// Copyright 2020 The Dawn Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef DAWNNATIVE_D3D12_SAMPLERHEAPCACHE_H_
#define DAWNNATIVE_D3D12_SAMPLERHEAPCACHE_H_

#include "dawn/common/RefCounted.h"
#include "dawn/native/BindingInfo.h"
#include "dawn/native/d3d12/CPUDescriptorHeapAllocationD3D12.h"
#include "dawn/native/d3d12/GPUDescriptorHeapAllocationD3D12.h"

#include <unordered_set>

// |SamplerHeapCacheEntry| maintains a cache of sampler descriptor heap allocations.
// Each entry represents one or more sampler descriptors that co-exist in a CPU and
// GPU descriptor heap. The CPU-side allocation is deallocated once the final reference
// has been released while the GPU-side allocation is deallocated when the GPU is finished.
//
// The BindGroupLayout hands out these entries upon constructing the bindgroup. If the entry is not
// invalid, it will allocate and initialize so it may be reused by another bindgroup.
//
// The cache is primary needed for the GPU sampler heap, which is much smaller than the view heap
// and switches incur expensive pipeline flushes.
namespace dawn::native::d3d12 {

    class BindGroup;
    class Device;
    class Sampler;
    class SamplerHeapCache;
    class StagingDescriptorAllocator;
    class ShaderVisibleDescriptorAllocator;

    // Wraps sampler descriptor heap allocations in a cache.
    class SamplerHeapCacheEntry : public RefCounted {
      public:
        SamplerHeapCacheEntry() = default;
        SamplerHeapCacheEntry(std::vector<Sampler*> samplers);
        SamplerHeapCacheEntry(SamplerHeapCache* cache,
                              StagingDescriptorAllocator* allocator,
                              std::vector<Sampler*> samplers,
                              CPUDescriptorHeapAllocation allocation);
        ~SamplerHeapCacheEntry() override;

        D3D12_GPU_DESCRIPTOR_HANDLE GetBaseDescriptor() const;

        std::vector<Sampler*>&& AcquireSamplers();

        bool Populate(Device* device, ShaderVisibleDescriptorAllocator* allocator);

        // Functors necessary for the unordered_map<SamplerHeapCacheEntry*>-based cache.
        struct HashFunc {
            size_t operator()(const SamplerHeapCacheEntry* entry) const;
        };

        struct EqualityFunc {
            bool operator()(const SamplerHeapCacheEntry* a, const SamplerHeapCacheEntry* b) const;
        };

      private:
        CPUDescriptorHeapAllocation mCPUAllocation;
        GPUDescriptorHeapAllocation mGPUAllocation;

        // Storing raw pointer because the sampler object will be already hashed
        // by the device and will already be unique.
        std::vector<Sampler*> mSamplers;

        StagingDescriptorAllocator* mAllocator = nullptr;
        SamplerHeapCache* mCache = nullptr;
    };

    // Cache descriptor heap allocations so that we don't create duplicate ones for every
    // BindGroup.
    class SamplerHeapCache {
      public:
        SamplerHeapCache(Device* device);
        ~SamplerHeapCache();

        ResultOrError<Ref<SamplerHeapCacheEntry>> GetOrCreate(
            const BindGroup* group,
            StagingDescriptorAllocator* samplerAllocator);

        void RemoveCacheEntry(SamplerHeapCacheEntry* entry);

      private:
        Device* mDevice;

        using Cache = std::unordered_set<SamplerHeapCacheEntry*,
                                         SamplerHeapCacheEntry::HashFunc,
                                         SamplerHeapCacheEntry::EqualityFunc>;

        Cache mCache;
    };

}  // namespace dawn::native::d3d12

#endif  // DAWNNATIVE_D3D12_SAMPLERHEAPCACHE_H_