feat: support IN operator for local evaluation (#128)

* feat: support `IN` operator for local evaluation

* fix: coerce trait values to `Strings` for `NOT_CONTAINS`, `CONTAINS`, `IN` and `REGEX` operators

* feat: implement delimiter logic for the `IN` operator

* feat: add docs

Author: khvn26

src/main/java/com/flagsmith/flagengine/segments/SegmentEvaluator.java

@@ -174,15 +174,24 @@ private static Boolean traitMatchesSegmentCondition(Optional<TraitModel> trait,
    */
   public static Boolean conditionMatchesTraitValue(SegmentConditionModel condition, Object value) {
     SegmentConditions operator = condition.getOperator();
-    if (operator.equals(SegmentConditions.NOT_CONTAINS)) {
-      return ((String) value).indexOf(condition.getValue()) == -1;
-    } else if (operator.equals(SegmentConditions.CONTAINS)) {
-      return ((String) value).indexOf(condition.getValue()) > -1;
-    } else if (operator.equals(SegmentConditions.REGEX)) {
-      Pattern pattern = Pattern.compile(condition.getValue());
-      return pattern.matcher((String) value).find();
-    } else {
-      return TypeCasting.compare(operator, value, condition.getValue());
+    switch (operator) {
+      case NOT_CONTAINS:
+        return (String.valueOf(value)).indexOf(condition.getValue()) == -1;
+      case CONTAINS:
+        return (String.valueOf(value)).indexOf(condition.getValue()) > -1;
+      case IN:
+        if (value instanceof String) {
+          return Arrays.asList(condition.getValue().split(",")).contains(value);
+        }
+        if (value instanceof Integer) {
+          return Arrays.asList(condition.getValue().split(",")).contains(String.valueOf(value));
+        }
+        return false;
+      case REGEX:
+        Pattern pattern = Pattern.compile(condition.getValue());
+        return pattern.matcher(String.valueOf(value)).find();
+      default:
+        return TypeCasting.compare(operator, value, condition.getValue());
     }
   }
-}
+}

src/main/java/com/flagsmith/flagengine/segments/constants/SegmentConditions.java

@@ -3,5 +3,5 @@
 public enum SegmentConditions {
   EQUAL, GREATER_THAN, LESS_THAN, LESS_THAN_INCLUSIVE, CONTAINS,
   GREATER_THAN_INCLUSIVE, NOT_CONTAINS, NOT_EQUAL, REGEX, PERCENTAGE_SPLIT,
-  MODULO, IS_SET, IS_NOT_SET;
+  MODULO, IS_SET, IS_NOT_SET, IN;
 }

src/test/java/com/flagsmith/flagengine/unit/segments/SegmentModelTest.java

@@ -61,17 +61,35 @@ private static Stream<Arguments> conditionTestData() {
         Arguments.of(SegmentConditions.CONTAINS, "bar", "b", true),
         Arguments.of(SegmentConditions.CONTAINS, "bar", "bar", true),
         Arguments.of(SegmentConditions.CONTAINS, "bar", "baz", false),
+        Arguments.of(SegmentConditions.CONTAINS, 1, "2", false),
+        Arguments.of(SegmentConditions.CONTAINS, 12, "1", true),
         Arguments.of(SegmentConditions.NOT_CONTAINS, "bar", "b", false),
         Arguments.of(SegmentConditions.NOT_CONTAINS, "bar", "bar", false),
         Arguments.of(SegmentConditions.NOT_CONTAINS, "bar", "baz", true),
+        Arguments.of(SegmentConditions.NOT_CONTAINS, 1, "2", true),
+        Arguments.of(SegmentConditions.NOT_CONTAINS, 12, "1", false),
         Arguments.of(SegmentConditions.REGEX, "foo", "[a-z]+", true),
         Arguments.of(SegmentConditions.REGEX, "FOO", "[a-z]+", false),
+        Arguments.of(SegmentConditions.REGEX, 42, "[a-z]+", false),
+        Arguments.of(SegmentConditions.REGEX, 42, "\\d+", true),
         Arguments.of(SegmentConditions.MODULO, 2, "2|0", true),
         Arguments.of(SegmentConditions.MODULO, 3, "2|0", false),
         Arguments.of(SegmentConditions.MODULO, 2.0, "2|0", true),
         Arguments.of(SegmentConditions.MODULO, 2.0, "2.0|0.0", true),
         Arguments.of(SegmentConditions.MODULO, "foo", "2|0", false),
-        Arguments.of(SegmentConditions.MODULO, "foo", "foo|bar", false)
+        Arguments.of(SegmentConditions.MODULO, "foo", "foo|bar", false),
+        Arguments.of(SegmentConditions.IN, "foo", "", false),
+        Arguments.of(SegmentConditions.IN, "foo", "foo,bar", true),
+        Arguments.of(SegmentConditions.IN, "bar", "foo,bar", true),
+        Arguments.of(SegmentConditions.IN, "ba", "foo,bar", false),
+        Arguments.of(SegmentConditions.IN, "foo", "foo", true),
+        Arguments.of(SegmentConditions.IN, 1, "1,2,3,4", true),
+        Arguments.of(SegmentConditions.IN, 1, "", false),
+        Arguments.of(SegmentConditions.IN, 1, "1", true),
+        // Flagsmith's engine does not evaluate `IN` condition for floats/doubles and booleans
+        // due to ambiguous serialization across supported platforms.
+        Arguments.of(SegmentConditions.IN, 1.5, "1.5", false),
+        Arguments.of(SegmentConditions.IN, false, "false", false)
     );
   }
 
@@ -131,9 +149,7 @@ private static Stream<Arguments> semverTestData() {
         Arguments.of(SegmentConditions.GREATER_THAN_INCLUSIVE, "1.0.1", "1.0.1:semver", true),
         Arguments.of(SegmentConditions.LESS_THAN_INCLUSIVE, "1.0.0", "1.0.1:semver", true),
         Arguments.of(SegmentConditions.LESS_THAN_INCLUSIVE, "1.0.0", "1.0.0:semver", true),
-        Arguments.of(SegmentConditions.LESS_THAN_INCLUSIVE, "1.0.1", "1.0.0:semver", false)
-    );
+        Arguments.of(SegmentConditions.LESS_THAN_INCLUSIVE, "1.0.1", "1.0.0:semver", false));
   }
 
-
 }