Add DateTimeFieldRenderer to show human-friendly timestamps.

This leverages the `humanize` package to do so.  Unfortunately that doesn't
seem to handle tz-aware times though, so we may need to revisit that at
some point...?

setup.py

@@ -75,6 +75,7 @@ requires = [
     # deprecated 'paster create' (and friends).
     'pyramid>=1.3a1',                   # 1.3b2                 1.4.5
 
+    'humanize',                         # 0.5.1
     'Mako',                             # 0.6.2
     'pyramid_beaker>=0.6',              #                       0.6.1
     'pyramid_debugtoolbar',             # 1.0

tailbone/forms/renderers/__init__.py

@@ -1,9 +1,8 @@
-#!/usr/bin/env python
-# -*- coding: utf-8  -*-
+# -*- coding: utf-8 -*-
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2012 Lance Edgar
+#  Copyright © 2010-2014 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -21,11 +20,16 @@
 #  along with Rattail.  If not, see <http://www.gnu.org/licenses/>.
 #
 ################################################################################
-
 """
 FormAlchemy Field Renderers
 """
 
-from .common import *
+from tailbone.forms.renderers.common import (
+    AutocompleteFieldRenderer,
+    DateTimeFieldRenderer,
+    EnumFieldRenderer,
+    YesNoFieldRenderer,
+    )
+
 from .people import *
 from .products import *

tailbone/forms/renderers/common.py

@@ -1,9 +1,8 @@
-#!/usr/bin/env python
-# -*- coding: utf-8  -*-
+# -*- coding: utf-8 -*-
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2012 Lance Edgar
+#  Copyright © 2010-2014 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -21,16 +20,21 @@
 #  along with Rattail.  If not, see <http://www.gnu.org/licenses/>.
 #
 ################################################################################
-
 """
 Common Field Renderers
 """
 
+from __future__ import unicode_literals
+
+import pytz
+import humanize
+
+import formalchemy
 from formalchemy.fields import FieldRenderer, SelectFieldRenderer, CheckBoxFieldRenderer
 from pyramid.renderers import render
+from webhelpers.html import HTML
 
-
-__all__ = ['AutocompleteFieldRenderer', 'EnumFieldRenderer', 'YesNoFieldRenderer']
+from rattail.time import timezone
 
 
 class AutocompleteFieldRenderer(FieldRenderer):
@@ -76,6 +80,54 @@ class AutocompleteFieldRenderer(FieldRenderer):
         return unicode(value)
 
 
+def pretty_datetime(config, value):
+    """
+    Formats a datetime as a "pretty" human-readable string, with a tooltip
+    showing the ISO string value.
+
+    :param config: Reference to a config object.
+
+    :param value: A ``datetime.datetime`` instance.  Note that if this instance
+       is not timezone-aware, its timezone is assumed to be UTC.
+    """
+    if not value:
+        return ''
+
+    # Make sure we're dealing with a tz-aware value.  If we're given a naive
+    # value, we assume it to be local to the UTC timezone.
+    if not value.tzinfo:
+        value = pytz.utc.localize(value)
+
+    # Convert value to local timezone, and make a naive copy.
+    local = timezone(config)
+    value = local.normalize(value.astimezone(local))
+    naive_value = value.replace(tzinfo=None)
+
+    return HTML.tag('span',
+                    title=value.strftime('%Y-%m-%d %H:%M:%S %Z%z'),
+                    c=humanize.naturaltime(naive_value))
+
+
+class DateTimeFieldRenderer(formalchemy.DateTimeFieldRenderer):
+    """
+    Custom date/time field renderer, which displays a "pretty" value in
+    read-only mode, leveraging config to show the correct timezone.
+    """
+
+    def __init__(self, config):
+        self.config = config
+
+    def __call__(self, field):
+        super(DateTimeFieldRenderer, self).__init__(field)
+        return self
+
+    def render_readonly(self, **kwargs):
+        value = self.raw_value
+        if not value:
+            return ''
+        return pretty_datetime(self.config, value)
+
+
 class EnumFieldRenderer(SelectFieldRenderer):
     """
     Renderer for simple enumeration fields.