--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifact-database/src/main/java/org/dive4elements/artifactdatabase/transition/TransitionEngine.java	Thu Apr 25 10:57:18 2013 +0200
@@ -0,0 +1,141 @@
+package de.intevation.artifactdatabase.transition;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.log4j.Logger;
+
+import de.intevation.artifacts.Artifact;
+
+import de.intevation.artifactdatabase.state.State;
+import de.intevation.artifactdatabase.state.StateEngine;
+
+
+/**
+ * The TransitionEngine stores all transitions for each Artifact and should be
+ * used to determine, if an Artifact is able to advance from one to another
+ * state.
+ *
+ * @author <a href="mailto:ingo.weinzierl@intevation.de">Ingo Weinzierl</a>
+ */
+public class TransitionEngine {
+
+    /** The logger used in this class. */
+    private static Logger logger = Logger.getLogger(TransitionEngine.class);
+
+    /**
+     * A map that contains the transitions of the artifacts. The key is the name
+     * of the artifact, its value is a list of all transitions of this artifact.
+     */
+    protected Map<String, List> transitions;
+
+
+    /**
+     * The default constructor.
+     */
+    public TransitionEngine() {
+        transitions = new HashMap<String, List>();
+    }
+
+
+    /**
+     * Add new transitions for a specific artifact.
+     *
+     * @param stateId the name of the Artifact.
+     * @param transition the list of transition of the artifact.
+     *
+     * @return true, if the transitions were added, otherwise false.
+     */
+    public boolean addTransition(String stateId, Transition transition) {
+        List tmp = transitions.get(stateId);
+
+        if (tmp == null) {
+            tmp = new ArrayList<Transition>();
+        }
+
+        tmp.add(transition);
+
+        logger.debug("Add new transitions for state '" + stateId + "'");
+
+        return transitions.put(stateId, tmp) != null;
+    }
+
+
+    /**
+     * This method returns all existing transitions of a state.
+     *
+     * @param state The state
+     *
+     * @return the existing transition of <i>state</i>.
+     */
+    public List<Transition> getTransitions(State state) {
+        return transitions.get(state.getID());
+    }
+
+
+    /**
+     * This method returns the reachable states of <i>state</i>.
+     *
+     * @param state The current state.
+     * @param engine The state engine.
+     *
+     * @return a list of reachable states.
+     */
+    public List<State> getReachableStates(
+        Artifact    artifact,
+        State       state,
+        StateEngine engine) {
+        List<Transition> transitions = getTransitions(state);
+        List<State>      reachable   = new ArrayList<State>();
+
+        if (transitions == null) {
+            return reachable;
+        }
+
+        for (Transition t: transitions) {
+            State target = engine.getState(t.getTo());
+
+            if (t.isValid(artifact, state, target)) {
+                reachable.add(target);
+            }
+        }
+
+        return reachable;
+    }
+
+
+    /**
+     * Determines if a state with a given identifier is reachable from a current
+     * state.
+     *
+     * @param artifact The owner artifact of state <i>state</i>.
+     * @param targetId The identifier of the target state.
+     * @param state The start state.
+     * @param stateEngine The StateEngine.
+     *
+     * @return true, if the target state is reachable, otherwise false.
+     */
+    public boolean isStateReachable(
+        Artifact    artifact,
+        String      targetId,
+        State       state,
+        StateEngine stateEngine)
+    {
+        List<State> reachable = getReachableStates(artifact, state,stateEngine);
+
+        if (reachable == null || reachable.size() == 0) {
+            return false;
+        }
+
+        for (State s: reachable) {
+            if (targetId.equals(s.getID())) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :