Add option to sort by last modification date (close #88)

Store the metadate “last-modified” for a track and an album and add an
option sort by it.

src/client.py

@@ -3,6 +3,7 @@
 
 import concurrent.futures
 import configparser
+import dateutil.parser
 import logging
 import os
 import queue
@@ -937,6 +938,8 @@ class Client(Base):
                 track.set_date(song['date'])
             if 'albumartist' in song:
                 track.set_albumartists(song['albumartist'])
+            if 'last-modified' in song:
+                track.set_last_modified(song['last-modified'])
         return track
 
 
@@ -998,6 +1001,7 @@ class MCGAlbum:
         self._host = host
         self._tracks = []
         self._length = 0
+        self._last_modified = None
         self._id = Utils.generate_id(title)
 
 
@@ -1057,6 +1061,9 @@ class MCGAlbum:
         path = os.path.dirname(track.get_file())
         if path not in self._pathes:
             self._pathes.append(path)
+        if track.get_last_modified():
+            if not self._last_modified or track.get_last_modified() > self._last_modified:
+                self._last_modified = track.get_last_modified()
 
 
     def get_tracks(self):
@@ -1067,6 +1074,10 @@ class MCGAlbum:
         return self._length
 
 
+    def get_last_modified(self):
+        return self._last_modified
+
+
     def filter(self, filter_string):
         if len(filter_string) == 0:
             return True
@@ -1102,6 +1113,8 @@ class MCGAlbum:
             value_function = "get_title"
         elif criterion == SortOrder.YEAR:
             value_function = "get_date"
+        elif criterion == SortOrder.MODIFIED:
+            value_function = "get_last_modified"
 
         value1 = getattr(album1, value_function)()
         value2 = getattr(album2, value_function)()
@@ -1137,6 +1150,7 @@ class MCGTrack:
         self._track = None
         self._length = 0
         self._date = None
+        self._last_modified = None
 
 
     def __eq__(self, other):
@@ -1208,6 +1222,18 @@ class MCGTrack:
         return self._file
 
 
+    def set_last_modified(self, date_string):
+        if date_string:
+            try:
+                self._last_modified = dateutil.parser.isoparse(date_string)
+            except ValueError as e:
+                self._logger.debug("Invalid date format: %s", date_string)
+
+
+    def get_last_modified(self):
+        return self._last_modified
+
+
 
 
 class MCGPlaylistTrack(MCGTrack):