From 7b20a28803f5cb06e1d5b2625739ef2bab75a86d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20P=C3=A9ters?= <fpeters@entrouvert.com>
Date: Sat, 28 Jul 2018 20:55:26 +0200
Subject: [PATCH 4/4] add live field conditions (#436)

---
 tests/test_admin_pages.py                     |   2 +-
 tests/test_backoffice_pages.py                |  12 +-
 tests/test_fields.py                          |  22 ++--
 tests/test_form_pages.py                      | 112 +++++++++++++++++-
 wcs/backoffice/submission.py                  |   2 +-
 wcs/fields.py                                 |  63 +++++++---
 wcs/formdef.py                                |  11 +-
 wcs/forms/root.py                             |  64 +++++++++-
 wcs/qommon/form.py                            |   7 +-
 wcs/qommon/static/js/qommon.forms.js          |  24 ++++
 wcs/qommon/templates/qommon/forms/widget.html |   6 +-
 11 files changed, 272 insertions(+), 53 deletions(-)

diff --git a/tests/test_admin_pages.py b/tests/test_admin_pages.py
index 92d2d8f1..dbe9bd9b 100644
--- a/tests/test_admin_pages.py
+++ b/tests/test_admin_pages.py
@@ -984,7 +984,7 @@ def test_form_new_field(pub):
 
     # check it's in the preview
     resp = app.get('/backoffice/forms/1/')
-    assert '<h3>baz</h3>' in resp.body
+    assert '<h3 data-field-id="1">baz</h3>' in resp.body
 
 def test_form_delete_field(pub):
     create_role()
diff --git a/tests/test_backoffice_pages.py b/tests/test_backoffice_pages.py
index 61a3f270..022f911a 100644
--- a/tests/test_backoffice_pages.py
+++ b/tests/test_backoffice_pages.py
@@ -4120,7 +4120,7 @@ def test_backoffice_formdata_named_wscall(http_requests, pub):
     app = login(get_app(pub))
 
     resp = app.get('/backoffice/submission/test/')
-    assert '<p class="comment-field ">XbarY</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">XbarY</p>' in resp.body
 
     # check with publisher variable in named webservice call
     if not pub.site_options.has_section('variables'):
@@ -4135,13 +4135,13 @@ def test_backoffice_formdata_named_wscall(http_requests, pub):
     wscall.store()
 
     resp = app.get('/backoffice/submission/test/')
-    assert '<p class="comment-field ">XbarY</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">XbarY</p>' in resp.body
 
     # django-templated URL
     wscall.request = {'url': '{{ example_url }}json'}
     wscall.store()
     resp = app.get('/backoffice/submission/test/')
-    assert '<p class="comment-field ">XbarY</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">XbarY</p>' in resp.body
 
     # webservice call in django template
     formdef.fields = [
@@ -4150,7 +4150,7 @@ def test_backoffice_formdata_named_wscall(http_requests, pub):
     formdef.store()
     formdef.data_class().wipe()
     resp = app.get('/backoffice/submission/test/')
-    assert '<p class="comment-field ">dja-bar-ngo</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">dja-bar-ngo</p>' in resp.body
 
 def test_backoffice_session_var(pub):
     open(os.path.join(pub.app_dir, 'site-options.cfg'), 'w').write('''[options]
@@ -4174,7 +4174,7 @@ query_string_allowed_vars = foo,bar
     resp = app.get('/backoffice/submission/test/?session_var_foo=bar')
     assert resp.location.endswith('/backoffice/submission/test/')
     resp = resp.follow()
-    assert '<p class="comment-field ">XbarY</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">XbarY</p>' in resp.body
 
     # django template
     formdef.fields = [
@@ -4185,7 +4185,7 @@ query_string_allowed_vars = foo,bar
     resp = app.get('/backoffice/submission/test/?session_var_foo=jang')
     assert resp.location.endswith('/backoffice/submission/test/')
     resp = resp.follow()
-    assert '<p class="comment-field ">django</p>' in resp.body
+    assert '<p data-field-id="7" class="comment-field ">django</p>' in resp.body
 
 def test_backoffice_display_message(pub):
     user = create_user(pub)
diff --git a/tests/test_fields.py b/tests/test_fields.py
index 951c47c4..1f4ff884 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -133,65 +133,65 @@ def test_title():
     field = fields.TitleField(label='Foobar')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<h3>Foobar</h3>' in str(form.render())
+    assert '<h3 data-field-id="None">Foobar</h3>' in str(form.render())
 
     field = fields.TitleField(label='Foobar', extra_css_class='test')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<h3 class="test">Foobar</h3>' in str(form.render())
+    assert '<h3 data-field-id="None" class="test">Foobar</h3>' in str(form.render())
 
 def test_subtitle():
     field = fields.SubtitleField(label='Foobar')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<h4>Foobar</h4>' in str(form.render())
+    assert '<h4 data-field-id="None">Foobar</h4>' in str(form.render())
 
     field = fields.SubtitleField(label='Foobar', extra_css_class='test')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<h4 class="test">Foobar</h4>' in str(form.render())
+    assert '<h4 data-field-id="None" class="test">Foobar</h4>' in str(form.render())
 
 def test_comment():
     field = fields.CommentField(label='Foobar')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<p class="comment-field ">Foobar</p>' in str(form.render())
+    assert '<p data-field-id="None" class="comment-field ">Foobar</p>' in str(form.render())
 
     field = fields.CommentField(label='Foo\n\nBar\n\nBaz')
     form = Form(use_tokens=False)
     field.add_to_form(form)
     assert '<p>Foo</p>\n<p>Bar</p>\n<p>Baz</p>' in str(form.render())
-    assert '<div class="comment-field "' in str(form.render())
+    assert '<div data-field-id="None" class="comment-field "' in str(form.render())
 
     # test for variable substitution
     pub.substitutions.feed(MockSubstitutionVariables())
     field = fields.CommentField(label='{{ bar }}')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<p class="comment-field ">Foobar</p>' in str(form.render())
+    assert '<p data-field-id="None" class="comment-field ">Foobar</p>' in str(form.render())
 
     field = fields.CommentField(label='[bar]')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<p class="comment-field ">Foobar</p>' in str(form.render())
+    assert '<p data-field-id="None" class="comment-field ">Foobar</p>' in str(form.render())
 
     # test for proper escaping of substitution variables
     field = fields.CommentField(label='{{ foo }}')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<p class="comment-field ">1 &lt; 3</p>' in str(form.render())
+    assert '<p data-field-id="None" class="comment-field ">1 &lt; 3</p>' in str(form.render())
 
     field = fields.CommentField(label='[foo]')
     form = Form(use_tokens=False)
     field.add_to_form(form)
-    assert '<p class="comment-field ">1 &lt; 3</p>' in str(form.render())
+    assert '<p data-field-id="None" class="comment-field ">1 &lt; 3</p>' in str(form.render())
 
     # test for html content
     field = fields.CommentField(label='<p>Foobar</p>')
     form = Form(use_tokens=False)
     field.add_to_form(form)
     assert '<p>Foobar</p>' in str(form.render())
-    assert '<div class="comment-field "' in str(form.render())
+    assert '<div data-field-id="None" class="comment-field "' in str(form.render())
     assert field.unhtmled_label == 'Foobar'
 
     field = fields.CommentField(label='<p>Foobar&eacute;</p>')
diff --git a/tests/test_form_pages.py b/tests/test_form_pages.py
index dcd2798c..6e528a51 100644
--- a/tests/test_form_pages.py
+++ b/tests/test_form_pages.py
@@ -1084,15 +1084,15 @@ def test_form_titles(pub):
     formdef.data_class().wipe()
 
     resp = get_app(pub).get('/test/')
-    assert not '<h3>1st page/h3>' in resp.body
-    assert '<h4>subtitle of 1st page</h4>' in resp.body
+    assert not '<h3 data-field-id="0">1st page/h3>' in resp.body
+    assert '<h4 data-field-id="5">subtitle of 1st page</h4>' in resp.body
     resp.form['f1'] = 'foo'
     resp = resp.form.submit('submit')
-    assert '<h3>title of second page</h3>' in resp.body
+    assert '<h3 data-field-id="6">title of second page</h3>' in resp.body
     resp = resp.form.submit('submit')  # -> validation page
     assert '<h3>1st page</h3>' in resp.body
-    assert '<h4>subtitle of 1st page</h4>' in resp.body
-    assert '<h3>title of second page</h3>' in resp.body
+    assert '<h4 data-field-id="5">subtitle of 1st page</h4>' in resp.body
+    assert '<h3 data-field-id="6">title of second page</h3>' in resp.body
     resp.form['f3'] = 'foo'
     resp = resp.form.submit('submit').follow()  # -> submit
     assert '<h3>1st page</h3>' in resp.body
@@ -5030,3 +5030,105 @@ def test_field_condition(pub):
     resp = resp.follow()
     assert '<span class="label">Bar</span>' in resp.body
     assert '<span class="label">Foo</span>' not in resp.body
+
+def test_field_live_condition(pub):
+    FormDef.wipe()
+    formdef = FormDef()
+    formdef.name = 'Foo'
+    formdef.fields = [
+        fields.StringField(type='string', id='1', label='Bar', size='40',
+            required=True, varname='bar'),
+        fields.StringField(type='string', id='2', label='Foo', size='40',
+            required=True, varname='foo',
+            condition={'type': 'django', 'value': 'form_var_bar == "bye"'}),
+    ]
+    formdef.store()
+
+    app = get_app(pub)
+    resp = app.get('/foo/')
+    assert 'f1' in resp.form.fields
+    assert 'f2' in resp.form.fields
+    assert resp.html.find('div', {'data-field-id': '1'}).attrs['data-live-source'] == 'true'
+    assert resp.html.find('div', {'data-field-id': '2'}).attrs.get('style') == 'display: none'
+    resp.form['f1'] = 'hello'
+    live_resp = app.post('/foo/live', params=resp.form.submit_fields())
+    assert live_resp.json['result']['1']['visible']
+    assert not live_resp.json['result']['2']['visible']
+    resp.form['f1'] = 'bye'
+    live_resp = app.post('/foo/live', params=resp.form.submit_fields())
+    assert live_resp.json['result']['1']['visible']
+    assert live_resp.json['result']['2']['visible']
+    resp.form['f1'] = 'hello'
+    resp = resp.form.submit('submit')
+    assert 'Check values then click submit.' in resp.body
+    assert 'name="f1"' in resp.body
+    assert 'name="f2"' not in resp.body
+    resp = resp.form.submit('submit')
+    resp = resp.follow()
+    assert '<span class="label">Bar</span>' in resp.body
+    assert '<span class="label">Foo</span>' not in resp.body
+
+    resp = get_app(pub).get('/foo/')
+    assert 'f1' in resp.form.fields
+    assert 'f2' in resp.form.fields
+    resp.form['f1'] = 'bye'
+    resp = resp.form.submit('submit')
+    assert 'There were errors' in resp.body
+    assert resp.html.find('div', {'data-field-id': '2'}).attrs.get('style') is None
+    resp.form['f2'] = 'bye'
+    resp = resp.form.submit('submit')
+    assert 'Check values then click submit.' in resp.body
+    assert 'name="f1"' in resp.body
+    assert 'name="f2"' in resp.body
+    resp = resp.form.submit('submit')
+    resp = resp.follow()
+    assert '<span class="label">Bar</span>' in resp.body
+    assert '<span class="label">Foo</span>' in resp.body
+
+def test_field_live_condition_multipages(pub):
+    FormDef.wipe()
+    formdef = FormDef()
+    formdef.name = 'Foo'
+    formdef.fields = [
+        fields.PageField(id='0', label='2nd page', type='page'),
+        fields.StringField(type='string', id='1', label='Bar', size='40',
+            required=True, varname='bar'),
+        fields.StringField(type='string', id='2', label='Foo', size='40',
+            required=True, varname='foo',
+            condition={'type': 'django', 'value': 'form_var_bar == "bye"'}),
+        fields.PageField(id='3', label='1st page', type='page'),
+        fields.StringField(type='string', id='4', label='Baz', size='40',
+            required=True, varname='baz'),
+    ]
+    formdef.store()
+
+    app = get_app(pub)
+    resp = app.get('/foo/')
+    assert 'f1' in resp.form.fields
+    assert 'f2' in resp.form.fields
+    assert resp.html.find('div', {'data-field-id': '1'}).attrs['data-live-source'] == 'true'
+    assert resp.html.find('div', {'data-field-id': '2'}).attrs.get('style') == 'display: none'
+    resp.form['f1'] = 'hello'
+    live_resp = app.post('/foo/live', params=resp.form.submit_fields())
+    assert live_resp.json['result']['1']['visible']
+    assert not live_resp.json['result']['2']['visible']
+    resp.form['f1'] = 'bye'
+    live_resp = app.post('/foo/live', params=resp.form.submit_fields())
+    assert live_resp.json['result']['1']['visible']
+    assert live_resp.json['result']['2']['visible']
+    resp.form['f1'] = 'bye'
+    resp.form['f2'] = 'bye'
+    resp = resp.form.submit('submit')
+    resp = resp.form.submit('previous')
+    assert resp.html.find('div', {'data-field-id': '2'}).attrs.get('style') is None
+    live_resp = app.post('/foo/live', params=resp.form.submit_fields())
+    assert live_resp.json['result']['1']['visible']
+    assert live_resp.json['result']['2']['visible']
+    resp = resp.form.submit('submit')
+    resp.form['f4'] = 'plop'
+    resp = resp.form.submit('submit')
+    assert 'Check values then click submit.' in resp.body
+    assert 'name="f1"' in resp.body
+    assert 'name="f2"' in resp.body
+    assert 'name="f4"' in resp.body
+    resp = resp.form.submit('submit')
diff --git a/wcs/backoffice/submission.py b/wcs/backoffice/submission.py
index 44b8df12..d4dfbb56 100644
--- a/wcs/backoffice/submission.py
+++ b/wcs/backoffice/submission.py
@@ -76,7 +76,7 @@ class RemoveDraftDirectory(Directory):
 
 class FormFillPage(PublicFormFillPage):
     _q_exports = ['', 'tempfile', 'autosave', 'code',
-            ('remove', 'remove_draft')]
+            ('remove', 'remove_draft'), 'live']
 
     filling_templates = ['wcs/formdata_filling.html']
     validation_templates = ['wcs/formdata_validation.html']
diff --git a/wcs/fields.py b/wcs/fields.py
index 26b5ca6e..4afa7a52 100644
--- a/wcs/fields.py
+++ b/wcs/fields.py
@@ -381,6 +381,29 @@ class Field(object):
         except RuntimeError:
             return True
 
+    def get_condition_varnames(self):
+        return re.findall(r'\bform[_\.]var[_\.]([a-zA-Z0-9_]+?)(?:_raw|\b)', self.condition['value'])
+
+    def has_live_conditions(self, formdef):
+        varnames = self.get_condition_varnames()
+        if not varnames:
+            return False
+        field_position = formdef.fields.index(self)
+        # rewind to field page
+        for field_position in range(field_position, -1, -1):
+            if formdef.fields[field_position].type == 'page':
+                break
+        else:
+            field_position = -1  # form with no page
+        # start from there
+        for field in formdef.fields[field_position+1:]:
+            if field.type == 'page':
+                # stop at next page
+                break
+            if field.varname in varnames:
+                return True
+        return False
+
 
 class WidgetField(Field):
     hint = None
@@ -413,6 +436,7 @@ class WidgetField(Field):
                 widget.extra_css_class = self.extra_css_class
         if self.varname:
             widget.div_id = 'var_%s' % self.varname
+        return widget
 
     def perform_more_widget_changes(self, form, kwargs, edit = True):
         pass
@@ -519,12 +543,12 @@ class TitleField(Field):
     description = N_('Title')
 
     def add_to_form(self, form, value = None):
+        extra_attributes = ' data-field-id="%s"' % self.id
         if self.extra_css_class:
-            extra_css_class = ' class="%s"' % self.extra_css_class
-        else:
-            extra_css_class = ''
-        form.widgets.append(HtmlWidget(
-                    htmltext('<h3%s>%s</h3>' % (extra_css_class, self.label))))
+            extra_attributes += ' class="%s"' % self.extra_css_class
+        widget = HtmlWidget(htmltext('<h3%s>%s</h3>' % (extra_attributes, self.label)))
+        form.widgets.append(widget)
+        return widget
     add_to_view_form = add_to_form
 
     def fill_admin_form(self, form):
@@ -547,12 +571,12 @@ class SubtitleField(TitleField):
     description = N_('Subtitle')
 
     def add_to_form(self, form, value = None):
+        extra_attributes = ' data-field-id="%s"' % self.id
         if self.extra_css_class:
-            extra_css_class = ' class="%s"' % self.extra_css_class
-        else:
-            extra_css_class = ''
-        form.widgets.append(HtmlWidget(
-                    htmltext('<h4%s>%s</h4>' % (extra_css_class, self.label))))
+            extra_attributes += ' class="%s"' % self.extra_css_class
+        widget = HtmlWidget(htmltext('<h4%s>%s</h4>' % (extra_attributes, self.label)))
+        form.widgets.append(widget)
+        return widget
     add_to_view_form = add_to_form
 
 register_field_class(SubtitleField)
@@ -563,7 +587,8 @@ class CommentField(Field):
     description = N_('Comment')
 
     def add_to_form(self, form, value = None):
-        class_attribute = 'class="comment-field %s"' % (self.extra_css_class or '')
+        tag_attributes = 'data-field-id="%s" class="comment-field %s"' % (
+                self.id, self.extra_css_class or '')
 
         if '\n\n' in self.label:
             label = '<p>' + re.sub('\n\n+', '</p>\n<p>', self.label) + '</p>'
@@ -579,9 +604,10 @@ class CommentField(Field):
                 enclosing_tag = 'div'
                 break
 
-        form.widgets.append(HtmlWidget(
-                    htmltext('<%s %s>%s</%s>' % (enclosing_tag, class_attribute,
-                    label, enclosing_tag))))
+        widget = HtmlWidget(htmltext('<%s %s>%s</%s>' % (
+            enclosing_tag, tag_attributes, label, enclosing_tag)))
+        form.widgets.append(widget)
+        return widget
 
     def add_to_view_form(self, *args):
         pass
@@ -1050,7 +1076,7 @@ class DateField(WidgetField):
     def add_to_form(self, form, value=None):
         if value and type(value) is not str:
             value = self.convert_value_to_str(value)
-        WidgetField.add_to_form(self, form, value=value)
+        return WidgetField.add_to_form(self, form, value=value)
 
     def add_to_view_form(self, form, value = None):
         value = localstrftime(value)
@@ -1531,8 +1557,11 @@ class PageCondition(Condition):
         # create variables with values currently being evaluated, not yet
         # available in the formdata.
         from formdata import get_dict_with_varnames
-        live_data = get_dict_with_varnames(formdef.fields, dict_vars)
-        form_live_data = dict(('form_' + x, y) for x, y in live_data.items())
+        live_data = {}
+        form_live_data = {}
+        if dict_vars is not None:
+            live_data = get_dict_with_varnames(formdef.fields, dict_vars)
+            form_live_data = dict(('form_' + x, y) for x, y in live_data.items())
 
         # 1) feed the form_var_* variables in the global substitution system,
         # they will shadow formdata context variables with their new "live"
diff --git a/wcs/formdef.py b/wcs/formdef.py
index b0fe1bf0..2e9cfc86 100644
--- a/wcs/formdef.py
+++ b/wcs/formdef.py
@@ -532,14 +532,19 @@ class FormDef(StorableObject):
                 continue
             if not on_page:
                 continue
-            if not field.is_visible(form_data, self):
-                continue
+            visible = field.is_visible(form_data, self)
+            if not visible:
+                if not field.has_live_conditions(self):
+                    # no live conditions so field can be skipped
+                    continue
             if type(displayed_fields) is list:
                 displayed_fields.append(field)
             value = None
             if form_data:
                 value = form_data.get(field.id)
-            field.add_to_form(form, value)
+            widget = field.add_to_form(form, value)
+            widget.is_hidden = not(visible)
+            widget.field = field
 
     def get_page(self, page_no):
         return [x for x in self.fields if x.type == 'page'][page_no]
diff --git a/wcs/forms/root.py b/wcs/forms/root.py
index 491cb3dd..830d6a93 100644
--- a/wcs/forms/root.py
+++ b/wcs/forms/root.py
@@ -16,6 +16,7 @@
 
 import copy
 import json
+import re
 import time
 from StringIO import StringIO
 import sys
@@ -171,7 +172,7 @@ class TrackingCodesDirectory(Directory):
 
 class FormPage(Directory, FormTemplateMixin):
     _q_exports = ['', 'tempfile', 'schema', 'tryauth',
-            'auth', 'qrcode', 'autosave', 'code', 'removedraft']
+            'auth', 'qrcode', 'autosave', 'code', 'removedraft', 'live']
 
     filling_templates = ['wcs/front/formdata_filling.html', 'wcs/formdata_filling.html']
     validation_templates = ['wcs/front/formdata_validation.html', 'wcs/formdata_validation.html']
@@ -378,16 +379,30 @@ class FormPage(Directory, FormTemplateMixin):
             if not one:
                 req.form = {}
 
+        live_condition_fields = {}
         for field in displayed_fields:
             if field.prefill:
                 # always set additional attributes as they will be used for
                 # "live prefill", regardless of existing data.
                 form.get_widget('f%s' % field.id).prefill_attributes = field.get_prefill_attributes()
+            if field.condition:
+                field.varnames = field.get_condition_varnames()
+                for varname in field.varnames:
+                    if not varname in live_condition_fields:
+                        live_condition_fields[varname] = []
+                    live_condition_fields[varname].append(field)
+
+        for field in displayed_fields:
+            if field.varname not in live_condition_fields:
+                continue
+            form.get_widget('f%s' % field.id).live_condition_source = True
 
         self.html_top(self.formdef.name)
 
         form.add_hidden('step', '0')
         form.add_hidden('page', self.pages.index(page))
+        if page:
+            form.add_hidden('page_id', page.id)
 
         form.add_submit('cancel', _('Cancel'), css_class = 'cancel')
         if self.formdef.enable_tracking_codes and not self.edit_mode:
@@ -696,7 +711,8 @@ class FormPage(Directory, FormTemplateMixin):
 
             self.feed_current_data(magictoken)
 
-            form = self.create_form(page=page)
+            submitted_fields = []
+            form = self.create_form(page=page, displayed_fields=submitted_fields)
             form.add_submit('previous')
             if self.formdef.enable_tracking_codes:
                 form.add_submit('removedraft')
@@ -708,13 +724,18 @@ class FormPage(Directory, FormTemplateMixin):
             if self.formdef.enable_tracking_codes and form.get_submit() == 'removedraft':
                 return self.removedraft()
 
+            form_data = session.get_by_magictoken(magictoken, {})
+            data = self.formdef.get_data(form)
+            form_data.update(data)
+
             if self.formdef.enable_tracking_codes and form.get_submit() == 'savedraft':
-                form_data = session.get_by_magictoken(magictoken, {})
-                data = self.formdef.get_data(form)
-                form_data.update(data)
                 filled = self.save_draft(form_data, page_no)
                 return redirect(filled.get_url().rstrip('/'))
 
+            for field in submitted_fields:
+                if not field.is_visible(form_data, self.formdef):
+                    del form._names['f%s' % field.id]
+
             page_error_messages = []
             if form.get_submit() == 'submit' and page:
                 post_conditions = page.post_conditions or []
@@ -988,6 +1009,39 @@ class FormPage(Directory, FormTemplateMixin):
                     pass
         return None
 
+    def live(self):
+        get_request().ignore_session = True
+        # live evaluation of fields
+        get_response().set_content_type('application/json')
+        def result_error(reason):
+            return json.dumps({'result': 'error', 'reason': reason})
+
+        session = get_session()
+        if not session:
+            return result_error('missing session')
+
+        formdata = self.get_transient_formdata()
+        get_publisher().substitutions.feed(formdata)
+
+        page_id = get_request().form.get('page_id')
+        if page_id:
+            for field in self.formdef.fields:
+                if str(field.id) == page_id:
+                    page = field
+                    break
+        else:
+            page = None
+
+        displayed_fields = []
+        form = self.create_form(page=page, displayed_fields=displayed_fields)
+        formdata.data.update(self.formdef.get_data(form))
+
+        result = {}
+        for field in displayed_fields:
+            result[field.id] = {'visible': field.is_visible(formdata.data, self.formdef)}
+
+        return json.dumps({'result': result})
+
     def submitted(self, form, existing_formdata = None):
         if existing_formdata: # modifying
             filled = existing_formdata
diff --git a/wcs/qommon/form.py b/wcs/qommon/form.py
index 1e2adcba..fe1a573b 100644
--- a/wcs/qommon/form.py
+++ b/wcs/qommon/form.py
@@ -417,9 +417,10 @@ class HtmlWidget(object):
         return self.render_content()
 
     def render_content(self):
-        if self.title:
-            return htmltext(self.title)
-        return htmltext(self.string)
+        content = self.title or self.string or ''
+        if getattr(self, 'is_hidden', False):
+            content = htmltext(str(content).replace('>', ' style="display: none">', 1))
+        return htmltext(content)
 
     def has_error(self, request):
         return False
diff --git a/wcs/qommon/static/js/qommon.forms.js b/wcs/qommon/static/js/qommon.forms.js
index cb2213ce..eee6e5bd 100644
--- a/wcs/qommon/static/js/qommon.forms.js
+++ b/wcs/qommon/static/js/qommon.forms.js
@@ -67,4 +67,28 @@ $(function() {
     }
     return true;
   });
+  var live_evaluation = null;
+  $('form div[data-live-source] input, form div[data-live-source] select').on('change keyup paste', function() {
+    var new_data = $(this).parents('form').serialize();
+    if (live_evaluation) {
+      live_evaluation.abort();
+    }
+    live_evaluation = $.ajax({
+      type: 'POST',
+      url: window.location.pathname + 'live',
+      dataType: 'json',
+      data: new_data,
+      headers: {'accept': 'application/json'},
+      success: function(json) {
+        $.each(json.result, function(key, value) {
+          var $widget = $('[data-field-id="' + key + '"]');
+          if (value.visible) {
+            $widget.show();
+          } else {
+            $widget.hide();
+          }
+        });
+      }
+    });
+  });
 });
diff --git a/wcs/qommon/templates/qommon/forms/widget.html b/wcs/qommon/templates/qommon/forms/widget.html
index e205ad49..35e1ea97 100644
--- a/wcs/qommon/templates/qommon/forms/widget.html
+++ b/wcs/qommon/templates/qommon/forms/widget.html
@@ -4,6 +4,8 @@
      {% if widget.get_error %}widget-with-error{% endif %}
      {% if widget.is_required %}widget-required{% else %}widget-optional{% endif %}
      {% if widget.is_prefilled %}widget-prefilled{% endif %}"
+     {% if widget.is_hidden %}style="display: none"{% endif %}
+     {% if widget.field %}data-field-id="{{ widget.field.id }}"{% endif %}
      {% if widget.div_id %}id="{{widget.div_id}}" data-valuecontainerid="form_{{widget.name}}"{% endif %}
      {% for attr in widget.prefill_attributes %}
      data-{{attr}}="{{widget.prefill_attributes|get:attr}}"
@@ -13,7 +15,9 @@
      {% endif %}
      {% if "data-dynamic-display-value" in widget.attrs %}
      data-dynamic-display-value="{{widget.attrs|get:"data-dynamic-display-value"}}"
-     {% endif %}>
+     {% endif %}
+     {% if widget.live_condition_source %}data-live-source="true"{% endif %}
+     >
   {% block widget-title %}
   {{widget.rendered_title}}
   {% endblock %}
-- 
2.18.0