") due to uniform layout constraints");
                    panic!("{}", msg.as_str());
                }

                if !MEMBER_OFFSET.is_multiple_of(MEMBER_ALIGN_CONSTRAINT) {
                    let mut msg = $crate::internal::MsgBuf::<256>::new();
                    msg.write_str("Failed to impl `ShaderLayoutCompat`: field `")
                        .write_str(stringify!($struct_name))
                        .write_str("::")
                        .write_str(stringify!($field_name))
                        .write_str("` (`")
                        .write_str(stringify!($field_ty))
                        .write_str("`) is not properly aligned. The offset is ")
                        .write_u64(MEMBER_OFFSET)
                        .write_str(" but required align is `ALIGN_CONSTRAINT` (")
                        .write_u64(MEMBER_ALIGN_CONSTRAINT)
                        .write_str(")");
                    panic!("{}", msg.as_str());
                }
            };
        )*

        impl $crate::ShaderLayoutCompat for $struct_name {
            const ALIGN_CONSTRAINT: ::core::num::NonZero<u64> = {
                const MEMBER_ALIGNS: &[u64] = &[$(
                    (<$field_ty as $crate::ShaderLayoutCompat>::ALIGN_CONSTRAINT.get())
                ),*];

                let mut max = MEMBER_ALIGNS[0];
                let mut i = 1;
                while i < MEMBER_ALIGNS.len() {
                    if MEMBER_ALIGNS[i] > max {
                        max = MEMBER_ALIGNS[i];
                    }
                    i += 1;
                }
                ::core::num::NonZero::new(max.next_multiple_of(16)).unwrap()
            };
            const SIZE_CONSTRAINT: ::core::num::NonZero<u64> = {
                const MEMBER_SIZES: &[u64] = &[$(
                    (<$field_ty as $crate::ShaderLayoutCompat>::SIZE_CONSTRAINT.get())
                ),*];

                let mut sum = MEMBER_SIZES[0];
                let mut i = 1;
                while i < MEMBER_SIZES.len() {
                    sum += MEMBER_SIZES[i];
                    i += 1;
                }
                ::core::num::NonZero::new(sum.next_multiple_of(16)).unwrap()
            };
        }
    };
}

/// Checks if all the struct's fields conform to shader layout then implements [`ShaderLayoutCompat`] for this struct, or fails at compile-time.
///
/// Different from [`ShaderLayout`], the alignment of struct must be a multiple of 16.
///
/// Checks at compile-time:
/// * For each field, `core::mem::offset_of!(struct, field)` must be equal to its [`ShaderLayoutCompat::ALIGN_CONSTRAINT`].
/// * Struct size must be equal to `roundUp(16, roundUp(AlignOf(S), SizeOf(S))))`.
///
/// See also <https://www.w3.org/TR/WGSL/#alignment-and-size> and <https://www.w3.org/TR/WGSL/#address-space-layout-constraints>
#[macro_export]
macro_rules! shader_layout_compat {
    (
        $(#[$attr:meta])*
        $vis:vis struct $struct_name:ident {
            $(
                $(#[$field_attr:meta])*
                $field_vis:vis $field_name:ident : $field_ty:ty
            ),* $(,)?
        }
   ) => {
       #[derive(Copy, Clone)]
       #[repr(C)]
       $(#[$attr])*
       $vis struct $struct_name {
           $(
               $(#[$field_attr])*
               $field_vis $field_name: $field_ty
           ),*
       }

       $crate::impl_shader_layout_compat_struct!{
           $(#[$attr])*
           $vis struct $struct_name {
               $(
                   $(#[$field_attr])*
                   $field_vis $field_name: $field_ty
               ),*
           }
       }
    };
}