/*-------------------------------------------------------------------------

 *

 * conversioncmds.c

 *    conversion creation command support code

 *

 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group

 * Portions Copyright (c) 1994, Regents of the University of California

 *

 *

 * IDENTIFICATION

 *    src/backend/commands/conversioncmds.c

 *

 *-------------------------------------------------------------------------

 */

#include "postgres.h"

#include "catalog/pg_conversion.h"

#include "catalog/pg_namespace.h"

#include "catalog/pg_proc.h"

#include "catalog/pg_type.h"

#include "commands/conversioncmds.h"

#include "mb/pg_wchar.h"

#include "miscadmin.h"

#include "parser/parse_func.h"

#include "utils/acl.h"

#include "utils/lsyscache.h"

/*

 * CREATE CONVERSION

 */

ObjectAddress

CreateConversionCommand(CreateConversionStmt *stmt)

{

  Oid     namespaceId;

  char     *conversion_name;

  AclResult aclresult;

  int     from_encoding;

  int     to_encoding;

  Oid     funcoid;

  const char *from_encoding_name = stmt->for_encoding_name;

  const char *to_encoding_name = stmt->to_encoding_name;

  List     *func_name = stmt->func_name;

  static const Oid funcargs[] = {INT4OID, INT4OID, CSTRINGOID, INTERNALOID, INT4OID, BOOLOID};

  char    result[1];

  Datum   funcresult;

  /* Convert list of names to a name and namespace */

  namespaceId = QualifiedNameGetCreationNamespace(stmt->conversion_name,

                          &conversion_name);

  /* Check we have creation rights in target namespace */

  aclresult = object_aclcheck(NamespaceRelationId, namespaceId, GetUserId(), ACL_CREATE);

  if (aclresult != ACLCHECK_OK)

    aclcheck_error(aclresult, OBJECT_SCHEMA,

             get_namespace_name(namespaceId));

  /* Check the encoding names */

  from_encoding = pg_char_to_encoding(from_encoding_name);

  if (from_encoding < 0)

    ereport(ERROR,

        (errcode(ERRCODE_UNDEFINED_OBJECT),

         errmsg("source encoding \"%s\" does not exist",

            from_encoding_name)));

  to_encoding = pg_char_to_encoding(to_encoding_name);

  if (to_encoding < 0)

    ereport(ERROR,

        (errcode(ERRCODE_UNDEFINED_OBJECT),

         errmsg("destination encoding \"%s\" does not exist",

            to_encoding_name)));

  /*

   * We consider conversions to or from SQL_ASCII to be meaningless.  (If

   * you wish to change this, note that pg_do_encoding_conversion() and its

   * sister functions have hard-wired fast paths for any conversion in which

   * the source or target encoding is SQL_ASCII, so that an encoding

   * conversion function declared for such a case will never be used.)

   */

  if (from_encoding == PG_SQL_ASCII || to_encoding == PG_SQL_ASCII)

    ereport(ERROR,

        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

         errmsg("encoding conversion to or from \"SQL_ASCII\" is not supported")));

  /*

   * Check the existence of the conversion function. Function name could be

   * a qualified name.

   */

  funcoid = LookupFuncName(func_name, sizeof(funcargs) / sizeof(Oid),

               funcargs, false);

  /* Check it returns int4, else it's probably the wrong function */

  if (get_func_rettype(funcoid) != INT4OID)

    ereport(ERROR,

        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

         errmsg("encoding conversion function %s must return type %s",

            NameListToString(func_name), "integer")));

  /* Check we have EXECUTE rights for the function */

  aclresult = object_aclcheck(ProcedureRelationId, funcoid, GetUserId(), ACL_EXECUTE);

  if (aclresult != ACLCHECK_OK)

    aclcheck_error(aclresult, OBJECT_FUNCTION,

             NameListToString(func_name));

  /*

   * Check that the conversion function is suitable for the requested source

   * and target encodings. We do that by calling the function with an empty

   * string; the conversion function should throw an error if it can't

   * perform the requested conversion.

   */

  funcresult = OidFunctionCall6(funcoid,

                  Int32GetDatum(from_encoding),

                  Int32GetDatum(to_encoding),

                  CStringGetDatum(""),

                  CStringGetDatum(result),

                  Int32GetDatum(0),

                  BoolGetDatum(false));

  /*

   * The function should return 0 for empty input. Might as well check that,

   * too.

   */

  if (DatumGetInt32(funcresult) != 0)

    ereport(ERROR,

        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

         errmsg("encoding conversion function %s returned incorrect result for empty input",

            NameListToString(func_name))));

  /*

   * All seem ok, go ahead (possible failure would be a duplicate conversion

   * name)

   */

  return ConversionCreate(conversion_name, namespaceId, GetUserId(),

              from_encoding, to_encoding, funcoid, stmt->def);

}