Add tsstats.cache.Cache

tsstats/cache.py

@@ -0,0 +1,59 @@
+# -*- coding: utf-8 -*-
+import hashlib
+import logging
+import os
+import pickle
+from collections import MutableMapping, namedtuple
+
+logger = logging.getLogger('tsstats')
+CachedLog = namedtuple('CachedLog', ['path', 'hash', 'events'])
+
+
+def _calculate_hash(path):
+    with open(path, 'rb') as f:
+        return hashlib.sha256(f.read()).hexdigest()
+
+
+class Cache(MutableMapping):
+    def __init__(self, path, data={}):
+        self.path = path
+        self.store = data
+
+    @classmethod
+    def read(cls, path):
+        data = {}
+        if os.path.exists(path):
+            logger.debug('Reading cache from %s', path)
+            with open(path, 'rb') as f:
+                try:
+                    data = pickle.load(f)
+                except EOFError:
+                    logger.debug('Couldn\'t read cache')
+        return cls(path, data)
+
+    def write(self, path=None):
+        if not path:
+            path = self.path
+        logger.debug('Writing cache to %s', path)
+        with open(path, 'wb') as f:
+            pickle.dump(self.store, f)
+
+    def needs_parsing(self, path):
+        if path not in self.store:
+            return True
+        return _calculate_hash(path) != self.store[path].hash
+
+    def __setitem__(self, path, events):
+        self.store[path] = CachedLog(path, _calculate_hash(path), list(events))
+
+    def __getitem__(self, path):
+        return self.store[path]
+
+    def __delitem__(self, path):
+        del self.store[path]
+
+    def __iter__(self):
+        return iter(self.store.keys())
+
+    def __len__(self):
+        return len(self.store)