Add frequency + fallback value selector

solver/src/main/java/org/chocosolver/solver/search/strategy/selectors/values/IntDomainBest.java

@@ -18,6 +18,7 @@
 import org.chocosolver.solver.variables.IntVar;
 
 import java.util.function.BiPredicate;
+import java.util.function.Function;
 
 /**
  * Value selector for optimization problems:
@@ -43,6 +44,10 @@ public final class IntDomainBest implements IntValueSelector {
      */
     private final BiPredicate<IntVar, Integer> condition;
 
+    private final IntValueSelector fallbackValueSelector;
+
+    private final Function<IntVar, Boolean> trigger;
+
     /**
      * Create a value selector that returns the best value wrt to the objective to optimize.
      * When an enumerated variable domain exceeds {@link #maxdom}, only bounds are considered.
@@ -54,14 +59,40 @@ public final class IntDomainBest implements IntValueSelector {
      * is kept.
      * </p>
      *
-     * @param maxdom    a maximum domain size to satisfy to use this value selector.
-     * @param dop       the decision operator used to make the decision
-     * @param condition predicate to break ties
+     * @param maxdom           a maximum domain size to satisfy to use this value selector
+     * @param intValueSelector fallback value selector
+     * @param trigger          the function that indicates when the best value selector is applied.
+     *                         When it returns true, the best value selector is applied.
+     *                         Otherwise, the fallback value selector is applied.
+     * @param dop              the decision operator used to make the decision
+     * @param condition        predicate to break ties
      */
-    public IntDomainBest(int maxdom, DecisionOperator<IntVar> dop, BiPredicate<IntVar, Integer> condition) {
+    public IntDomainBest(int maxdom, IntValueSelector intValueSelector, Function<IntVar, Boolean> trigger, DecisionOperator<IntVar> dop, BiPredicate<IntVar, Integer> condition) {
         this.maxdom = maxdom;
         this.dop = dop;
         this.condition = condition;
+        this.fallbackValueSelector = intValueSelector;
+        this.trigger = trigger;
+    }
+
+    /**
+     * Create a value selector that returns the best value wrt to the objective to optimize.
+     * When an enumerated variable domain exceeds {@link #maxdom}, only bounds are considered.
+     *
+     * <p>
+     * {@code condition} is called when the evaluated {@code value} returns a score
+     * equals to the current best one. In that case, if {@code condition} returns {@code true}
+     * then {@code value} is retained as the new best candidate, otherwise the previous one
+     * is kept.
+     * </p>
+     *
+     * @param intValueSelector fallback value selector
+     * @param trigger          the function that indicates when the best value selector is applied.
+     *                         When it returns true, the best value selector is applied.
+     *                         Otherwise, the fallback value selector is applied.
+     */
+    public IntDomainBest(IntValueSelector intValueSelector, Function<IntVar, Boolean> trigger) {
+        this(100, intValueSelector, trigger, DecisionOperatorFactory.makeIntEq(), (k, v) -> false);
     }
 
     /**
@@ -76,26 +107,51 @@ public IntDomainBest(int maxdom, DecisionOperator<IntVar> dop, BiPredicate<IntVa
      * </p>
      *
      * @param condition predicate to break ties
+     * @apiNote The default values are:
+     * <ul>
+     *     <li>maxdom is set to 100</li>
+     *     <li>the trigger is set to restart count % 16 == 0</li>
+     *     <li>the decision operator is set to '='</li>
+     * </ul>
      */
     public IntDomainBest(BiPredicate<IntVar, Integer> condition) {
-        this(100, DecisionOperatorFactory.makeIntEq(), condition);
+        this(100,
+                new IntDomainMin(),
+                v -> true,
+                DecisionOperatorFactory.makeIntEq(),
+                condition);
     }
 
 
     /**
      * Create a value selector for assignments that returns the best value wrt to the objective to
      * optimize. When an enumerated variable domain exceeds 100, only bounds are considered.
      * Always-false condition is set by default.
+     *
+     * @apiNote The default values are:
+     * <ul>
+     *     <li>maxdom is set to 100</li>
+     *     <li>the trigger is set to restart count % 16 == 0</li>
+     *     <li>the decision operator is set to '='</li>
+     *     <li>the predicate to break ties is lexico</li>
+     * </ul>
      */
     public IntDomainBest() {
-        this(100, DecisionOperatorFactory.makeIntEq(), (k, v) -> false);
+        this(100,
+                new IntDomainMin(),
+                v -> true,
+                DecisionOperatorFactory.makeIntEq(),
+                (k, v) -> false);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public int selectValue(IntVar var) {
+        if (!trigger.apply(var)) {
+            return fallbackValueSelector.selectValue(var);
+        }
         assert var.getModel().getObjective() != null;
         if (var.hasEnumeratedDomain() && var.getDomainSize() < maxdom) {
             int bestCost = Integer.MAX_VALUE;