/* Copyright 2015 The TensorFlow 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.
==============================================================================*/

#ifndef TENSORFLOW_CORE_FRAMEWORK_READER_INTERFACE_H_
#define TENSORFLOW_CORE_FRAMEWORK_READER_INTERFACE_H_

#include <memory>
#include <string>
#include "tensorflow/core/framework/op_kernel.h"
#include "tensorflow/core/framework/resource_mgr.h"
#include "tensorflow/core/framework/tensor.h"
#include "tensorflow/core/lib/core/status.h"
#include "tensorflow/core/platform/types.h"

namespace tensorflow {

class QueueInterface;
class ReaderInterface;

// Readers are the mechanism for reading records from files in
// TensorFlow graphs.  Each supported file format has a corresponding
// ReaderInterface descendant and a corresponding Op & OpKernel
// (implemented using ReaderOpKernel from reader_op_kernel.h).
//
// To use a Reader, you first encode "work" (some string, typically a
// filename) in the Reader's "work queue".  It then processes the
// "work" (reading records from the file), to produce key/value
// strings.  The methods of this class are called by ReaderFoo ops,
// so see ../ops/io_ops.cc for detailed descriptions.
//
// All descendants of this class must be thread-safe.
class ReaderInterface : public ResourceBase {
 public:
  // Read a single record into *key / *value.  May get more work from
  // *queue if the current work is complete.  Sets the status on
  // *context with an OutOfRange Status if the current work is
  // complete and the queue is done (closed and empty).
  // This method may block.
  virtual void Read(QueueInterface* queue, string* key, string* value,
                    OpKernelContext* context) = 0;

  // Read up to num_records records into keys / values. May get more work from
  // *queue if the current work is complete.  Sets the status on
  // *context with an OutOfRange Status if the current work is
  // complete and the queue is done (closed and empty).
  // This method may block.
  // The std::vector keys/value pointers are assumed to point to empty
  // structures (that have most likely been reserve(num_records)).
  // Returns how many records were actually read.
  virtual int64 ReadUpTo(const int64 num_records, QueueInterface* queue,
                         std::vector<string>* keys, std::vector<string>* value,
                         OpKernelContext* context) = 0;

  // Restore this reader to its newly-constructed state.
  virtual Status Reset() = 0;

  // Accessors
  virtual int64 NumRecordsProduced() = 0;
  virtual int64 NumWorkUnitsCompleted() = 0;

  // -- Serialization/Restoration support --
  // Not all readers will support saving and restoring state.
  virtual Status SerializeState(string* state) = 0;
  // Note: Must Reset on error.
  virtual Status RestoreState(const string& state) = 0;

  string DebugString() override { return "a reader"; }

 protected:
  virtual ~ReaderInterface() {}
};

}  // namespace tensorflow

#endif  // TENSORFLOW_CORE_FRAMEWORK_READER_INTERFACE_H_
