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    // Copyright (c) 2016 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::cmp;

    use proc_macro2::TokenStream;

    use crate::enums::{Dim, Decoration, StorageClass, ImageFormat};
    use crate::parse::{Instruction, Spirv};
    use crate::spirv_search;

    pub fn write_descriptor_sets(doc: &Spirv) -> TokenStream {
        // TODO: not implemented correctly

        // Finding all the descriptors.
        let mut descriptors = Vec::new();
        struct Descriptor {
            set: u32,
            binding: u32,
            desc_ty: TokenStream,
            array_count: u64,
            readonly: bool,
        }

        // Looping to find all the elements that have the `DescriptorSet` decoration.
        for set_decoration in doc.get_decorations(Decoration::DecorationDescriptorSet) {
            let variable_id = set_decoration.target_id;
            let set = set_decoration.params[0];

            // Find which type is pointed to by this variable.
            let pointed_ty = pointer_variable_ty(doc, variable_id);
            // Name of the variable.
            let name = spirv_search::name_from_id(doc, variable_id);

            // Find the binding point of this descriptor.
            // TODO: There was a previous todo here, I think it was asking for this to be implemented for member decorations? check git history
            let binding = doc.get_decoration_params(variable_id, Decoration::DecorationBinding).unwrap()[0];

            // Find information about the kind of binding for this descriptor.
            let (desc_ty, readonly, array_count) = descriptor_infos(doc, pointed_ty, false)
                .expect(&format!(
                    "Couldn't find relevant type for uniform `{}` (type {}, maybe unimplemented)",
                    name,
                    pointed_ty
                ));
            descriptors.push(Descriptor { desc_ty, set, binding, array_count, readonly });
        }

        // Looping to find all the push constant structs.
        let mut push_constants_size = 0;
        for instruction in doc.instructions.iter() {
            let type_id = match instruction {
                &Instruction::TypePointer { type_id, storage_class: StorageClass::StorageClassPushConstant, .. }
                  => type_id,
                _ => continue,
            };

            let (_, size, _) = crate::structs::type_from_id(doc, type_id);
            let size = size.expect("Found runtime-sized push constants");
            push_constants_size = cmp::max(push_constants_size, size);
        }

        // Writing the body of the `descriptor` method.
        let descriptor_body = descriptors
            .iter()
            .map(|d| {
                let set = d.set as usize;
                let binding = d.binding as usize;
                let desc_ty = &d.desc_ty;
                let array_count = d.array_count as u32;
                let readonly = d.readonly;
                quote!{
                    (#set, #binding) => Some(DescriptorDesc {
                        ty: #desc_ty,
                        array_count: #array_count,
                        stages: self.0.clone(),
                        readonly: #readonly,
                    }),
                }
            })
            .collect::<Vec<_>>();

        let num_sets = descriptors.iter().fold(0, |s, d| cmp::max(s, d.set + 1)) as usize;

        // Writing the body of the `num_bindings_in_set` method.
        let num_bindings_in_set_body = (0 .. num_sets)
            .map(|set| {
                 let num = descriptors
                     .iter()
                     .filter(|d| d.set == set as u32)
                     .fold(0, |s, d| cmp::max(s, 1 + d.binding)) as usize;
                 quote!{ #set => Some(#num), }
             })
            .collect::<Vec<_>>();

        // Writing the body of the `num_push_constants_ranges` method.
        let num_push_constants_ranges_body = if push_constants_size == 0 { 0 } else { 1 } as usize;

        // Writing the body of the `push_constants_range` method.
        let push_constants_range_body = quote!(
            if num != 0 || #push_constants_size == 0 {
                None
            } else {
                Some(PipelineLayoutDescPcRange {
                    offset: 0,                   // FIXME: not necessarily true
                    size: #push_constants_size,
                    stages: ShaderStages::all(), // FIXME: wrong
                })
            }
        );

        quote!{
            #[derive(Debug, Clone)]
            pub struct Layout(pub ShaderStages);

            #[allow(unsafe_code)]
            unsafe impl PipelineLayoutDesc for Layout {
                fn num_sets(&self) -> usize {
                    #num_sets
                }

                fn num_bindings_in_set(&self, set: usize) -> Option<usize> {
                    match set {
                        #( #num_bindings_in_set_body )*
                        _ => None
                    }
                }

                fn descriptor(&self, set: usize, binding: usize) -> Option<DescriptorDesc> {
                    match (set, binding) {
                        #( #descriptor_body )*
                        _ => None
                    }
                }

                fn num_push_constants_ranges(&self) -> usize {
                    #num_push_constants_ranges_body
                }

                fn push_constants_range(&self, num: usize) -> Option<PipelineLayoutDescPcRange> {
                    #push_constants_range_body
                }
            }
        }
    }

    /// Assumes that `variable` is a variable with a `TypePointer` and returns the id of the pointed
    /// type.
    fn pointer_variable_ty(doc: &Spirv, variable: u32) -> u32 {
        let var_ty = doc.instructions
            .iter()
            .filter_map(|i| match i {
                &Instruction::Variable { result_type_id, result_id, .. }
                    if result_id == variable => Some(result_type_id),
                _ => None,
            })
            .next()
            .unwrap();

        doc.instructions
            .iter()
            .filter_map(|i| match i {
                &Instruction::TypePointer { result_id, type_id, .. }
                    if result_id == var_ty => Some(type_id),
                _ => None,
            })
            .next()
            .unwrap()
    }

    /// Returns a `DescriptorDescTy` constructor, a bool indicating whether the descriptor is
    /// read-only, and the number of array elements.
    ///
    /// See also section 14.5.2 of the Vulkan specs: Descriptor Set Interface
    fn descriptor_infos(doc: &Spirv, pointed_ty: u32, force_combined_image_sampled: bool)
        -> Option<(TokenStream, bool, u64)>
    {
        doc.instructions.iter().filter_map(|i| {
            match i {
                &Instruction::TypeStruct { result_id, .. } if result_id == pointed_ty => {
                    // Determine whether there's a Block or BufferBlock decoration.
                    let decoration_buffer_block = doc.get_decoration_params(pointed_ty, Decoration::DecorationBufferBlock).is_some();
                    let decoration_block = doc.get_decoration_params(pointed_ty, Decoration::DecorationBlock).is_some();
                    assert!(decoration_buffer_block ^ decoration_block, "Found a buffer uniform with neither the Block nor BufferBlock decorations, or both.");
                    let is_ssbo = decoration_buffer_block && !decoration_block;

                    // Determine whether there's a NonWritable decoration.
                    //let non_writable = false;       // TODO: tricky because the decoration is on struct members

                    let desc = quote!{
                        DescriptorDescTy::Buffer(DescriptorBufferDesc {
                            dynamic: Some(false),
                            storage: #is_ssbo,
                        })
                    };

                    Some((desc, true, 1))
                }
                &Instruction::TypeImage { result_id, ref dim, arrayed, ms, sampled, ref format, .. }
                    if result_id == pointed_ty =>
                {
                    let sampled = sampled.expect("Vulkan requires that variables of type OpTypeImage \
                                                  have a Sampled operand of 1 or 2");

                    let arrayed = match arrayed {
                        true  => quote!{ DescriptorImageDescArray::Arrayed { max_layers: None } },
                        false => quote!{ DescriptorImageDescArray::NonArrayed }
                    };

                    match dim {
                        Dim::DimSubpassData => {
                            // We are an input attachment.
                            assert!(!force_combined_image_sampled, "An OpTypeSampledImage can't point to \
                                                                    an OpTypeImage whose dimension is \
                                                                    SubpassData");
                            assert!(if let &ImageFormat::ImageFormatUnknown = format { true }
                                    else { false }, "If Dim is SubpassData, Image Format must be Unknown");
                            assert!(!sampled, "If Dim is SubpassData, Sampled must be 2");

                            let desc = quote!{
                                DescriptorDescTy::InputAttachment {
                                    multisampled: #ms,
                                    array_layers: #arrayed
                                }
                            };

                            Some((desc, true, 1))
                        }
                        Dim::DimBuffer => {
                            // We are a texel buffer.
                            let not_sampled = !sampled;
                            let desc = quote!{
                                DescriptorDescTy::TexelBuffer {
                                    storage: #not_sampled,
                                    format: None, // TODO: specify format if known
                                }
                            };

                            Some((desc, true, 1))
                        }
                        _ => {
                            // We are a sampled or storage image.
                            let ty = match force_combined_image_sampled {
                                true  => quote!{ DescriptorDescTy::CombinedImageSampler },
                                false => quote!{ DescriptorDescTy::Image }
                            };
                            let dim = match *dim {
                                Dim::Dim1D => quote!{ DescriptorImageDescDimensions::OneDimensional },
                                Dim::Dim2D => quote!{ DescriptorImageDescDimensions::TwoDimensional },
                                Dim::Dim3D => quote!{ DescriptorImageDescDimensions::ThreeDimensional },
                                Dim::DimCube => quote!{ DescriptorImageDescDimensions::Cube },
                                Dim::DimRect => panic!("Vulkan doesn't support rectangle textures"),
                                _ => unreachable!()
                            };

                            let desc = quote!{
                                #ty(DescriptorImageDesc {
                                    sampled: #sampled,
                                    dimensions: #dim,
                                    format: None,       // TODO: specify format if known
                                    multisampled: #ms,
                                    array_layers: #arrayed,
                                })
                            };

                            Some((desc, true, 1))
                        }
                    }
                }

                &Instruction::TypeSampledImage { result_id, image_type_id } if result_id == pointed_ty
                    => descriptor_infos(doc, image_type_id, true),

                &Instruction::TypeSampler { result_id } if result_id == pointed_ty => {
                    let desc = quote!{ DescriptorDescTy::Sampler };
                    Some((desc, true, 1))
                }
                &Instruction::TypeArray { result_id, type_id, length_id } if result_id == pointed_ty => {
                    let (desc, readonly, arr) = match descriptor_infos(doc, type_id, false) {
                        None => return None,
                        Some(v) => v,
                    };
                    assert_eq!(arr, 1);     // TODO: implement?
                    let len = doc.instructions.iter().filter_map(|e| {
                        match e {
                            &Instruction::Constant { result_id, ref data, .. }
                                if result_id == length_id => Some(data.clone()),
                            _ => None
                        }
                    }).next().expect("failed to find array length");
                    let len = len.iter().rev().fold(0, |a, &b| (a << 32) | b as u64);
                    Some((desc, readonly, len))
                }
                _ => None, // TODO: other types
            }
        }).next()
    }

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