From 8a2738ca8ad28ed11cae842f1dec48da86a0a985 Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Thu, 6 Sep 2012 00:07:40 -0400
Subject: [PATCH] Add backend for caching image state

---
 imagekit/conf.py                     |  2 ++
 imagekit/generators.py               | 16 +++++----
 imagekit/imagecache/backends/base.py | 49 +++++++++++++++++++++++++---
 imagekit/models/fields/files.py      |  3 ++
 4 files changed, 58 insertions(+), 12 deletions(-)

diff --git a/imagekit/conf.py b/imagekit/conf.py
index 5618bcb..6c09232 100644
--- a/imagekit/conf.py
+++ b/imagekit/conf.py
@@ -3,5 +3,7 @@ from appconf import AppConf
 
 class ImageKitConf(AppConf):
     DEFAULT_IMAGE_CACHE_BACKEND = 'imagekit.imagecache.backends.Simple'
+    CACHE_BACKEND = None
     VALIDATE_ON_ACCESS = True
     CACHE_DIR = 'CACHE/images'
+    CACHE_PREFIX = 'ik-'
diff --git a/imagekit/generators.py b/imagekit/generators.py
index 344fc67..6c4a974 100644
--- a/imagekit/generators.py
+++ b/imagekit/generators.py
@@ -49,18 +49,20 @@ class SpecFileGenerator(object):
         content = IKContentFile(filename, imgfile.read(), format=format)
         return img, content
 
+    def get_hash(self, source_file):
+        return md5(''.join([
+            pickle.dumps(self.get_processors(source_file)),
+            self.format,
+            pickle.dumps(self.options),
+            str(self.autoconvert),
+        ])).hexdigest()
+
     def generate_filename(self, source_file):
         source_filename = source_file.name
         filename = None
         if source_filename:
-            hash = md5(''.join([
-                pickle.dumps(self.get_processors(source_file)),
-                self.format,
-                pickle.dumps(self.options),
-                str(self.autoconvert),
-            ])).hexdigest()
+            hash = self.get_hash(source_file)
             extension = suggest_extension(source_filename, self.format)
-
             filename = os.path.normpath(os.path.join(
                     settings.IMAGEKIT_CACHE_DIR,
                     os.path.splitext(source_filename)[0],
diff --git a/imagekit/imagecache/backends/base.py b/imagekit/imagecache/backends/base.py
index 91a319f..a489f6d 100644
--- a/imagekit/imagecache/backends/base.py
+++ b/imagekit/imagecache/backends/base.py
@@ -1,4 +1,6 @@
 from ...utils import get_singleton
+from django.core.cache import get_cache
+from django.core.cache.backends.dummy import DummyCache
 from django.core.exceptions import ImproperlyConfigured
 
 
@@ -16,7 +18,39 @@ class InvalidImageCacheBackendError(ImproperlyConfigured):
     pass
 
 
-class Simple(object):
+class CachedValidationBackend(object):
+    @property
+    def cache(self):
+        if not getattr(self, '_cache', None):
+            from django.conf import settings
+            alias = settings.IMAGEKIT_CACHE_BACKEND
+            self._cache = get_cache(alias) if alias else DummyCache(None, {})
+        return self._cache
+
+    def get_key(self, file):
+        from django.conf import settings
+        return '%s%s-valid' % (settings.IMAGEKIT_CACHE_PREFIX, file.get_hash())
+
+    def is_invalid(self, file):
+        key = self.get_key(file)
+        cached_value = self.cache.get(key)
+        if cached_value is None:
+            cached_value = self._is_invalid(file)
+            self.cache.set(key, cached_value)
+        return cached_value
+
+    def validate(self, file):
+        if self.is_invalid(file):
+            self._validate(file)
+            self.cache.set(self.get_key(file), True)
+
+    def invalidate(self, file):
+        if not self.is_invalid(file):
+            self._invalidate(file)
+            self.cache.set(self.get_key(file), False)
+
+
+class Simple(CachedValidationBackend):
     """
     The most basic image cache backend. Files are considered valid if they
     exist. To invalidate a file, it's deleted; to validate one, it's generated
@@ -24,21 +58,26 @@ class Simple(object):
 
     """
 
-    def is_invalid(self, file):
+    def _is_invalid(self, file):
         if not getattr(file, '_file', None):
             # No file on object. Have to check storage.
             return not file.storage.exists(file.name)
         return False
 
-    def validate(self, file):
+    def _validate(self, file):
         """
         Generates a new image by running the processors on the source file.
 
         """
-        if self.is_invalid(file):
-            file.generate(save=True)
+        file.generate(save=True)
 
     def invalidate(self, file):
+        """
+        Invalidate the file by deleting it. We override ``invalidate()``
+        instead of ``_invalidate()`` because we don't really care to check
+        whether the file is invalid or not.
+
+        """
         file.delete(save=False)
 
     def clear(self, file):
diff --git a/imagekit/models/fields/files.py b/imagekit/models/fields/files.py
index b46d813..687295f 100644
--- a/imagekit/models/fields/files.py
+++ b/imagekit/models/fields/files.py
@@ -6,6 +6,9 @@ class ImageSpecFieldFile(ImageFieldFile):
         super(ImageSpecFieldFile, self).__init__(instance, field, None)
         self.attname = attname
 
+    def get_hash(self):
+        return self.field.generator.get_hash(self.source_file)
+
     @property
     def source_file(self):
         field_name = getattr(self.field, 'image_field', None)