From 23de4d00d7db32f622eb46b3597dd62a13f562eb Mon Sep 17 00:00:00 2001
From: "D. Berge" <dberge@aaltronav.eu>
Date: Thu, 12 May 2022 21:51:00 +0200
Subject: [PATCH] Add database upgrade file 23.

This defines a interpolate_geometry_from_tstamp(), taking a timestamp
and a maximum timespan in seconds. It will then interpolate a position
at the exact timestamp based on data from real_time_inputs, provided
that the effective interpolation timespan does not exceed the maximum
requested.

Fixes #243.
---
 ...3.10-add-interpolate-geometry-function.sql | 127 ++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 etc/db/upgrades/upgrade23-v0.3.10-add-interpolate-geometry-function.sql

diff --git a/etc/db/upgrades/upgrade23-v0.3.10-add-interpolate-geometry-function.sql b/etc/db/upgrades/upgrade23-v0.3.10-add-interpolate-geometry-function.sql
new file mode 100644
index 0000000..54b4a71
--- /dev/null
+++ b/etc/db/upgrades/upgrade23-v0.3.10-add-interpolate-geometry-function.sql
@@ -0,0 +1,127 @@
+-- Fix not being able to edit a time-based event.
+--
+-- New schema version: 0.3.10
+--
+-- ATTENTION:
+--
+-- ENSURE YOU HAVE BACKED UP THE DATABASE BEFORE RUNNING THIS SCRIPT.
+--
+--
+-- NOTE: This upgrade affects only the public schema.
+-- NOTE: Each application starts a transaction, which must be committed
+-- or rolled back.
+--
+-- This defines a interpolate_geometry_from_tstamp(), taking a timestamp
+-- and a maximum timespan in seconds. It will then interpolate a position
+-- at the exact timestamp based on data from real_time_inputs, provided
+-- that the effective interpolation timespan does not exceed the maximum
+-- requested.
+--
+-- To apply, run as the dougal user:
+--
+-- psql <<EOF
+-- \i $THIS_FILE
+-- COMMIT;
+-- EOF
+--
+-- NOTE: It can be applied multiple times without ill effect.
+--
+
+BEGIN;
+
+CREATE OR REPLACE PROCEDURE pg_temp.show_notice (notice text) AS $$
+BEGIN
+	RAISE NOTICE '%', notice;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE PROCEDURE pg_temp.upgrade () AS $outer$
+BEGIN
+
+	CALL pg_temp.show_notice('Defining interpolate_geometry_from_tstamp()');
+
+	CREATE OR REPLACE FUNCTION public.interpolate_geometry_from_tstamp(
+		IN ts timestamptz,
+		IN maxspan numeric
+	)
+	RETURNS geometry
+	AS $$
+	DECLARE
+		ts0 timestamptz;
+		ts1 timestamptz;
+		geom0 geometry;
+		geom1 geometry;
+		span numeric;
+		fraction numeric;
+	BEGIN
+
+		SELECT tstamp, geometry
+		INTO ts0, geom0
+		FROM real_time_inputs
+		WHERE tstamp <= ts
+		ORDER BY tstamp DESC
+		LIMIT 1;
+
+		SELECT tstamp, geometry
+		INTO ts1, geom1
+		FROM real_time_inputs
+		WHERE tstamp >= ts
+		ORDER BY tstamp ASC
+		LIMIT 1;
+
+		IF geom0 IS NULL OR geom1 IS NULL THEN
+			RAISE NOTICE 'Interpolation failed (no straddling data)';
+			RETURN NULL;
+		END IF;
+
+		-- See if we got an exact match
+		IF ts0 = ts THEN
+			RETURN geom0;
+		ELSIF ts1 = ts THEN
+			RETURN geom1;
+		END IF;
+
+		span := extract('epoch' FROM ts1 - ts0);
+
+		IF span > maxspan THEN
+			RAISE NOTICE 'Interpolation timespan % outside maximum requested (%)', span, maxspan;
+			RETURN NULL;
+		END IF;
+
+		fraction := extract('epoch' FROM ts - ts0) / span;
+
+		IF fraction < 0 OR fraction > 1 THEN
+			RAISE NOTICE 'Requested timestamp % outside of interpolation span (fraction: %)', ts, fraction;
+			RETURN NULL;
+		END IF;
+
+		RETURN ST_LineInterpolatePoint(St_MakeLine(geom0, geom1), fraction);
+
+	END;
+	$$ LANGUAGE plpgsql;
+
+	COMMENT ON FUNCTION public.interpolate_geometry_from_tstamp(timestamptz, numeric) IS
+	'Interpolate a position over a given maximum timespan (in seconds)
+	based on real-time inputs. Returns a POINT geometry.';
+
+
+END;
+$outer$ LANGUAGE plpgsql;
+
+CALL pg_temp.upgrade();
+
+CALL pg_temp.show_notice('Cleaning up');
+DROP PROCEDURE pg_temp.upgrade ();
+
+CALL pg_temp.show_notice('Updating db_schema version');
+INSERT INTO public.info VALUES ('version', '{"db_schema": "0.3.10"}')
+ON CONFLICT (key) DO UPDATE
+	SET value = public.info.value || '{"db_schema": "0.3.10"}' WHERE public.info.key = 'version';
+
+
+CALL pg_temp.show_notice('All done. You may now run "COMMIT;" to persist the changes');
+DROP PROCEDURE pg_temp.show_notice (notice text);
+
+--
+--NOTE Run `COMMIT;` now if all went well
+--