/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.

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. */

// NOTE: This file was originally created by tensorflow
//       (https://github.com/tensorflow/tensorflow/) we borrow this
//       file and did some modifications so that we can send gRPC
//       requests without too much copying of the tensor data.

#pragma once

#include <vector>

#include "google/protobuf/io/coded_stream.h"
#include "google/protobuf/io/zero_copy_stream.h"
#include "grpc++/grpc++.h"

namespace grpc {
// A ZeroCopyInputStream that reads from grpc_byte_buffer
class GrpcBufferReader final
    : public ::google::protobuf::io::ZeroCopyInputStream {
  typedef void (CoreCodegenInterface::*OldReaderInitAPI)(
      grpc_byte_buffer_reader* reader, grpc_byte_buffer* buffer);
  typedef int (CoreCodegenInterface::*NewReaderInitAPI)(
      grpc_byte_buffer_reader* reader, grpc_byte_buffer* buffer);
  void ReaderInit(OldReaderInitAPI ptr, grpc_byte_buffer_reader* reader,
                  grpc_byte_buffer* buffer) {
    (g_core_codegen_interface->*ptr)(reader, buffer);
  }
  void ReaderInit(NewReaderInitAPI ptr, grpc_byte_buffer_reader* reader,
                  grpc_byte_buffer* buffer) {
    int result = (g_core_codegen_interface->*ptr)(reader, buffer);
    (void)result;
  }

 public:
  explicit GrpcBufferReader(grpc_byte_buffer* buffer)
      : byte_count_(0), backup_count_(0) {
    ReaderInit(&CoreCodegenInterface::grpc_byte_buffer_reader_init, &reader_,
               buffer);
  }
  ~GrpcBufferReader() override {
    g_core_codegen_interface->grpc_byte_buffer_reader_destroy(&reader_);
  }

  bool Next(const void** data, int* size) override {
    if (backup_count_ > 0) {
      *data = GRPC_SLICE_START_PTR(slice_) + GRPC_SLICE_LENGTH(slice_) -
              backup_count_;
      GPR_CODEGEN_ASSERT(backup_count_ <= INT_MAX);
      *size = static_cast<int>(backup_count_);
      backup_count_ = 0;
      return true;
    }
    if (!g_core_codegen_interface->grpc_byte_buffer_reader_next(&reader_,
                                                                &slice_)) {
      return false;
    }
    g_core_codegen_interface->grpc_slice_unref(slice_);
    *data = GRPC_SLICE_START_PTR(slice_);
    // On win x64, int is only 32bit
    GPR_CODEGEN_ASSERT(GRPC_SLICE_LENGTH(slice_) <= INT_MAX);
    byte_count_ += * size = static_cast<int>(GRPC_SLICE_LENGTH(slice_));
    return true;
  }

  void BackUp(int count) override { backup_count_ = count; }

  bool Skip(int count) override {
    const void* data;
    int size;
    while (Next(&data, &size)) {
      if (size >= count) {
        BackUp(size - count);
        return true;
      }
      // size < count;
      count -= size;
    }
    // error or we have too large count;
    return false;
  }

  ::google::protobuf::int64 ByteCount() const override {
    return byte_count_ - backup_count_;
  }

 private:
  int64_t byte_count_;
  int64_t backup_count_;
  grpc_byte_buffer_reader reader_;
  grpc_slice slice_;
};

};  // namespace grpc

namespace paddle {
namespace operators {
namespace distributed {
// Source provides a way for a particular RPC implementation to provide
// received data to ParseFrom.
class Source {
 public:
  virtual ~Source() {}

  // Return the stream that contains the data to be parsed.
  // Note that this method might be invoked more than once if
  // ParseFrom needs to fall back to a more expensive parsing method.
  // Every call must return a stream pointing at the beginning of
  // the serialized RecvTensorResponse.
  //
  // Note that a subsequent call to contents() invalidates previous
  // results of contents().
  //
  // Ownership of the returned stream is retained by the Source and
  // should not be deleted by the caller.
  virtual ::google::protobuf::io::ZeroCopyInputStream* contents() = 0;
};

// A ZeroCopyInputStream that reads from a grpc::ByteBuffer.
class GrpcByteBufferSource
    : public ::google::protobuf::io::ZeroCopyInputStream {
 public:
  GrpcByteBufferSource();
  bool Init(const ::grpc::ByteBuffer& src);  // Can be called multiple times.
  bool Next(const void** data, int* size) override;
  void BackUp(int count) override;
  bool Skip(int count) override;
  ::google::protobuf::int64 ByteCount() const override;

 private:
  std::vector<::grpc::Slice> slices_;
  size_t cur_;       // Current slice index.
  int left_;         // Number of bytes in slices_[cur_] left to yield.
  const char* ptr_;  // Address of next byte in slices_[cur_] to yield.
  ::google::protobuf::int64 byte_count_;
};

class GrpcByteBufferSourceWrapper : public Source {
 public:
  explicit GrpcByteBufferSourceWrapper(GrpcByteBufferSource* source)
      : source_(source) {}
  ::google::protobuf::io::ZeroCopyInputStream* contents() override {
    return source_;
  }

 private:
  GrpcByteBufferSource* source_;
};

class GrpcByteSource : public Source {
 public:
  explicit GrpcByteSource(grpc_byte_buffer* buffer) : buffer_(buffer) {}
  ~GrpcByteSource() override { DeleteStream(); }

  typedef ::grpc::GrpcBufferReader Reader;

  ::google::protobuf::io::ZeroCopyInputStream* contents() override {
    DeleteStream();
    stream_ = new (&space_) Reader(buffer_);
    return stream_;
  }

 private:
  void DeleteStream() {
    if (stream_) {
      stream_->~Reader();
    }
  }

  grpc_byte_buffer* buffer_;  // Not owned
  Reader* stream_ = nullptr;  // Points into space_ if non-nullptr
  char space_[sizeof(Reader)];
};

}  // namespace distributed
}  // namespace operators
}  // namespace paddle
