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use crate::{DeviceExt, SizedBuffer};

use replace_with::replace_with_or_abort;

/// A [`wgpu::Buffer`] Pool (dynamic supply).
pub struct BufferPool {
    buffers: Vec<SizedBuffer>,
    occupied: usize,

    label: crate::OwnedLabel,
    usage: wgpu::BufferUsage,
}

impl BufferPool {
    /// Creates a new pool.
    pub fn new(descriptor: &BufferPoolDescriptor) -> Self {
        Self {
            buffers: Vec::new(),
            occupied: 0,

            label: descriptor.label.map(|l| l.to_owned()),
            usage: descriptor.usage,
        }
    }

    /// Get uploaded buffer by index.
    pub fn get(&self, i: usize) -> Option<&wgpu::Buffer> {
        self.buffers.get(i).map(|b| &b.buffer)
    }

    /// Upload data to buffer. Returns buffer index.
    pub fn upload(&mut self, device: &wgpu::Device, queue: &wgpu::Queue, data: &[u8]) -> usize {
        if self.occupied < self.buffers.len() {
            let buffer = &mut self.buffers[self.occupied];

            // CCDF
            let label = self.label.as_deref();
            let usage = self.usage;
            replace_with_or_abort(buffer, |buffer| {
                crate::write(
                    device,
                    queue,
                    buffer,
                    &crate::WriteDescriptor { label, data, usage },
                )
            });

            self.occupied += 1;
            self.occupied
        } else {
            self.buffers.push(self.create_buffer(device, data));
            self.occupied += 1;
            self.occupied
        }
    }

    /// Clear whole buffer. Buffers are marked as reusable.
    pub fn clear(&mut self) {
        self.occupied = 0;
    }

    fn create_buffer(&self, device: &wgpu::Device, data: &[u8]) -> SizedBuffer {
        let buffer = device.create_buffer_init(&crate::BufferInitDescriptor {
            label: self.label.as_deref(),
            contents: data,
            usage: self.usage,
            size: None,
        });
        SizedBuffer::new(data.len() as wgpu::BufferAddress, buffer)
    }
}

/// Descriptor for [`BufferPool`]
pub struct BufferPoolDescriptor<'a> {
    /// Label assigned to all buffers
    pub label: wgpu::Label<'a>,
    /// Usages for all buffer
    pub usage: wgpu::BufferUsage,
}