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// Copyright (c) 2017 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

use std::error;
use std::fmt;

use VulkanObject;
use buffer::BufferAccess;
use buffer::TypedBufferAccess;
use device::Device;
use device::DeviceOwned;
use pipeline::input_assembly::Index;

/// Checks whether an index buffer can be bound.
///
/// # Panic
///
/// - Panics if the buffer was not created with `device`.
///
pub fn check_index_buffer<B, I>(device: &Device, buffer: &B)
                                -> Result<CheckIndexBuffer, CheckIndexBufferError>
    where B: ?Sized + BufferAccess + TypedBufferAccess<Content = [I]>,
          I: Index
{
    assert_eq!(buffer.inner().buffer.device().internal_object(),
               device.internal_object());

    if !buffer.inner().buffer.usage_index_buffer() {
        return Err(CheckIndexBufferError::BufferMissingUsage);
    }

    // TODO: The sum of offset and the address of the range of VkDeviceMemory object that is
    //       backing buffer, must be a multiple of the type indicated by indexType

    // TODO: fullDrawIndexUint32 feature

    Ok(CheckIndexBuffer { num_indices: buffer.len() })
}

/// Information returned if `check_index_buffer` succeeds.
pub struct CheckIndexBuffer {
    /// Number of indices in the index buffer.
    pub num_indices: usize,
}

/// Error that can happen when checking whether binding an index buffer is valid.
#[derive(Debug, Copy, Clone)]
pub enum CheckIndexBufferError {
    /// The "index buffer" usage must be enabled on the index buffer.
    BufferMissingUsage,
    /// The data or size must be 4-bytes aligned.
    WrongAlignment,
    /// The type of the indices is not supported by the device.
    UnsupportIndexType,
}

impl error::Error for CheckIndexBufferError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            CheckIndexBufferError::BufferMissingUsage => {
                "the index buffer usage must be enabled on the index buffer"
            },
            CheckIndexBufferError::WrongAlignment => {
                "the sum of offset and the address of the range of VkDeviceMemory object that is \
                 backing buffer, must be a multiple of the type indicated by indexType"
            },
            CheckIndexBufferError::UnsupportIndexType => {
                "the type of the indices is not supported by the device"
            },
        }
    }
}

impl fmt::Display for CheckIndexBufferError {
    #[inline]
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", error::Error::description(self))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use buffer::BufferUsage;
    use buffer::CpuAccessibleBuffer;

    #[test]
    fn num_indices() {
        let (device, queue) = gfx_dev_and_queue!();
        let buffer = CpuAccessibleBuffer::from_iter(device.clone(),
                                                    BufferUsage::index_buffer(),
                                                    0 .. 500u32)
            .unwrap();

        match check_index_buffer(&device, &buffer) {
            Ok(CheckIndexBuffer { num_indices }) => {
                assert_eq!(num_indices, 500);
            },
            _ => panic!(),
        }
    }

    #[test]
    fn missing_usage() {
        let (device, queue) = gfx_dev_and_queue!();
        let buffer = CpuAccessibleBuffer::from_iter(device.clone(),
                                                    BufferUsage::vertex_buffer(),
                                                    0 .. 500u32)
            .unwrap();

        match check_index_buffer(&device, &buffer) {
            Err(CheckIndexBufferError::BufferMissingUsage) => (),
            _ => panic!(),
        }
    }

    #[test]
    fn wrong_device() {
        let (dev1, queue) = gfx_dev_and_queue!();
        let (dev2, _) = gfx_dev_and_queue!();

        let buffer = CpuAccessibleBuffer::from_iter(dev1, BufferUsage::all(), 0 .. 500u32).unwrap();

        assert_should_panic!({
                                 let _ = check_index_buffer(&dev2, &buffer);
                             });
    }
}