Starting to implement alerts #17

alertproviders/http_alert_provider.py

@@ -0,0 +1,61 @@
+import logging
+from datetime import datetime
+from threading import Timer, Thread
+from time import sleep
+
+import pytz
+import requests
+
+from alertproviders.alert_provider import AlertProvider
+
+
+# Generic alert provider class for providers that request data via HTTP(S). Just for convenience to avoid code
+# duplication. Subclasses of this query the individual APIs for data.
+class HTTPAlertProvider(AlertProvider):
+
+    def __init__(self, provider_config, url, poll_interval):
+        super().__init__(provider_config)
+        self.url = url
+        self.poll_interval = poll_interval
+        self.poll_timer = None
+
+    def start(self):
+        # Fire off a one-shot thread to run poll() for the first time, just to ensure start() returns immediately and
+        # the application can continue starting. The thread itself will then die, and the timer will kick in on its own
+        # thread.
+        logging.info("Set up query of " + self.name + " alert API every " + str(self.poll_interval) + " seconds.")
+        thread = Thread(target=self.poll)
+        thread.daemon = True
+        thread.start()
+
+    def stop(self):
+        self.poll_timer.cancel()
+
+    def poll(self):
+        try:
+            # Request data from API
+            logging.debug("Polling " + self.name + " alert API...")
+            http_response = requests.get(self.url, headers=self.HTTP_HEADERS)
+            # Pass off to the subclass for processing
+            new_alerts = self.http_response_to_alerts(http_response)
+            # Submit the new alerts for processing. There might not be any alerts for the less popular programs.
+            if new_alerts:
+                self.submit_batch(new_alerts)
+
+            self.status = "OK"
+            self.last_update_time = datetime.now(pytz.UTC)
+            logging.debug("Received data from " + self.name + " alert API.")
+
+        except Exception as e:
+            self.status = "Error"
+            logging.exception("Exception in HTTP JSON Alert Provider (" + self.name + ")")
+            sleep(1)
+
+        self.poll_timer = Timer(self.poll_interval, self.poll)
+        self.poll_timer.start()
+
+    # Convert an HTTP response returned by the API into alert data. The whole response is provided here so the subclass
+    # implementations can check for HTTP status codes if necessary, and handle the response as JSON, XML, text, whatever
+    # the API actually provides.
+    def http_response_to_alerts(self, http_response):
+        raise NotImplementedError("Subclasses must implement this method")