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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,
   as published by the Free Software Foundation.

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   as designated in a particular file or component or in included license
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   permission to link the program and your derivative works with the
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   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
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#ifndef SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_
#define SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_

#include <sys/types.h>

#include "sql/range_optimizer/index_range_scan.h"
#include "sql/range_optimizer/range_optimizer.h"
#include "sql/sql_list.h"

/**
  An iterator much like IndexRangeScanIterator, but it scans in the reverse
  order. This makes it at times more complicated, but since it doesn't support
  being a part of a ROR scan, it is also less complicated in many ways.

  One could argue that this and IndexRangeScanIterator should be factored into
  a common base class with separate _ASC and _DESC classes, but they don't
  actually duplicate that much code.
 */
class ReverseIndexRangeScanIterator : public TableRowIterator {
 public:
  ReverseIndexRangeScanIterator(THD *thd, TABLE *table, ha_rows *examined_rows,
                                double expected_rows, int index,
                                MEM_ROOT *return_mem_root, uint mrr_flags,
                                Bounds_checked_array<QUICK_RANGE *> ranges,
                                bool using_extended_key_parts);
  ~ReverseIndexRangeScanIterator() override;
  int Read() override;
  bool Init() override;

 private:
  static range_seq_t quick_range_rev_seq_init(void *init_param, uint, uint);

  const uint m_index; /* Index this quick select uses */
  ha_rows m_expected_rows;
  ha_rows *m_examined_rows;

  MEM_ROOT *mem_root;
  bool inited = false;

  // TODO: pre-allocate space to avoid malloc/free for small number of columns.
  MY_BITMAP column_bitmap;

  uint m_mrr_flags; /* Flags to be used with MRR interface */

  Bounds_checked_array<QUICK_RANGE *> ranges; /* ordered array of range ptrs */
  /* Members needed to use the MRR interface */
  QUICK_RANGE_SEQ_CTX qr_traversal_ctx;

  QUICK_RANGE *last_range;  // The range we are currently scanning, or nullptr.
  int current_range_idx;

  /* Info about index we're scanning */
  KEY_PART_INFO *key_part_info;

  // Whether this reverse scan uses extended keyparts (in case of Innodb,
  // secondary index is extended to include primary key).
  bool m_using_extended_key_parts{false};

  bool range_reads_after_key(QUICK_RANGE *range);
  int cmp_prev(QUICK_RANGE *range);
};

#endif  // SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_