Add Sleep duration string.

api/serializers.py

@@ -22,4 +22,4 @@ class BabySerializer(serializers.HyperlinkedModelSerializer):
 class SleepSerializer(serializers.HyperlinkedModelSerializer):
     class Meta:
         model = Sleep
-        fields = ('baby', 'start', 'end')
+        fields = ('baby', 'start', 'end', 'duration')

core/admin.py

@@ -14,5 +14,5 @@ class BabyAdmin(admin.ModelAdmin):
 
 @admin.register(Sleep)
 class SleepAdmin(admin.ModelAdmin):
-    list_display = ('baby', 'start', 'end',)
+    list_display = ('baby', 'start', 'end', 'duration',)
     search_fields = ('baby__first_name', 'baby__last_name',)

core/models.py

@@ -1,3 +1,9 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from datetime import datetime
+from math import floor
+
 from django.db import models
 
 
@@ -30,9 +36,32 @@ class Sleep(models.Model):
         verbose_name_plural = 'Sleep'
 
     def __str__(self):
-        return '{} slept from {} to {} on {}'.format(
+        return '{} slept for {}'.format(
             self.baby,
-            self.start.time(),
-            self.end.time(),
-            self.end.date(),
+            self.duration()
         )
+
+    def duration(self):
+        diff = self.end - self.start
+        if diff.seconds < 60:
+            duration = '{} second{}'.format(
+                diff.seconds,
+                's' if diff.seconds > 1 else ''
+            )
+        elif diff.seconds < 3600:
+            duration = '{} minute{}, {} second{}'.format(
+                floor(diff.seconds / 60),
+                's' if floor(diff.seconds / 60) > 1 else '',
+                diff.seconds % 60,
+                's' if diff.seconds % 60 > 1 else ''
+            )
+        else:
+            duration = '{} hour{}, {} minute{}, {} second{}'.format(
+                floor(diff.seconds / 3600),
+                's' if floor(diff.seconds / 3600) > 1 else '',
+                floor((diff.seconds - 3600) / 60),
+                's' if floor((diff.seconds - 3600) / 60) > 1 else '',
+                diff.seconds % 60,
+                's' if diff.seconds % 60 > 1 else ''
+            )
+        return duration