use std::marker::PhantomData;

use bytemuck::Pod;
use wgpu::*;

pub struct ArrBuf<T: Pod> {
    label: &'static str,
    usage: BufferUsages,
    pub buffer: Buffer,
    len: usize,
    _pd: PhantomData<T>,
}

impl<T: Pod> ArrBuf<T> {
    pub fn new(device: &Device, usage: BufferUsages, label: &'static str) -> Self {
        Self {
            label,
            usage,
            buffer: Self::init_buf(device, 0, usage, label),
            len: 0,
            _pd: PhantomData,
        }
    }
    /// Returns whether the `Buffer` was recreated, which stales any cached
    /// `BindGroup` holding it.
    pub fn update(&mut self, device: &Device, queue: &Queue, data: &[T]) -> bool {
        let resized = self.len != data.len();
        if resized {
            self.len = data.len();
            self.buffer =
                Self::init_buf(device, std::mem::size_of_val(data), self.usage, self.label);
        }
        queue.write_buffer(&self.buffer, 0, bytemuck::cast_slice(data));
        resized
    }
    pub fn len(&self) -> usize {
        self.len
    }
    fn init_buf(device: &Device, size: usize, usage: BufferUsages, label: &'static str) -> Buffer {
        let mut size = size as u64;
        if usage.contains(BufferUsages::STORAGE) {
            // A binding cannot be empty or under the layout's minimum.
            size = size.max(std::mem::size_of::<T>() as u64);
        }
        device.create_buffer(&BufferDescriptor {
            label: Some(label),
            size,
            mapped_at_creation: false,
            usage,
        })
    }
}