Generate a date range in Snowflake within a tabular UDF - snowflake-cloud-data-platform

Question

I'm trying to replace a PostGres function that generates a list of timestamps using the current timestamp that starts [X] [start datepart]s ago and ends with the current timestamp with an interval of [end datepart]s. For example, a user could ask for a series that starts five days ago and returns a timestamp for every hour.
I've found plenty of examples that do something like this using the GENERATOR function. This is how it is done now:
CREATE OR REPLACE FUNCTION fn_get_timestamps_in_range(grain VARCHAR, start_tsmp TIMESTAMP_TZ, maxrange NUMERIC(38,0))
RETURNS TABLE(out_tsmp TIMESTAMP_TZ)
LANGUAGE SQL
STRICT
AS
$$
SELECT CONVERT_TIMEZONE('UTC', CASE LOWER(grain)
WHEN 'min' THEN DATEADD('min', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'hour' THEN DATEADD('hour', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'day' THEN DATEADD('day', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'month' THEN DATEADD('month',ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'year' THEN DATEADD('year', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
END) FROM TABLE(GENERATOR(ROWCOUNT=>maxrange)) ORDER BY 1
$$
;
However, to use that function I have to provide maxrange -- i.e. know how many rows are going to be returned -- so I have to do a DATEDIFF([datepart], start, end). I have this in a function:
CREATE OR REPLACE FUNCTION fn_get_datediff(grain VARCHAR, start_tsmp TIMESTAMP_TZ, end_tsmp TIMESTAMP_TZ)
RETURNS NUMBER(18,0)
LANGUAGE SQL
STRICT
AS
$$
CASE LOWER(grain)
WHEN 'min' THEN DATEDIFF('min', start_tsmp, end_tsmp)
WHEN 'hour' THEN DATEDIFF('hour', start_tsmp, end_tsmp)
WHEN 'day' THEN DATEDIFF('day', start_tsmp, end_tsmp)
WHEN 'month' THEN DATEDIFF('month',start_tsmp, end_tsmp)
WHEN 'year' THEN DATEDIFF('year', start_tsmp, end_tsmp)
ELSE -1
END + 1::NUMERIC(18,0)
$$
;
Try as I may, the GENERATOR will not accept that result -- I keep getting "argument 1 to function GENERATOR needs to be constant" error. Even if the calc is performed in a calling UDF, the error still returns.
For example:
SELECT * FROM TABLE(fn_get_timestamps_in_range(
$end_grain
,fn_get_offset_start_tsmp($start_grain, 1 - $start_range, $time_zone)
,fn_get_datediff($end_grain
,etl.fn_get_offset_start_tsmp($start_grain, 1 - $start_range, $time_zone)
,etl.fn_normalize_date($end_grain, CURRENT_TIMESTAMP, $time_zone))
)
)
;
...returns the error:
SQL compilation error: argument 1 to function GENERATOR needs to be constant, found '(CAST(DATE_DIFFTIMESTAMPINMINUTES(DATE_ADDMINUTESTOTIMESTAMP(-19, ENSURE_NULLABLE('2022-01-05 21:01:00.000000000Ztz=1080')), ENSURE_NULLABLE('2022-01-05 21:01:00.000000000Ztz=1080')) AS NUMBER(18,0))) + 1'
If I replace the datediff call with a number, it works fine.
How can I get the GENERATOR function to accept the values I need?

Answer 1

Found the solution -- I set a static value for the GENERATOR and then put a QUALIFY statement on it to limit the values to the first maxrange returned. Sorry if I wasted anyone's time.
The resulting code looked like:
CREATE OR REPLACE FUNCTION fn_get_timestamps_in_range(grain VARCHAR, start_tsmp TIMESTAMP_TZ, end_tsmp TIMESTAMP_TZ)
RETURNS TABLE(out_tsmp TIMESTAMP_TZ)
LANGUAGE SQL
STRICT
AS
$$
SELECT CONVERT_TIMEZONE('UTC', CASE LOWER(grain)
WHEN 'min' THEN DATEADD('min', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'hour' THEN DATEADD('hour', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'day' THEN DATEADD('day', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'month' THEN DATEADD('month',ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
WHEN 'year' THEN DATEADD('year', ROW_NUMBER() OVER(ORDER BY NULL) - 1, start_tsmp)
END) AS tsmp
FROM TABLE(GENERATOR(ROWCOUNT=>10000))
QUALIFY ROW_NUMBER() OVER(ORDER BY NULL) < fn_get_datediff(grain, start_tsmp, end_tsmp) + 1
ORDER BY 1
$$
;