Fix annoying off by one bug that could cause collation to not happen in

a timely fashion even if there were plenty of samples.

waveform-reader/src/main/java/uk/ac/ucl/rits/inform/datasources/waveform/WaveformCollator.java

@@ -164,6 +164,7 @@ private WaveformMessage collateContiguousData(SortedMap<Instant, WaveformMessage
         // existing values are not necessarily in mutable lists so use a new ArrayList
         List<Double> newNumericValues = new ArrayList<>();
         Iterator<Map.Entry<Instant, WaveformMessage>> perPatientMapIter = perPatientMap.entrySet().iterator();
+        // keep track of incoming message sizes for general interest (does not affect collation algorithm)
         Map<Integer, Integer> uncollatedMessageSizes = new HashMap<>();
         int messagesToCollate = 0;
         while (perPatientMapIter.hasNext()) {
@@ -178,13 +179,19 @@ private WaveformMessage collateContiguousData(SortedMap<Instant, WaveformMessage
             int messageSizeCount = uncollatedMessageSizes.getOrDefault(thisMessageSampleCount, 0);
             uncollatedMessageSizes.put(thisMessageSampleCount, messageSizeCount + 1);
 
-            if (sampleCount + thisMessageSampleCount > targetCollatedMessageSamples) {
-                logger.debug("Reached sample target ({} + {} > {}), collated message span: {} -> {}",
-                        sampleCount, thisMessageSampleCount, targetCollatedMessageSamples,
+            // Ideally this code would be reworked, but for now it's important for sampleCount to meet or exceed
+            // targetCollatedMessageSamples even if we break out here (and thus don't include the current message).
+            // This is needed to prevent the check later on that would say the total sample count isn't big enough
+            // to make a message unless the data is old enough that we should collate regardless.
+            // Essentially, the later code is failing to realise that you can "meet" the target even if you're slightly
+            // short of it, because the next message would take us over the target.
+            sampleCount += thisMessageSampleCount;
+            if (sampleCount > targetCollatedMessageSamples) {
+                logger.debug("Reached sample target ({} > {}), collated message size {}, collated message span: {} -> {}",
+                        sampleCount, targetCollatedMessageSamples, sampleCount - thisMessageSampleCount,
                         firstMsg.getObservationTime(), msg.getObservationTime());
                 break;
             }
-            sampleCount += thisMessageSampleCount;
 
             if (previousMsg != null) {
                 Instant expectedNextDatetime = previousMsg.getExpectedNextObservationDatetime();

waveform-reader/src/test/java/uk/ac/ucl/rits/inform/datasources/waveform/TestWaveformCollation.java

@@ -77,9 +77,10 @@ private void makeAndAddTestMessages() throws WaveformCollator.CollationException
     }
 
     static Stream<Arguments> noGapsData() {
-        // We are adjusting the target number of samples config option rather than
-        // the actual number of samples supplied, which may be a bit unintuitive but
-        // is easier and amounts to the same thing.
+        // There is a fixed quantity of 3000 samples in messages containing 5 samples each.
+        // We are adjusting the *target* number of samples config option rather than
+        // the actual number of messages/samples supplied, which may be unintuitive but
+        // amounts to the same thing and means we can use the same test data each time.
         return Stream.of(
                 // only just happened
                 Arguments.of(3000, 10000, List.of(3000), 0),