--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/model/river/MainWstValues.java	Tue Oct 02 13:25:52 2018 +0200
@@ -0,0 +1,102 @@
+/** Copyright (C) 2017 by Bundesanstalt für Gewässerkunde
+ * Software engineering by
+ *  Björnsen Beratende Ingenieure GmbH
+ *  Dr. Schumacher Ingenieurbüro für Wasser und Umwelt
+ *
+ * This file is Free Software under the GNU AGPL (>=v3)
+ * and comes with ABSOLUTELY NO WARRANTY! Check out the
+ * documentation coming with Dive4Elements River for details.
+ */
+package org.dive4elements.river.artifacts.model.river;
+
+import java.math.BigDecimal;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.dive4elements.river.artifacts.model.WstValueTable;
+import org.dive4elements.river.artifacts.model.WstValueTable.QPosition;
+import org.dive4elements.river.artifacts.model.WstValueTableFactory;
+import org.dive4elements.river.model.Gauge;
+import org.dive4elements.river.model.MainValue;
+import org.dive4elements.river.model.MainValueType;
+import org.dive4elements.river.model.NamedMainValue;
+import org.dive4elements.river.model.River;
+
+/**
+ * @author Gernot Belger
+ */
+public final class MainWstValues {
+
+    private static final Map<String, MainWstValues> values = new HashMap<>();
+
+    public synchronized static MainWstValues forRiver(final River river) {
+
+        final String riverName = river.getName();
+        if (values.containsKey(riverName))
+            return values.get(riverName);
+
+        /* determine q main values of first upstream gauge */
+        final Gauge gauge = river.firstUpstreamGauge();
+
+        /* determine reference station */
+        // REAMRK: we will be using the station of the gauge (not the start of the range) to determine the q-Position,
+        // because we are using the discharge of the main value of the gauge. Hopefully .wt file and main values are always
+        // synchrone...
+        final BigDecimal referenceStation = gauge.getStation();
+
+        /* determine q-positions for all main values */
+        // REMARK: wst is cached, so we get it when we need it and do not remember it
+        final WstValueTable wst = WstValueTableFactory.getTable(river);
+
+        final Map<String, QPosition> mainValuePositions = new HashMap<>();
+
+        final List<MainValue> mainValues = gauge.getMainValues();
+        for (final MainValue mainValue : mainValues) {
+            final NamedMainValue nmv = mainValue.getMainValue();
+            if (nmv.getType().getName().equals(MainValueType.MainValueTypeKey.Q.getName())) {
+                final BigDecimal discharge = mainValue.getValue();
+                final String name = nmv.getName();
+
+                final QPosition qPosition = wst.getQPosition(referenceStation.doubleValue(), discharge.doubleValue());
+                mainValuePositions.put(name.toUpperCase(), qPosition);
+            }
+        }
+
+        final MainWstValues mainWstValues = new MainWstValues(river.getName(), mainValuePositions);
+        values.put(riverName, mainWstValues);
+        return mainWstValues;
+    }
+
+    private final Map<String, QPosition> mainValuePositions;
+
+    private final String riverName;
+
+    private MainWstValues(final String riverName, final Map<String, QPosition> mainValuePositions) {
+        this.riverName = riverName;
+        this.mainValuePositions = mainValuePositions;
+    }
+
+    public boolean hasPosition(final String mainValueName) {
+
+        final QPosition qPosition = this.mainValuePositions.get(mainValueName.toUpperCase());
+        return qPosition != null;
+    }
+
+    public double getW(final River river, final String mainValueName, final double station) {
+        // REMARK: we do not keep the river, as it is a hibernate object and this instance is statically cached.
+        // However, we need to make sure we are not misused with another river
+        // We also do not look up the river by its name here, because thats a database access
+        if (!river.getName().equals(this.riverName))
+            throw new IllegalStateException();
+
+        // REMARK: wst is cached, so we get it when we need it and do not remember it
+        final WstValueTable wst = WstValueTableFactory.getTable(river);
+
+        final QPosition qPosition = this.mainValuePositions.get(mainValueName.toUpperCase());
+        if (qPosition == null)
+            return Double.NaN;
+
+        return wst.interpolateW(station, qPosition);
+    }
+}
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