--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pngtile/store.py	Sat Oct 04 01:01:43 2014 +0300
@@ -0,0 +1,153 @@
+
+import pypngtile
+
+import os.path
+import threading
+
+class Error (Exception):
+    pass
+
+class NotFound (KeyError):
+    pass
+
+class InvalidImage (Exception):
+    pass
+
+class UncachedImage (Exception):
+    pass
+
+class PNGTileStore (object):
+    """
+        Access pypngtile.Image's on a filesystem.
+        
+        Intended to be threadsafe for open()
+    """
+
+    IMAGE_TYPES = (
+        'png',
+    )
+
+    def __init__ (self, image_root):
+        if not os.path.isdir(image_root) :
+            raise Error("Given image_root does not exist: {image_root}".format(image_root=image_root))
+
+        self.image_root = os.path.abspath(image_root)
+        
+        # cache opened Images
+        self.images = { }
+        self.images_lock = threading.Lock()
+
+    def lookup (self, url):
+        """
+            Lookup image by request path.
+
+            Returns name, path, type. For dirs, type will be None.
+
+            Raises Error, NotFound, InvalidImage
+
+            Threadless.
+        """
+
+        if not os.path.isdir(self.image_root):
+            raise Error("Server image_root has gone missing")
+    
+        # path to image
+        name = url.lstrip('/')
+        
+        # build absolute path
+        path = os.path.abspath(os.path.join(self.image_root, name))
+
+        # ensure the path points inside the data root
+        if not path.startswith(self.image_root):
+            raise NotFound(name)
+        
+        if not os.path.exists(path):
+            raise NotFound(name)
+        
+        # determine time
+        if os.path.isdir(path):
+            return name, path, None
+        else:
+            basename, type = path.rsplit('.', 1)
+
+            if type not in self.IMAGE_TYPES:
+                raise InvalidImage(name)
+ 
+            return name, path, type
+
+    def list (self, url):
+        """
+            Yield a series of valid sub-names for the given directory:
+                foo.type
+                foo/
+            
+            The yielded items should be sorted before use.
+        """
+
+        name, root, type = self.lookup(url)
+
+        if type:
+            raise InvalidImage(name)
+
+        for name in os.listdir(root):
+            path = os.path.join(root, name)
+
+            # skip dotfiles
+            if name.startswith('.'):
+                continue
+            
+            # show dirs
+            if os.path.isdir(path):
+                if not os.access(path, os.R_OK):
+                    # skip inaccessible dirs
+                    continue
+
+                yield name + '/'
+
+            # examine ext
+            if '.' in name:
+                name_base, name_type = name.rsplit('.', 1)
+            else:
+                name_base = name
+                name_type = None
+
+            # show .png files with a .cache file
+            if name_type in self.IMAGE_TYPES and os.path.exists(os.path.join(root, name_base + '.cache')):
+                yield name
+
+    def open (self, url):
+        """
+            Return Image object for given URL.
+
+            Raises UncachedImage, pypngtile.Error
+
+            Threadsafe.
+        """
+
+        name, path, type = self.lookup(url)
+
+        if not type:
+            raise InvalidImage(name)
+
+        # get Image object
+        with self.images_lock:
+            image = self.images.get(path)
+
+        if not image:
+            # open
+            image = pypngtile.Image(path)
+
+            # check
+            if image.status() not in (pypngtile.CACHE_FRESH, pypngtile.CACHE_STALE):
+                raise UncachedImage(name)
+
+            # load
+            image.open()
+
+            # cache
+            with self.images_lock:
+                # we don't really care if some other thread raced us on the same Image and opened it up concurrently...
+                # this is just a cache
+                self.images[path] = image
+        
+        return image, name