feat(core): add resilient fixed-window throttling

tests/test_throttling.py

@@ -0,0 +1,130 @@
+from __future__ import annotations
+
+import unittest
+
+from redis.exceptions import RedisError
+
+from govoplan_core.core.throttling import (
+    FixedWindowBucket,
+    FixedWindowThrottle,
+    InMemoryFixedWindowStore,
+    ResilientFixedWindowStore,
+    ThrottleDimension,
+    build_fixed_window_throttle,
+)
+
+
+class _Clock:
+    def __init__(self) -> None:
+        self.value = 100.0
+
+    def __call__(self) -> float:
+        return self.value
+
+
+class _RecordingStore:
+    def __init__(self) -> None:
+        self.values: dict[str, int] = {}
+
+    def read(self, key: str) -> FixedWindowBucket:
+        return FixedWindowBucket(self.values.get(key, 0), 60)
+
+    def increment(self, key: str, *, window_seconds: int) -> FixedWindowBucket:
+        del window_seconds
+        self.values[key] = self.values.get(key, 0) + 1
+        return FixedWindowBucket(self.values[key], 60)
+
+    def delete(self, key: str) -> None:
+        self.values.pop(key, None)
+
+
+class _FailingStore(_RecordingStore):
+    def read(self, key: str) -> FixedWindowBucket:
+        del key
+        raise RedisError("offline")
+
+    def increment(self, key: str, *, window_seconds: int) -> FixedWindowBucket:
+        del key, window_seconds
+        raise RedisError("offline")
+
+    def delete(self, key: str) -> None:
+        del key
+        raise RedisError("offline")
+
+
+class FixedWindowThrottleTests(unittest.TestCase):
+    def test_blocks_at_limit_and_expires_without_sleeping(self) -> None:
+        clock = _Clock()
+        store = InMemoryFixedWindowStore(clock=clock)
+        throttle = FixedWindowThrottle(store, window_seconds=60)
+        dimensions = (ThrottleDimension("password", "secret-subject", 3),)
+
+        self.assertTrue(throttle.check(dimensions).allowed)
+        self.assertTrue(throttle.record(dimensions).allowed)
+        self.assertTrue(throttle.record(dimensions).allowed)
+        blocked = throttle.record(dimensions)
+        self.assertFalse(blocked.allowed)
+        self.assertEqual(blocked.retry_after_seconds, 60)
+        self.assertFalse(throttle.check(dimensions).allowed)
+
+        clock.value += 61
+        self.assertTrue(throttle.check(dimensions).allowed)
+
+    def test_subject_is_hashed_and_success_can_reset_it(self) -> None:
+        store = _RecordingStore()
+        throttle = FixedWindowThrottle(store, window_seconds=60)
+        dimensions = (ThrottleDimension("poll-participation-password", "tenant:token-secret", 2),)
+
+        throttle.record(dimensions)
+
+        self.assertEqual(len(store.values), 1)
+        stored_key = next(iter(store.values))
+        self.assertNotIn("tenant:token-secret", stored_key)
+        self.assertIn(":poll-participation-password:", stored_key)
+        throttle.reset(dimensions)
+        self.assertEqual(store.values, {})
+
+    def test_resilient_store_uses_bounded_local_fallback(self) -> None:
+        clock = _Clock()
+        fallback = InMemoryFixedWindowStore(max_entries=2, clock=clock)
+        store = ResilientFixedWindowStore(
+            _FailingStore(),
+            fallback,
+            retry_seconds=30,
+            clock=clock,
+        )
+
+        first = store.increment("first", window_seconds=60)
+        second = store.increment("first", window_seconds=60)
+        store.increment("second", window_seconds=60)
+        store.increment("third", window_seconds=60)
+
+        self.assertEqual(first.count, 1)
+        self.assertEqual(second.count, 2)
+        self.assertEqual(fallback.read("first").count, 0)
+        self.assertEqual(fallback.read("third").count, 1)
+
+    def test_builder_operates_without_redis(self) -> None:
+        throttle = build_fixed_window_throttle(
+            redis_url=None,
+            window_seconds=30,
+            max_local_entries=10,
+        )
+        dimensions = (ThrottleDimension("test", "subject", 1),)
+
+        self.assertFalse(throttle.record(dimensions).allowed)
+        self.assertFalse(throttle.check(dimensions).allowed)
+
+    def test_rejects_invalid_dimensions(self) -> None:
+        throttle = FixedWindowThrottle(_RecordingStore(), window_seconds=60)
+
+        with self.assertRaisesRegex(ValueError, "At least one"):
+            throttle.check(())
+        with self.assertRaisesRegex(ValueError, "positive"):
+            throttle.check((ThrottleDimension("test", "subject", 0),))
+        with self.assertRaisesRegex(ValueError, "namespaces"):
+            throttle.check((ThrottleDimension("Invalid namespace", "subject", 1),))
+
+
+if __name__ == "__main__":
+    unittest.main()