--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/potd/tools.py	Sat May 05 17:10:48 2012 -0500
@@ -0,0 +1,96 @@
+"""
+Tools for the Photo of the Day (potd) application.
+
+"""
+import random
+import logging
+
+from potd.models import Current, Sequence, Photo
+
+
+logger = logging.getLogger(__name__)
+
+
+def get_sequence():
+    """
+    Reads the photo sequence object from the database and converts it into a
+    list of photo IDs. If the sequence object is not found, and empty list is
+    returned.
+
+    """
+    try:
+        s = Sequence.objects.get(pk=1)
+    except Sequence.DoesNotExist:
+        return []
+
+    return [int(x) for x in s.seq.split(',')]
+
+
+def new_sequence():
+    """
+    Generates a new random sequence of photos and saves it to the database.
+    The sequence is returned as a list of photo IDs.
+
+    """
+    ids = list(Photo.objects.values_list('id', flat=True))
+    random.shuffle(ids)
+
+    try:
+        s = Sequence.objects.get(pk=1)
+    except Sequence.DoesNotExist:
+        s = Sequence()
+
+    s.seq = ','.join([str(n) for n in ids])
+    s.save()
+    return ids
+
+
+def pick_potd():
+    """
+    Chooses the next POTD. Run this command at midnight to update the POTD.
+
+    """
+    # Get the "current" record for the now old POTD:
+    try:
+        c = Current.objects.get(pk=1)
+        current = c.potd.pk
+    except Current.DoesNotExist:
+        c = Current()
+        current = None
+
+    # Get the sequence of photo ID's:
+    seq = get_sequence()
+
+    # If there is no current object, sequence, or if this was the last POTD in
+    # the sequence, generate a new random sequence:
+
+    if current is None or not seq or current == seq[-1]:
+        # time to generate a new random sequence
+        seq = new_sequence()
+        # set current to the first one in the sequence
+        if seq:
+            try:
+                c.potd = Photo.objects.get(pk=seq[0])
+            except Photo.DoesNotExist:
+                logger.error("POTD: missing photo %d", seq[0])
+            else:
+                c.potd.potd_count += 1
+                c.potd.save()
+                c.save()
+    else:
+        # find current in the sequence, pick the next one
+        try:
+            i = seq.index(current)
+        except ValueError:
+            logger.error("POTD: current photo (%d) not in sequence", current)
+            return
+
+        n = i + 1
+        try:
+            c.potd = Photo.objects.get(pk=seq[n])
+        except Photo.DoesNotExist:
+            logger.error("POTD: missing next photo %d", n)
+        else:
+            c.potd.potd_count += 1
+            c.potd.save()
+            c.save()