1 files changed, 61 insertions, 2 deletions
diff --git a/lib/utils/cache.py b/lib/utils/cache.py
index c0313ebe..1ede8ce1 100644
--- a/lib/utils/cache.py
+++ b/lib/utils/cache.py
@@ -2,14 +2,73 @@
 #
 # Copyright (c) 2010 Authors
 # Licensed under the GNU GPL version 3.0 or later.  See the file LICENSE for details.
+import os
+import atexit
+import hashlib
+import pickle
+
+import appdirs
+import diskcache
+
+from lib.utils.settings import global_settings
 
 try:
     from functools import lru_cache
 except ImportError:
     from backports.functools_lru_cache import lru_cache
 
-# simplify use of lru_cache decorator
-
 
+# simplify use of lru_cache decorator
 def cache(*args, **kwargs):
     return lru_cache(maxsize=None)(*args, **kwargs)
+
+
+__stitch_plan_cache = None
+
+
+def get_stitch_plan_cache():
+    global __stitch_plan_cache
+
+    if __stitch_plan_cache is None:
+        cache_dir = os.path.join(appdirs.user_config_dir('inkstitch'), 'cache', 'stitch_plan')
+        size_limit = global_settings['cache_size'] * 1024 * 1024
+        __stitch_plan_cache = diskcache.Cache(cache_dir, size=size_limit)
+        __stitch_plan_cache.size_limit = size_limit
+        atexit.register(__stitch_plan_cache.close)
+
+    return __stitch_plan_cache
+
+
+class CacheKeyGenerator(object):
+    """Generate cache keys given arbitrary data.
+
+    Given arbitrary data, generate short cache key that is extremely likely
+    to be unique.
+
+    Use example:
+
+        >>> generator = CacheKeyGenerator()
+        >>> generator.update(b'12345')
+        >>> generator.update([1, 2, 3, {4, 5, 6}])
+        >>> generator.get_cache_key()
+    """
+
+    def __init__(self):
+        # SHA1 is chosen for speed.  We don't need cryptography-grade hashing
+        # for this use case.
+        self._hasher = hashlib.sha1()
+
+    def update(self, data):
+        """Provide data to be hashed into a cache key.
+
+        Arguments:
+            data -- a bytes object or any object that can be pickled
+        """
+
+        if not isinstance(data, bytes):
+            data = pickle.dumps(data)
+
+        self._hasher.update(data)
+
+    def get_cache_key(self):
+        return self._hasher.hexdigest()