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#ifndef BINLOG_DECOMPRESSING_EVENT_OBJECT_ISTREAM_H_
#define BINLOG_DECOMPRESSING_EVENT_OBJECT_ISTREAM_H_

#include <queue>

#include "libbinlogevents/include/compression/payload_event_buffer_istream.h"
#include "libbinlogevents/include/nodiscard.h"
#include "sql/binlog_reader.h"
#include "sql/raii/targeted_stringstream.h"

/// @addtogroup Replication
/// @{
///
/// @file decompressing_event_object_istream.h
///
/// Stream class that yields Log_event objects, including events
/// contained in Transaction_payload_log_events.

namespace binlog {

/// Stream class that yields Log_event objects from a source.  The
/// source can be a Transaction_payload_log_event, in which case it will
/// produce the contained events.  Or it can be a file, in which case it
/// will yield all events in the file, and if there is a
/// Transaction_payload_log_event, it will yield first that and then all
/// the contained events.
///
/// The recommended use pattern is:
///
/// @code
///   while (stream >> event) {
///     // handle event
///   }
///   if (stream.has_error()) {
///     // handle error
///   }
/// @endcode
///
/// This class actually enforces that you call `has_error` after the
/// loop; failure to do so will result in an assertion in debug mode.
/// In the unlikely case that your code doesn't need to check for
/// errors, you can get rid of the assert by calling has_error() and
/// discarding the return value.
class Decompressing_event_object_istream {
 public:
  using Buffer_stream_t =
      binary_log::transaction::compression::Payload_event_buffer_istream;
  using Buffer_view_t = Buffer_stream_t::Buffer_view_t;
  using Buffer_ptr_t = Buffer_stream_t::Buffer_ptr_t;
  using Event_ptr_t = std::shared_ptr<Log_event>;
  using Tple_ptr_t = std::shared_ptr<const Transaction_payload_log_event>;
  using Fde_ref_t = const Format_description_event &;
  using Status_t = binary_log::transaction::compression::Decompress_status;
  using Grow_calculator_t = Buffer_stream_t::Grow_calculator_t;

  /// Construct stream over a file, decompressing payload events.
  ///
  /// This will produce all events in the file, and in addition, each
  /// Transaction_payload_log_event is followed by the contained
  /// events.
  ///
  /// @param reader The source file to read from.
  explicit Decompressing_event_object_istream(
      IBasic_binlog_file_reader &reader);

  /// Construct stream over a Transaction_payload_log_event.
  ///
  /// This will produce all events contained in the event, but not the
  /// event itself.
  ///
  /// This Decompressing_event_object_istream will, during its entire
  /// life time, hold shared ownership of the Transaction_payload_log_event.
  ///
  /// @param transaction_payload_log_event The source file to read from.
  ///
  /// @param format_description_event The FD event used to parse events.
  Decompressing_event_object_istream(
      const Tple_ptr_t &transaction_payload_log_event,
      Fde_ref_t format_description_event);

  /// Construct stream over a Transaction_payload_log_event.
  ///
  /// This will produce all events contained in the event, but not the
  /// event itself.
  ///
  /// This Decompressing_event_object_istream will, during its entire
  /// life time, hold a pointer to the Transaction_payload_log_event,
  /// and the caller must ensure that the event outlives the stream.
  ///
  /// @param transaction_payload_log_event The source file to read from.
  ///
  /// @param format_description_event The FD event used to parse events.
  Decompressing_event_object_istream(
      const Transaction_payload_log_event &transaction_payload_log_event,
      Fde_ref_t format_description_event);

#ifdef NDEBUG
  ~Decompressing_event_object_istream() = default;
#else
  ~Decompressing_event_object_istream();
#endif

  Decompressing_event_object_istream(Decompressing_event_object_istream &) =
      delete;
  Decompressing_event_object_istream(Decompressing_event_object_istream &&) =
      delete;
  Decompressing_event_object_istream &operator=(
      Decompressing_event_object_istream &) = delete;
  Decompressing_event_object_istream &operator=(
      Decompressing_event_object_istream &&) = delete;

  /// Specify whether checksums shall be verified or not.
  ///
  /// @param verify_checksum If true, verify checksums; otherwise
  /// don't.
  void set_verify_checksum(bool verify_checksum = true);

  /// Read an event from the stream.
  ///
  /// @param out Shared pointer to the produced event.  If this is a
  /// Transaction_payload_log_event, the stream will keep a shared
  /// pointer to it, until it has produced all the contained events.
  ///
  /// @return This object.
  Decompressing_event_object_istream &operator>>(Event_ptr_t &out);

  /// Indicate if EOF or error has not happened.
  ///
  /// @retval true last read was successful (or there was no last
  /// read).
  ///
  /// @retval false last read resulted in end-of-stream or error.
  explicit operator bool() const;

  /// Indicate if EOF or error has happened. This is the negation of
  /// `operator bool`.
  ///
  /// @retval false last read was successful, or there was no last
  /// read.
  ///
  /// @retval true last read resulted in end-of-stream or error.
  bool operator!() const;

  /// Return true if an error has happened.
  bool has_error() const;

  /// Return a message describing the last error.
  ///
  /// @retval "" No error
  ///
  /// @retval string Error
  std::string get_error_str() const;

  /// Return the status
  Status_t get_status() const;

  /// Return const reference to Grow_calculator to the internal event buffer.
  const Grow_calculator_t &get_grow_calculator() const;

  /// Set the Grow_calculator for the internal event buffer.
  void set_grow_calculator(const Grow_calculator_t &grow_calculator);

 private:
  /// Stream of events to read from
  IBasic_binlog_file_reader *m_binlog_reader{nullptr};
  /// Whether we should verify checksum. Unused!
  bool m_verify_checksum{false};
  /// Error from last operation
  std::string m_error_str;
  /// True if we have reached EOF, false otherwise.
  bool m_end{false};
  /// Status
  Status_t m_status{Status_t::success};
  /// Position of last event
  my_off_t m_event_position{0};
#ifndef NDEBUG
  /// True if a read has failed but neither `get_error_str` nor
  /// `has_error` has been called.
  mutable bool m_outstanding_error{false};
#endif

  /// Policy for growing buffers in the decompressing stream
  Grow_calculator_t m_grow_calculator;
  /// The decompression stream; non-null while we are positioned in a TPLE.
  std::unique_ptr<Buffer_stream_t> m_buffer_istream{nullptr};
  /// end_log_pos for the currently processed TPLE, if any
  my_off_t m_transaction_payload_event_offset{0};
  /// 0 when not processing a TPLE; N>0 when positioned before the Nth
  /// embedded event of a TPLE.
  int m_embedded_event_number{0};

  /// Return the current FDE.
  std::function<Fde_ref_t()> m_get_format_description_event;

  /// Report an error
  ///
  /// This sets the status as specified, and returns a stringstream to
  /// which the caller shall write a message.
  ///
  /// @param status The status
  ///
  /// @returns Targeted_stringstream object; the error for this stream
  /// will be set to the given status.
  [[NODISCARD]] raii::Targeted_stringstream error_stream(Status_t status);

  /// Prepare to unfold a given Transaction_payload_log_event by
  /// setting state variables and creating the
  /// Payload_event_buffer_istream object.
  ///
  /// This object will not hold ownership of the event. The caller
  /// must ensure that the event outlives the stream.
  ///
  /// @param tple Event to unfold
  void begin_payload_event(const Transaction_payload_log_event &tple) {
    do_begin_payload_event(tple, tple);
  }

  /// Prepare to unfold a given Transaction_payload_log_event by
  /// setting state variables and creating the
  /// Payload_event_buffer_istream object.
  ///
  /// This object will hold shared ownership of the event.
  ///
  /// @param tple Event to unfold
  void begin_payload_event(const Tple_ptr_t &tple) {
    do_begin_payload_event(*tple, tple);
  }

  /// Worker function implementing both forms of begin_payload_event.
  ///
  /// @tparam Event_ref_or_ptr Either reference-to-event or
  /// shared-pointer-to-event.
  ///
  /// @param tple Event to unfold.
  ///
  /// @param ownership_tple Ownership handle for the event. This can
  /// be a shared_ptr if this object should hold shared ownership, or
  /// a reference otherwise.
  template <class Event_ref_or_ptr>
  void do_begin_payload_event(const Transaction_payload_log_event &tple,
                              const Event_ref_or_ptr &ownership_tple) {
    DBUG_TRACE;
    m_transaction_payload_event_offset = tple.header()->log_pos;
    m_embedded_event_number = 1;
    assert(!m_buffer_istream);
    try {
      m_buffer_istream = std::make_unique<Buffer_stream_t>(ownership_tple);
    } catch (...) {
      // Leave m_buffer_istream empty.
      // Report error on next invocation of `operator>>`.
    }
  }

  /// Worker that deserializes an event from the buffer.
  ///
  /// @param[in] buffer Input byte buffer.
  ///
  /// @param[out] out Pointer to output event.
  ///
  /// @retval false success
  /// @retval true error
  [[NODISCARD]] bool decode_from_buffer(Buffer_view_t &buffer,
                                        Event_ptr_t &out);

  /// Status from read_from_payload_stream
  enum class Read_status { success, eof, error };

  /// Read and decode next event from the Payload_log_event stream
  ///
  /// @param[out] out Pointer to output event.
  ///
  /// @retval success The event was successfully read and decoded
  ///
  /// @retval error An error occurred. `get_error_str` will contain
  /// the reason.
  ///
  /// @retval eof Nothing was read because the read position was at
  /// the end of the event.
  [[NODISCARD]] Read_status read_from_payload_stream(Event_ptr_t &out);

  /// Read and decode the next event from the binlog stream.
  ///
  /// @param[out] out Pointer to the output event.
  ///
  /// @retval false The event was successfully read and decoded.
  ///
  /// @retval true Error or EOF occurred.  In case of error,
  /// `get_error_str` will contain the reason.
  [[NODISCARD]] bool read_from_binlog_stream(Event_ptr_t &out);
};

}  // namespace binlog

/// @} (end of group Replication)

#endif  // ifdef BINLOG_DECOMPRESSING_EVENT_OBJECT_ISTREAM_H_