// 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 std::sync::Arc;

use OomError;
use VulkanObject;
use buffer::BufferAccess;
use buffer::BufferViewRef;
use descriptor::descriptor::DescriptorDesc;
use descriptor::descriptor::DescriptorDescTy;
use descriptor::descriptor::DescriptorImageDesc;
use descriptor::descriptor::DescriptorImageDescArray;
use descriptor::descriptor::DescriptorImageDescDimensions;
use descriptor::descriptor::DescriptorType;
use descriptor::descriptor_set::DescriptorPool;
use descriptor::descriptor_set::DescriptorPoolAlloc;
use descriptor::descriptor_set::DescriptorSet;
use descriptor::descriptor_set::DescriptorSetDesc;
use descriptor::descriptor_set::DescriptorWrite;
use descriptor::descriptor_set::StdDescriptorPoolAlloc;
use descriptor::descriptor_set::UnsafeDescriptorSet;
use descriptor::descriptor_set::UnsafeDescriptorSetLayout;
use descriptor::pipeline_layout::PipelineLayoutAbstract;
use device::Device;
use device::DeviceOwned;
use format::Format;
use image::ImageViewAccess;
use sampler::Sampler;

/// An immutable descriptor set that is expected to be long-lived.
///
/// Creating a persistent descriptor set allocates from a pool, and can't be modified once created.
/// You are therefore encouraged to create them at initialization and not the during
/// performance-critical paths.
///
/// > **Note**: You can control of the pool that is used to create the descriptor set, if you wish
/// > so. By creating a implementation of the `DescriptorPool` trait that doesn't perform any
/// > actual allocation, you can skip this allocation and make it acceptable to use a persistent
/// > descriptor set in performance-critical paths..
///
/// The template parameter of the `PersistentDescriptorSet` is complex, and you shouldn't try to
/// express it explicitly. If you want to store your descriptor set in a struct or in a `Vec` for
/// example, you are encouraged to turn the `PersistentDescriptorSet` into a `Box<DescriptorSet>`
/// or a `Arc<DescriptorSet>`.
///
/// # Example
// TODO:
pub struct PersistentDescriptorSet<L, R, P = StdDescriptorPoolAlloc> {
    inner: P,
    resources: R,
    pipeline_layout: L,
    set_id: usize,
    layout: Arc<UnsafeDescriptorSetLayout>,
}

impl<L> PersistentDescriptorSet<L, ()> {
    /// Starts the process of building a `PersistentDescriptorSet`. Returns a builder.
    ///
    /// # Panic
    ///
    /// - Panics if the set id is out of range.
    ///
    pub fn start(layout: L, set_id: usize) -> PersistentDescriptorSetBuilder<L, ()>
        where L: PipelineLayoutAbstract
    {
        assert!(layout.num_sets() > set_id);

        let cap = layout.num_bindings_in_set(set_id).unwrap_or(0);

        PersistentDescriptorSetBuilder {
            layout: layout,
            set_id: set_id,
            binding_id: 0,
            writes: Vec::with_capacity(cap),
            resources: (),
        }
    }
}

unsafe impl<L, R, P> DescriptorSet for PersistentDescriptorSet<L, R, P>
    where L: PipelineLayoutAbstract,
          P: DescriptorPoolAlloc,
          R: PersistentDescriptorSetResources
{
    #[inline]
    fn inner(&self) -> &UnsafeDescriptorSet {
        self.inner.inner()
    }

    #[inline]
    fn num_buffers(&self) -> usize {
        self.resources.num_buffers()
    }

    #[inline]
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)> {
        self.resources.buffer(index)
    }

    #[inline]
    fn num_images(&self) -> usize {
        self.resources.num_images()
    }

    #[inline]
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        self.resources.image(index)
    }
}

unsafe impl<L, R, P> DescriptorSetDesc for PersistentDescriptorSet<L, R, P>
    where L: PipelineLayoutAbstract
{
    #[inline]
    fn num_bindings(&self) -> usize {
        self.pipeline_layout
            .num_bindings_in_set(self.set_id)
            .unwrap()
    }

    #[inline]
    fn descriptor(&self, binding: usize) -> Option<DescriptorDesc> {
        self.pipeline_layout.descriptor(self.set_id, binding)
    }
}

unsafe impl<L, R, P> DeviceOwned for PersistentDescriptorSet<L, R, P>
    where L: DeviceOwned
{
    #[inline]
    fn device(&self) -> &Arc<Device> {
        self.layout.device()
    }
}

/// Prototype of a `PersistentDescriptorSet`.
///
/// The template parameter `L` is the pipeline layout to use, and the template parameter `R` is
/// an unspecified type that represents the list of resources.
///
/// See the docs of `PersistentDescriptorSet` for an example.
pub struct PersistentDescriptorSetBuilder<L, R> {
    // The pipeline layout.
    layout: L,
    // Id of the set within the pipeline layout.
    set_id: usize,
    // Binding currently being filled.
    binding_id: usize,
    // The writes to perform on a descriptor set in order to put the resources in it.
    writes: Vec<DescriptorWrite>,
    // Holds the resources alive.
    resources: R,
}

// TODO: lots of checks are still missing, see the docs of
//       VkDescriptorImageInfo and VkWriteDescriptorSet

impl<L, R> PersistentDescriptorSetBuilder<L, R>
    where L: PipelineLayoutAbstract
{
    /// Builds a `PersistentDescriptorSet` from the builder.
    #[inline]
    pub fn build(self)
                 -> Result<PersistentDescriptorSet<L, R, StdDescriptorPoolAlloc>,
                           PersistentDescriptorSetBuildError> {
        let mut pool = Device::standard_descriptor_pool(self.layout.device());
        self.build_with_pool(&mut pool)
    }

    /// Builds a `PersistentDescriptorSet` from the builder.
    ///
    /// # Panic
    ///
    /// Panics if the pool doesn't have the same device as the pipeline layout.
    ///
    pub fn build_with_pool<P>(
        self, pool: &mut P)
        -> Result<PersistentDescriptorSet<L, R, P::Alloc>, PersistentDescriptorSetBuildError>
        where P: ?Sized + DescriptorPool
    {
        assert_eq!(self.layout.device().internal_object(),
                   pool.device().internal_object());

        let expected_desc = self.layout.num_bindings_in_set(self.set_id).unwrap();

        if expected_desc > self.binding_id {
            return Err(PersistentDescriptorSetBuildError::MissingDescriptors {
                           expected: expected_desc as u32,
                           obtained: self.binding_id as u32,
                       });
        }

        debug_assert_eq!(expected_desc, self.binding_id);

        let set_layout = self.layout
            .descriptor_set_layout(self.set_id)
            .expect("Unable to get the descriptor set layout")
            .clone();

        let set = unsafe {
            let mut set = pool.alloc(&set_layout)?;
            set.inner_mut()
                .write(pool.device(), self.writes.into_iter());
            set
        };

        Ok(PersistentDescriptorSet {
               inner: set,
               resources: self.resources,
               pipeline_layout: self.layout,
               set_id: self.set_id,
               layout: set_layout,
           })
    }

    /// Call this function if the next element of the set is an array in order to set the value of
    /// each element.
    ///
    /// Returns an error if the descriptor is empty.
    ///
    /// This function can be called even if the descriptor isn't an array, and it is valid to enter
    /// the "array", add one element, then leave.
    #[inline]
    pub fn enter_array(
        self)
        -> Result<PersistentDescriptorSetBuilderArray<L, R>, PersistentDescriptorSetError> {
        let desc = match self.layout.descriptor(self.set_id, self.binding_id) {
            Some(d) => d,
            None => return Err(PersistentDescriptorSetError::EmptyExpected),
        };

        Ok(PersistentDescriptorSetBuilderArray {
               builder: self,
               desc,
               array_element: 0,
           })
    }

    /// Skips the current descriptor if it is empty.
    #[inline]
    pub fn add_empty(
        mut self)
        -> Result<PersistentDescriptorSetBuilder<L, R>, PersistentDescriptorSetError> {
        match self.layout.descriptor(self.set_id, self.binding_id) {
            None => (),
            Some(desc) => return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                                         expected: desc.ty.ty().unwrap(),
                                     }),
        }

        self.binding_id += 1;
        Ok(self)
    }

    /// Binds a buffer as the next descriptor.
    ///
    /// An error is returned if the buffer isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the buffer doesn't have the same device as the pipeline layout.
    ///
    #[inline]
    pub fn add_buffer<T>(self, buffer: T)
                         -> Result<PersistentDescriptorSetBuilder<L,
                                                                  (R,
                                                                   PersistentDescriptorSetBuf<T>)>,
                                   PersistentDescriptorSetError>
        where T: BufferAccess
    {
        self.enter_array()?.add_buffer(buffer)?.leave_array()
    }

    /// Binds a buffer view as the next descriptor.
    ///
    /// An error is returned if the buffer isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the buffer view doesn't have the same device as the pipeline layout.
    ///
    pub fn add_buffer_view<T>(self, view: T)
        -> Result<PersistentDescriptorSetBuilder<L, (R, PersistentDescriptorSetBufView<T>)>, PersistentDescriptorSetError>
        where T: BufferViewRef
    {
        self.enter_array()?.add_buffer_view(view)?.leave_array()
    }

    /// Binds an image view as the next descriptor.
    ///
    /// An error is returned if the image view isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the image view doesn't have the same device as the pipeline layout.
    ///
    #[inline]
    pub fn add_image<T>(self, image_view: T)
                        -> Result<PersistentDescriptorSetBuilder<L,
                                                                 (R,
                                                                  PersistentDescriptorSetImg<T>)>,
                                  PersistentDescriptorSetError>
        where T: ImageViewAccess
    {
        self.enter_array()?.add_image(image_view)?.leave_array()
    }

    /// Binds an image view with a sampler as the next descriptor.
    ///
    /// An error is returned if the image view isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the image view or the sampler doesn't have the same device as the pipeline layout.
    ///
    #[inline]
    pub fn add_sampled_image<T>(self, image_view: T, sampler: Arc<Sampler>)
        -> Result<PersistentDescriptorSetBuilder<L, ((R, PersistentDescriptorSetImg<T>), PersistentDescriptorSetSampler)>, PersistentDescriptorSetError>
        where T: ImageViewAccess
    {
        self.enter_array()?
            .add_sampled_image(image_view, sampler)?
            .leave_array()
    }

    /// Binds a sampler as the next descriptor.
    ///
    /// An error is returned if the sampler isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the sampler doesn't have the same device as the pipeline layout.
    ///
    #[inline]
    pub fn add_sampler(self, sampler: Arc<Sampler>)
                       -> Result<PersistentDescriptorSetBuilder<L,
                                                                (R,
                                                                 PersistentDescriptorSetSampler)>,
                                 PersistentDescriptorSetError> {
        self.enter_array()?.add_sampler(sampler)?.leave_array()
    }
}

/// Same as `PersistentDescriptorSetBuilder`, but we're in an array.
pub struct PersistentDescriptorSetBuilderArray<L, R> {
    // The original builder.
    builder: PersistentDescriptorSetBuilder<L, R>,
    // Current array elements.
    array_element: usize,
    // Description of the descriptor.
    desc: DescriptorDesc,
}

impl<L, R> PersistentDescriptorSetBuilderArray<L, R>
    where L: PipelineLayoutAbstract
{
    /// Leaves the array. Call this once you added all the elements of the array.
    pub fn leave_array(
        mut self)
        -> Result<PersistentDescriptorSetBuilder<L, R>, PersistentDescriptorSetError> {
        if self.desc.array_count > self.array_element as u32 {
            return Err(PersistentDescriptorSetError::MissingArrayElements {
                           expected: self.desc.array_count,
                           obtained: self.array_element as u32,
                       });
        }

        debug_assert_eq!(self.desc.array_count, self.array_element as u32);

        self.builder.binding_id += 1;
        Ok(self.builder)
    }

    /// Binds a buffer as the next element in the array.
    ///
    /// An error is returned if the buffer isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the buffer doesn't have the same device as the pipeline layout.
    ///
    pub fn add_buffer<T>(mut self, buffer: T)
        -> Result<PersistentDescriptorSetBuilderArray<L, (R, PersistentDescriptorSetBuf<T>)>, PersistentDescriptorSetError>
        where T: BufferAccess
    {
        assert_eq!(self.builder.layout.device().internal_object(),
                   buffer.inner().buffer.device().internal_object());

        if self.array_element as u32 >= self.desc.array_count {
            return Err(PersistentDescriptorSetError::ArrayOutOfBounds);
        }

        self.builder.writes.push(match self.desc.ty {
            DescriptorDescTy::Buffer(ref buffer_desc) => {
                // Note that the buffer content is not checked. This is technically not unsafe as
                // long as the data in the buffer has no invalid memory representation (ie. no
                // bool, no enum, no pointer, no str) and as long as the robust buffer access
                // feature is enabled.
                // TODO: this is not checked ^

                // TODO: eventually shouldn't be an assert ; for now robust_buffer_access is always
                //       enabled so this assert should never fail in practice, but we put it anyway
                //       in case we forget to adjust this code
                assert!(self.builder
                            .layout
                            .device()
                            .enabled_features()
                            .robust_buffer_access);

                if buffer_desc.storage {
                    if !buffer.inner().buffer.usage_storage_buffer() {
                        return Err(PersistentDescriptorSetError::MissingBufferUsage(
                                   MissingBufferUsage::StorageBuffer));
                    }

                    unsafe {
                        DescriptorWrite::storage_buffer(self.builder.binding_id as u32,
                                                        self.array_element as u32,
                                                        &buffer)
                    }
                } else {
                    if !buffer.inner().buffer.usage_uniform_buffer() {
                        return Err(PersistentDescriptorSetError::MissingBufferUsage(
                                   MissingBufferUsage::UniformBuffer));
                    }

                    unsafe {
                        DescriptorWrite::uniform_buffer(self.builder.binding_id as u32,
                                                        self.array_element as u32,
                                                        &buffer)
                    }
                }
            },
            ref d => {
                return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                               expected: d.ty().unwrap(),
                           });
            },
        });

        Ok(PersistentDescriptorSetBuilderArray {
               builder: PersistentDescriptorSetBuilder {
                   layout: self.builder.layout,
                   set_id: self.builder.set_id,
                   binding_id: self.builder.binding_id,
                   writes: self.builder.writes,
                   resources: (self.builder.resources,
                               PersistentDescriptorSetBuf {
                                   buffer: buffer,
                                   descriptor_num: self.builder.binding_id as u32,
                               }),
               },
               desc: self.desc,
               array_element: self.array_element + 1,
           })
    }

    /// Binds a buffer view as the next element in the array.
    ///
    /// An error is returned if the buffer isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the buffer view doesn't have the same device as the pipeline layout.
    ///
    pub fn add_buffer_view<T>(mut self, view: T)
        -> Result<PersistentDescriptorSetBuilderArray<L, (R, PersistentDescriptorSetBufView<T>)>, PersistentDescriptorSetError>
        where T: BufferViewRef
    {
        assert_eq!(self.builder.layout.device().internal_object(),
                   view.view().device().internal_object());

        if self.array_element as u32 >= self.desc.array_count {
            return Err(PersistentDescriptorSetError::ArrayOutOfBounds);
        }

        self.builder.writes.push(match self.desc.ty {
            DescriptorDescTy::TexelBuffer { storage, .. } => {
                if storage {
                    // TODO: storage_texel_buffer_atomic

                    if !view.view().storage_texel_buffer() {
                        return Err(PersistentDescriptorSetError::MissingBufferUsage(
                                   MissingBufferUsage::StorageTexelBuffer));
                    }

                    DescriptorWrite::storage_texel_buffer(self.builder.binding_id as u32,
                                                          self.array_element as u32,
                                                          view.view())
                } else {
                    if !view.view().uniform_texel_buffer() {
                        return Err(PersistentDescriptorSetError::MissingBufferUsage(
                                   MissingBufferUsage::UniformTexelBuffer));
                    }

                    DescriptorWrite::uniform_texel_buffer(self.builder.binding_id as u32,
                                                          self.array_element as u32,
                                                          view.view())
                }
            },
            ref d => {
                return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                               expected: d.ty().unwrap(),
                           });
            },
        });

        Ok(PersistentDescriptorSetBuilderArray {
               builder: PersistentDescriptorSetBuilder {
                   layout: self.builder.layout,
                   set_id: self.builder.set_id,
                   binding_id: self.builder.binding_id,
                   writes: self.builder.writes,
                   resources: (self.builder.resources,
                               PersistentDescriptorSetBufView {
                                   view: view,
                                   descriptor_num: self.builder.binding_id as u32,
                               }),
               },
               desc: self.desc,
               array_element: self.array_element + 1,
           })
    }

    /// Binds an image view as the next element in the array.
    ///
    /// An error is returned if the image view isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the image view doesn't have the same device as the pipeline layout.
    ///
    pub fn add_image<T>(mut self, image_view: T)
        -> Result<PersistentDescriptorSetBuilderArray<L, (R, PersistentDescriptorSetImg<T>)>, PersistentDescriptorSetError>
        where T: ImageViewAccess
    {
        assert_eq!(self.builder.layout.device().internal_object(),
                   image_view.parent().inner().image.device().internal_object());

        if self.array_element as u32 >= self.desc.array_count {
            return Err(PersistentDescriptorSetError::ArrayOutOfBounds);
        }

        let desc = match self.builder
            .layout
            .descriptor(self.builder.set_id, self.builder.binding_id) {
            Some(d) => d,
            None => return Err(PersistentDescriptorSetError::EmptyExpected),
        };

        self.builder.writes.push(match desc.ty {
            DescriptorDescTy::Image(ref desc) => {
                image_match_desc(&image_view, &desc)?;

                if desc.sampled {
                    DescriptorWrite::sampled_image(self.builder.binding_id as u32,
                                                   self.array_element as u32,
                                                   &image_view)
                } else {
                    DescriptorWrite::storage_image(self.builder.binding_id as u32,
                                                   self.array_element as u32,
                                                   &image_view)
                }
            },
            DescriptorDescTy::InputAttachment {
                multisampled,
                array_layers,
            } => {
                if !image_view.parent().inner().image.usage_input_attachment() {
                    return Err(PersistentDescriptorSetError::MissingImageUsage(
                                   MissingImageUsage::InputAttachment));
                }

                if multisampled && image_view.samples() == 1 {
                    return Err(PersistentDescriptorSetError::ExpectedMultisampled);
                } else if !multisampled && image_view.samples() != 1 {
                    return Err(PersistentDescriptorSetError::UnexpectedMultisampled);
                }

                let image_layers = image_view.dimensions().array_layers();

                match array_layers {
                    DescriptorImageDescArray::NonArrayed => {
                        if image_layers != 1 {
                            return Err(PersistentDescriptorSetError::ArrayLayersMismatch {
                                           expected: 1,
                                           obtained: image_layers,
                                       });
                        }
                    },
                    DescriptorImageDescArray::Arrayed { max_layers: Some(max_layers) } => {
                        if image_layers > max_layers {
                            // TODO: is this correct? "max" layers? or is it in fact min layers?
                            return Err(PersistentDescriptorSetError::ArrayLayersMismatch {
                                           expected: max_layers,
                                           obtained: image_layers,
                                       });
                        }
                    },
                    DescriptorImageDescArray::Arrayed { max_layers: None } => {},
                };

                DescriptorWrite::input_attachment(self.builder.binding_id as u32,
                                                  self.array_element as u32,
                                                  &image_view)
            },
            ty => {
                return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                               expected: ty.ty().unwrap(),
                           });
            },
        });

        Ok(PersistentDescriptorSetBuilderArray {
               builder: PersistentDescriptorSetBuilder {
                   layout: self.builder.layout,
                   set_id: self.builder.set_id,
                   binding_id: self.builder.binding_id,
                   writes: self.builder.writes,
                   resources: (self.builder.resources,
                               PersistentDescriptorSetImg {
                                   image: image_view,
                                   descriptor_num: self.builder.binding_id as u32,
                               }),
               },
               desc: self.desc,
               array_element: self.array_element + 1,
           })
    }

    /// Binds an image view with a sampler as the next element in the array.
    ///
    /// An error is returned if the image view isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the image or the sampler doesn't have the same device as the pipeline layout.
    ///
    pub fn add_sampled_image<T>(mut self, image_view: T, sampler: Arc<Sampler>)
        -> Result<PersistentDescriptorSetBuilderArray<L, ((R, PersistentDescriptorSetImg<T>), PersistentDescriptorSetSampler)>, PersistentDescriptorSetError>
        where T: ImageViewAccess
    {
        assert_eq!(self.builder.layout.device().internal_object(),
                   image_view.parent().inner().image.device().internal_object());
        assert_eq!(self.builder.layout.device().internal_object(),
                   sampler.device().internal_object());

        if self.array_element as u32 >= self.desc.array_count {
            return Err(PersistentDescriptorSetError::ArrayOutOfBounds);
        }

        let desc = match self.builder
            .layout
            .descriptor(self.builder.set_id, self.builder.binding_id) {
            Some(d) => d,
            None => return Err(PersistentDescriptorSetError::EmptyExpected),
        };

        if !image_view.can_be_sampled(&sampler) {
            return Err(PersistentDescriptorSetError::IncompatibleImageViewSampler);
        }

        self.builder.writes.push(match desc.ty {
            DescriptorDescTy::CombinedImageSampler(ref desc) => {
                image_match_desc(&image_view, &desc)?;
                DescriptorWrite::combined_image_sampler(self.builder.binding_id as u32,
                                                        self.array_element as u32,
                                                        &sampler,
                                                        &image_view)
            },
            ty => {
                return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                               expected: ty.ty().unwrap(),
                           });
            },
        });

        Ok(PersistentDescriptorSetBuilderArray {
               builder: PersistentDescriptorSetBuilder {
                   layout: self.builder.layout,
                   set_id: self.builder.set_id,
                   binding_id: self.builder.binding_id,
                   writes: self.builder.writes,
                   resources: ((self.builder.resources,
                                PersistentDescriptorSetImg {
                                    image: image_view,
                                    descriptor_num: self.builder.binding_id as u32,
                                }),
                               PersistentDescriptorSetSampler { sampler: sampler }),
               },
               desc: self.desc,
               array_element: self.array_element + 1,
           })
    }

    /// Binds a sampler as the next element in the array.
    ///
    /// An error is returned if the sampler isn't compatible with the descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the sampler doesn't have the same device as the pipeline layout.
    ///
    pub fn add_sampler(mut self, sampler: Arc<Sampler>)
        -> Result<PersistentDescriptorSetBuilderArray<L, (R, PersistentDescriptorSetSampler)>, PersistentDescriptorSetError>
    {
        assert_eq!(self.builder.layout.device().internal_object(),
                   sampler.device().internal_object());

        if self.array_element as u32 >= self.desc.array_count {
            return Err(PersistentDescriptorSetError::ArrayOutOfBounds);
        }

        let desc = match self.builder
            .layout
            .descriptor(self.builder.set_id, self.builder.binding_id) {
            Some(d) => d,
            None => return Err(PersistentDescriptorSetError::EmptyExpected),
        };

        self.builder.writes.push(match desc.ty {
            DescriptorDescTy::Sampler => {
                DescriptorWrite::sampler(self.builder.binding_id as u32,
                                         self.array_element as u32,
                                         &sampler)
            },
            ty => {
                return Err(PersistentDescriptorSetError::WrongDescriptorTy {
                               expected: ty.ty().unwrap(),
                           });
            },
        });

        Ok(PersistentDescriptorSetBuilderArray {
               builder: PersistentDescriptorSetBuilder {
                   layout: self.builder.layout,
                   set_id: self.builder.set_id,
                   binding_id: self.builder.binding_id,
                   writes: self.builder.writes,
                   resources: (self.builder.resources,
                               PersistentDescriptorSetSampler { sampler: sampler }),
               },
               desc: self.desc,
               array_element: self.array_element + 1,
           })
    }
}

// Checks whether an image view matches the descriptor.
fn image_match_desc<I>(image_view: &I, desc: &DescriptorImageDesc)
                       -> Result<(), PersistentDescriptorSetError>
    where I: ?Sized + ImageViewAccess
{
    if desc.sampled && !image_view.parent().inner().image.usage_sampled() {
        return Err(PersistentDescriptorSetError::MissingImageUsage(
                       MissingImageUsage::Sampled));
    } else if !desc.sampled && !image_view.parent().inner().image.usage_storage() {
        return Err(PersistentDescriptorSetError::MissingImageUsage(
                       MissingImageUsage::Storage));
    }

    let image_view_ty = DescriptorImageDescDimensions::from_dimensions(image_view.dimensions());
    if image_view_ty != desc.dimensions {
        return Err(PersistentDescriptorSetError::ImageViewTypeMismatch {
                       expected: desc.dimensions,
                       obtained: image_view_ty,
                   });
    }

    if let Some(format) = desc.format {
        if image_view.format() != format {
            return Err(PersistentDescriptorSetError::ImageViewFormatMismatch {
                           expected: format,
                           obtained: image_view.format(),
                       });
        }
    }

    if desc.multisampled && image_view.samples() == 1 {
        return Err(PersistentDescriptorSetError::ExpectedMultisampled);
    } else if !desc.multisampled && image_view.samples() != 1 {
        return Err(PersistentDescriptorSetError::UnexpectedMultisampled);
    }

    let image_layers = image_view.dimensions().array_layers();

    match desc.array_layers {
        DescriptorImageDescArray::NonArrayed => {
            // TODO: when a non-array is expected, can we pass an image view that is in fact an
            // array with one layer? need to check
            if image_layers != 1 {
                return Err(PersistentDescriptorSetError::ArrayLayersMismatch {
                               expected: 1,
                               obtained: image_layers,
                           });
            }
        },
        DescriptorImageDescArray::Arrayed { max_layers: Some(max_layers) } => {
            if image_layers > max_layers {
                // TODO: is this correct? "max" layers? or is it in fact min layers?
                return Err(PersistentDescriptorSetError::ArrayLayersMismatch {
                               expected: max_layers,
                               obtained: image_layers,
                           });
            }
        },
        DescriptorImageDescArray::Arrayed { max_layers: None } => {},
    };

    Ok(())
}

pub unsafe trait PersistentDescriptorSetResources {
    fn num_buffers(&self) -> usize;
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)>;
    fn num_images(&self) -> usize;
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)>;
}

unsafe impl PersistentDescriptorSetResources for () {
    #[inline]
    fn num_buffers(&self) -> usize {
        0
    }

    #[inline]
    fn buffer(&self, _: usize) -> Option<(&dyn BufferAccess, u32)> {
        None
    }

    #[inline]
    fn num_images(&self) -> usize {
        0
    }

    #[inline]
    fn image(&self, _: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        None
    }
}

/// Internal object related to the `PersistentDescriptorSet` system.
pub struct PersistentDescriptorSetBuf<B> {
    buffer: B,
    descriptor_num: u32,
}

unsafe impl<R, B> PersistentDescriptorSetResources for (R, PersistentDescriptorSetBuf<B>)
    where R: PersistentDescriptorSetResources,
          B: BufferAccess
{
    #[inline]
    fn num_buffers(&self) -> usize {
        self.0.num_buffers() + 1
    }

    #[inline]
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)> {
        if let Some(buf) = self.0.buffer(index) {
            Some(buf)
        } else if index == self.0.num_buffers() {
            Some((&self.1.buffer, self.1.descriptor_num))
        } else {
            None
        }
    }

    #[inline]
    fn num_images(&self) -> usize {
        self.0.num_images()
    }

    #[inline]
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        self.0.image(index)
    }
}

/// Internal object related to the `PersistentDescriptorSet` system.
pub struct PersistentDescriptorSetBufView<V>
    where V: BufferViewRef
{
    view: V,
    descriptor_num: u32,
}

unsafe impl<R, V> PersistentDescriptorSetResources for (R, PersistentDescriptorSetBufView<V>)
    where R: PersistentDescriptorSetResources,
          V: BufferViewRef
{
    #[inline]
    fn num_buffers(&self) -> usize {
        self.0.num_buffers() + 1
    }

    #[inline]
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)> {
        if let Some(buf) = self.0.buffer(index) {
            Some(buf)
        } else if index == self.0.num_buffers() {
            Some((self.1.view.view().buffer(), self.1.descriptor_num))
        } else {
            None
        }
    }

    #[inline]
    fn num_images(&self) -> usize {
        self.0.num_images()
    }

    #[inline]
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        self.0.image(index)
    }
}

/// Internal object related to the `PersistentDescriptorSet` system.
pub struct PersistentDescriptorSetImg<I> {
    image: I,
    descriptor_num: u32,
}

unsafe impl<R, I> PersistentDescriptorSetResources for (R, PersistentDescriptorSetImg<I>)
    where R: PersistentDescriptorSetResources,
          I: ImageViewAccess
{
    #[inline]
    fn num_buffers(&self) -> usize {
        self.0.num_buffers()
    }

    #[inline]
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)> {
        self.0.buffer(index)
    }

    #[inline]
    fn num_images(&self) -> usize {
        self.0.num_images() + 1
    }

    #[inline]
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        if let Some(img) = self.0.image(index) {
            Some(img)
        } else if index == self.0.num_images() {
            Some((&self.1.image, self.1.descriptor_num))
        } else {
            None
        }
    }
}

/// Internal object related to the `PersistentDescriptorSet` system.
pub struct PersistentDescriptorSetSampler {
    sampler: Arc<Sampler>,
}

unsafe impl<R> PersistentDescriptorSetResources for (R, PersistentDescriptorSetSampler)
    where R: PersistentDescriptorSetResources
{
    #[inline]
    fn num_buffers(&self) -> usize {
        self.0.num_buffers()
    }

    #[inline]
    fn buffer(&self, index: usize) -> Option<(&dyn BufferAccess, u32)> {
        self.0.buffer(index)
    }

    #[inline]
    fn num_images(&self) -> usize {
        self.0.num_images()
    }

    #[inline]
    fn image(&self, index: usize) -> Option<(&dyn ImageViewAccess, u32)> {
        self.0.image(index)
    }
}

// Part of the PersistentDescriptorSetError for the case
// of missing usage on a buffer.
#[derive(Debug, Clone)]
pub enum MissingBufferUsage {
    StorageBuffer, UniformBuffer, StorageTexelBuffer, UniformTexelBuffer
}

// Part of the PersistentDescriptorSetError for the case
// of missing usage on an image.
#[derive(Debug, Clone)]
pub enum MissingImageUsage {
    InputAttachment, Sampled, Storage
}

/// Error related to the persistent descriptor set.
#[derive(Debug, Clone)]
pub enum PersistentDescriptorSetError {
    /// Expected one type of resource but got another.
    WrongDescriptorTy {
        /// The expected descriptor type.
        expected: DescriptorType,
    },

    /// Expected nothing.
    EmptyExpected,

    /// Tried to add too many elements to an array.
    ArrayOutOfBounds,

    /// Didn't fill all the elements of an array before leaving.
    MissingArrayElements {
        /// Number of expected elements.
        expected: u32,
        /// Number of elements that were added.
        obtained: u32,
    },

    /// The image view isn't compatible with the sampler.
    IncompatibleImageViewSampler,

    /// The buffer is missing the correct usage.
    MissingBufferUsage(MissingBufferUsage),

    /// The image is missing the correct usage.
    MissingImageUsage(MissingImageUsage),

    /// Expected a multisampled image, but got a single-sampled image.
    ExpectedMultisampled,

    /// Expected a single-sampled image, but got a multisampled image.
    UnexpectedMultisampled,

    /// The number of array layers of an image doesn't match what was expected.
    ArrayLayersMismatch {
        /// Number of expected array layers for the image.
        expected: u32,
        /// Number of array layers of the image that was added.
        obtained: u32,
    },

    /// The format of an image view doesn't match what was expected.
    ImageViewFormatMismatch {
        /// Expected format.
        expected: Format,
        /// Format of the image view that was passed.
        obtained: Format,
    },

    /// The type of an image view doesn't match what was expected.
    ImageViewTypeMismatch {
        /// Expected type.
        expected: DescriptorImageDescDimensions,
        /// Type of the image view that was passed.
        obtained: DescriptorImageDescDimensions,
    },
}

impl error::Error for PersistentDescriptorSetError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            PersistentDescriptorSetError::WrongDescriptorTy { .. } => {
                "expected one type of resource but got another"
            },
            PersistentDescriptorSetError::EmptyExpected => {
                "expected an empty descriptor but got something"
            },
            PersistentDescriptorSetError::ArrayOutOfBounds => {
                "tried to add too many elements to an array"
            },
            PersistentDescriptorSetError::MissingArrayElements { .. } => {
                "didn't fill all the elements of an array before leaving"
            },
            PersistentDescriptorSetError::IncompatibleImageViewSampler => {
                "the image view isn't compatible with the sampler"
            },
            PersistentDescriptorSetError::MissingBufferUsage { .. } => {
                "the buffer is missing the correct usage"
            },
            PersistentDescriptorSetError::MissingImageUsage { .. } => {
                "the image is missing the correct usage"
            },
            PersistentDescriptorSetError::ExpectedMultisampled => {
                "expected a multisampled image, but got a single-sampled image"
            },
            PersistentDescriptorSetError::UnexpectedMultisampled => {
                "expected a single-sampled image, but got a multisampled image"
            },
            PersistentDescriptorSetError::ArrayLayersMismatch { .. } => {
                "the number of array layers of an image doesn't match what was expected"
            },
            PersistentDescriptorSetError::ImageViewFormatMismatch { .. } => {
                "the format of an image view doesn't match what was expected"
            },
            PersistentDescriptorSetError::ImageViewTypeMismatch { .. } => {
                "the type of an image view doesn't match what was expected"
            },
        }
    }
}

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

/// Error when building a persistent descriptor set.
#[derive(Debug, Clone)]
pub enum PersistentDescriptorSetBuildError {
    /// Out of memory.
    OomError(OomError),

    /// Didn't fill all the descriptors before building.
    MissingDescriptors {
        /// Number of expected descriptors.
        expected: u32,
        /// Number of descriptors that were added.
        obtained: u32,
    },
}

impl error::Error for PersistentDescriptorSetBuildError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            PersistentDescriptorSetBuildError::MissingDescriptors { .. } => {
                "didn't fill all the descriptors before building"
            },
            PersistentDescriptorSetBuildError::OomError(_) => {
                "not enough memory available"
            },
        }
    }
}

impl From<OomError> for PersistentDescriptorSetBuildError {
    #[inline]
    fn from(err: OomError) -> PersistentDescriptorSetBuildError {
        PersistentDescriptorSetBuildError::OomError(err)
    }
}

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