Add posthog local eval support

feature_gate/adapters/memory.py

@@ -57,7 +57,7 @@ def features(self):
     self._logger.info("Lists features {features}")
     return features
 
-  def is_enabled(self, feature_key):
+  def is_enabled(self, feature_key, **kwargs):
     for feature in self._features:
       if feature["key"] == feature_key:
         is_enabled = feature["gates"]["boolean"]["enabled"]

feature_gate/adapters/posthog.py

@@ -21,8 +21,8 @@ def features(self):
     key='key'
     return [item[key] for item in resp["data"] if key in item]
 
-  def is_enabled(self, feature_key):
-    return self.client.is_enabled(feature_key)
+  def is_enabled(self, feature_key, **kwargs):
+    return self.client.is_enabled(feature_key, **kwargs)
 
   def enable(self, feature_key):
     resp = self.client.enable_feature(feature_key)

feature_gate/client.py

@@ -17,8 +17,8 @@ def remove(self, feature):
   def features(self):
     return self.adapter.features()
 
-  def is_enabled(self, feature):
-    return self.adapter.is_enabled(feature)
+  def is_enabled(self, feature, **kwargs):
+    return self.adapter.is_enabled(feature, **kwargs)
 
   def enable(self, feature):
     return self.adapter.enable(feature)

feature_gate/clients/posthog_api_client.py

@@ -2,6 +2,7 @@
 import os
 import requests
 import structlog
+from posthog import Posthog
 
 from pathlib import Path
 from feature_gate.client import FeatureNotFound
@@ -16,7 +17,7 @@ class PosthogAPIClientError(Exception):
   pass
 
 class PosthogAPIClient:
-  def __init__(self, api_base=None, api_key=None, project_id=None):
+  def __init__(self, api_base=None, api_key=None, project_id=None, poll_interval=30):
     if api_base is None:
       self.api_base = os.environ.get("POSTHOG_API_BASE", "https://app.posthog.com")
     else:
@@ -31,6 +32,12 @@ def __init__(self, api_base=None, api_key=None, project_id=None):
       self.project_id = os.environ.get('POSTHOG_PROJECT_ID')
     else:
       self.project_id = project_id
+
+    self.posthog_client = Posthog(project_id,
+                             host=self.api_base,
+                             poll_interval=poll_interval, # local eval refresh interval
+                             personal_api_key=api_key
+    )
 
     bind_contextvars(klass="PosthogAPIClient", project_id=project_id)
     project_root = os.path.abspath(os.getenv('PROJECT_ROOT', '.'))
@@ -58,6 +65,31 @@ def api_key(self):
   def project_id(self):
     return self.project_id
 
+
+  def is_enabled(self, key, user_id=None, person_properties=None, only_evaluate_locally=False, **kwargs):
+    """
+    This uses posthog local evaluation to check if a feature flag is enabled 
+    for a user without making a server request.
+    See local eval docs here: https://posthog.com/docs/feature-flags/local-evaluation
+
+    Args:
+        name (String): the name/key of the feature flag
+        user (User): the user object
+
+    Returns:
+        bool: true or false
+    """
+    return self.posthog_client.get_feature_flag(
+      key,
+      user_id,
+      # Include any person properties, groups, or group properties required to evaluate the flag
+      person_properties=person_properties,
+      # Optional. Defaults to False. Set to True if you don't want PostHog to make a server request if it can't evaluate locally
+      only_evaluate_locally=only_evaluate_locally,
+      **kwargs
+    )
+
+
   def list_features(self):
     path = f'/api/projects/{self.project_id}/feature_flags'
     with bound_contextvars(method="list_features"):
@@ -96,13 +128,6 @@ def delete_feature(self, key):
         response = self._patch(path, payload)
         return self._map_single_response("PATCH", path, response)
 
-  def is_enabled(self, key):
-    feature = self.fetch_feature(key)
-    if feature == None:
-      raise FeatureNotFound(f"Feature {key} not found")
-    else:
-      return feature["active"]
-
   def enable_feature(self, key):
     feature = self.fetch_feature(key)
     if feature == None:

pyproject.toml

@@ -15,6 +15,7 @@ keywords = ["feature flags", "feature gate"]
 python = ">= 3.10"
 structlog = "^24.1.0"
 requests = "^2.31.0"
+posthog = "^3.5.0"
 
 [tool.poetry.group.test.dependencies]
 pytest = "^8.0.0"