From daaffb78e78bff2bdd739ff401b2b8217c2407c1 Mon Sep 17 00:00:00 2001
From: Thomas Vander Stichele <thomas (at) apestaart (dot) org>
Date: Sun, 3 May 2009 17:04:42 +0000
Subject: [PATCH] 	* morituri/common/common.py: 	  Create a Persister
 class to wrap a possible pickle path. 	* examples/trm.py: 	  Use it.

---
 ChangeLog                 |  7 ++++
 examples/trm.py           | 33 ++++++------------
 morituri/common/common.py | 72 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+), 23 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index daa3cd4..76f7528 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2009-05-03  Thomas Vander Stichele  <thomas at apestaart dot org>
+
+	* morituri/common/common.py:
+	  Create a Persister class to wrap a possible pickle path.
+	* examples/trm.py:
+	  Use it.
+
 2009-05-03  Thomas Vander Stichele  <thomas at apestaart dot org>
 
 	* morituri/program/cdparanoia.py:
diff --git a/examples/trm.py b/examples/trm.py
index eb34e5b..1e89865 100644
--- a/examples/trm.py
+++ b/examples/trm.py
@@ -31,7 +31,7 @@ import gobject
 gobject.threads_init()
 import gtk
 
-from morituri.common import checksum, task, taskgtk
+from morituri.common import checksum, task, taskgtk, common
 
 def gtkmain(runner, taskk):
     runner.connect('stop', lambda _: gtk.main_quit())
@@ -48,9 +48,8 @@ def climain(runner, taskk):
     runner.run(taskk)
 
 class Listener(object):
-    def __init__(self, path):
-        self.path = path
-        self.trms = {}
+    def __init__(self, persister):
+        self._persister = persister
 
     def progressed(self, task, value):
         pass
@@ -62,14 +61,9 @@ class Listener(object):
         pass
 
     def stopped(self, task):
-        self.trms[task.path] = task.trm
+        self._persister.object[task.path] = task.trm
         print task.path, task.trm
-
-        (fd, path) = tempfile.mkstemp(suffix='.morituri')
-        handle = os.fdopen(fd, 'wb')
-        pickle.dump(self.trms, handle, 2)
-        handle.close()
-        shutil.move(path, self.path)
+        self._persister.persist()
 
 
 def main(argv):
@@ -98,19 +92,12 @@ def main(argv):
 
     mtask = task.MultiCombinedTask()
     listener = None
-    trms = {}
-    if options.pickle:
-        listener = Listener(options.pickle)
-        print 'Opening pickle %s' % options.pickle
-        handle = open(options.pickle)
-        try:
-            trms = pickle.load(handle)
-        except Exception, e:
-            sys.stderr.write(
-                "Pickle file '%s' cannot be loaded.\n" % options.pickle)
-            sys.exit(1)
 
-        handle.close()
+    ptrms = common.Persister(options.pickle or None, {})
+    if options.pickle:
+        listener = Listener(ptrms)
+        print 'Using pickle %s' % options.pickle
+    trms = ptrms.object
 
     for path in paths:
         path = path.rstrip()
diff --git a/morituri/common/common.py b/morituri/common/common.py
index 6c6cdcb..32fc23d 100644
--- a/morituri/common/common.py
+++ b/morituri/common/common.py
@@ -20,6 +20,10 @@
 # You should have received a copy of the GNU General Public License
 # along with morituri.  If not, see <http://www.gnu.org/licenses/>.
 
+import os
+import tempfile
+import shutil
+
 def msfToFrames(msf):
     """
     Converts a string value in MM:SS:FF to frames
@@ -57,3 +61,71 @@ def framesToHMSF(frames):
     h = frames / 75 / 60 / 60
 
     return "%02d:%02d:%02d.%02d" % (h, m, s, f)
+
+class Persister(object):
+    """
+    I wrap an optional pickle to persist an object to disk.
+
+    Instantiate me with a path to automatically unpickle the object.
+    Call persist to store the object to disk; it will get stored if it
+    changed from the on-disk object.
+
+    @ivar object: the persistent object
+    """
+
+    def __init__(self, path=None, default=None):
+        """
+        If path is not given, the object will not be persisted.
+        This allows code to transparently deal with both persisted and
+        non-persisted objects, since the persist method will just end up
+        doing nothing.
+        """
+        self._path = path
+        self.object = None
+
+        self._unpickle(default)
+
+    def persist(self, object=None):
+        """
+        Persist the given object, if we have a persistence path and the
+        object changed.
+
+        If object is not given, re-persist our object, always.
+        If object is given, only persist if it was changed.
+        """
+        # don't pickle if it's already ok
+        if object and object == self.object:
+            return
+
+        # don't pickle if there is no path
+        if not self._path:
+            return
+
+        # default to pickling our object again
+        if object is None:
+            object = self.object
+
+        # pickle
+        self.object = object
+        (fd, path) = tempfile.mkstemp(suffix='.morituri.pickle')
+        handle = os.fdopen(fd, 'wb')
+        print 'pickle'
+        import pickle
+        pickle.dump(object, handle, 2)
+        handle.close()
+        # do an atomic move
+        shutil.move(path, self._path)
+
+    def _unpickle(self, default=None):
+        self.object = default
+
+        if not self._path:
+            return None
+
+        if not os.path.exists(self._path):
+            return None
+
+        handle = open(self._path)
+        import pickle
+        print 'unpickle'
+        self.object = pickle.load(handle)