Introduce ts_date_trunc function

ts_date_trunc() is similar to date_trunc() in PostgreSQL, but
supports intervals like '2 months' or '1 year 6 months'.

sql/CMakeLists.txt

@@ -39,6 +39,7 @@ set(SOURCE_FILES
   ddl_triggers.sql
   bookend.sql
   time_bucket.sql
+  ts_date_trunc.sql
   version.sql
   size_utils.sql
   histogram.sql

sql/ts_date_trunc.sql

@@ -0,0 +1,23 @@
+-- This file and its contents are licensed under the Apache License 2.0.
+-- Please see the included NOTICE for copyright information and
+-- LICENSE-APACHE for a copy of the license.
+
+-- ts_date_trunc() is similar to date_trunc() in PostgreSQL but supports intervals like 'N months'
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts DATE) RETURNS DATE
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;
+
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts DATE, origin DATE) RETURNS DATE
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;
+
+-- utility functions
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts TIMESTAMP) RETURNS TIMESTAMP
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc_timestamp' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;
+
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts TIMESTAMP, origin TIMESTAMP) RETURNS TIMESTAMP
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc_timestamp' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;
+
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts TIMESTAMPTZ) RETURNS TIMESTAMPTZ
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc_timestamptz' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;
+
+CREATE OR REPLACE FUNCTION ts_date_trunc(bucket_width INTERVAL, ts TIMESTAMPTZ, origin TIMESTAMPTZ) RETURNS TIMESTAMPTZ
+	AS '@MODULE_PATHNAME@', 'ts_date_trunc_timestamptz' LANGUAGE C IMMUTABLE PARALLEL SAFE STRICT;

src/CMakeLists.txt

@@ -48,6 +48,7 @@ set(SOURCES
   subspace_store.c
   tablespace.c
   time_bucket.c
+  ts_date_trunc.c
   time_utils.c
   custom_type_cache.c
   trigger.c

src/ts_date_trunc.c

@@ -0,0 +1,136 @@
+/*
+ * This file and its contents are licensed under the Apache License 2.0.
+ * Please see the included NOTICE for copyright information and
+ * LICENSE-APACHE for a copy of the license.
+ */
+#include <postgres.h>
+#include <utils/date.h>
+#include <utils/datetime.h>
+#include <utils/fmgrprotos.h>
+
+#include "ts_date_trunc.h"
+
+TS_FUNCTION_INFO_V1(ts_date_trunc);
+TS_FUNCTION_INFO_V1(ts_date_trunc_timestamp);
+TS_FUNCTION_INFO_V1(ts_date_trunc_timestamptz);
+
+TSDLLEXPORT Datum
+ts_date_trunc_timestamp(PG_FUNCTION_ARGS)
+{
+	DateADT result;
+	Datum interval = PG_GETARG_DATUM(0);
+	DateADT ts_date = DatumGetDateADT(DirectFunctionCall1(timestamp_date, PG_GETARG_DATUM(1)));
+
+	if (PG_NARGS() > 2)
+	{
+		DateADT origin = DatumGetDateADT(DirectFunctionCall1(timestamp_date, PG_GETARG_DATUM(2)));
+		result = DatumGetDateADT(DirectFunctionCall3(ts_date_trunc, interval, DateADTGetDatum(ts_date), DateADTGetDatum(origin)));
+	}
+	else
+	{
+		result = DatumGetDateADT(DirectFunctionCall2(ts_date_trunc, interval, DateADTGetDatum(ts_date)));
+	}
+
+	return DirectFunctionCall1(date_timestamp, DateADTGetDatum(result));
+}
+
+TSDLLEXPORT Datum
+ts_date_trunc_timestamptz(PG_FUNCTION_ARGS)
+{
+	DateADT result;
+	Datum interval = PG_GETARG_DATUM(0);
+	DateADT ts_date = DatumGetDateADT(DirectFunctionCall1(timestamptz_date, PG_GETARG_DATUM(1)));
+
+	if (PG_NARGS() > 2)
+	{
+		DateADT origin = DatumGetDateADT(DirectFunctionCall1(timestamptz_date, PG_GETARG_DATUM(2)));
+		result = DatumGetDateADT(DirectFunctionCall3(ts_date_trunc, interval, DateADTGetDatum(ts_date), DateADTGetDatum(origin)));
+	}
+	else
+	{
+		result = DatumGetDateADT(DirectFunctionCall2(ts_date_trunc, interval, DateADTGetDatum(ts_date)));
+	}
+
+	return DirectFunctionCall1(date_timestamptz, DateADTGetDatum(result));
+}
+
+TSDLLEXPORT Datum
+ts_date_trunc(PG_FUNCTION_ARGS)
+{
+	Interval *interval = PG_GETARG_INTERVAL_P(0);
+	DateADT date = PG_GETARG_DATEADT(1);
+	DateADT origin_date = 0; // 2000-01-01
+	int origin_year = 2000, origin_month = 1, origin_day = 1;
+	int year, month, day;
+	int delta, bucket_number;
+
+	if ((interval->time != 0) || ((interval->month != 0) && (interval->day != 0)))
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("unsupported interval: use either days and weeks, or months and years")));
+	}
+
+	if ((interval->month == 0) && (interval->day == 0))
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("unsupported interval: at least one day expected")));
+	}
+
+	if (PG_NARGS() > 2)
+	{
+		origin_date = PG_GETARG_DATUM(2);
+		j2date(origin_date + POSTGRES_EPOCH_JDATE, &origin_year, &origin_month, &origin_day);
+	}
+
+	if ((origin_day != 1) && (interval->month != 0))
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("Invalid `origin` day, YYYY-MM-01 UTC expected")));
+	}
+
+	if (DATE_NOT_FINITE(date))
+		PG_RETURN_DATEADT(date);
+
+	if(interval->month != 0)
+	{
+		/* Handle months and years */
+
+		j2date(date + POSTGRES_EPOCH_JDATE, &year, &month, &day);
+
+		if ((year < origin_year) || ((year == origin_year) && (month < origin_month)))
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("`date` < `origin` not supported, choose another `origin`")));
+		}
+
+		delta = (year * 12 + month) - (origin_year * 12 + origin_month);
+		bucket_number = delta / interval->month;
+		year = origin_year + (bucket_number * interval->month) / 12;
+		month =
+			(((origin_year * 12 + (origin_month - 1)) + (bucket_number * interval->month)) % 12) + 1;
+		day = 1;
+
+		date = date2j(year, month, day) - POSTGRES_EPOCH_JDATE;
+	}
+	else
+	{
+		/* Handle days and weeks */
+
+		if (date < origin_date)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("`date` < `origin` not supported, choose another `origin`")));
+		}
+
+		delta = date - origin_date;
+		bucket_number = delta / interval->day;
+		date = bucket_number * interval->day;
+	}
+
+	PG_RETURN_DATEADT(date);
+}

src/ts_date_trunc.h

@@ -0,0 +1,18 @@
+/*
+ * This file and its contents are licensed under the Apache License 2.0.
+ * Please see the included NOTICE for copyright information and
+ * LICENSE-APACHE for a copy of the license.
+ */
+#ifndef TIMESCALEDB_DATE_TRUNC_H
+#define TIMESCALEDB_DATE_TRUNC_H
+
+#include <postgres.h>
+#include <fmgr.h>
+
+#include "export.h"
+
+extern TSDLLEXPORT Datum ts_date_trunc(PG_FUNCTION_ARGS);
+extern TSDLLEXPORT Datum ts_date_trunc_timestamp(PG_FUNCTION_ARGS);
+extern TSDLLEXPORT Datum ts_date_trunc_timestamptz(PG_FUNCTION_ARGS);
+
+#endif /* TIMESCALEDB_DATE_TRUNC_H */

test/expected/extension.out

@@ -75,5 +75,6 @@ WHERE oid IN (
  timescaledb_fdw_validator
  timescaledb_post_restore
  timescaledb_pre_restore
-(56 rows)
+ ts_date_trunc
+(57 rows)