Add FilenameMunger class to processing, with tests.

Munging filenames is something all media type processors want to be able to
do, so I'm refactoring it out into a nice bite-sized class.

mediagoblin/processing.py

@@ -15,6 +15,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import logging
+import os
 
 from celery.task import Task
 
@@ -42,6 +43,21 @@ def create_pub_filepath(entry, filename):
 # Media processing initial steps
 ################################
 
+class FilenameMunger(object):
+    MAX_FILENAME_LENGTH = 255
+
+    def __init__(self, path):
+        self.dirpath, self.basename = os.path.split(path)
+        self.basename, self.ext = os.path.splitext(self.basename)
+        self.ext = self.ext.lower()
+
+    def munge(self, fmtstr):
+        basename_len = (self.MAX_FILENAME_LENGTH -
+                        len(fmtstr.format(basename='', ext=self.ext)))
+        return fmtstr.format(basename=self.basename[:basename_len],
+                             ext=self.ext)
+
+
 class ProcessMedia(Task):
     """
     DEPRECATED -- This now resides in the individual media plugins

mediagoblin/tests/test_processing.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+from nose.tools import assert_equal, assert_true, assert_false
+
+from mediagoblin import processing
+
+class TestProcessing(object):
+    def run_munge(self, input, format, output=None):
+        munger = processing.FilenameMunger(input)
+        result = munger.munge(format)
+        if output is None:
+            return result
+        assert_equal(output, result)
+        
+    def test_easy_filename_munge(self):
+        self.run_munge('/home/user/foo.TXT', '{basename}bar{ext}', 'foobar.txt')
+
+    def test_long_filename_munge(self):
+        self.run_munge('{0}.png'.format('A' * 300), 'image-{basename}{ext}',
+                       'image-{0}.png'.format('A' * 245))