/* Copyright (c) 2000, 2025, Oracle and/or its affiliates.

   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.

   This program is designed to work with certain software (including
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   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
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   the program or referenced in the documentation.

   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
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file
  Implementations of basic iterators, ie. those that have no children
  and don't take any refs (they typically read directly from a table
  in some way). See row_iterator.h.
*/

#include "sql/iterators/basic_row_iterators.h"

#include <assert.h>
#include <atomic>
#include <string>
#include <utility>
#include <vector>

#include "my_base.h"
#include "my_inttypes.h"
#include "my_sys.h"
#include "mysqld_error.h"
#include "sql/debug_sync.h"
#include "sql/handler.h"
#include "sql/iterators/row_iterator.h"
#include "sql/mem_root_array.h"
#include "sql/sql_bitmap.h"
#include "sql/sql_class.h"  // THD
#include "sql/sql_executor.h"
#include "sql/sql_tmp_table.h"
#include "sql/system_variables.h"
#include "sql/table.h"

using std::string;
using std::vector;

template <bool Reverse>
IndexScanIterator<Reverse>::IndexScanIterator(THD *thd, TABLE *table, int idx,
                                              bool use_order,
                                              double expected_rows,
                                              ha_rows *examined_rows)
    : TableRowIterator(thd, table),
      m_record(table->record[0]),
      m_idx(idx),
      m_use_order(use_order),
      m_expected_rows(expected_rows),
      m_examined_rows(examined_rows) {}

template <bool Reverse>
IndexScanIterator<Reverse>::~IndexScanIterator() {
  if (table() && table()->key_read) {
    table()->set_keyread(false);
  }
}

template <bool Reverse>
bool IndexScanIterator<Reverse>::Init() {
  if (!table()->file->inited) {
    if (table()->covering_keys.is_set(m_idx) && !table()->no_keyread) {
      table()->set_keyread(true);
    }

    int error = table()->file->ha_index_init(m_idx, m_use_order);
    if (error) {
      PrintError(error);
      return true;
    }

    if (set_record_buffer(table(), m_expected_rows)) {
      return true;
    }
  }
  m_first = true;
  return false;
}

// Doxygen gets confused by the explicit specializations.

//! @cond
template <>
int IndexScanIterator<false>::Read() {  // Forward read.
  int error;
  if (m_first) {
    error = table()->file->ha_index_first(m_record);
    m_first = false;
  } else {
    error = table()->file->ha_index_next(m_record);
  }
  if (error) return HandleError(error);
  if (m_examined_rows != nullptr) {
    ++*m_examined_rows;
  }
  return 0;
}

template <>
int IndexScanIterator<true>::Read() {  // Backward read.
  int error;
  if (m_first) {
    error = table()->file->ha_index_last(m_record);
    m_first = false;
  } else {
    error = table()->file->ha_index_prev(m_record);
  }
  if (error) return HandleError(error);
  if (m_examined_rows != nullptr) {
    ++*m_examined_rows;
  }
  return 0;
}
//! @endcond

template class IndexScanIterator<true>;
template class IndexScanIterator<false>;

/**
  The default implementation of unlock-row method of RowIterator,
  used in all access methods except EQRefIterator.
*/
void TableRowIterator::UnlockRow() { m_table->file->unlock_row(); }

void TableRowIterator::SetNullRowFlag(bool is_null_row) {
  if (is_null_row) {
    m_table->set_null_row();
  } else {
    m_table->reset_null_row();
  }
}

int TableRowIterator::HandleError(int error) {
  if (thd()->killed) {
    thd()->send_kill_message();
    return 1;
  }

  if (error == HA_ERR_END_OF_FILE || error == HA_ERR_KEY_NOT_FOUND) {
    m_table->set_no_row();
    return -1;
  } else {
    PrintError(error);
    return 1;
  }
}

void TableRowIterator::PrintError(int error) {
  m_table->file->print_error(error, MYF(0));
}

void TableRowIterator::StartPSIBatchMode() {
  m_table->file->start_psi_batch_mode();
}

void TableRowIterator::EndPSIBatchModeIfStarted() {
  m_table->file->end_psi_batch_mode_if_started();
}

TableScanIterator::TableScanIterator(THD *thd, TABLE *table,
                                     double expected_rows,
                                     ha_rows *examined_rows)
    : TableRowIterator(thd, table),
      m_record(table->record[0]),
      m_expected_rows(expected_rows),
      m_examined_rows(examined_rows),
      m_limit_rows(table->set_counter() != nullptr ? table->m_limit_rows
                                                   : HA_POS_ERROR) {}

TableScanIterator::~TableScanIterator() {
  if (table()->file != nullptr) {
    table()->file->ha_index_or_rnd_end();
  }
}

bool TableScanIterator::Init() {
  empty_record(table());

  /*
    Only attempt to allocate a record buffer the first time the handler is
    initialized.
  */
  const bool first_init = !table()->file->inited;

  int error = table()->file->ha_rnd_init(true);
  if (error) {
    PrintError(error);
    return true;
  }

  if (first_init && set_record_buffer(table(), m_expected_rows)) {
    return true; /* purecov: inspected */
  }

  m_stored_rows = 0;

  return false;
}

int TableScanIterator::Read() {
  int tmp;
  if (table()->is_union_or_table()) {
    while ((tmp = table()->file->ha_rnd_next(m_record))) {
      /*
       ha_rnd_next can return RECORD_DELETED for MyISAM when one thread is
       reading and another deleting without locks.
       */
      if (tmp == HA_ERR_RECORD_DELETED && !thd()->killed) continue;
      return HandleError(tmp);
    }
    if (m_examined_rows != nullptr) {
      ++*m_examined_rows;
    }
  } else {
    while (true) {
      if (m_remaining_dups == 0) {  // always initially
        while ((tmp = table()->file->ha_rnd_next(m_record))) {
          if (tmp == HA_ERR_RECORD_DELETED && !thd()->killed) continue;
          return HandleError(tmp);
        }
        if (m_examined_rows != nullptr) {
          ++*m_examined_rows;
        }

        // Filter out rows not qualifying for INTERSECT, EXCEPT by reading
        // the counter.
        const ulonglong cnt =
            static_cast<ulonglong>(table()->set_counter()->val_int());
        if (table()->is_except()) {
          if (table()->is_distinct()) {
            // EXCEPT DISTINCT: any counter value larger than one yields
            // exactly one row
            if (cnt >= 1) break;
          } else {
            // EXCEPT ALL: we use m_remaining_dups to yield as many rows
            // as found in the counter.
            m_remaining_dups = cnt;
          }
        } else {
          // INTERSECT
          if (table()->is_distinct()) {
            if (cnt == 0) break;
          } else {
            HalfCounter c(cnt);
            // Use min(left side counter, right side counter)
            m_remaining_dups = std::min(c[0], c[1]);
          }
        }
      } else {
        --m_remaining_dups;  // return the same row once more.
        break;
      }
      // Skipping this row
    }
    if (++m_stored_rows > m_limit_rows) {
      return HandleError(HA_ERR_END_OF_FILE);
    }
  }
  return 0;
}

ZeroRowsIterator::ZeroRowsIterator(THD *thd,
                                   Mem_root_array<TABLE *> pruned_tables)
    : RowIterator(thd), m_pruned_tables(std::move(pruned_tables)) {}

void ZeroRowsIterator::SetNullRowFlag(bool is_null_row) {
  assert(!m_pruned_tables.empty());
  for (TABLE *table : m_pruned_tables) {
    if (is_null_row) {
      table->set_null_row();
    } else {
      table->reset_null_row();
    }
  }
}

FollowTailIterator::FollowTailIterator(THD *thd, TABLE *table,
                                       double expected_rows,
                                       ha_rows *examined_rows)
    : TableRowIterator(thd, table),
      m_record(table->record[0]),
      m_expected_rows(expected_rows),
      m_examined_rows(examined_rows) {}

FollowTailIterator::~FollowTailIterator() {
  if (table()->file != nullptr) {
    table()->file->ha_index_or_rnd_end();
  }
}

bool FollowTailIterator::Init() {
  empty_record(table());

  // BeginMaterialization() must be called before this.
  assert(m_stored_rows != nullptr);

  /*
    Only attempt to allocate a record buffer the first time the handler is
    initialized.
  */
  const bool first_init = !table()->file->inited;

  if (first_init) {
    // Before starting a new WITH RECURSIVE execution,
    // MaterializeIterator::Init() does ha_index_or_rnd_end() on all read
    // cursors of recursive members, which sets file->inited = false, so we can
    // use that as a signal.
    if (!table()->is_created()) {
      // Recursive references always refer to a temporary table,
      // which do not exist at resolution time; thus, we need to
      // connect to it on first run here.
      assert(table()->in_use == nullptr || table()->in_use == thd());
      table()->in_use = thd();
      if (open_tmp_table(table())) {
        return true;
      }
    }

    int error = table()->file->ha_rnd_init(true);
    if (error) {
      PrintError(error);
      return true;
    }

    if (first_init && set_record_buffer(table(), m_expected_rows)) {
      return true; /* purecov: inspected */
    }

    // The first seen record will start a new iteration.
    m_read_rows = 0;
    m_recursive_iteration_count = 0;
    m_end_of_current_iteration = 0;
  } else {
    // Just continue where we left off last time.
  }

  m_inited = true;
  return false;
}

int FollowTailIterator::Read() {
  if (m_read_rows == *m_stored_rows) {
    /*
      Return EOF without even checking if there are more rows
      (there isn't), so that we can continue reading when there are.
      There are two underlying reasons why we need to do this,
      depending on the storage engine in use:

      1. For both MEMORY and InnoDB, when they report EOF,
         the scan stays blocked at EOF forever even if new rows
         are inserted later. (InnoDB has a supremum record, and
         MEMORY increments info->current_record unconditionally.)

      2. Specific to MEMORY, inserting records that are deduplicated
         away can corrupt cursors that hit EOF. Consider the following
         scenario:

         - write 'A'
         - write 'A': allocates a record, hits a duplicate key error, leaves
           the allocated place as "deleted record".
         - init scan
         - read: finds 'A' at #0
         - read: finds deleted record at #1, properly skips over it, moves to
           EOF
         - even if we save the read position at this point, it's "after #1"
         - close scan
         - write 'B': takes the place of deleted record, i.e. writes at #1
         - write 'C': writes at #2
         - init scan, reposition at saved position
         - read: still after #1, so misses 'B'.

         In this scenario, the table is formed of real records followed by
         deleted records and then EOF.

       To avoid these problems, we keep track of the number of rows in the
       table by holding the m_stored_rows pointer into the MaterializeIterator,
       and simply avoid hitting EOF.
     */
    return -1;
  }

  if (m_read_rows == m_end_of_current_iteration) {
    // We have started a new iteration. Check to see if we have passed the
    // user-set limit.
    if (++m_recursive_iteration_count >
        thd()->variables.cte_max_recursion_depth) {
      my_error(ER_CTE_MAX_RECURSION_DEPTH, MYF(0), m_recursive_iteration_count);
      return 1;
    }
    m_end_of_current_iteration = *m_stored_rows;

#ifdef ENABLED_DEBUG_SYNC
    if (m_recursive_iteration_count == 4) {
      DEBUG_SYNC(thd(), "in_WITH_RECURSIVE");
    }
#endif
  }

  // Read the actual row.
  //
  // We can never have MyISAM here, so we don't need the checks
  // for HA_ERR_RECORD_DELETED that TableScanIterator has.
  int err = table()->file->ha_rnd_next(m_record);
  if (err) {
    return HandleError(err);
  }

  ++m_read_rows;

  if (m_examined_rows != nullptr) {
    ++*m_examined_rows;
  }
  return 0;
}

bool FollowTailIterator::RepositionCursorAfterSpillToDisk() {
  if (!m_inited) {
    // Spill-to-disk happened before we got to read a single row,
    // so the table has not been initialized yet. It will start
    // at the first row when we actually get to Init(), which is fine.
    return false;
  }
  return reposition_innodb_cursor(table(), m_read_rows);
}