/* Copyright (c) 2011, 2021, 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 also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   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
   separately licensed software that they have included with MySQL.

   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,
   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */


#ifndef OPT_EXPLAIN_INCLUDED
#define OPT_EXPLAIN_INCLUDED

/** @file "EXPLAIN <command>" 

Single table UPDATE/DELETE commands are explained by the 
explain_single_table_modification() function.

A query expression (complete SELECT query possibly including
subqueries and unions), INSERT...SELECT and multitable UPDATE/DELETE
commands are explained like this:

(1) explain_query_expression()

Is the entry point. Forwards the job to explain_unit().

(2) explain_unit()

Is for a SELECT_LEX_UNIT, prepares, optimizes, explains one JOIN for
each "top-level" SELECT_LEXs of the unit (like: all SELECTs of a
UNION; but not subqueries), and one JOIN for the fake SELECT_LEX of
UNION); each JOIN explain (JOIN::exec()) calls explain_query_specification()

(3) explain_query_specification()

Is for a single SELECT_LEX (fake or not). It needs a prepared and
optimized JOIN, for which it builds the EXPLAIN rows. But it also
launches the EXPLAIN process for "inner units" (==subqueries of this
SELECT_LEX), by calling explain_unit() for each of them. 
*/

#include <my_base.h>
#include "opt_explain_format.h"

class JOIN;
class Query_result;
class Query_result_interceptor;
struct TABLE;
class THD;
typedef class st_select_lex_unit SELECT_LEX_UNIT;
typedef class st_select_lex SELECT_LEX;

extern const char *join_type_str[];

/** Table modification plan for JOIN-less statements (update/delete) */
class Modification_plan
{
public:
  THD *const thd;           ///< Owning thread
  const enum_mod_type mod_type;///< Modification type - MT_INSERT/MT_UPDATE/etc
  TABLE *table;             ///< Table to modify

  QEP_TAB *tab;             ///< QUICK access method + WHERE clause
  uint key;                 ///< Key to use
  ha_rows limit;            ///< Limit
  bool need_tmp_table;      ///< Whether tmp table needs to be used
  bool need_sort;           ///< Whether to use filesort
  bool used_key_is_modified;///< Whether the key used to scan is modified
  const char *message;      ///< Arbitrary message
  bool zero_result;         ///< TRUE <=> plan will not be executed
  ha_rows examined_rows;    ///< # of rows expected to be examined in the table

  Modification_plan(THD *thd_arg,
                    enum_mod_type mt, QEP_TAB *qep_tab,
                    uint key_arg, ha_rows limit_arg, bool need_tmp_table_arg,
                    bool need_sort_arg, bool used_key_is_modified_arg,
                    ha_rows rows);

  Modification_plan(THD *thd_arg,
                    enum_mod_type mt, TABLE *table_arg,
                    const char *message_arg, bool zero_result_arg,
                    ha_rows rows);

  ~Modification_plan();

private:
  void register_in_thd();
};


/**
  EXPLAIN functionality for Query_result_insert, Query_result_update and
  Query_result_delete.

  This class objects substitute Query_result_insert, Query_result_update and
  Query_result_delete data interceptor objects to implement EXPLAIN for INSERT,
  REPLACE and multi-table UPDATE and DELETE queries.
  Query_result_explain class object initializes tables like Query_result_insert,
  Query_result_update or Query_result_delete data interceptor do, but it suppress
  table data modification by the underlying interceptor object.
  Thus, we can use Query_result_explain object in the context of EXPLAIN INSERT/
  REPLACE/UPDATE/DELETE query like we use Query_result_send in the context of
  EXPLAIN SELECT command:
    1) in presence of lex->describe flag we pass Query_result_explain object to the
       handle_query() function,
    2) it call prepare(), prepare2() and initialize_tables() functions to
       mark modified tables etc.

*/

class Query_result_explain : public Query_result_send {
protected:
  /*
    As far as we use Query_result_explain object in a place of Query_result_send,
    Query_result_explain have to pass multiple invocation of its prepare(),
    prepare2() and initialize_tables() functions, since JOIN::exec() of
    subqueries runs these functions of Query_result_send multiple times by design.
    Query_result_insert, Query_result_update and Query_result_delete class
    functions are not intended for multiple invocations, so "prepared",
    "prepared2" and "initialized" flags guard data interceptor object from
    function re-invocation.
  */
  bool prepared;    ///< prepare() is done
  bool prepared2;   ///< prepare2() is done
  bool initialized; ///< initialize_tables() is done

  /**
    Pointer to underlying Query_result_insert, Query_result_update or
    Query_result_delete object.
  */
  Query_result *interceptor;

public:
  Query_result_explain(st_select_lex_unit *unit_arg, Query_result *interceptor_arg)
  : prepared(false), prepared2(false), initialized(false),
    interceptor(interceptor_arg)
  { unit= unit_arg; }

protected:
  virtual int prepare(List<Item> &list, SELECT_LEX_UNIT *u)
  {
    if (prepared)
      return false;
    prepared= true;
    return Query_result_send::prepare(list, u) || interceptor->prepare(list, u);
  }

  virtual int prepare2(void)
  {
    if (prepared2)
      return false;
    prepared2= true;
    return Query_result_send::prepare2() || interceptor->prepare2();
  }

  virtual bool initialize_tables(JOIN *join)
  {
    if (initialized)
      return false;
    initialized= true;
    return Query_result_send::initialize_tables(join) ||
           interceptor->initialize_tables(join);
  }

  virtual void cleanup()
  {
    Query_result_send::cleanup();
    interceptor->cleanup();
  }
};


bool explain_no_table(THD *thd, SELECT_LEX *select_lex, const char *message,
                      enum_parsing_context ctx);
bool explain_single_table_modification(THD *ethd,
                                       const Modification_plan *plan,
                                       SELECT_LEX *select);
bool explain_query(THD *thd, SELECT_LEX_UNIT *unit);
bool explain_query_specification(THD *ethd, SELECT_LEX *select_lex,
                                 enum_parsing_context ctx);
void mysql_explain_other(THD *thd);

#endif /* OPT_EXPLAIN_INCLUDED */
