/* 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
   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 either included with
   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 */

/*
** example file of UDF (user definable functions) that are dynamically loaded
** into the standard mysqld core.
**
** The functions name, type and shared library is saved in the new system
** table 'func'.  To be able to create new functions one must have write
** privilege for the database 'mysql'.	If one starts MySQL with
** --skip-grant-tables, then UDF initialization will also be skipped.
**
** Syntax for the new commands are:
** create function <function_name> returns {string|real|integer}
**		  soname <name_of_shared_library>
** drop function <function_name>
**
** Each defined function may have a xxxx_init function and a xxxx_deinit
** function.  The init function should alloc memory for the function
** and tell the main function about the max length of the result
** (for string functions), number of decimals (for double functions) and
** if the result may be a null value.
**
** If a function sets the 'error' argument to 1 the function will not be
** called anymore and mysqld will return NULL for all calls to this copy
** of the function.
**
** All strings arguments to functions are given as string pointer + length
** to allow handling of binary data.
** Remember that all functions must be thread safe. This means that one is not
** allowed to alloc any global or static variables that changes!
** If one needs memory one should alloc this in the init function and free
** this on the __deinit function.
**
** Note that the init and __deinit functions are only called once per
** SQL statement while the value function may be called many times
**
** Function 'metaphon' returns a metaphon string of the string argument.
** This is something like a soundex string, but it's more tuned for English.
**
** Function 'myfunc_double' returns summary of codes of all letters
** of arguments divided by summary length of all its arguments.
**
** Function 'myfunc_int' returns summary length of all its arguments.
**
** Function 'sequence' returns an sequence starting from a certain number.
**
** Function 'myfunc_argument_name' returns name of argument.
**
** On the end is a couple of functions that converts hostnames to ip and
** vice versa.
**
** A dynamically loadable file should be compiled shared.
** (something like: gcc -shared -o my_func.so myfunc.cc).
** You can easily get all switches right by doing:
** cd sql ; make udf_example.o
** Take the compile line that make writes, remove the '-c' near the end of
** the line and add -shared -o udf_example.so to the end of the compile line.
** The resulting library (udf_example.so) should be copied to some dir
** searched by ld. (/usr/lib ?)
** If you are using gcc, then you should be able to create the udf_example.so
** by simply doing 'make udf_example.so'.
**
** After the library is made one must notify mysqld about the new
** functions with the commands:
**
** CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so";
** CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so";
** CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so";
** CREATE FUNCTION sequence RETURNS INTEGER SONAME "udf_example.so";
** CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so";
** CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so";
** CREATE AGGREGATE FUNCTION avgcost RETURNS REAL SONAME "udf_example.so";
** CREATE FUNCTION myfunc_argument_name RETURNS STRING SONAME "udf_example.so";
**
** After this the functions will work exactly like native MySQL functions.
** Functions should be created only once.
**
** The functions can be deleted by:
**
** DROP FUNCTION metaphon;
** DROP FUNCTION myfunc_double;
** DROP FUNCTION myfunc_int;
** DROP FUNCTION lookup;
** DROP FUNCTION reverse_lookup;
** DROP FUNCTION avgcost;
** DROP FUNCTION myfunc_argument_name;
**
** The CREATE FUNCTION and DROP FUNCTION update the func@mysql table. All
** Active function will be reloaded on every restart of server
** (if --skip-grant-tables is not given)
**
** If you ge problems with undefined symbols when loading the shared
** library, you should verify that mysqld is compiled with the -rdynamic
** option.
**
** If you can't get AGGREGATES to work, check that you have the column
** 'type' in the mysql.func table.  If not, run 'mysql_upgrade'.
**
*/

#include <assert.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <mutex>
#include <new>
#include <regex>
#include <string>
#include <vector>

#include "mysql.h"  // IWYU pragma: keep
#include "mysql/udf_registration_types.h"

#ifdef _WIN32
/* inet_aton needs winsock library */
#pragma comment(lib, "ws2_32")
#endif

/*
  Not all platforms have gethostbyaddr_r, so we use a global lock here instead.
  Production-quality code should use getaddrinfo where available.
*/
static std::mutex *LOCK_hostname{nullptr};

/* All function signatures must be right or mysqld will not find the symbol! */

/*************************************************************************
** Example of init function
** Arguments:
** initid	Points to a structure that the init function should fill.
**		This argument is given to all other functions.
**	bool maybe_null	1 if function can return NULL
**				Default value is 1 if any of the arguments
**				is declared maybe_null.
**	unsigned int decimals	Number of decimals.
**				Default value is max decimals in any of the
**				arguments.
**	unsigned int max_length  Length of string result.
**				The default value for integer functions is 21
**				The default value for real functions is 13+
**				default number of decimals.
**				The default value for string functions is
**				the longest string argument.
**	char *ptr;		A pointer that the function can use.
**
** args		Points to a structure which contains:
**	unsigned int arg_count		Number of arguments
**	enum Item_result *arg_type	Types for each argument.
**					Types are STRING_RESULT, REAL_RESULT
**					and INT_RESULT.
**	char **args			Pointer to constant arguments.
**					Contains 0 for not constant argument.
**	unsigned long *lengths;		max string length for each argument
**	char *maybe_null		Information of which arguments
**					may be NULL
**
** message	Error message that should be passed to the user on fail.
**		The message buffer is MYSQL_ERRMSG_SIZE big, but one should
**		try to keep the error message less than 80 bytes long!
**
** This function should return 1 if something goes wrong. In this case
** message should contain something useful!
**************************************************************************/

#define MAXMETAPH 8

extern "C" bool metaphon_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  if (args->arg_count != 1 || args->arg_type[0] != STRING_RESULT) {
    strcpy(message, "Wrong arguments to metaphon;  Use the source");
    return true;
  }
  initid->max_length = MAXMETAPH;
  return false;
}

/****************************************************************************
** Deinit function. This should free all resources allocated by
** this function.
** Arguments:
** initid	Return value from xxxx_init
****************************************************************************/

extern "C" void metaphon_deinit(UDF_INIT *) {}

/***************************************************************************
** UDF string function.
** Arguments:
** initid	Structure filled by xxx_init
** args		The same structure as to xxx_init. This structure
**		contains values for all parameters.
**		Note that the functions MUST check and convert all
**		to the type it wants!  Null values are represented by
**		a NULL pointer
** result	Possible buffer to save result. At least 255 byte long.
** length	Pointer to length of the above buffer.	In this the function
**		should save the result length
** is_null	If the result is null, one should store 1 here.
** error	If something goes fatally wrong one should store 1 here.
**
** This function should return a pointer to the result string.
** Normally this is 'result' but may also be an allocated string.
***************************************************************************/

/* Character coding array */
static char codes[26] = {
    1, 16, 4, 16, 9, 2, 4, 16, 9, 2, 0, 2, 2, 2,
    1, 4,  0, 2,  4, 4, 1, 0,  0, 0, 8, 0
    /* A  B C  D E F G  H I J K L M N O P Q R S T U V W X Y Z*/
};

/*--- Macros to access character coding array -------------*/

#define ISVOWEL(x) (codes[(x) - 'A'] & 1) /* AEIOU */

/* Following letters are not changed */
#define NOCHANGE(x) (codes[(x) - 'A'] & 2) /* FJLMNR */

/* These form diphthongs when preceding H */
#define AFFECTH(x) (codes[(x) - 'A'] & 4) /* CGPST */

/* These make C and G soft */
#define MAKESOFT(x) (codes[(x) - 'A'] & 8) /* EIY */

/* These prevent GH from becoming F */
#define NOGHTOF(x) (codes[(x) - 'A'] & 16) /* BDH */

extern "C" char *metaphon(UDF_INIT *, UDF_ARGS *args, char *result,
                          unsigned long *length, unsigned char *is_null,
                          unsigned char *) {
  const char *word = args->args[0];
  const char *w_end;
  char *org_result;
  char *n, *n_start, *n_end; /* pointers to string */
  char *metaph_end;          /* pointers to end of metaph */
  char ntrans[32];           /* word with uppercase letters */
  int KSflag;                /* state flag for X to KS */

  if (!word) /* Null argument */
  {
    /* The length is expected to be zero when the argument is NULL. */
    assert(args->lengths[0] == 0);
    *is_null = 1;
    return nullptr;
  }

  w_end = word + args->lengths[0];
  org_result = result;

  /*--------------------------------------------------------
   *  Copy word to internal buffer, dropping non-alphabetic
   *  characters and converting to uppercase.
   *-------------------------------------------------------*/

  for (n = ntrans + 1, n_end = ntrans + sizeof(ntrans) - 2;
       word != w_end && n < n_end; word++)
    if (isalpha(*word)) *n++ = toupper(*word);

  if (n == ntrans + 1) /* return empty string if 0 bytes */
  {
    *length = 0;
    return result;
  }
  n_end = n;       /* set n_end to end of string */
  ntrans[0] = 'Z'; /* ntrans[0] should be a neutral char */
  n[0] = n[1] = 0; /* pad with nulls */
  n = ntrans + 1;  /* assign pointer to start */

  /*------------------------------------------------------------
   *  check for all prefixes:
   *		PN KN GN AE WR WH and X at start.
   *----------------------------------------------------------*/

  switch (*n) {
    case 'P':
    case 'K':
    case 'G':
      if (n[1] == 'N') *n++ = 0;
      break;
    case 'A':
      if (n[1] == 'E') *n++ = 0;
      break;
    case 'W':
      if (n[1] == 'R')
        *n++ = 0;
      else if (*(n + 1) == 'H') {
        n[1] = *n;
        *n++ = 0;
      }
      break;
    case 'X':
      *n = 'S';
      break;
  }

  /*------------------------------------------------------------
   *  Now, loop step through string, stopping at end of string
   *  or when the computed metaph is MAXMETAPH characters long
   *----------------------------------------------------------*/

  KSflag = 0; /* state flag for KS translation */

  for (metaph_end = result + MAXMETAPH, n_start = n;
       n < n_end && result < metaph_end; n++) {
    if (KSflag) {
      KSflag = 0;
      *result++ = *n;
    } else {
      /* drop duplicates except for CC */
      if (*(n - 1) == *n && *n != 'C') continue;

      /* check for F J L M N R or first letter vowel */
      if (NOCHANGE(*n) || (n == n_start && ISVOWEL(*n)))
        *result++ = *n;
      else
        switch (*n) {
          case 'B': /* check for -MB */
            if (n < n_end || *(n - 1) != 'M') *result++ = *n;
            break;

          case 'C': /* C = X ("sh" sound) in CH and CIA */
            /*   = S in CE CI and CY	      */
            /*	 dropped in SCI SCE SCY       */
            /* else K			      */
            if (*(n - 1) != 'S' || !MAKESOFT(n[1])) {
              if (n[1] == 'I' && n[2] == 'A')
                *result++ = 'X';
              else if (MAKESOFT(n[1]))
                *result++ = 'S';
              else if (n[1] == 'H')
                *result++ =
                    ((n == n_start && !ISVOWEL(n[2])) || *(n - 1) == 'S') ? 'K'
                                                                          : 'X';
              else
                *result++ = 'K';
            }
            break;

          case 'D': /* J before DGE, DGI, DGY, else T */
            *result++ = (n[1] == 'G' && MAKESOFT(n[2])) ? 'J' : 'T';
            break;

          case 'G': /* complicated, see table in text */
            if ((n[1] != 'H' || ISVOWEL(n[2])) &&
                (n[1] != 'N' ||
                 ((n + 1) < n_end && (n[2] != 'E' || *(n + 3) != 'D'))) &&
                (*(n - 1) != 'D' || !MAKESOFT(n[1])))
              *result++ = (MAKESOFT(*(n + 1)) && n[2] != 'G') ? 'J' : 'K';
            else if (n[1] == 'H' && !NOGHTOF(*(n - 3)) && *(n - 4) != 'H')
              *result++ = 'F';
            break;

          case 'H': /* H if before a vowel and not after */
            /* C, G, P, S, T */

            if (!AFFECTH(*(n - 1)) && (!ISVOWEL(*(n - 1)) || ISVOWEL(n[1])))
              *result++ = 'H';
            break;

          case 'K': /* K = K, except dropped after C */
            if (*(n - 1) != 'C') *result++ = 'K';
            break;

          case 'P': /* PH = F, else P = P */
            *result++ = *(n + 1) == 'H' ? 'F' : 'P';
            break;
          case 'Q': /* Q = K (U after Q is already gone */
            *result++ = 'K';
            break;

          case 'S': /* SH, SIO, SIA = X ("sh" sound) */
            *result++ = (n[1] == 'H' ||
                         (*(n + 1) == 'I' && (n[2] == 'O' || n[2] == 'A')))
                            ? 'X'
                            : 'S';
            break;

          case 'T': /* TIO, TIA = X ("sh" sound) */
            /* TH = 0, ("th" sound ) */
            if (*(n + 1) == 'I' && (n[2] == 'O' || n[2] == 'A'))
              *result++ = 'X';
            else if (n[1] == 'H')
              *result++ = '0';
            else if (*(n + 1) != 'C' || n[2] != 'H')
              *result++ = 'T';
            break;

          case 'V': /* V = F */
            *result++ = 'F';
            break;

          case 'W': /* only exist if a vowel follows */
          case 'Y':
            if (ISVOWEL(n[1])) *result++ = *n;
            break;

          case 'X': /* X = KS, except at start */
            if (n == n_start)
              *result++ = 'S';
            else {
              *result++ = 'K'; /* insert K, then S */
              KSflag = 1;      /* this flag will cause S to be
                                  inserted on next pass thru loop */
            }
            break;

          case 'Z':
            *result++ = 'S';
            break;
        }
    }
  }
  *length = (unsigned long)(result - org_result);
  return org_result;
}

/***************************************************************************
** UDF double function.
** Arguments:
** initid	Structure filled by xxx_init
** args		The same structure as to xxx_init. This structure
**		contains values for all parameters.
**		Note that the functions MUST check and convert all
**		to the type it wants!  Null values are represented by
**		a NULL pointer
** is_null	If the result is null, one should store 1 here.
** error	If something goes fatally wrong one should store 1 here.
**
** This function should return the result.
***************************************************************************/

extern "C" bool myfunc_double_init(UDF_INIT *initid, UDF_ARGS *args,
                                   char *message) {
  unsigned i;

  if (!args->arg_count) {
    strcpy(message, "myfunc_double must have at least one argument");
    return true;
  }
  /*
  ** As this function wants to have everything as strings, force all arguments
  ** to strings.
  */
  for (i = 0; i < args->arg_count; i++) args->arg_type[i] = STRING_RESULT;
  initid->maybe_null = true; /* The result may be null */
  initid->decimals = 2;      /* We want 2 decimals in the result */
  initid->max_length = 6;    /* 3 digits + . + 2 decimals */
  return false;
}

extern "C" double myfunc_double(UDF_INIT *, UDF_ARGS *args,
                                unsigned char *is_null, unsigned char *) {
  unsigned long val = 0;
  unsigned long v = 0;
  unsigned i, j;

  for (i = 0; i < args->arg_count; i++) {
    if (args->args[i] == nullptr) continue;
    val += args->lengths[i];
    for (j = args->lengths[i]; j-- > 0;) v += args->args[i][j];
  }
  if (val) return (double)v / (double)val;
  *is_null = 1;
  return 0.0;
}

/***************************************************************************
** UDF long long function.
** Arguments:
** initid	Return value from xxxx_init
** args		The same structure as to xxx_init. This structure
**		contains values for all parameters.
**		Note that the functions MUST check and convert all
**		to the type it wants!  Null values are represented by
**		a NULL pointer
** is_null	If the result is null, one should store 1 here.
** error	If something goes fatally wrong one should store 1 here.
**
** This function should return the result as a long long
***************************************************************************/

/* This function returns the sum of all arguments */

extern "C" long long myfunc_int(UDF_INIT *, UDF_ARGS *args, unsigned char *,
                                unsigned char *) {
  long long val = 0;
  unsigned i;

  for (i = 0; i < args->arg_count; i++) {
    if (args->args[i] == nullptr) continue;
    switch (args->arg_type[i]) {
      case STRING_RESULT: /* Add string lengths */
        val += args->lengths[i];
        break;
      case INT_RESULT: /* Add numbers */
        val += *((long long *)args->args[i]);
        break;
      case REAL_RESULT: /* Add numbers as long long */
        val += (long long)*((double *)args->args[i]);
        break;
      default:
        break;
    }
  }
  return val;
}

/*
  At least one of _init/_deinit is needed unless the server is started
  with --allow_suspicious_udfs.
*/
extern "C" bool myfunc_int_init(UDF_INIT *, UDF_ARGS *, char *) {
  return false;
}

/*
  Simple example of how to get a sequences starting from the first argument
  or 1 if no arguments have been given
*/

extern "C" bool sequence_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  if (args->arg_count > 1) {
    strcpy(message, "This function takes none or 1 argument");
    return true;
  }
  if (args->arg_count)
    args->arg_type[0] = INT_RESULT; /* Force argument to int */

  if (!(initid->ptr = (char *)malloc(sizeof(long long)))) {
    strcpy(message, "Couldn't allocate memory");
    return true;
  }
  memset(initid->ptr, 0, sizeof(long long));
  /*
    sequence() is a non-deterministic function : it has different value
    even if called with the same arguments.
  */
  initid->const_item = false;
  return false;
}

extern "C" void sequence_deinit(UDF_INIT *initid) {
  if (initid->ptr) free(initid->ptr);
}

extern "C" long long sequence(UDF_INIT *initid, UDF_ARGS *args, unsigned char *,
                              unsigned char *) {
  unsigned long long val = 0;
  if (args->arg_count) val = *((long long *)args->args[0]);
  return ++*((long long *)initid->ptr) + val;
}

/****************************************************************************
** Some functions that handles IP and hostname conversions
** The original function was from Zeev Suraski.
**
** CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so";
** CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so";
**
****************************************************************************/

#ifndef _WIN32
#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/socket.h>
#endif

/****************************************************************************
** lookup IP for an hostname.
**
** This code assumes that inet_ntoa() is thread safe (As it is in Solaris)
****************************************************************************/

extern "C" bool lookup_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  if (args->arg_count != 1 || args->arg_type[0] != STRING_RESULT) {
    strcpy(message, "Wrong arguments to lookup;  Use the source");
    return true;
  }
  initid->max_length = 11;
  initid->maybe_null = true;
  LOCK_hostname = new std::mutex;
  return false;
}

extern "C" void lookup_deinit(UDF_INIT *) {
  delete LOCK_hostname;
  LOCK_hostname = nullptr;
}

extern "C" char *lookup(UDF_INIT *, UDF_ARGS *args, char *result,
                        unsigned long *res_length, unsigned char *null_value,
                        unsigned char *) {
  unsigned length;
  char name_buff[256];
  struct hostent *hostent;
  struct in_addr in;

  if (!args->args[0] || !(length = args->lengths[0])) {
    *null_value = 1;
    return nullptr;
  }
  if (length >= sizeof(name_buff)) length = sizeof(name_buff) - 1;
  memcpy(name_buff, args->args[0], length);
  name_buff[length] = 0;
  {
    std::lock_guard<std::mutex> lock(*LOCK_hostname);
    if (!(hostent = gethostbyname((char *)name_buff))) {
      *null_value = 1;
      return nullptr;
    }
  }
  memcpy(&in, *hostent->h_addr_list, sizeof(in.s_addr));
  strcpy(result, inet_ntoa(in));
  *res_length = strlen(result);
  return result;
}

/****************************************************************************
** return hostname for an IP number.
** The functions can take as arguments a string "xxx.xxx.xxx.xxx" or
** four numbers.
****************************************************************************/

extern "C" bool reverse_lookup_init(UDF_INIT *initid, UDF_ARGS *args,
                                    char *message) {
  if (args->arg_count == 1)
    args->arg_type[0] = STRING_RESULT;
  else if (args->arg_count == 4)
    args->arg_type[0] = args->arg_type[1] = args->arg_type[2] =
        args->arg_type[3] = INT_RESULT;
  else {
    strcpy(message,
           "Wrong number of arguments to reverse_lookup;  Use the source");
    return true;
  }
  initid->max_length = 32;
  initid->maybe_null = true;
  LOCK_hostname = new std::mutex;
  return false;
}

extern "C" void reverse_lookup_deinit(UDF_INIT *) {
  delete LOCK_hostname;
  LOCK_hostname = nullptr;
}

extern "C" char *reverse_lookup(UDF_INIT *, UDF_ARGS *args, char *result,
                                unsigned long *res_length,
                                unsigned char *null_value, unsigned char *) {
  struct hostent *hp;
  unsigned long taddr;
  unsigned length;

  if (args->arg_count == 4) {
    if (!args->args[0] || !args->args[1] || !args->args[2] || !args->args[3]) {
      *null_value = 1;
      return nullptr;
    }
    sprintf(result, "%d.%d.%d.%d", (int)*((long long *)args->args[0]),
            (int)*((long long *)args->args[1]),
            (int)*((long long *)args->args[2]),
            (int)*((long long *)args->args[3]));
  } else {              /* string argument */
    if (!args->args[0]) /* Return NULL for NULL values */
    {
      *null_value = 1;
      return nullptr;
    }
    length = args->lengths[0];
    if (length >= (unsigned)*res_length - 1) length = (unsigned)*res_length;
    memcpy(result, args->args[0], length);
    result[length] = 0;
  }

  taddr = inet_addr(result);
  if (taddr == (unsigned long)-1L) {
    *null_value = 1;
    return nullptr;
  }
  {
    std::lock_guard<std::mutex> lock(*LOCK_hostname);
    if (!(hp = gethostbyaddr((char *)&taddr, sizeof(taddr), AF_INET))) {
      *null_value = 1;
      return nullptr;
    }
  }
  strcpy(result, hp->h_name);
  *res_length = strlen(result);
  return result;
}

/*
** Syntax for the new aggregate commands are:
** create aggregate function <function_name> returns {string|real|integer}
**		  soname <name_of_shared_library>
**
** Syntax for avgcost: avgcost( t.quantity, t.price )
**	with t.quantity=integer, t.price=double
** (this example is provided by Andreas F. Bobak <bobak@relog.ch>)
*/

struct avgcost_data {
  unsigned long long count;
  long long totalquantity;
  double totalprice;
};

/*
** Average Cost Aggregate Function.
*/
extern "C" bool avgcost_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  struct avgcost_data *data;

  if (args->arg_count != 2) {
    strcpy(message,
           "wrong number of arguments: AVGCOST() requires two arguments");
    return true;
  }

  if ((args->arg_type[0] != INT_RESULT) || (args->arg_type[1] != REAL_RESULT)) {
    strcpy(message,
           "wrong argument type: AVGCOST() requires an INT and a REAL");
    return true;
  }

  /*
  **	force arguments to double.
  */
  /*args->arg_type[0]	= REAL_RESULT;
    args->arg_type[1]	= REAL_RESULT;*/

  initid->maybe_null = false; /* The result may be null */
  initid->decimals = 4;       /* We want 4 decimals in the result */
  initid->max_length = 20;    /* 6 digits + . + 10 decimals */

  if (!(data = new (std::nothrow) avgcost_data)) {
    strcpy(message, "Couldn't allocate memory");
    return true;
  }
  data->totalquantity = 0;
  data->totalprice = 0.0;

  initid->ptr = (char *)data;

  return false;
}

extern "C" void avgcost_deinit(UDF_INIT *initid) {
  void *void_ptr = initid->ptr;
  avgcost_data *data = static_cast<avgcost_data *>(void_ptr);
  delete data;
}

/* This is needed to get things to work in MySQL 4.1.1 and above */

extern "C" void avgcost_clear(UDF_INIT *initid, unsigned char *,
                              unsigned char *) {
  struct avgcost_data *data = (struct avgcost_data *)initid->ptr;
  data->totalprice = 0.0;
  data->totalquantity = 0;
  data->count = 0;
}

extern "C" void avgcost_add(UDF_INIT *initid, UDF_ARGS *args, unsigned char *,
                            unsigned char *) {
  if (args->args[0] && args->args[1]) {
    struct avgcost_data *data = (struct avgcost_data *)initid->ptr;
    long long quantity = *((long long *)args->args[0]);
    long long newquantity = data->totalquantity + quantity;
    double price = *((double *)args->args[1]);

    data->count++;

    if (((data->totalquantity >= 0) && (quantity < 0)) ||
        ((data->totalquantity < 0) && (quantity > 0))) {
      /*
      **	passing from + to - or from - to +
      */
      if (((quantity < 0) && (newquantity < 0)) ||
          ((quantity > 0) && (newquantity > 0))) {
        data->totalprice = price * (double)newquantity;
      }
      /*
      **	sub q if totalq > 0
      **	add q if totalq < 0
      */
      else {
        price = data->totalprice / (double)data->totalquantity;
        data->totalprice = price * (double)newquantity;
      }
      data->totalquantity = newquantity;
    } else {
      data->totalquantity += quantity;
      data->totalprice += price * (double)quantity;
    }

    if (data->totalquantity == 0) data->totalprice = 0.0;
  }
}

extern "C" double avgcost(UDF_INIT *initid, UDF_ARGS *, unsigned char *is_null,
                          unsigned char *) {
  struct avgcost_data *data = (struct avgcost_data *)initid->ptr;
  if (!data->count || !data->totalquantity) {
    *is_null = 1;
    return 0.0;
  }

  *is_null = 0;
  return data->totalprice / (double)data->totalquantity;
}

extern "C" bool myfunc_argument_name_init(UDF_INIT *initid, UDF_ARGS *args,
                                          char *message) {
  if (args->arg_count != 1) {
    strcpy(message, "myfunc_argument_name_init accepts only one argument");
    return true;
  }
  initid->max_length = args->attribute_lengths[0];
  initid->maybe_null = true;
  initid->const_item = true;
  return false;
}

extern "C" char *myfunc_argument_name(UDF_INIT *, UDF_ARGS *args, char *result,
                                      unsigned long *length,
                                      unsigned char *null_value,
                                      unsigned char *) {
  if (!args->attributes[0]) {
    *null_value = 1;
    return nullptr;
  }
  (*length)--; /* space for ending \0 (for debugging purposes) */
  if (*length > args->attribute_lengths[0])
    *length = args->attribute_lengths[0];
  memcpy(result, args->attributes[0], *length);
  result[*length] = 0;
  return result;
}

extern "C" bool is_const_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  if (args->arg_count != 1) {
    strcpy(message, "IS_CONST accepts only one argument");
    return true;
  }
  initid->ptr = (char *)((args->args[0] != nullptr) ? 1ULL : 0);
  return false;
}

extern "C" char *is_const(UDF_INIT *initid, UDF_ARGS *, char *result,
                          unsigned long *length, unsigned char *is_null,
                          unsigned char *) {
  if (initid->ptr != nullptr) {
    sprintf(result, "const");
  } else {
    sprintf(result, "not const");
  }
  *is_null = 0;
  *length = (unsigned)strlen(result);
  return result;
}

extern "C" bool check_const_len_init(UDF_INIT *initid, UDF_ARGS *args,
                                     char *message) {
  if (args->arg_count != 1) {
    strcpy(message, "CHECK_CONST_LEN accepts only one argument");
    return true;
  }
  if (args->args[0] == nullptr) {
    initid->ptr = const_cast<char *>("Not constant");
  } else if (strlen(args->args[0]) == args->lengths[0]) {
    initid->ptr = const_cast<char *>("Correct length");
  } else {
    initid->ptr = const_cast<char *>("Wrong length");
  }
  initid->max_length = 100;
  return false;
}

extern "C" char *check_const_len(UDF_INIT *initid, UDF_ARGS *, char *result,
                                 unsigned long *length, unsigned char *is_null,
                                 unsigned char *) {
  strcpy(result, initid->ptr);
  *length = strlen(result);
  *is_null = 0;
  return result;
}

struct My_median_data {
  std::vector<long long> vec;
};

extern "C" bool my_median_init(UDF_INIT *initid, UDF_ARGS *, char *message) {
  My_median_data *data = new (std::nothrow) My_median_data;
  if (!data) {
    strcpy(message, "Could not allocate memory");
    return true;
  }
  initid->ptr = static_cast<char *>(static_cast<void *>(data));
  return false;
}

extern "C" void my_median_deinit(UDF_INIT *initid) {
  My_median_data *data =
      static_cast<My_median_data *>(static_cast<void *>(initid->ptr));
  delete data;
}

extern "C" void my_median_add(UDF_INIT *initid, UDF_ARGS *args, unsigned char *,
                              unsigned char *) {
  My_median_data *data =
      static_cast<My_median_data *>(static_cast<void *>(initid->ptr));
  if (args->args[0]) {
    void *arg0 = args->args[0];
    long long number = *(static_cast<long long *>(arg0));
    data->vec.push_back(number);
  }
}

extern "C" void my_median_clear(UDF_INIT *initid, unsigned char *,
                                unsigned char *) {
  My_median_data *data =
      static_cast<My_median_data *>(static_cast<void *>(initid->ptr));
  data->vec.clear();
}

extern "C" long long my_median(UDF_INIT *initid, UDF_ARGS *,
                               unsigned char *is_null, unsigned char *) {
  My_median_data *data =
      static_cast<My_median_data *>(static_cast<void *>(initid->ptr));
  if (data->vec.size() == 0) {
    *is_null = 1;
    return 0;
  }
  const size_t ix = data->vec.size() / 2;
  std::nth_element(data->vec.begin(), data->vec.begin() + ix, data->vec.end());
  return data->vec[ix];
}