/* Copyright (c) 2021, 2024, 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.

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   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
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "sql/join_optimizer/replace_item.h"
#include "sql/item.h"
#include "sql/sql_resolver.h"
#include "sql/temp_table_param.h"

/**
  Check what field the given item will be materialized into under the given
  temporary table parameters.

  If the item is materialized (ie., found in items_to_copy), we return a
  canonical Item_field for that field; ie., the same every time. This means
  that you can do the same replacement in a SELECT list and then in
  items_to_copy itself, and still have them match. This is used in particular
  when updating Temp_table_param itself, in FinalizePlanForQueryBlock().

  Normally, we want to search for only the same item, up to references
  (need_exact_match=true). However, in ORDER BY specifications of windows,
  we can sometimes have the same field referred to by different Item_field,
  and the callers may need to set need_exact_match=false, which compares
  using Item::eq() instead. This also disables the behavior of checking
  and propagating Item::hidden.
 */
static Item *FindReplacementItem(Item *item,
                                 const Func_ptr_array &items_to_copy,
                                 bool need_exact_match) {
  if (item->const_for_execution()) {
    // Stop traversing (which we do with a fake replacement with ourselves).
    // This is the only case where we can return an Item that is not an
    // Item_field.
    return item;
  }

  for (const Func_ptr &func : items_to_copy) {
    bool match;
    if (need_exact_match) {
      // For nearly all cases, just comparing the items (by pointer) would
      // be sufficient, but in rare cases involving CTEs (see e.g. the test for
      // bug #26907753), we can have a ref in func.func(), so we need to call
      // real_item() before comparing.
      match = func.func()->hidden == item->hidden &&
              func.func()->real_item() == item->real_item();
    } else {
      match =
          func.func()->real_item() == item->real_item() ||
          func.func()->real_item()->eq(item->real_item(), /*binary_cmp=*/true);
    }
    if (match) {
      Item_field *item_field = func.result_item();
      if (item_field == nullptr) return nullptr;
      if (need_exact_match) {
        item_field->hidden = item->hidden;
      }
      return item_field;
    }
  }
  return nullptr;
}

Item *FindReplacementOrReplaceMaterializedItems(
    THD *thd, Item *item, const Func_ptr_array &items_to_copy,
    bool need_exact_match) {
  Item *replacement =
      FindReplacementItem(item, items_to_copy, need_exact_match);
  if (replacement != nullptr) {
    return replacement;
  } else {
    // We don't need to care about the hidden flag when modifying the arguments
    // to an item (ie., the item itself isn't in the SELECT list). Non-exact
    // matches are important when modifying arguments within rollup group
    // wrappers, since e.g. rollup_group_item(t1.a) will create a hidden item
    // t1.a, and if we materialize t1.a -> <temporary>.a, we'll need to modify
    // the argument to the rollup group wrapper as well.
    ReplaceMaterializedItems(thd, item, items_to_copy,
                             /*need_exact_match=*/false);
    return item;
  }
}

void ReplaceMaterializedItems(THD *thd, Item *item,
                              const Func_ptr_array &items_to_copy,
                              bool need_exact_match) {
  bool modified = false;
  const auto replace_functor = [&modified, &items_to_copy, need_exact_match](
                                   Item *sub_item, Item *,
                                   unsigned) -> ReplaceResult {
    Item *replacement = FindReplacementItem(sub_item->real_item(),
                                            items_to_copy, need_exact_match);
    if (replacement != nullptr) {
      modified = true;
      return {ReplaceResult::REPLACE, replacement};
    } else {
      return {ReplaceResult::KEEP_TRAVERSING, nullptr};
    }
  };
  WalkAndReplace(thd, item, std::move(replace_functor));

  // If the item was modified to reference temporary tables, we need to update
  // its used tables to account for that.
  if (modified) {
    item->update_used_tables();
  }
}