/*
 * This file and its contents are licensed under the Timescale License.
 * Please see the included NOTICE for copyright information and
 * LICENSE-TIMESCALE for a copy of the license.
 */

#include <postgres.h>
#include <access/htup_details.h>
#include <catalog/pg_type.h>
#include <utils/builtins.h>
#include <utils/datum.h>
#include <utils/numeric.h>
#include <utils/typcache.h>

#include "compat/compat.h"
#include "gapfill_internal.h"
#include "interpolate.h"

#define INTERPOLATE(x, x0, x1, y0, y1) (((y0) * ((x1) - (x)) + (y1) * ((x) - (x0))) / ((x1) - (x0)))

/*
 * gapfill_interpolate_initialize gets called when plan is initialized for every interpolate column
 */
void
gapfill_interpolate_initialize(GapFillInterpolateColumnState *interpolate, GapFillState *state,
							   FuncExpr *function)
{
	interpolate->prev.isnull = true;
	interpolate->next.isnull = true;
	if (list_length(function->args) > 1)
		interpolate->lookup_before = gapfill_adjust_varnos(state, lsecond(function->args));
	if (list_length(function->args) > 2)
		interpolate->lookup_after = gapfill_adjust_varnos(state, lthird(function->args));
}

/*
 * gapfill_interpolate_group_change gets called when a new aggregation group becomes active
 */
void
gapfill_interpolate_group_change(GapFillInterpolateColumnState *column, int64 time, Datum value,
								 bool isnull)
{
	column->prev.isnull = true;
	column->next.isnull = isnull;
	if (!isnull)
	{
		column->next.time = time;
		column->next.value = datumCopy(value, column->base.typbyval, column->base.typlen);
	}
}

/*
 * gapfill_interpolate_tuple_fetched gets called when a new tuple is fetched from subplan
 */
void
gapfill_interpolate_tuple_fetched(GapFillInterpolateColumnState *column, int64 time, Datum value,
								  bool isnull)
{
	column->next.isnull = isnull;
	if (!isnull)
	{
		column->next.time = time;
		column->next.value = datumCopy(value, column->base.typbyval, column->base.typlen);
	}
}

/*
 * gapfill_interpolate_tuple_returned gets called when subplan tuple is returned
 */
void
gapfill_interpolate_tuple_returned(GapFillInterpolateColumnState *column, int64 time, Datum value,
								   bool isnull)
{
	column->next.isnull = true;
	column->prev.isnull = isnull;
	if (!isnull)
	{
		column->prev.time = time;
		column->prev.value = datumCopy(value, column->base.typbyval, column->base.typlen);
	}
}

/*
 * Do out of bounds lookup for interpolation
 */
static void
gapfill_fetch_sample(GapFillState *state, GapFillInterpolateColumnState *column,
					 GapFillInterpolateSample *sample, Expr *lookup)
{
	HeapTupleHeader th;
	HeapTupleData tuple;
	TupleDesc tupdesc;
	Datum value;
	bool isnull;
	Datum datum = gapfill_exec_expr(state, lookup, &isnull);

	if (isnull)
	{
		sample->isnull = true;
		return;
	}

	th = DatumGetHeapTupleHeader(datum);
	if (HeapTupleHeaderGetNatts(th) != 2)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("interpolate RECORD arguments must have 2 elements")));

	/* Extract type information from the tuple itself */
	Assert(RECORDOID == HeapTupleHeaderGetTypeId(th));
	tupdesc = lookup_rowtype_tupdesc(HeapTupleHeaderGetTypeId(th), HeapTupleHeaderGetTypMod(th));

	/* Build a temporary HeapTuple control structure */
	tuple.t_len = HeapTupleHeaderGetDatumLength(th);
	ItemPointerSetInvalid(&(tuple.t_self));
	tuple.t_tableOid = InvalidOid;
	tuple.t_data = th;

	/* check first element in record matches timestamp datatype */
	if (TupleDescAttr(tupdesc, 0)->atttypid != state->columns[state->time_index]->typid)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("first argument of interpolate returned record must match used timestamp "
						"datatype"),
				 errdetail("Returned type %s does not match expected type %s.",
						   format_type_be(TupleDescAttr(tupdesc, 0)->atttypid),
						   format_type_be(column->base.typid))));

	/* check second element in record matches interpolate datatype */
	if (TupleDescAttr(tupdesc, 1)->atttypid != column->base.typid)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("second argument of interpolate returned record must match used "
						"interpolate datatype"),
				 errdetail("Returned type %s does not match expected type %s.",
						   format_type_be(TupleDescAttr(tupdesc, 1)->atttypid),
						   format_type_be(column->base.typid))));

	value = heap_getattr(&tuple, 1, tupdesc, &sample->isnull);
	if (!sample->isnull)
	{
		sample->time = gapfill_datum_get_internal(value, state->gapfill_typid);

		value = heap_getattr(&tuple, 2, tupdesc, &sample->isnull);
		if (!sample->isnull)
			sample->value = datumCopy(value, column->base.typbyval, column->base.typlen);
	}

	ReleaseTupleDesc(tupdesc);
}

/* Calculate the interpolation using numerics, returning the result as a numeric datum */
static Datum
interpolate_numeric(int64 x_i, int64 x0_i, int64 x1_i, Datum y0, Datum y1)
{
	Datum x0 = DirectFunctionCall1(int8_numeric, Int64GetDatum(x0_i));
	Datum x1 = DirectFunctionCall1(int8_numeric, Int64GetDatum(x1_i));
	Datum x = DirectFunctionCall1(int8_numeric, Int64GetDatum(x_i));

	Datum x1_sub_x = DirectFunctionCall2(numeric_sub, x1, x);
	Datum x_sub_x0 = DirectFunctionCall2(numeric_sub, x, x0);
	Datum y0_mul_x1_sub_x = DirectFunctionCall2(numeric_mul, y0, x1_sub_x);
	Datum y1_mul_x_sub_x0 = DirectFunctionCall2(numeric_mul, y1, x_sub_x0);

	Datum numerator = DirectFunctionCall2(numeric_add, y0_mul_x1_sub_x, y1_mul_x_sub_x0);
	Datum denominator = DirectFunctionCall2(numeric_sub, x1, x0);

	return DirectFunctionCall2(numeric_div, numerator, denominator);
}

/*
 * gapfill_interpolate_calculate gets called for every gapfilled tuple to calculate values
 *
 * Calculate linear interpolation value
 * y = (y0(x1-x) + y1(x-x0))/(x1-x0)
 */
void
gapfill_interpolate_calculate(GapFillInterpolateColumnState *column, GapFillState *state,
							  int64 time, Datum *value, bool *isnull)
{
	int64 x, x0, x1;
	Datum y0, y1;

	/* only evaluate expr for first tuple */
	if (column->prev.isnull && column->lookup_before && time == state->gapfill_start)
		gapfill_fetch_sample(state, column, &column->prev, column->lookup_before);

	if (column->next.isnull && column->lookup_after &&
		(FETCHED_LAST == state->state || FETCHED_NEXT_GROUP == state->state))
		gapfill_fetch_sample(state, column, &column->next, column->lookup_after);

	*isnull = column->prev.isnull || column->next.isnull;
	if (*isnull)
		return;

	y0 = column->prev.value;
	y1 = column->next.value;

	x = time;
	x0 = column->prev.time;
	x1 = column->next.time;

	switch (column->base.typid)
	{
		/* All integer types must use numeric-based interpolation calculations since they are
		 * multiplied by int64 and this could cause an overflow. numerics also interpolate better
		 * because the answer is rounded and not truncated. We can't use float8 because that
		 doesn't handle really big ints exactly. We can't use the Postgres INT128 implementation
		 because it doesn't support division. */
		case INT2OID:
			*value =
				DirectFunctionCall1(numeric_int2,
									interpolate_numeric(x,
														x0,
														x1,
														DirectFunctionCall1(int2_numeric, y0),
														DirectFunctionCall1(int2_numeric, y1)));
			break;
		case INT4OID:
			*value =
				DirectFunctionCall1(numeric_int4,
									interpolate_numeric(x,
														x0,
														x1,
														DirectFunctionCall1(int4_numeric, y0),
														DirectFunctionCall1(int4_numeric, y1)));
			break;
		case INT8OID:
			*value =
				DirectFunctionCall1(numeric_int8,
									interpolate_numeric(x,
														x0,
														x1,
														DirectFunctionCall1(int8_numeric, y0),
														DirectFunctionCall1(int8_numeric, y1)));
			break;
		case FLOAT4OID:
			/* Shortcircuit calculation when y0 == y1 for float because otherwise
			 * output will be unstable for certain values due to float rounding. */
			if (DatumGetFloat4(y0) == DatumGetFloat4(y1))
				*value = y0;
			else
				*value =
					Float4GetDatum(INTERPOLATE(x, x0, x1, DatumGetFloat4(y0), DatumGetFloat4(y1)));
			break;
		case FLOAT8OID:
			/* Shortcircuit calculation when y0 == y1 for float because otherwise
			 * output will be unstable for certain values due to float rounding. */
			if (DatumGetFloat8(y0) == DatumGetFloat8(y1))
				*value = y0;
			else
				*value =
					Float8GetDatum(INTERPOLATE(x, x0, x1, DatumGetFloat8(y0), DatumGetFloat8(y1)));
			break;
		default:

			/*
			 * should never happen since interpolate is not defined for other
			 * datatypes
			 */
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("unsupported datatype for interpolate: %s",
							format_type_be(column->base.typid))));
			pg_unreachable();
			break;
	}
}
