/* Copyright 2016 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_PLATFORM_GCS_FILE_SYSTEM_H_
#define TENSORFLOW_CORE_PLATFORM_GCS_FILE_SYSTEM_H_

#include <string>
#include <vector>
#include "tensorflow/core/lib/core/status.h"
#include "tensorflow/core/platform/cloud/auth_provider.h"
#include "tensorflow/core/platform/cloud/file_block_cache.h"
#include "tensorflow/core/platform/cloud/http_request.h"
#include "tensorflow/core/platform/cloud/retrying_file_system.h"
#include "tensorflow/core/platform/file_system.h"

namespace tensorflow {

/// Google Cloud Storage implementation of a file system.
///
/// The clients should use RetryingGcsFileSystem defined below,
/// which adds retry logic to GCS operations.
class GcsFileSystem : public FileSystem {
 public:
  GcsFileSystem();
  GcsFileSystem(std::unique_ptr<AuthProvider> auth_provider,
                std::unique_ptr<HttpRequest::Factory> http_request_factory,
                size_t block_size, uint32 block_count, uint64 max_staleness,
                int64 initial_retry_delay_usec);

  Status NewRandomAccessFile(
      const string& filename,
      std::unique_ptr<RandomAccessFile>* result) override;

  Status NewWritableFile(const string& fname,
                         std::unique_ptr<WritableFile>* result) override;

  Status NewAppendableFile(const string& fname,
                           std::unique_ptr<WritableFile>* result) override;

  Status NewReadOnlyMemoryRegionFromFile(
      const string& filename,
      std::unique_ptr<ReadOnlyMemoryRegion>* result) override;

  Status FileExists(const string& fname) override;

  Status Stat(const string& fname, FileStatistics* stat) override;

  Status GetChildren(const string& dir, std::vector<string>* result) override;

  Status GetMatchingPaths(const string& pattern,
                          std::vector<string>* results) override;

  Status DeleteFile(const string& fname) override;

  Status CreateDir(const string& dirname) override;

  Status DeleteDir(const string& dirname) override;

  Status GetFileSize(const string& fname, uint64* file_size) override;

  Status RenameFile(const string& src, const string& target) override;

  Status IsDirectory(const string& fname) override;

  Status DeleteRecursively(const string& dirname, int64* undeleted_files,
                           int64* undeleted_dirs) override;
  size_t block_size() const { return block_size_; }
  uint32 block_count() const { return block_count_; }
  uint64 max_staleness() const { return max_staleness_; }

 private:
  /// \brief Checks if the bucket exists. Returns OK if the check succeeded.
  ///
  /// 'result' is set if the function returns OK. 'result' cannot be nullptr.
  Status BucketExists(const string& bucket, bool* result);

  /// \brief Checks if the object exists. Returns OK if the check succeeded.
  ///
  /// 'result' is set if the function returns OK. 'result' cannot be nullptr.
  Status ObjectExists(const string& bucket, const string& object, bool* result);

  /// \brief Checks if the folder exists. Returns OK if the check succeeded.
  ///
  /// 'result' is set if the function returns OK. 'result' cannot be nullptr.
  Status FolderExists(const string& dirname, bool* result);

  /// \brief Internal version of GetChildren with more knobs.
  ///
  /// If 'recursively' is true, returns all objects in all subfolders.
  /// Otherwise only returns the immediate children in the directory.
  ///
  /// If 'include_self_directory_marker' is true and there is a GCS directory
  /// marker at the path 'dir', GetChildrenBound will return an empty string
  /// as one of the children that represents this marker.
  Status GetChildrenBounded(const string& dir, uint64 max_results,
                            std::vector<string>* result, bool recursively,
                            bool include_self_directory_marker);
  /// Retrieves file statistics assuming fname points to a GCS object.
  Status StatForObject(const string& bucket, const string& object,
                       FileStatistics* stat);
  Status RenameObject(const string& src, const string& target);

  /// Loads file contents from GCS for a given bucket and object.
  Status LoadBufferFromGCS(const string& bucket, const string& object,
                           uint64_t offset, size_t n, std::vector<char>* out);

  std::unique_ptr<AuthProvider> auth_provider_;
  std::unique_ptr<HttpRequest::Factory> http_request_factory_;

  /// Guards access to the file cache.
  mutex mu_;

  /// Cache from filename to FileBlockCache. Populated iff max_staleness_ > 0.
  std::map<string, std::shared_ptr<FileBlockCache>> file_cache_ GUARDED_BY(mu_);

  /// The block size for block-aligned reads in the RandomAccessFile
  /// implementation. Defaults to 256Mb.
  size_t block_size_ = 256 * 1024 * 1024;

  /// The block count for the LRU cache of blocks in the RandomAccessFile
  /// implementation.  Defaults to 1.
  uint32 block_count_ = 1;

  /// The maximum staleness of cached file blocks across close/open boundaries.
  /// Defaults to 0, meaning that file blocks do not persist across close/open
  /// boundaries.
  uint64 max_staleness_ = 0;

  /// The initial delay for exponential backoffs when retrying failed calls.
  const int64 initial_retry_delay_usec_ = 1000000L;

  TF_DISALLOW_COPY_AND_ASSIGN(GcsFileSystem);
};

/// Google Cloud Storage implementation of a file system with retry on failures.
class RetryingGcsFileSystem : public RetryingFileSystem {
 public:
  RetryingGcsFileSystem()
      : RetryingFileSystem(std::unique_ptr<FileSystem>(new GcsFileSystem)) {}
};

}  // namespace tensorflow

#endif  // TENSORFLOW_CORE_PLATFORM_GCS_FILE_SYSTEM_H_
