//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

//

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

#pragma once

#include <stdint.h>

#include <cstdint>

#include <memory>

#include <unordered_map>

#include <vector>

#include "db/log_format.h"

#include "file/sequence_file_reader.h"

#include "rocksdb/options.h"

#include "rocksdb/slice.h"

#include "rocksdb/status.h"

#include "util/compression.h"

#include "util/hash_containers.h"

#include "util/udt_util.h"

#include "util/xxhash.h"

namespace ROCKSDB_NAMESPACE {

class Logger;

namespace log {

/**

 * Reader is a general purpose log stream reader implementation. The actual job

 * of reading from the device is implemented by the SequentialFile interface.

 *

 * Please see Writer for details on the file and record layout.

 */

class Reader {

 public:

  // Interface for reporting errors.

  class Reporter {

   public:

    virtual ~Reporter();

    // Some corruption was detected.  "size" is the approximate number

    // of bytes dropped due to the corruption.

    virtual void Corruption(size_t bytes, const Status& status,

                            uint64_t log_number = kMaxSequenceNumber) = 0;

    virtual void OldLogRecord(size_t /*bytes*/) {}

  };

  // Create a reader that will return log records from "*file".

  // "*file" must remain live while this Reader is in use.

  //

  // If "reporter" is non-nullptr, it is notified whenever some data is

  // dropped due to a detected corruption.  "*reporter" must remain

  // live while this Reader is in use.

  //

  // If "checksum" is true, verify checksums if available.

  // TODO(hx235): separate WAL related parameters from general `Reader`

  // parameters

  Reader(std::shared_ptr<Logger> info_log,

         std::unique_ptr<SequentialFileReader>&& file, Reporter* reporter,

         bool checksum, uint64_t log_num, bool track_and_verify_wals = false,

         bool stop_replay_for_corruption = false,

         uint64_t min_wal_number_to_keep = std::numeric_limits<uint64_t>::max(),

         const PredecessorWALInfo& observed_predecessor_wal_info =

             PredecessorWALInfo());

  // No copying allowed

  Reader(const Reader&) = delete;

  void operator=(const Reader&) = delete;

  virtual ~Reader();

  // Read the next record into *record.  Returns true if read

  // successfully, false if we hit end of the input.  May use

  // "*scratch" as temporary storage. The contents filled in *record

  // will only be valid until the next mutating operation on this

  // reader or the next mutation to *scratch.

  // If record_checksum is not nullptr, then this function will calculate the

  // checksum of the record read and set record_checksum to it. The checksum is

  // calculated from the original buffers that contain the contents of the

  // record.

  virtual bool ReadRecord(Slice* record, std::string* scratch,

                          WALRecoveryMode wal_recovery_mode =

                              WALRecoveryMode::kTolerateCorruptedTailRecords,

                          uint64_t* record_checksum = nullptr);

  // Return the recorded user-defined timestamp size that have been read so

  // far. This only applies to WAL logs.

  const UnorderedMap<uint32_t, size_t>& GetRecordedTimestampSize() const {

    return recorded_cf_to_ts_sz_;

  }

  // Returns the physical offset of the last record returned by ReadRecord.

  //

  // Undefined before the first call to ReadRecord.

  uint64_t LastRecordOffset();

  // Returns the first physical offset after the last record returned by

  // ReadRecord, or zero before first call to ReadRecord. This can also be

  // thought of as the "current" position in processing the file bytes.

  uint64_t LastRecordEnd();

  // returns true if the reader has encountered an eof condition.

  bool IsEOF() { return eof_; }

  // returns true if the reader has encountered read error.

  bool hasReadError() const { return read_error_; }

  // when we know more data has been written to the file. we can use this

  // function to force the reader to look again in the file.

  // Also aligns the file position indicator to the start of the next block

  // by reading the rest of the data from the EOF position to the end of the

  // block that was partially read.

  virtual void UnmarkEOF();

  SequentialFileReader* file() { return file_.get(); }

  Reporter* GetReporter() const { return reporter_; }

  uint64_t GetLogNumber() const { return log_number_; }

  size_t GetReadOffset() const {

    return static_cast<size_t>(end_of_buffer_offset_);

  }

  bool IsCompressedAndEmptyFile() {

    return !first_record_read_ && compression_type_record_read_;

  }

 protected:

  std::shared_ptr<Logger> info_log_;

  const std::unique_ptr<SequentialFileReader> file_;

  Reporter* const reporter_;

  bool const checksum_;

  char* const backing_store_;

  // Internal state variables used for reading records

  Slice buffer_;

  bool eof_;         // Last Read() indicated EOF by returning < kBlockSize

  bool read_error_;  // Error occurred while reading from file

  // Offset of the file position indicator within the last block when an

  // EOF was detected.

  size_t eof_offset_;

  // Offset of the last record returned by ReadRecord.

  uint64_t last_record_offset_;

  // Offset of the first location past the end of buffer_.

  uint64_t end_of_buffer_offset_;

  // which log number this is

  uint64_t const log_number_;

  // See `Options::track_and_verify_wals`

  bool track_and_verify_wals_;

  // Below variables are used for WAL verification

  // TODO(hx235): To revise `stop_replay_for_corruption_` inside `LogReader`

  // since we have `observed_predecessor_wal_info_` to verify against the

  // `recorded_predecessor_wal_info_` recorded in current WAL. If there is no

  // WAL hole, we can revise `stop_replay_for_corruption_` to be false.

  bool stop_replay_for_corruption_;

  uint64_t min_wal_number_to_keep_;

  PredecessorWALInfo observed_predecessor_wal_info_;

  // Whether this is a recycled log file

  bool recycled_;

  // Whether the first record has been read or not.

  bool first_record_read_;

  // Type of compression used

  CompressionType compression_type_;

  // Track whether the compression type record has been read or not.

  bool compression_type_record_read_;

  StreamingUncompress* uncompress_;

  // Reusable uncompressed output buffer

  std::unique_ptr<char[]> uncompressed_buffer_;

  // Reusable uncompressed record

  std::string uncompressed_record_;

  // Used for stream hashing fragment content in ReadRecord()

  XXH3_state_t* hash_state_;

  // Used for stream hashing uncompressed buffer in ReadPhysicalRecord()

  XXH3_state_t* uncompress_hash_state_;

  // The recorded user-defined timestamp sizes that have been read so far. This

  // is only for WAL logs.

  UnorderedMap<uint32_t, size_t> recorded_cf_to_ts_sz_;

  // Extend record types with the following special values

  enum : uint8_t {

    kEof = kMaxRecordType + 1,

    // Returned whenever we find an invalid physical record.

    // Currently there are three situations in which this happens:

    // * The record has an invalid CRC (ReadPhysicalRecord reports a drop)

    // * The record is a 0-length record (No drop is reported)

    kBadRecord = kMaxRecordType + 2,

    // Returned when we fail to read a valid header.

    kBadHeader = kMaxRecordType + 3,

    // Returned when we read an old record from a previous user of the log.

    kOldRecord = kMaxRecordType + 4,

    // Returned when we get a bad record length

    kBadRecordLen = kMaxRecordType + 5,

    // Returned when we get a bad record checksum

    kBadRecordChecksum = kMaxRecordType + 6,

  };

  // Return type, or one of the preceding special values

  // If WAL compression is enabled, fragment_checksum is the checksum of the

  // fragment computed from the original buffer containing uncompressed

  // fragment.

  uint8_t ReadPhysicalRecord(Slice* result, size_t* drop_size,

                             uint64_t* fragment_checksum = nullptr);

  // Read some more

  bool ReadMore(size_t* drop_size, uint8_t* error);

  void UnmarkEOFInternal();

  // Reports dropped bytes to the reporter.

  // buffer_ must be updated to remove the dropped bytes prior to invocation.

  void ReportCorruption(size_t bytes, const char* reason,

                        uint64_t log_number = kMaxSequenceNumber);

  void ReportDrop(size_t bytes, const Status& reason,

                  uint64_t log_number = kMaxSequenceNumber);

  void ReportOldLogRecord(size_t bytes);

  void InitCompression(const CompressionTypeRecord& compression_record);

  Status UpdateRecordedTimestampSize(

      const std::vector<std::pair<uint32_t, size_t>>& cf_to_ts_sz);

  void MaybeVerifyPredecessorWALInfo(

      WALRecoveryMode wal_recovery_mode, Slice fragment,

      const PredecessorWALInfo& recorded_predecessor_wal_info);

};

class FragmentBufferedReader : public Reader {

 public:

  FragmentBufferedReader(std::shared_ptr<Logger> info_log,

                         std::unique_ptr<SequentialFileReader>&& _file,

                         Reporter* reporter, bool checksum, uint64_t log_num)

      : Reader(info_log, std::move(_file), reporter, checksum, log_num,

               false /*verify_and_track_wals*/,

               false /*stop_replay_for_corruption*/,

               std::numeric_limits<uint64_t>::max() /*min_wal_number_to_keep*/,

               PredecessorWALInfo() /*observed_predecessor_wal_info*/),

        fragments_(),

        in_fragmented_record_(false) {}

  ~FragmentBufferedReader() override {}

  bool ReadRecord(Slice* record, std::string* scratch,

                  WALRecoveryMode wal_recovery_mode =

                      WALRecoveryMode::kTolerateCorruptedTailRecords,

                  uint64_t* record_checksum = nullptr) override;

  void UnmarkEOF() override;

 private:

  std::string fragments_;

  bool in_fragmented_record_;

  bool TryReadFragment(Slice* result, size_t* drop_size,

                       uint8_t* fragment_type_or_err);

  bool TryReadMore(size_t* drop_size, uint8_t* error);

  // No copy allowed

  FragmentBufferedReader(const FragmentBufferedReader&);

  void operator=(const FragmentBufferedReader&);

};

}  // namespace log

}  // namespace ROCKSDB_NAMESPACE