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package jrummikub.ai.fdsolver;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class Solver {
Set<Var<?>> vars = new HashSet<Var<?>>();
Set<Var<?>> dirtyVars = new HashSet<Var<?>>();
Set<Var<?>> unsolvedVars = new HashSet<Var<?>>();
Set<Constraint> constraints = new HashSet<Constraint>();
ArrayList<StackFrame> stack = new ArrayList<StackFrame>();
boolean contradiction = false;
static private class StackFrame {
Map<Var<?>, HashSet<?>> invalidatedValues = new HashMap<Var<?>, HashSet<?>>();
Var<?> branchVar;
Object branchValue;
public <T> void invalidate(Var<T> var, T invalid) {
HashSet<T> values = (HashSet<T>) invalidatedValues.get(var);
if (values == null) {
invalidatedValues.put(var,
new HashSet<T>(Arrays.asList(invalid)));
} else {
values.add(invalid);
}
}
@Override
public String toString() {
return "StackItem [invalidatedValues=" + invalidatedValues + "]";
}
}
public Solver() {
stack.add(new StackFrame());
}
public boolean solve() {
do {
solveStep();
} while (!(contradiction || (dirtyVars.isEmpty() && unsolvedVars
.isEmpty())));
return !contradiction;
}
public void solveStep() {
if (unsolvedVars.isEmpty() && dirtyVars.isEmpty()) {
contradiction = true;
} else {
propagateAll();
}
if (contradiction) {
if (stack.size() == 1) {
return;
}
backtrack();
} else if (unsolvedVars.isEmpty()) {
return;
} else {
branch();
}
}
public void propagateOnce() {
Iterator<Var<?>> it = dirtyVars.iterator();
Var<?> dirtyVar = it.next();
it.remove();
outerLoop: for (Constraint constraint : constraints) {
if (constraint.getWatchedVars().contains(dirtyVar)) {
for (Propagator propagator : constraint.getPropagators(false)) {
if (propagator.getWatchedVars().contains(dirtyVar)) {
propagator.propagate();
if (contradiction) {
break outerLoop;
}
}
}
}
}
}
public void propagateAll() {
while (!(dirtyVars.isEmpty() || contradiction)) {
propagateOnce();
}
}
public void addVar(Var<?> var) {
vars.add(var);
if (var.getRange().size() != 1) {
unsolvedVars.add(var);
}
}
public void addConstraint(Constraint constraint) {
constraints.add(constraint);
for (Var<?> var : constraint.getWatchedVars()) {
var.makeDirty();
}
}
// backtracking and logging
void branch() {
branchOn(unsolvedVars.iterator().next());
}
@SuppressWarnings("unchecked")
void branchOn(Var<?> var) {
Object value = var.getRange().iterator().next();
branchWith((Var<Object>) var, value);
}
<T> void branchWith(Var<T> var, T value) {
StackFrame stackFrame = new StackFrame();
stackFrame.branchVar = var;
stackFrame.branchValue = value;
stack.add(stackFrame);
var.choose(value);
}
private StackFrame getTopStackFrame() {
return stack.get(stack.size() - 1);
}
<T> void logInvalidation(Var<T> var, T invalid) {
getTopStackFrame().invalidate(var, invalid);
if (var.getRange().size() == 1) {
unsolvedVars.remove(var);
}
}
@SuppressWarnings("unchecked")
// This would need rank-2 types which java lacks
private void rollback(StackFrame item) {
for (Map.Entry<Var<?>, HashSet<?>> entry : item.invalidatedValues
.entrySet()) {
Var<Object> var = (Var<Object>) entry.getKey();
HashSet<Object> values = (HashSet<Object>) entry.getValue();
var.getRange().addAll(values);
if (var.getRange().size() != 1) {
unsolvedVars.add(var);
} else {
unsolvedVars.remove(var);
}
}
}
@SuppressWarnings("unchecked")
void backtrack() {
contradiction = false;
StackFrame topFrame = getTopStackFrame();
rollback(topFrame);
stack.remove(stack.size() - 1);
((Var<Object>) topFrame.branchVar).invalidate(topFrame.branchValue);
}
// factory methods for vars
public Var<Integer> makeRangeVar(int low, int high) {
ArrayList<Integer> range = new ArrayList<Integer>();
for (int i = low; i <= high; i++) {
range.add(i);
}
return makeVar(range);
}
public Var<Boolean> makeBoolVar() {
return makeVar(true, false);
}
public <T> Var<T> makeVar(Collection<T> range) {
Var<T> var = new Var<T>(this, range);
addVar(var);
return var;
}
public <T> Var<T> makeVar(T... range) {
return makeVar(Arrays.asList(range));
}
}
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