feat: Change fractional custom op from percentage-based to relative weighting. (#91)

Signed-off-by: Simon Schrottner <simon.schrottner@dynatrace.com>

providers/openfeature-provider-flagd/src/openfeature/contrib/provider/flagd/resolvers/process/custom_ops.py

@@ -1,5 +1,6 @@
 import logging
 import typing
+from dataclasses import dataclass
 
 import mmh3
 import semver
@@ -10,6 +11,12 @@ JsonLogicArg = typing.Union[JsonPrimitive, typing.Sequence[JsonPrimitive]]
 logger = logging.getLogger("openfeature.contrib")
 
 
+@dataclass
+class Fraction:
+    variant: str
+    weight: int = 1
+
+
 def fractional(data: dict, *args: JsonLogicArg) -> typing.Optional[str]:
     if not args:
         logger.error("No arguments provided to fractional operator.")
@@ -32,28 +39,51 @@ def fractional(data: dict, *args: JsonLogicArg) -> typing.Optional[str]:
         return None
 
     hash_ratio = abs(mmh3.hash(bucket_by)) / (2**31 - 1)
-    bucket = int(hash_ratio * 100)
+    bucket = hash_ratio * 100
 
+    total_weight = 0
+    fractions = []
     for arg in args:
-        if (
-            not isinstance(arg, (tuple, list))
-            or len(arg) != 2
-            or not isinstance(arg[0], str)
-            or not isinstance(arg[1], int)
-        ):
-            logger.error("Fractional variant weights must be (str, int) tuple")
-            return None
-    variant_weights: typing.Tuple[typing.Tuple[str, int]] = args  # type: ignore[assignment]
+        fraction = _parse_fraction(arg)
+        if fraction:
+            fractions.append(fraction)
+            total_weight += fraction.weight
 
-    range_end = 0
-    for variant, weight in variant_weights:
-        range_end += weight
+    range_end: float = 0
+    for fraction in fractions:
+        range_end += fraction.weight * 100 / total_weight
         if bucket < range_end:
-            return variant
+            return fraction.variant
 
     return None
 
 
+def _parse_fraction(arg: JsonLogicArg) -> typing.Optional[Fraction]:
+    if not isinstance(arg, (tuple, list)) or not arg:
+        logger.error(
+            "Fractional variant weights must be (str, int) tuple or [str] list"
+        )
+        return None
+
+    if not isinstance(arg[0], str):
+        logger.error(
+            "Fractional variant identifier (first element) isn't of type 'str'"
+        )
+        return None
+
+    if len(arg) >= 2 and not isinstance(arg[1], int):
+        logger.error(
+            "Fractional variant weight value (second element) isn't of type 'int'"
+        )
+        return None
+
+    fraction = Fraction(variant=arg[0])
+    if len(arg) >= 2:
+        fraction.weight = arg[1]
+
+    return fraction
+
+
 def starts_with(data: dict, *args: JsonLogicArg) -> typing.Optional[bool]:
     def f(s1: str, s2: str) -> bool:
         return s1.startswith(s2)

providers/openfeature-provider-flagd/tests/flags/invalid-fractional-args-wrong-content.json

@@ -0,0 +1,16 @@
+{
+  "flags": {
+    "basic-flag": {
+      "state": "ENABLED",
+      "variants": {
+        "default": "default",
+        "true": "true",
+        "false": "false"
+      },
+      "defaultVariant": "default",
+      "targeting": {
+        "fractional": [[]]
+      }
+    }
+  }
+}

providers/openfeature-provider-flagd/tests/flags/invalid-fractional-weights-strings.json

@@ -0,0 +1,19 @@
+{
+  "flags": {
+    "basic-flag": {
+      "state": "ENABLED",
+      "variants": {
+        "default": "default",
+        "true": "true",
+        "false": "false"
+      },
+      "defaultVariant": "default",
+      "targeting": {
+        "fractional": [
+          ["a", "one"],
+          ["b", "one"]
+        ]
+      }
+    }
+  }
+}

providers/openfeature-provider-flagd/tests/test_errors.py

@@ -48,7 +48,9 @@ def test_file_load_errors(file_name: str):
         "invalid-semver-args.json",
         "invalid-stringcomp-args.json",
         "invalid-fractional-args.json",
+        "invalid-fractional-args-wrong-content.json",
         "invalid-fractional-weights.json",
+        "invalid-fractional-weights-strings.json",
     ],
 )
 def test_json_logic_parse_errors(file_name: str):