[rrd4j] Fix restore on startup

bundles/org.openhab.persistence.rrd4j/src/main/java/org/openhab/persistence/rrd4j/internal/RRD4jPersistenceService.java

@@ -64,12 +64,14 @@
 import org.openhab.core.persistence.FilterCriteria;
 import org.openhab.core.persistence.FilterCriteria.Ordering;
 import org.openhab.core.persistence.HistoricItem;
+import org.openhab.core.persistence.PersistedItem;
 import org.openhab.core.persistence.PersistenceItemInfo;
 import org.openhab.core.persistence.PersistenceService;
 import org.openhab.core.persistence.QueryablePersistenceService;
 import org.openhab.core.persistence.strategy.PersistenceCronStrategy;
 import org.openhab.core.persistence.strategy.PersistenceStrategy;
 import org.openhab.core.types.State;
+import org.openhab.core.types.UnDefType;
 import org.osgi.framework.Constants;
 import org.osgi.service.component.annotations.Activate;
 import org.osgi.service.component.annotations.Component;
@@ -539,6 +541,118 @@ public Iterable<HistoricItem> query(FilterCriteria filter, @Nullable String alia
         }
     }
 
+    /**
+     * Returns a {@link PersistedItem} representing the persisted state, last update and change timestamps and previous
+     * persisted state. This can be used to restore the full state of an item.
+     * The default implementation queries the service and iterates backward to find the last change and previous
+     * persisted state. Persistence services can override this default implementation with a more specific or efficient
+     * algorithm.
+     *
+     * This method overrides the default implementation in the interface as queries without a begin date are not allowed
+     * in the rrd4j database. If the last change cannot be found in half the length of the first archive, a null value
+     * for the last change and previous persisted state will be returned with {@link PersistedItem}.
+     *
+     * @param itemName name of item
+     * @param alias alias of item
+     *
+     * @return a {@link PersistedItem} or null if the item has not been persisted
+     */
+    @Override
+    public @Nullable PersistedItem persistedItem(String itemName, @Nullable String alias) {
+        State currentState = UnDefType.NULL;
+        State previousState = null;
+        ZonedDateTime lastUpdate = null;
+        ZonedDateTime lastChange = null;
+
+        // Avoid query with open begin date. Don't look further back than half of the first archive.
+        // Only half of the archive is considered to avoid accidently querying the next archive with lower granularity.
+        String localAlias = alias != null ? alias : itemName;
+        RrdDefConfig rrdDefConfig = getRrdDefConfig(localAlias);
+        if (rrdDefConfig == null) {
+            logger.warn("No rrd4j database definition found for {}", itemName);
+            return null;
+        }
+        List<RrdArchiveDef> rrdArchiveDefs = rrdDefConfig.archives;
+        if (rrdArchiveDefs.isEmpty()) {
+            logger.warn("No rrd4j archive definition found for {}", itemName);
+            return null;
+        }
+        RrdArchiveDef rrdArchiveDef = rrdArchiveDefs.get(0);
+        long archiveLength = (rrdArchiveDef.rows * rrdArchiveDef.steps) / 2;
+        ZonedDateTime endDate = ZonedDateTime.now();
+        ZonedDateTime beginDate = endDate.minusSeconds(archiveLength);
+
+        int pageNumber = 0;
+        FilterCriteria filter = new FilterCriteria().setItemName(itemName).setBeginDate(beginDate).setEndDate(endDate)
+                .setOrdering(Ordering.DESCENDING).setPageSize(1000).setPageNumber(pageNumber);
+        Iterable<HistoricItem> items = query(filter, alias);
+        while (items != null) {
+            Iterator<HistoricItem> it = items.iterator();
+            int itemCount = 0;
+            if (UnDefType.NULL.equals(currentState) && it.hasNext()) {
+                HistoricItem historicItem = it.next();
+                itemCount++;
+                currentState = historicItem.getState();
+                lastUpdate = historicItem.getTimestamp();
+                lastChange = lastUpdate;
+            }
+            while (it.hasNext()) {
+                HistoricItem historicItem = it.next();
+                itemCount++;
+                if (!historicItem.getState().equals(currentState)) {
+                    previousState = historicItem.getState();
+                    items = null;
+                    break;
+                }
+                lastChange = historicItem.getTimestamp();
+            }
+            if (itemCount == filter.getPageSize()) {
+                filter.setPageNumber(++pageNumber);
+                items = query(filter);
+            } else {
+                items = null;
+            }
+        }
+
+        if (UnDefType.NULL.equals(currentState) || lastUpdate == null) {
+            return null;
+        }
+
+        final State state = currentState;
+        final ZonedDateTime lastStateUpdate = lastUpdate;
+        final State lastState = previousState;
+        // if we don't find a previous state in persistence, we also don't know when it last changed
+        final ZonedDateTime lastStateChange = previousState != null ? lastChange : null;
+
+        return new PersistedItem() {
+
+            @Override
+            public ZonedDateTime getTimestamp() {
+                return lastStateUpdate;
+            }
+
+            @Override
+            public State getState() {
+                return state;
+            }
+
+            @Override
+            public String getName() {
+                return itemName;
+            }
+
+            @Override
+            public @Nullable ZonedDateTime getLastStateChange() {
+                return lastStateChange;
+            }
+
+            @Override
+            public @Nullable State getLastState() {
+                return lastState;
+            }
+        };
+    }
+
     @Override
     public Set<PersistenceItemInfo> getItemInfo() {
         return Set.of();