use std::mem::size_of;

use bytemuck::{Pod, Zeroable};

#[repr(C)]
#[derive(Copy, Clone, Debug, PartialEq, Pod, Zeroable)]
pub struct Instance {
	/// Position on the screen
	pub position: [f32; 2],
	/// Relative size
	pub size: [f32; 2],
	/// Rotation, in radians
	pub rotation: f32,
	/// z-index
	pub z_index: i32,
}

impl Default for Instance {
	fn default() -> Self {
		Self {
			position: [0.0; 2],
			size: [1.0; 2],
			rotation: 0.0,
			z_index: 0,
		}
	}
}

impl Instance {
	// whenever this is updated, please also update `sprite.wgsl`
	const ATTRIBUTES: [wgpu::VertexAttribute; 4] =
		wgpu::vertex_attr_array![1 => Float32x2, 2 => Float32x2, 3 => Float32, 4 => Sint32];

	pub(crate) fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
		// make sure these two don't conflict
		debug_assert_eq!(
			Self::ATTRIBUTES[0].shader_location as usize,
			crate::Vertex::ATTRIBUTES.len()
		);
		wgpu::VertexBufferLayout {
			array_stride: size_of::<Self>() as wgpu::BufferAddress,
			step_mode: wgpu::VertexStepMode::Instance,
			attributes: &Self::ATTRIBUTES,
		}
	}
}