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   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
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   This program is distributed in the hope that it will be useful,
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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   You should have received a copy of the GNU General Public License
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#ifndef MYSQL_BINLOG_EVENT_COMPRESSION_COMPRESSOR_H
#define MYSQL_BINLOG_EVENT_COMPRESSION_COMPRESSOR_H

#include <cstddef>
#include <tuple>
#include "mysql/binlog/event/compression/base.h"                    // type
#include "mysql/binlog/event/compression/buffer/grow_constraint.h"  // Grow_constraint
#include "mysql/binlog/event/compression/buffer/managed_buffer_sequence.h"  // Managed_buffer_sequence
#include "mysql/binlog/event/nodiscard.h"  // NODISCARD

#include <limits>  // std::numeric_limits

namespace mysql::binlog::event::compression {

using Compress_status = mysql::binlog::event::compression::buffer::Grow_status;

/// Abstract base class for compressors.
///
/// Each subclass normally corresponds to a compression algorithm, and
/// maintains the algorithm-specific state for it.
///
/// An instance of this class can be reused to compress several
/// *frames*.  A frame is a self-contained segment of data, in the
/// sense that it can be decompressed without knowing about other
/// frames, and compression does not take advantage of patterns that
/// repeat between frames.
///
/// Input for a frame can be provided in pieces.  All pieces for a
/// frame will be compressed together; the decompressor will take
/// advantage of patterns across in different pieces within the frame.
/// Providing a frame in pieces is useful when not all input is known
/// at once.
///
/// To compress one frame, use the API as follows:
///
/// 1. Repeat as many times as needed:
///    1.1. Call @c feed to provide a piece of input.
///    1.2. Call @c compress to consume the piece of input and possibly
///         produce a prefix of the output.
/// 2. Choose one of the following:
///    2.1. Call @c finish to produce the remainder of the output for this
///         frame.
///    2.2. Call @c reset to abort this frame.
///
/// @note After 1.2, although the compression library has read all
/// input given so far, it may not have produced all corresponding
/// output.  It usually holds some data in internal buffers, since it
/// may be more compressible when more data has been given. Therefore,
/// step 2.1 is always necessary in order to complete the frame.
///
/// @note To reuse the compressor object for another input, repeat the
/// above procedure as many times as needed.
///
/// This class requires that the user provides a @c
/// mysql::binlog::event::compression::buffer::Managed_buffer_sequence to
/// store output.
class Compressor {
 public:
  using Managed_buffer_sequence_t =
      mysql::binlog::event::compression::buffer::Managed_buffer_sequence<>;
  using Char_t = Managed_buffer_sequence_t::Char_t;
  using Size_t = Managed_buffer_sequence_t::Size_t;
  using Grow_constraint_t =
      mysql::binlog::event::compression::buffer::Grow_constraint;
  static constexpr Size_t pledged_input_size_unset =
      std::numeric_limits<Size_t>::max();

  Compressor() = default;
  Compressor(const Compressor &other) = delete;
  Compressor(Compressor &&other) = delete;
  Compressor &operator=(const Compressor &other) = delete;
  Compressor &operator=(Compressor &&other) = delete;

  virtual ~Compressor() = default;

  /// @return the compression type.
  type get_type_code() const;

  /// Reset the frame.
  ///
  /// This cancels the current frame and starts a new one.
  ///
  /// This is allowed but unnecessary if the current frame has been
  /// reset by @c finish or by an out_of_memory error from @c
  /// compress.
  void reset();

  /// Submit data to be compressed.
  ///
  /// This will not consume any of the input; it should be followed by
  /// a call to @c compress or @c finish.
  ///
  /// @note This object will not copy the input; the caller must
  /// ensure that the input lives until it has been consumed or the
  /// frame has been reset.
  ///
  /// @note Must not be called when there is still non-consumed input
  /// left after a previous call to @c feed.
  ///
  /// @param input_data Data to be compressed. This object will keep a
  /// shallow copy of the data and use it in subsequent calls to @c
  /// compress or @c finish.
  ///
  /// @param input_size Size of data to be compressed.
  template <class Input_char_t>
  void feed(const Input_char_t *input_data, Size_t input_size) {
    feed_char_t(reinterpret_cast<const Char_t *>(input_data), input_size);
  }

  /// Consume all input previously given in the feed function.
  ///
  /// This will consume the input, but may not produce all output;
  /// there may be output still in compression library buffers.  Use
  /// the @c finish function to flush the output and end the frame.
  ///
  /// @param out Storage for compressed bytes.  This may grow, if
  /// needed.
  ///
  /// @retval success All input was consumed.
  ///
  /// @retval out_of_memory The operation failed due to an out of
  /// memory error.  The frame has been reset.
  ///
  /// @retval exceeds_max_size The @c out buffer was already at its
  /// max capacity, and filled, and there were more bytes left to
  /// produce.  The frame has not been reset and it is not guaranteed
  /// that all input has been consumed.  The caller may resume
  /// compression e.g.  after increasing the capacity, or resetting
  /// the output buffer (perhaps after moving existing data
  /// elsewhere), or using a different output buffer, or similar.
  [[NODISCARD]] Compress_status compress(Managed_buffer_sequence_t &out);

  /// Consume all input, produce all output, and end the frame.
  ///
  /// This will consume all input previously given by @c feed (it
  /// internally calls @c compress).  Then it ends the frame and
  /// flushes the output, ensuring that all data that may reside in
  /// the compression library's internal buffers gets compressed and
  /// written to the output.
  ///
  /// The next call to @c feed will start a new frame.
  ///
  /// @param out Storage for compressed bytes.  This may grow, if
  /// needed.
  ///
  /// @retval success All input was consumed, all output was produced,
  /// and the frame was reset.
  ///
  /// @retval out_of_memory The operation failed due to an out of
  /// memory error, and the frame has been reset.
  ///
  /// @retval exceeds_max_size The @c out buffer was already at its
  /// max capacity, and filled, and there were more bytes left to
  /// produce.  The frame has not been reset and it is not guaranteed
  /// that all input has been consumed.  The caller may resume
  /// compression e.g.  after increasing the capacity, or resetting
  /// the output buffer (perhaps after moving existing data
  /// elsewhere), or using a different output buffer, or similar.
  [[NODISCARD]] Compress_status finish(Managed_buffer_sequence_t &out);

  /// Return a `Grow_constraint` that may be used with the
  /// Managed_buffer_sequence storing the output, in order to
  /// optimize memory usage for a particular compression algorithm.
  ///
  /// This may be implemented by subclasses such that it depends on
  /// the pledged input size.  Therefore, for the most optimal grow
  /// constraint, call this after set_pledged_input_size.
  Grow_constraint_t get_grow_constraint_hint() const;

  /// Declare that the input size will be exactly as given.
  ///
  /// This may allow compressors and decompressors to use memory more
  /// efficiently.
  ///
  /// This function may only be called if `feed` has never been
  /// called, or if the compressor has been reset since the last call
  /// to `feed`.  The pledged size will be set back to
  /// pledged_input_size_unset next time this compressor is reset.
  ///
  /// It is required that the total number of bytes passed to `feed`
  /// before the call to `finish` matches the pledged number.
  /// Otherwise, the behavior of `finish` is undefined.
  void set_pledged_input_size(Size_t size);

  /// Return the size previously provided to `set_pledged_input_size`,
  /// or `pledged_input_size_unset` if no pledged size has been set.
  Size_t get_pledged_input_size() const;

 private:
  /// Worker function for @c feed, requiring the correct Char_t type.
  ///
  /// @see feed.
  void feed_char_t(const Char_t *input_data, Size_t input_size);

  /// implement @c get_type_code.
  virtual type do_get_type_code() const = 0;

  /// Implement @c reset.
  virtual void do_reset() = 0;

  /// Implement @c feed.
  ///
  /// This differs from @c feed in that it does not have to reset the
  /// frame when returning out_of_memory; the caller does that.
  virtual void do_feed(const Char_t *input_data, Size_t input_size) = 0;

  /// Implement @c compress.
  ///
  /// This differs from @c compress in that it does not have to reset
  /// the frame when returning out_of_memory; the caller does that.
  [[NODISCARD]] virtual Compress_status do_compress(
      Managed_buffer_sequence_t &out) = 0;

  /// Implement @c finish.
  ///
  /// This differs from @c finish in that it does not have to reset
  /// the frame when returning out_of_memory; the caller does that.
  ///
  /// Implementations may assume that @c compress has been called,
  /// since @c finish does that.
  [[NODISCARD]] virtual Compress_status do_finish(
      Managed_buffer_sequence_t &out) = 0;

  /// Implement @c get_grow_constraint_hint.
  ///
  /// In this base class, the function returns a default-constructed
  /// Grow_constraint, i.e., one which does not limit the
  /// Grow_calculator.
  virtual Grow_constraint_t do_get_grow_constraint_hint() const;

  /// Implement @c set_pledged_input_size
  ///
  /// By default, this does nothing.
  virtual void do_set_pledged_input_size([[maybe_unused]] Size_t size);

  /// True when user has provided input that has not yet been consumed.
  bool m_pending_input = false;

  /// True when user has not provided any input since the last reset.
  bool m_empty = true;

  /// The number of bytes
  Size_t m_pledged_input_size = pledged_input_size_unset;
};

}  // namespace mysql::binlog::event::compression

#endif  // MYSQL_BINLOG_EVENT_COMPRESSION_COMPRESSOR_H