fixed prometheus statistics to correctly use labels

src/c3nav/mapdata/metrics.py

@@ -1,4 +1,6 @@
 import re
+from typing import Optional, Sequence
+
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.core.cache import cache
@@ -18,15 +20,54 @@ if settings.METRCIS:
     reports_open.set_function(lambda: Report.objects.filter(open=True).count()),
 
     class APIStatsCollector(Collector):
+
+        name_registry: dict[str, None | Sequence[str]] = dict()
+
         def collect(self):
+            metrics: dict[str, CounterMetricFamily] = dict()
             if settings.CACHES['default']['BACKEND'] == 'django.core.cache.backends.redis.RedisCache':
                 client = cache._cache.get_client()
                 for key in client.keys(f"*{settings.CACHES['default'].get('KEY_PREFIX', '')}apistats__*"):
-                    key = key.decode('utf-8').split(':', 2)[2]
-                    key = re.sub(r'[^a-zA-Z0-9_]', '_', key)
-                    yield CounterMetricFamily(f'c3nav_{key}', key, value=cache.get(key))
+                    key: str = key.decode('utf-8').split(':', 2)[2]
+                    value = cache.get(key)
+                    key = key[10:]  # trim apistats__ from the beginning
+
+                    # some routing stats don't use double underscores to separate fields, workaround for now
+                    if key.startswith('route_tuple_'):
+                        key = re.sub(r'^route_tuple_(.*)_(.*)$', r'route_tuple__\1__\2', key)
+                    if key.startswith('route_origin_') or key.startswith('route_destination_'):
+                        key = re.sub(r'^route_(origin|destination)_(.*)$', r'route_\1__\2', key)
+
+                    name, *labels = key.split('__')
+                    try:
+                        label_names = self.name_registry[name]
+                    except KeyError:
+                        continue
+
+                    if label_names is None:
+                        label_names = list()
+
+                    if len(label_names) != len(labels):
+                        raise ValueError('configured labels and number of extracted labels doesn\'t match.')
+
+                    try:
+                        counter = metrics[name]
+                    except KeyError:
+                        counter = metrics[name] = CounterMetricFamily(f'c3nav_{name}', f'c3nav_{name}',
+                                                                      labels=label_names)
+                    counter.add_metric(labels, value)
+            return metrics.values()
 
         def describe(self):
             return list()
 
+        @classmethod
+        def add_stat(cls, name:str, label_names: Optional[str | Sequence[str]] = None):
+            if isinstance(label_names, str):
+                label_names = [label_names]
+            if name in cls.name_registry and label_names != cls.name_registry[name]:
+                raise KeyError(f'{name} already exists')
+            cls.name_registry[name] = label_names
+
+
     REGISTRY.register(APIStatsCollector())