--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifact-database/src/main/java/org/dive4elements/artifactdatabase/state/FacetActivity.java	Thu Apr 25 10:57:18 2013 +0200
@@ -0,0 +1,111 @@
+package de.intevation.artifactdatabase.state;
+
+import de.intevation.artifacts.Artifact;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.log4j.Logger;
+
+
+/**
+ * System used in practice used by AttributeWriter in flys-artifacts to decide
+ * whether a facet is initially active.
+ * Provides a singleton Registry into which FacetActivities can be registered
+ * under a key (in practice the artifacts name.  This Registry is queried for
+ * new Facets in order to find whether they are active or inactive.
+ */
+public interface FacetActivity
+{
+    /** Static 'activity' that lets all facets be active. */
+    public static final FacetActivity ACTIVE = new FacetActivity() {
+        @Override
+        public Boolean isInitialActive(
+            Artifact artifact,
+            Facet    facet,
+            String   output
+        ) {
+            return Boolean.TRUE;
+        }
+    };
+
+    /** Static 'activity' that lets all facets be inactive. */
+    public static final FacetActivity INACTIVE = new FacetActivity() {
+        @Override
+        public Boolean isInitialActive(
+            Artifact artifact,
+            Facet    facet,
+            String   output
+        ) {
+            return Boolean.FALSE;
+        }
+    };
+
+    Boolean isInitialActive(Artifact artifact, Facet facet, String output);
+
+    /** Singleton registry, that maps artifact names to the activities, which
+     * decide whether or not a facet should be (initially) active. */
+    public static final class Registry {
+
+        /** The logger for this class. */
+        private static Logger logger = Logger.getLogger(Registry.class);
+
+        /** Singleton instance. */
+        private static final Registry INSTANCE = new Registry();
+
+        /** Map of keys (artifact names) to the activities. */
+        private Map<String, List<FacetActivity>> activities;
+
+        /** Private singleton constructor for the Facet-Activity-Registry. */
+        private Registry() {
+            activities = new HashMap<String, List<FacetActivity>>();
+        }
+
+        /** Access Singleton instance. */
+        public static Registry getInstance() {
+            return INSTANCE;
+        }
+
+        /** Queries whether a given facet should be active or not. */
+        public synchronized boolean isInitialActive(
+            String   key,
+            Artifact artifact,
+            Facet    facet,
+            String   output
+        ) {
+            List<FacetActivity> activityList = activities.get(key);
+            if (activityList == null) {
+                logger.debug("FacetActivity.Registry: No activity " +
+                             "registered for " + key);
+                return true;
+            }
+            if (activityList.size() != 1) {
+                logger.warn("FacetActivity.Registry: More than one " +
+                            "FacetActivity registered for " + key);
+            }
+            for (FacetActivity activity: activityList) {
+                Boolean isActive =
+                    activity.isInitialActive(artifact, facet, output);
+                // Nice. Only, in practice they never return NULL.
+                if (isActive != null) {
+                    return isActive;
+                }
+            }
+            return true;
+        }
+
+
+        /** Add a FacetActivity under given key (usually artifacts name). */
+        public synchronized void register(String key, FacetActivity activity) {
+            List<FacetActivity> activityList = activities.get(key);
+            if (activityList == null) {
+                activityList = new ArrayList<FacetActivity>(3);
+                activities.put(key, activityList);
+            }
+            activityList.add(activity);
+        }
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf-8 :