/*-------------------------------------------------------------------------
 *
 * array_userfuncs.c
 *	  Misc user-visible array support functions
 *
 * Copyright (c) 2003-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/backend/utils/adt/array_userfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_type.h"
#include "common/int.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"


static Datum array_position_common(FunctionCallInfo fcinfo);


/*
 * fetch_array_arg_replace_nulls
 *
 * Fetch an array-valued argument in expanded form; if it's null, construct an
 * empty array value of the proper data type.  Also cache basic element type
 * information in fn_extra.
 *
 * Caution: if the input is a read/write pointer, this returns the input
 * argument; so callers must be sure that their changes are "safe", that is
 * they cannot leave the array in a corrupt state.
 *
 * If we're being called as an aggregate function, make sure any newly-made
 * expanded array is allocated in the aggregate state context, so as to save
 * copying operations.
 */
static ExpandedArrayHeader *
fetch_array_arg_replace_nulls(FunctionCallInfo fcinfo, int argno)
{
	ExpandedArrayHeader *eah;
	Oid			element_type;
	ArrayMetaState *my_extra;
	MemoryContext resultcxt;

	/* If first time through, create datatype cache struct */
	my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
	if (my_extra == NULL)
	{
		my_extra = (ArrayMetaState *)
			MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
							   sizeof(ArrayMetaState));
		my_extra->element_type = InvalidOid;
		fcinfo->flinfo->fn_extra = my_extra;
	}

	/* Figure out which context we want the result in */
	if (!AggCheckCallContext(fcinfo, &resultcxt))
		resultcxt = CurrentMemoryContext;

	/* Now collect the array value */
	if (!PG_ARGISNULL(argno))
	{
		MemoryContext oldcxt = MemoryContextSwitchTo(resultcxt);

		eah = PG_GETARG_EXPANDED_ARRAYX(argno, my_extra);
		MemoryContextSwitchTo(oldcxt);
	}
	else
	{
		/* We have to look up the array type and element type */
		Oid			arr_typeid = get_fn_expr_argtype(fcinfo->flinfo, argno);

		if (!OidIsValid(arr_typeid))
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
					 errmsg("could not determine input data type")));
		element_type = get_element_type(arr_typeid);
		if (!OidIsValid(element_type))
			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg("input data type is not an array")));

		eah = construct_empty_expanded_array(element_type,
											 resultcxt,
											 my_extra);
	}

	return eah;
}

/*-----------------------------------------------------------------------------
 * array_append :
 *		push an element onto the end of a one-dimensional array
 *----------------------------------------------------------------------------
 */
Datum
array_append(PG_FUNCTION_ARGS)
{
	ExpandedArrayHeader *eah;
	Datum		newelem;
	bool		isNull;
	Datum		result;
	int		   *dimv,
			   *lb;
	int			indx;
	ArrayMetaState *my_extra;

	eah = fetch_array_arg_replace_nulls(fcinfo, 0);
	isNull = PG_ARGISNULL(1);
	if (isNull)
		newelem = (Datum) 0;
	else
		newelem = PG_GETARG_DATUM(1);

	if (eah->ndims == 1)
	{
		/* append newelem */
		lb = eah->lbound;
		dimv = eah->dims;

		/* index of added elem is at lb[0] + (dimv[0] - 1) + 1 */
		if (pg_add_s32_overflow(lb[0], dimv[0], &indx))
			ereport(ERROR,
					(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
					 errmsg("integer out of range")));
	}
	else if (eah->ndims == 0)
		indx = 1;
	else
		ereport(ERROR,
				(errcode(ERRCODE_DATA_EXCEPTION),
				 errmsg("argument must be empty or one-dimensional array")));

	/* Perform element insertion */
	my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;

	result = array_set_element(EOHPGetRWDatum(&eah->hdr),
							   1, &indx, newelem, isNull,
							   -1, my_extra->typlen, my_extra->typbyval, my_extra->typalign);

	PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_prepend :
 *		push an element onto the front of a one-dimensional array
 *----------------------------------------------------------------------------
 */
Datum
array_prepend(PG_FUNCTION_ARGS)
{
	ExpandedArrayHeader *eah;
	Datum		newelem;
	bool		isNull;
	Datum		result;
	int		   *lb;
	int			indx;
	int			lb0;
	ArrayMetaState *my_extra;

	isNull = PG_ARGISNULL(0);
	if (isNull)
		newelem = (Datum) 0;
	else
		newelem = PG_GETARG_DATUM(0);
	eah = fetch_array_arg_replace_nulls(fcinfo, 1);

	if (eah->ndims == 1)
	{
		/* prepend newelem */
		lb = eah->lbound;
		lb0 = lb[0];

		if (pg_sub_s32_overflow(lb0, 1, &indx))
			ereport(ERROR,
					(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
					 errmsg("integer out of range")));
	}
	else if (eah->ndims == 0)
	{
		indx = 1;
		lb0 = 1;
	}
	else
		ereport(ERROR,
				(errcode(ERRCODE_DATA_EXCEPTION),
				 errmsg("argument must be empty or one-dimensional array")));

	/* Perform element insertion */
	my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;

	result = array_set_element(EOHPGetRWDatum(&eah->hdr),
							   1, &indx, newelem, isNull,
							   -1, my_extra->typlen, my_extra->typbyval, my_extra->typalign);

	/* Readjust result's LB to match the input's, as expected for prepend */
	Assert(result == EOHPGetRWDatum(&eah->hdr));
	if (eah->ndims == 1)
	{
		/* This is ok whether we've deconstructed or not */
		eah->lbound[0] = lb0;
	}

	PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_cat :
 *		concatenate two nD arrays to form an nD array, or
 *		push an (n-1)D array onto the end of an nD array
 *----------------------------------------------------------------------------
 */
Datum
array_cat(PG_FUNCTION_ARGS)
{
	ArrayType  *v1,
			   *v2;
	ArrayType  *result;
	int		   *dims,
			   *lbs,
				ndims,
				nitems,
				ndatabytes,
				nbytes;
	int		   *dims1,
			   *lbs1,
				ndims1,
				nitems1,
				ndatabytes1;
	int		   *dims2,
			   *lbs2,
				ndims2,
				nitems2,
				ndatabytes2;
	int			i;
	char	   *dat1,
			   *dat2;
	bits8	   *bitmap1,
			   *bitmap2;
	Oid			element_type;
	Oid			element_type1;
	Oid			element_type2;
	int32		dataoffset;

	/* Concatenating a null array is a no-op, just return the other input */
	if (PG_ARGISNULL(0))
	{
		if (PG_ARGISNULL(1))
			PG_RETURN_NULL();
		result = PG_GETARG_ARRAYTYPE_P(1);
		PG_RETURN_ARRAYTYPE_P(result);
	}
	if (PG_ARGISNULL(1))
	{
		result = PG_GETARG_ARRAYTYPE_P(0);
		PG_RETURN_ARRAYTYPE_P(result);
	}

	v1 = PG_GETARG_ARRAYTYPE_P(0);
	v2 = PG_GETARG_ARRAYTYPE_P(1);

	element_type1 = ARR_ELEMTYPE(v1);
	element_type2 = ARR_ELEMTYPE(v2);

	/* Check we have matching element types */
	if (element_type1 != element_type2)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg("cannot concatenate incompatible arrays"),
				 errdetail("Arrays with element types %s and %s are not "
						   "compatible for concatenation.",
						   format_type_be(element_type1),
						   format_type_be(element_type2))));

	/* OK, use it */
	element_type = element_type1;

	/*----------
	 * We must have one of the following combinations of inputs:
	 * 1) one empty array, and one non-empty array
	 * 2) both arrays empty
	 * 3) two arrays with ndims1 == ndims2
	 * 4) ndims1 == ndims2 - 1
	 * 5) ndims1 == ndims2 + 1
	 *----------
	 */
	ndims1 = ARR_NDIM(v1);
	ndims2 = ARR_NDIM(v2);

	/*
	 * short circuit - if one input array is empty, and the other is not, we
	 * return the non-empty one as the result
	 *
	 * if both are empty, return the first one
	 */
	if (ndims1 == 0 && ndims2 > 0)
		PG_RETURN_ARRAYTYPE_P(v2);

	if (ndims2 == 0)
		PG_RETURN_ARRAYTYPE_P(v1);

	/* the rest fall under rule 3, 4, or 5 */
	if (ndims1 != ndims2 &&
		ndims1 != ndims2 - 1 &&
		ndims1 != ndims2 + 1)
		ereport(ERROR,
				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
				 errmsg("cannot concatenate incompatible arrays"),
				 errdetail("Arrays of %d and %d dimensions are not "
						   "compatible for concatenation.",
						   ndims1, ndims2)));

	/* get argument array details */
	lbs1 = ARR_LBOUND(v1);
	lbs2 = ARR_LBOUND(v2);
	dims1 = ARR_DIMS(v1);
	dims2 = ARR_DIMS(v2);
	dat1 = ARR_DATA_PTR(v1);
	dat2 = ARR_DATA_PTR(v2);
	bitmap1 = ARR_NULLBITMAP(v1);
	bitmap2 = ARR_NULLBITMAP(v2);
	nitems1 = ArrayGetNItems(ndims1, dims1);
	nitems2 = ArrayGetNItems(ndims2, dims2);
	ndatabytes1 = ARR_SIZE(v1) - ARR_DATA_OFFSET(v1);
	ndatabytes2 = ARR_SIZE(v2) - ARR_DATA_OFFSET(v2);

	if (ndims1 == ndims2)
	{
		/*
		 * resulting array is made up of the elements (possibly arrays
		 * themselves) of the input argument arrays
		 */
		ndims = ndims1;
		dims = (int *) palloc(ndims * sizeof(int));
		lbs = (int *) palloc(ndims * sizeof(int));

		dims[0] = dims1[0] + dims2[0];
		lbs[0] = lbs1[0];

		for (i = 1; i < ndims; i++)
		{
			if (dims1[i] != dims2[i] || lbs1[i] != lbs2[i])
				ereport(ERROR,
						(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
						 errmsg("cannot concatenate incompatible arrays"),
						 errdetail("Arrays with differing element dimensions are "
								   "not compatible for concatenation.")));

			dims[i] = dims1[i];
			lbs[i] = lbs1[i];
		}
	}
	else if (ndims1 == ndims2 - 1)
	{
		/*
		 * resulting array has the second argument as the outer array, with
		 * the first argument inserted at the front of the outer dimension
		 */
		ndims = ndims2;
		dims = (int *) palloc(ndims * sizeof(int));
		lbs = (int *) palloc(ndims * sizeof(int));
		memcpy(dims, dims2, ndims * sizeof(int));
		memcpy(lbs, lbs2, ndims * sizeof(int));

		/* increment number of elements in outer array */
		dims[0] += 1;

		/* make sure the added element matches our existing elements */
		for (i = 0; i < ndims1; i++)
		{
			if (dims1[i] != dims[i + 1] || lbs1[i] != lbs[i + 1])
				ereport(ERROR,
						(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
						 errmsg("cannot concatenate incompatible arrays"),
						 errdetail("Arrays with differing dimensions are not "
								   "compatible for concatenation.")));
		}
	}
	else
	{
		/*
		 * (ndims1 == ndims2 + 1)
		 *
		 * resulting array has the first argument as the outer array, with the
		 * second argument appended to the end of the outer dimension
		 */
		ndims = ndims1;
		dims = (int *) palloc(ndims * sizeof(int));
		lbs = (int *) palloc(ndims * sizeof(int));
		memcpy(dims, dims1, ndims * sizeof(int));
		memcpy(lbs, lbs1, ndims * sizeof(int));

		/* increment number of elements in outer array */
		dims[0] += 1;

		/* make sure the added element matches our existing elements */
		for (i = 0; i < ndims2; i++)
		{
			if (dims2[i] != dims[i + 1] || lbs2[i] != lbs[i + 1])
				ereport(ERROR,
						(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
						 errmsg("cannot concatenate incompatible arrays"),
						 errdetail("Arrays with differing dimensions are not "
								   "compatible for concatenation.")));
		}
	}

	/* Do this mainly for overflow checking */
	nitems = ArrayGetNItems(ndims, dims);
	ArrayCheckBounds(ndims, dims, lbs);

	/* build the result array */
	ndatabytes = ndatabytes1 + ndatabytes2;
	if (ARR_HASNULL(v1) || ARR_HASNULL(v2))
	{
		dataoffset = ARR_OVERHEAD_WITHNULLS(ndims, nitems);
		nbytes = ndatabytes + dataoffset;
	}
	else
	{
		dataoffset = 0;			/* marker for no null bitmap */
		nbytes = ndatabytes + ARR_OVERHEAD_NONULLS(ndims);
	}
	result = (ArrayType *) palloc0(nbytes);
	SET_VARSIZE(result, nbytes);
	result->ndim = ndims;
	result->dataoffset = dataoffset;
	result->elemtype = element_type;
	memcpy(ARR_DIMS(result), dims, ndims * sizeof(int));
	memcpy(ARR_LBOUND(result), lbs, ndims * sizeof(int));
	/* data area is arg1 then arg2 */
	memcpy(ARR_DATA_PTR(result), dat1, ndatabytes1);
	memcpy(ARR_DATA_PTR(result) + ndatabytes1, dat2, ndatabytes2);
	/* handle the null bitmap if needed */
	if (ARR_HASNULL(result))
	{
		array_bitmap_copy(ARR_NULLBITMAP(result), 0,
						  bitmap1, 0,
						  nitems1);
		array_bitmap_copy(ARR_NULLBITMAP(result), nitems1,
						  bitmap2, 0,
						  nitems2);
	}

	PG_RETURN_ARRAYTYPE_P(result);
}


/*
 * ARRAY_AGG(anynonarray) aggregate function
 */
Datum
array_agg_transfn(PG_FUNCTION_ARGS)
{
	Oid			arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
	MemoryContext aggcontext;
	ArrayBuildState *state;
	Datum		elem;

	if (arg1_typeid == InvalidOid)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not determine input data type")));

	/*
	 * Note: we do not need a run-time check about whether arg1_typeid is a
	 * valid array element type, because the parser would have verified that
	 * while resolving the input/result types of this polymorphic aggregate.
	 */

	if (!AggCheckCallContext(fcinfo, &aggcontext))
	{
		/* cannot be called directly because of internal-type argument */
		elog(ERROR, "array_agg_transfn called in non-aggregate context");
	}

	if (PG_ARGISNULL(0))
		state = initArrayResult(arg1_typeid, aggcontext, false);
	else
		state = (ArrayBuildState *) PG_GETARG_POINTER(0);

	elem = PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1);

	state = accumArrayResult(state,
							 elem,
							 PG_ARGISNULL(1),
							 arg1_typeid,
							 aggcontext);

	/*
	 * The transition type for array_agg() is declared to be "internal", which
	 * is a pass-by-value type the same size as a pointer.  So we can safely
	 * pass the ArrayBuildState pointer through nodeAgg.c's machinations.
	 */
	PG_RETURN_POINTER(state);
}

Datum
array_agg_finalfn(PG_FUNCTION_ARGS)
{
	Datum		result;
	ArrayBuildState *state;
	int			dims[1];
	int			lbs[1];

	/* cannot be called directly because of internal-type argument */
	Assert(AggCheckCallContext(fcinfo, NULL));

	state = PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0);

	if (state == NULL)
		PG_RETURN_NULL();		/* returns null iff no input values */

	dims[0] = state->nelems;
	lbs[0] = 1;

	/*
	 * Make the result.  We cannot release the ArrayBuildState because
	 * sometimes aggregate final functions are re-executed.  Rather, it is
	 * nodeAgg.c's responsibility to reset the aggcontext when it's safe to do
	 * so.
	 */
	result = makeMdArrayResult(state, 1, dims, lbs,
							   CurrentMemoryContext,
							   false);

	PG_RETURN_DATUM(result);
}

/*
 * ARRAY_AGG(anyarray) aggregate function
 */
Datum
array_agg_array_transfn(PG_FUNCTION_ARGS)
{
	Oid			arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
	MemoryContext aggcontext;
	ArrayBuildStateArr *state;

	if (arg1_typeid == InvalidOid)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not determine input data type")));

	/*
	 * Note: we do not need a run-time check about whether arg1_typeid is a
	 * valid array type, because the parser would have verified that while
	 * resolving the input/result types of this polymorphic aggregate.
	 */

	if (!AggCheckCallContext(fcinfo, &aggcontext))
	{
		/* cannot be called directly because of internal-type argument */
		elog(ERROR, "array_agg_array_transfn called in non-aggregate context");
	}


	if (PG_ARGISNULL(0))
		state = initArrayResultArr(arg1_typeid, InvalidOid, aggcontext, false);
	else
		state = (ArrayBuildStateArr *) PG_GETARG_POINTER(0);

	state = accumArrayResultArr(state,
								PG_GETARG_DATUM(1),
								PG_ARGISNULL(1),
								arg1_typeid,
								aggcontext);

	/*
	 * The transition type for array_agg() is declared to be "internal", which
	 * is a pass-by-value type the same size as a pointer.  So we can safely
	 * pass the ArrayBuildStateArr pointer through nodeAgg.c's machinations.
	 */
	PG_RETURN_POINTER(state);
}

Datum
array_agg_array_finalfn(PG_FUNCTION_ARGS)
{
	Datum		result;
	ArrayBuildStateArr *state;

	/* cannot be called directly because of internal-type argument */
	Assert(AggCheckCallContext(fcinfo, NULL));

	state = PG_ARGISNULL(0) ? NULL : (ArrayBuildStateArr *) PG_GETARG_POINTER(0);

	if (state == NULL)
		PG_RETURN_NULL();		/* returns null iff no input values */

	/*
	 * Make the result.  We cannot release the ArrayBuildStateArr because
	 * sometimes aggregate final functions are re-executed.  Rather, it is
	 * nodeAgg.c's responsibility to reset the aggcontext when it's safe to do
	 * so.
	 */
	result = makeArrayResultArr(state, CurrentMemoryContext, false);

	PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_position, array_position_start :
 *			return the offset of a value in an array.
 *
 * IS NOT DISTINCT FROM semantics are used for comparisons.  Return NULL when
 * the value is not found.
 *-----------------------------------------------------------------------------
 */
Datum
array_position(PG_FUNCTION_ARGS)
{
	return array_position_common(fcinfo);
}

Datum
array_position_start(PG_FUNCTION_ARGS)
{
	return array_position_common(fcinfo);
}

/*
 * array_position_common
 *		Common code for array_position and array_position_start
 *
 * These are separate wrappers for the sake of opr_sanity regression test.
 * They are not strict so we have to test for null inputs explicitly.
 */
static Datum
array_position_common(FunctionCallInfo fcinfo)
{
	ArrayType  *array;
	Oid			collation = PG_GET_COLLATION();
	Oid			element_type;
	Datum		searched_element,
				value;
	bool		isnull;
	int			position,
				position_min;
	bool		found = false;
	TypeCacheEntry *typentry;
	ArrayMetaState *my_extra;
	bool		null_search;
	ArrayIterator array_iterator;

	if (PG_ARGISNULL(0))
		PG_RETURN_NULL();

	array = PG_GETARG_ARRAYTYPE_P(0);
	element_type = ARR_ELEMTYPE(array);

	/*
	 * We refuse to search for elements in multi-dimensional arrays, since we
	 * have no good way to report the element's location in the array.
	 */
	if (ARR_NDIM(array) > 1)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("searching for elements in multidimensional arrays is not supported")));

	if (PG_ARGISNULL(1))
	{
		/* fast return when the array doesn't have nulls */
		if (!array_contains_nulls(array))
			PG_RETURN_NULL();
		searched_element = (Datum) 0;
		null_search = true;
	}
	else
	{
		searched_element = PG_GETARG_DATUM(1);
		null_search = false;
	}

	position = (ARR_LBOUND(array))[0] - 1;

	/* figure out where to start */
	if (PG_NARGS() == 3)
	{
		if (PG_ARGISNULL(2))
			ereport(ERROR,
					(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
					 errmsg("initial position must not be null")));

		position_min = PG_GETARG_INT32(2);
	}
	else
		position_min = (ARR_LBOUND(array))[0];

	/*
	 * We arrange to look up type info for array_create_iterator only once per
	 * series of calls, assuming the element type doesn't change underneath
	 * us.
	 */
	my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
	if (my_extra == NULL)
	{
		fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
													  sizeof(ArrayMetaState));
		my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
		my_extra->element_type = ~element_type;
	}

	if (my_extra->element_type != element_type)
	{
		get_typlenbyvalalign(element_type,
							 &my_extra->typlen,
							 &my_extra->typbyval,
							 &my_extra->typalign);

		typentry = lookup_type_cache(element_type, TYPECACHE_EQ_OPR_FINFO);

		if (!OidIsValid(typentry->eq_opr_finfo.fn_oid))
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_FUNCTION),
					 errmsg("could not identify an equality operator for type %s",
							format_type_be(element_type))));

		my_extra->element_type = element_type;
		fmgr_info_cxt(typentry->eq_opr_finfo.fn_oid, &my_extra->proc,
					  fcinfo->flinfo->fn_mcxt);
	}

	/* Examine each array element until we find a match. */
	array_iterator = array_create_iterator(array, 0, my_extra);
	while (array_iterate(array_iterator, &value, &isnull))
	{
		position++;

		/* skip initial elements if caller requested so */
		if (position < position_min)
			continue;

		/*
		 * Can't look at the array element's value if it's null; but if we
		 * search for null, we have a hit and are done.
		 */
		if (isnull || null_search)
		{
			if (isnull && null_search)
			{
				found = true;
				break;
			}
			else
				continue;
		}

		/* not nulls, so run the operator */
		if (DatumGetBool(FunctionCall2Coll(&my_extra->proc, collation,
										   searched_element, value)))
		{
			found = true;
			break;
		}
	}

	array_free_iterator(array_iterator);

	/* Avoid leaking memory when handed toasted input */
	PG_FREE_IF_COPY(array, 0);

	if (!found)
		PG_RETURN_NULL();

	PG_RETURN_INT32(position);
}

/*-----------------------------------------------------------------------------
 * array_positions :
 *			return an array of positions of a value in an array.
 *
 * IS NOT DISTINCT FROM semantics are used for comparisons.  Returns NULL when
 * the input array is NULL.  When the value is not found in the array, returns
 * an empty array.
 *
 * This is not strict so we have to test for null inputs explicitly.
 *-----------------------------------------------------------------------------
 */
Datum
array_positions(PG_FUNCTION_ARGS)
{
	ArrayType  *array;
	Oid			collation = PG_GET_COLLATION();
	Oid			element_type;
	Datum		searched_element,
				value;
	bool		isnull;
	int			position;
	TypeCacheEntry *typentry;
	ArrayMetaState *my_extra;
	bool		null_search;
	ArrayIterator array_iterator;
	ArrayBuildState *astate = NULL;

	if (PG_ARGISNULL(0))
		PG_RETURN_NULL();

	array = PG_GETARG_ARRAYTYPE_P(0);
	element_type = ARR_ELEMTYPE(array);

	position = (ARR_LBOUND(array))[0] - 1;

	/*
	 * We refuse to search for elements in multi-dimensional arrays, since we
	 * have no good way to report the element's location in the array.
	 */
	if (ARR_NDIM(array) > 1)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("searching for elements in multidimensional arrays is not supported")));

	astate = initArrayResult(INT4OID, CurrentMemoryContext, false);

	if (PG_ARGISNULL(1))
	{
		/* fast return when the array doesn't have nulls */
		if (!array_contains_nulls(array))
			PG_RETURN_DATUM(makeArrayResult(astate, CurrentMemoryContext));
		searched_element = (Datum) 0;
		null_search = true;
	}
	else
	{
		searched_element = PG_GETARG_DATUM(1);
		null_search = false;
	}

	/*
	 * We arrange to look up type info for array_create_iterator only once per
	 * series of calls, assuming the element type doesn't change underneath
	 * us.
	 */
	my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
	if (my_extra == NULL)
	{
		fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
													  sizeof(ArrayMetaState));
		my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
		my_extra->element_type = ~element_type;
	}

	if (my_extra->element_type != element_type)
	{
		get_typlenbyvalalign(element_type,
							 &my_extra->typlen,
							 &my_extra->typbyval,
							 &my_extra->typalign);

		typentry = lookup_type_cache(element_type, TYPECACHE_EQ_OPR_FINFO);

		if (!OidIsValid(typentry->eq_opr_finfo.fn_oid))
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_FUNCTION),
					 errmsg("could not identify an equality operator for type %s",
							format_type_be(element_type))));

		my_extra->element_type = element_type;
		fmgr_info_cxt(typentry->eq_opr_finfo.fn_oid, &my_extra->proc,
					  fcinfo->flinfo->fn_mcxt);
	}

	/*
	 * Accumulate each array position iff the element matches the given
	 * element.
	 */
	array_iterator = array_create_iterator(array, 0, my_extra);
	while (array_iterate(array_iterator, &value, &isnull))
	{
		position += 1;

		/*
		 * Can't look at the array element's value if it's null; but if we
		 * search for null, we have a hit.
		 */
		if (isnull || null_search)
		{
			if (isnull && null_search)
				astate =
					accumArrayResult(astate, Int32GetDatum(position), false,
									 INT4OID, CurrentMemoryContext);

			continue;
		}

		/* not nulls, so run the operator */
		if (DatumGetBool(FunctionCall2Coll(&my_extra->proc, collation,
										   searched_element, value)))
			astate =
				accumArrayResult(astate, Int32GetDatum(position), false,
								 INT4OID, CurrentMemoryContext);
	}

	array_free_iterator(array_iterator);

	/* Avoid leaking memory when handed toasted input */
	PG_FREE_IF_COPY(array, 0);

	PG_RETURN_DATUM(makeArrayResult(astate, CurrentMemoryContext));
}