[timer] Add Timer.getExecutionTime() (#2147)

Signed-off-by: Jimmy Tanagra <jcode@tanagra.id.au>

bundles/org.openhab.core.model.script/src/org/openhab/core/model/script/actions/Timer.java

@@ -30,6 +30,13 @@ public interface Timer {
      */
     public boolean cancel();
 
+    /**
+     * Gets the scheduled exection time
+     * 
+     * @return the scheduled execution time, or null if the timer was cancelled
+     */
+    public ZonedDateTime getExecutionTime();
+
     /**
      * Determines whether the scheduled execution is yet to happen.
      *
@@ -60,5 +67,4 @@ public interface Timer {
      * @return true, if the rescheduling was done successful
      */
     public boolean reschedule(ZonedDateTime newTime);
-
 }

bundles/org.openhab.core.model.script/src/org/openhab/core/model/script/internal/actions/TimerImpl.java

@@ -13,6 +13,7 @@
 package org.openhab.core.model.script.internal.actions;
 
 import java.time.ZonedDateTime;
+import java.util.concurrent.TimeUnit;
 
 import org.openhab.core.model.script.actions.Timer;
 import org.openhab.core.scheduler.ScheduledCompletableFuture;
@@ -63,6 +64,11 @@ public class TimerImpl implements Timer {
         }
     }
 
+    @Override
+    public ZonedDateTime getExecutionTime() {
+        return cancelled ? null : ZonedDateTime.now().plusNanos(future.getDelay(TimeUnit.NANOSECONDS));
+    }
+
     @Override
     public boolean isActive() {
         return !future.isDone() && !cancelled;