Add additional template for custom date formats (#3262)

I can live with a few visual line breaks 🐬

homeassistant/helpers/template.py

@@ -252,6 +252,20 @@ def multiply(value, amount):
         return value
 
 
+def timestamp_custom(value, date_format=DATE_STR_FORMAT, local=True):
+    """Filter to convert given timestamp to format."""
+    try:
+        date = dt_util.utc_from_timestamp(value)
+
+        if local:
+            date = dt_util.as_local(date)
+
+        return date.strftime(date_format)
+    except (ValueError, TypeError):
+        # If timestamp can't be converted
+        return value
+
+
 def timestamp_local(value):
     """Filter to convert given timestamp to local date/time."""
     try:
@@ -263,7 +277,7 @@ def timestamp_local(value):
 
 
 def timestamp_utc(value):
-    """Filter to convert gibrn timestamp to UTC date/time."""
+    """Filter to convert given timestamp to UTC date/time."""
     try:
         return dt_util.utc_from_timestamp(value).strftime(DATE_STR_FORMAT)
     except (ValueError, TypeError):
@@ -289,5 +303,6 @@ class TemplateEnvironment(ImmutableSandboxedEnvironment):
 ENV = TemplateEnvironment()
 ENV.filters['round'] = forgiving_round
 ENV.filters['multiply'] = multiply
+ENV.filters['timestamp_custom'] = timestamp_custom
 ENV.filters['timestamp_local'] = timestamp_local
 ENV.filters['timestamp_utc'] = timestamp_utc

tests/helpers/test_template.py

@@ -127,6 +127,30 @@ class TestUtilTemplate(unittest.TestCase):
                 template.render(self.hass,
                                 '{{ %s | multiply(10) | round }}' % inp))
 
+    def test_timestamp_custom(self):
+        """Test the timestamps to custom filter."""
+        tests = [
+            (None, None, None, 'None'),
+            (1469119144, None, True, '2016-07-21 16:39:04'),
+            (1469119144, '%Y', True, '2016'),
+            (1469119144, 'invalid', True, 'invalid'),
+            (dt_util.as_timestamp(dt_util.utcnow()), None, False,
+                dt_util.now().strftime('%Y-%m-%d %H:%M:%S'))
+        ]
+
+        for inp, fmt, local, out in tests:
+            if fmt:
+                fil = 'timestamp_custom(\'{}\')'.format(fmt)
+            elif fmt and local:
+                fil = 'timestamp_custom(\'{0}\', {1})'.format(fmt, local)
+            else:
+                fil = 'timestamp_custom'
+
+            self.assertEqual(
+                    out,
+                    template.render(self.hass, '{{ %s | %s }}' % (inp, fil))
+                )
+
     def test_timestamp_local(self):
         """Test the timestamps to local filter."""
         tests = {