// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_UI_LIB_ESCHER_RENDERER_BATCH_GPU_UPLOADER_H_
#define SRC_UI_LIB_ESCHER_RENDERER_BATCH_GPU_UPLOADER_H_

#include <lib/fit/function.h>

#include <variant>

#include "src/ui/lib/escher/escher.h"
#include "src/ui/lib/escher/renderer/buffer_cache.h"
#include "src/ui/lib/escher/renderer/frame.h"
#include "src/ui/lib/escher/vk/buffer.h"
#include "src/ui/lib/escher/vk/command_buffer.h"

#include <vulkan/vulkan.hpp>

namespace escher {

// Provides host-accessible GPU memory for clients to upload Images and Buffers
// to the GPU. Offers the ability to batch uploads into consolidated submissions
// to the GPU driver.
//
// About synchronization:
//   We use semaphore (usually generated by ChainedSemaphoreGenerator) for
// synchronization between BatchGpuDownloader/Uploader and other gfx components,
// so we only need the barrier to synchronize all transfer-related commands.
//
//   Currently users of BatchGpuUploader should manually enforce that the
// BatchGpuUploader waits on other BatchGpuUploader or gfx::Engine if they write
// to the images / buffers the BatchGpuUploader reads from, by using
// AddWaitSemaphore() function. Also, Submit() function will return a semaphore
// being signaled when command buffer finishes execution, which can be used for
// synchronization.
//
// TODO(SCN-1197) Add memory barriers so the BatchGpuUploader and
// BatchGpuDownloader can handle synchronization of reads and writes on the same
// Resource.
//
class BatchGpuUploader {
 public:
  static std::unique_ptr<BatchGpuUploader> New(EscherWeakPtr weak_escher,
                                               uint64_t frame_trace_number = 0);

  BatchGpuUploader(EscherWeakPtr weak_escher, uint64_t frame_trace_number = 0);
  ~BatchGpuUploader();

  // Returns true if the BatchGPUUploader has content to upload on the GPU.
  bool HasContentToUpload() const { return copy_info_records_.size() > 0; }

  // Returns true if BatchGpuUploader needs a command buffer, i.e. it needs to
  // uploading images/buffers, or it needs to wait on/signal semaphores.
  bool NeedsCommandBuffer() const {
    return HasContentToUpload() || !wait_semaphores_.empty() || !signal_semaphores_.empty();
  }

  // Callers of ScheduleWriteImage() and ScheduleWriteBuffer() may use
  // DataProviderCallback to defer writing if callers need to write to the
  // host-visible Vulkan buffers directly without copying data.
  using DataProviderCallback = std::function<void(uint8_t* host_buffer_ptr, size_t copy_size)>;

  // Schedule a buffer-to-buffer copy that will be submitted when Submit()
  // is called.  Reference will be retained in |resources_| until we call
  // Submit(), where we keep the resources alive until submitted CommandBuffer
  // is retired.
  //
  // |target_offset| is the starting offset in bytes from the start of the
  //   target buffer.
  // |copy_size| is the size to be copied to the buffer.
  //
  // These arguments are used to build VkBufferCopy struct.  See the Vulkan specs
  // VkBufferCopy for more details.
  //
  // |write_function| is a callback function which will be called at
  // GenerateCommands(), where we copy our data to the host-visible buffer.
  void ScheduleWriteBuffer(const BufferPtr& target, DataProviderCallback write_function,
                           vk::DeviceSize target_offset, vk::DeviceSize copy_size);

  // Schedule a buffer-to-buffer copy that will be submitted when Submit()
  // is called.  Reference will be retained in |resources_| until we call
  // Submit(), where we keep the resources alive until submitted CommandBuffer
  // is retired.
  //
  // |target_offset| is the starting offset in bytes from the start of the
  //   target buffer.
  // |copy_size| is the size to be copied to the buffer.
  // This argument is used to build VkBufferCopy struct.  See the Vulkan specs
  // VkBufferCopy for more details.
  //
  // |host_data| will be kept until GenerateCommands() where we copy the data
  // to the host-visible buffer.
  template <class T>
  void ScheduleWriteBuffer(const BufferPtr& target, std::vector<T> host_data,
                           vk::DeviceSize target_offset = 0U, vk::DeviceSize copy_size = 0U) {
    vk::DeviceSize real_copy_size = copy_size == 0U ? host_data.size() * sizeof(T) : copy_size;
    // The lambda needs to be mutable so that |host_data| can be moved out.
    ScheduleWriteBuffer(
        target,
        [host_data = std::move(host_data), requested_size = real_copy_size](
            uint8_t* host_buffer_ptr, size_t copy_size) mutable {
          FXL_DCHECK(copy_size >= requested_size);
          memcpy(static_cast<void*>(host_buffer_ptr), host_data.data(),
                 std::min(copy_size, requested_size));
        },
        target_offset, real_copy_size);
  }

  // Schedule a buffer-to-image copy that will be submitted when Submit()
  // is called.  Reference will be retained in |resources_| until we call
  // Submit(), where we keep the resources alive until submitted CommandBuffer
  // is retired.
  //
  // |region| specifies the buffer region which will be copied to the target
  // image.
  //   |region.bufferOffset| should be set to zero since the src buffer is
  //   managed internally by the uploader; currently |imageOffset| requires to
  //   be zero and |imageExtent| requires to be the whole image.
  // The default value of |region| is vk::BufferImageCopy(), in which case we
  // create a default copy region which writes to the color data of an image
  // of one mipmap layer.
  //
  // |write_function| is a callback function which will be called at
  // GenerateCommands(), where we copy our data to the host-visible buffer.
  void ScheduleWriteImage(const ImagePtr& target, DataProviderCallback write_function,
                          vk::ImageLayout final_layout = vk::ImageLayout::eShaderReadOnlyOptimal,
                          vk::BufferImageCopy region = vk::BufferImageCopy());

  // Schedule a buffer-to-image copy that will be submitted when Submit()
  // is called.  Reference will be retained in |resources_| until we call
  // Submit(), where we keep the resources alive until submitted CommandBuffer
  // is retired.
  //
  // |region| specifies the buffer region which will be copied to the target
  // image.
  //   |region.bufferOffset| should be set to zero since the src buffer is
  //   managed internally by the uploader; currently |imageOffset| requires to
  //   be zero and |imageExtent| requires to be the whole image.
  // The default value of |region| is vk::BufferImageCopy(), in which case we
  // create a default copy region which writes to the color data of an image
  // of one mipmap layer.
  //
  // |host_data| will be kept until GenerateCommands() where we copy the data
  // to the host-visible buffer.
  template <class T>
  void ScheduleWriteImage(const ImagePtr& target, std::vector<T> host_data,
                          vk::ImageLayout final_layout = vk::ImageLayout::eShaderReadOnlyOptimal,
                          vk::BufferImageCopy region = vk::BufferImageCopy()) {
    ScheduleWriteImage(
        target,
        [host_data = std::move(host_data)](uint8_t* host_buffer_ptr, size_t copy_size) mutable {
          auto requested_size = host_data.size() * sizeof(T);
          FXL_DCHECK(copy_size >= requested_size);
          memcpy(static_cast<void*>(host_buffer_ptr), host_data.data(),
                 std::min(copy_size, requested_size));
        },
        final_layout, std::move(region));
  }

  // Submits all pending work to the given CommandBuffer. Users need to call
  // cmds->Submit() after calling this function.
  //
  // CommandBuffer cannot be empty if there is any pending work, including
  // writing to buffer/images, waiting on/signaling semaphores.
  void GenerateCommands(CommandBuffer* cmds);

  // Submits all pending work to the given CommandBuffer.
  // Callback function will be called after all work is done.
  void Submit(fit::function<void()> callback = nullptr);

  // Submit() and GenerateCommands() will wait on all semaphores added by
  // AddWaitSemaphore().
  void AddWaitSemaphore(SemaphorePtr sema, vk::PipelineStageFlags flags);

  // Submit() and GenerateCommands() will signal all semaphores added by
  // AddSignalSemaphore().
  void AddSignalSemaphore(SemaphorePtr sema);

 private:
  enum class CopyType { COPY_IMAGE = 0, COPY_BUFFER = 1 };
  struct ImageCopyInfo {
    ImagePtr target;
    vk::BufferImageCopy region;
    vk::ImageLayout final_layout;
  };
  struct BufferCopyInfo {
    BufferPtr target;
    vk::BufferCopy region;
  };
  using CopyInfoVariant = std::variant<ImageCopyInfo, BufferCopyInfo>;

  struct CopyInfo {
    CopyType type;
    vk::DeviceSize offset;
    vk::DeviceSize size;
    DataProviderCallback write_function;
    // copy_info can either be a ImageCopyInfo or a BufferCopyInfo.
    CopyInfoVariant copy_info;
  };

  BufferPtr CreateBufferFromRecords();

  EscherWeakPtr escher_;

  // The trace number for the frame. Cached to support lazy frame creation.
  const uint64_t frame_trace_number_;
  BufferCacheWeakPtr buffer_cache_;

  vk::DeviceSize current_offset_ = 0U;

  std::vector<CopyInfo> copy_info_records_;
  std::vector<ResourcePtr> resources_;

  std::vector<std::pair<SemaphorePtr, vk::PipelineStageFlags>> wait_semaphores_;
  std::vector<SemaphorePtr> signal_semaphores_;

  FXL_DISALLOW_COPY_AND_ASSIGN(BatchGpuUploader);
};

}  // namespace escher

#endif  // SRC_UI_LIB_ESCHER_RENDERER_BATCH_GPU_UPLOADER_H_