feat: Change fractional custom op from percentage-based to relative weighting. #828

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/process/targeting/Fractional.java

@@ -50,37 +50,35 @@ public Object evaluate(List arguments, Object data) throws JsonLogicEvaluationEx
  }
 
  final List<FractionProperty> propertyList = new ArrayList<>();
+ int totalWeight = 0;
 
- double distribution = 0;
  try {
  for (Object dist : distibutions) {
  FractionProperty fractionProperty = new FractionProperty(dist);
  propertyList.add(fractionProperty);
- distribution += fractionProperty.getPercentage();
+ totalWeight += fractionProperty.getWeight();
  }
  } catch (JsonLogicException e) {
  log.debug("Error parsing fractional targeting rule", e);
  return null;
  }
 
- if (distribution != 100) {
- log.debug("Fractional properties do not sum to 100");
- return null;
- }
-
  // find distribution
- return distributeValue(bucketBy, propertyList);
+ return distributeValue(bucketBy, propertyList, totalWeight);
  }
 
- private static String distributeValue(final String hashKey, final List<FractionProperty> propertyList)
- throws JsonLogicEvaluationException {
+ private static String distributeValue(
+ final String hashKey,
+ final List<FractionProperty> propertyList,
+ int totalWeight
+ ) throws JsonLogicEvaluationException {
  byte[] bytes = hashKey.getBytes(StandardCharsets.UTF_8);
  int mmrHash = MurmurHash3.hash32x86(bytes, 0, bytes.length, 0);
- int bucket = (int) ((Math.abs(mmrHash) * 1.0f / Integer.MAX_VALUE) * 100);
+ float bucket = (Math.abs(mmrHash) * 1.0f / Integer.MAX_VALUE) * 100;
 
- int bucketSum = 0;
+ float bucketSum = 0;
  for (FractionProperty p : propertyList) {
- bucketSum += p.getPercentage();
+ bucketSum += p.getPercentage(totalWeight);
 
  if (bucket < bucketSum) {
  return p.getVariant();
@@ -95,7 +93,7 @@ private static String distributeValue(final String hashKey, final List<FractionP
  @SuppressWarnings({"checkstyle:NoFinalizer"})
  private static class FractionProperty {
  private final String variant;
- private final int percentage;
+ private final int weight;
 
  protected final void finalize() {
  // DO NOT REMOVE, spotbugs: CT_CONSTRUCTOR_THROW
@@ -108,23 +106,32 @@ protected final void finalize() {
 
  final List<?> array = (List) from;
 
- if (array.size() != 2) {
- throw new JsonLogicException("Fraction property does not have two elements");
+ if (array.isEmpty()) {
+ throw new JsonLogicException("Fraction property needs at least one element");
  }
 
  // first must be a string
  if (!(array.get(0) instanceof String)) {
  throw new JsonLogicException("First element of the fraction property is not a string variant");
  }
 
- // second element must be a number
- if (!(array.get(1) instanceof Number)) {
- throw new JsonLogicException("Second element of the fraction property is not a number");
- }
-
  variant = (String) array.get(0);
- percentage = ((Number) array.get(1)).intValue();
+ if (array.size() >= 2) {
+ // second element must be a number
+ if (!(array.get(1) instanceof Number)) {
+ throw new JsonLogicException("Second element of the fraction property is not a number");
+ }
+ weight = ((Number) array.get(1)).intValue();
+ } else {
+ weight = 1;
+ }
  }
 
+ float getPercentage(int totalWeight) {
+ if (weight == 0) {
+ return 0;
+ }
+ return (float) (weight * 100) / totalWeight;
+ }
  }
 }