use bytemuck::{Pod, Zeroable};
use std::mem;

pub const NUM_INSTANCES_PER_ROW: u32 = 10;
pub const NUM_INSTANCES: u32 = NUM_INSTANCES_PER_ROW * NUM_INSTANCES_PER_ROW;

pub const INSTANCE_DISPLACEMENT: cgmath::Vector3<f32> = cgmath::Vector3::new(
    NUM_INSTANCES_PER_ROW as f32 * 0.5,
    0.0,
    NUM_INSTANCES_PER_ROW as f32 * 0.5,
);

pub struct Instance {
    pub position: cgmath::Vector3<f32>,
    pub rotation: cgmath::Quaternion<f32>,
}

impl Instance {
    pub fn ToRaw(&self) -> InstanceRaw {
        InstanceRaw {
            model: (cgmath::Matrix4::from_translation(self.position)
                * cgmath::Matrix4::from(self.rotation))
            .into(),
        }
    }
}

#[repr(C)]
#[derive(Copy, Clone, Pod, Zeroable)]
pub struct InstanceRaw {
    pub model: [[f32; 4]; 4],
}

impl InstanceRaw {
    pub fn GetDescriptor<'a>() -> wgpu::VertexBufferLayout<'a> {
        wgpu::VertexBufferLayout {
            array_stride: mem::size_of::<InstanceRaw>() as wgpu::BufferAddress,
            // We need to switch from using a step mode of Vertex to Instance
            // This means that our shaders will only change to use the next
            // instance when the shader starts processing a new instance
            step_mode: wgpu::VertexStepMode::Instance,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0,
                    // While our vertex shader only uses locations 0, and 1 now, in later tutorials we'll
                    // be using 2, 3, and 4, for Vertex. We'll start at slot 5 not conflict with them later
                    shader_location: 5,
                    format: wgpu::VertexFormat::Float32x4,
                },
                // A mat4 takes up 4 vertex slots as it is technically 4 vec4s. We need to define a slot
                // for each vec4. We'll have to reassemble the mat4 in
                // the shader.
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 4]>() as wgpu::BufferAddress,
                    shader_location: 6,
                    format: wgpu::VertexFormat::Float32x4,
                },
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 8]>() as wgpu::BufferAddress,
                    shader_location: 7,
                    format: wgpu::VertexFormat::Float32x4,
                },
                wgpu::VertexAttribute {
                    offset: mem::size_of::<[f32; 12]>() as wgpu::BufferAddress,
                    shader_location: 8,
                    format: wgpu::VertexFormat::Float32x4,
                },
            ],
        }
    }
}