CREATE OR REPLACE FUNCTION sputnik.guessinit(t TIMESTAMP WITH TIME ZONE, sequence BIGINT, slope DOUBLE PRECISION)
RETURNS VOID
VOLATILE RETURNS NULL ON NULL INPUT SECURITY DEFINER
LANGUAGE 'plpythonu' AS
$$
GD["time"] = t
GD["sequence"] = sequence
GD["slope"] = slope
$$;

CREATE OR REPLACE FUNCTION sputnik.guessbest(state BIGINT, t TIMESTAMP WITH TIME ZONE, sequence BIGINT)
RETURNS BIGINT
VOLATILE CALLED ON NULL INPUT SECURITY DEFINER
LANGUAGE 'plpythonu' AS
$$
if (not GD.has_key("time")) or (not GD.has_key("sequence")) or (not GD.has_key("slope")):
	return None
if (t is None) or (sequence is None):
	return None

plan = plpy.prepare("""
SELECT (extract('epoch' FROM ($1::TIMESTAMP WITH TIME ZONE-$2::TIMESTAMP WITH TIME ZONE)))::float/($3::BIGINT-$4::BIGINT)::float AS slope
""", ["timestamptz", "timestamptz", "int8", "int8"])

result = sequence
if state is not None:
	r0 = plpy.execute(plan, [t, GD["time"], sequence, GD["sequence"]], 1)
	r1 = plpy.execute(plan, [t, GD["time"], state, GD["sequence"]], 1)
	if abs(r0[0]["slope"]-GD["slope"]) >= abs(r1[0]["slope"]-GD["slope"]):
		result = sequence
	else:
		result = state
return result
$$;

CREATE AGGREGATE sputnik.guesser (TIMESTAMP WITH TIME ZONE, BIGINT) (
	SFUNC = sputnik.guessbest,
	STYPE = BIGINT
);