Add validations to BroadcastMessage color and font

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/broadcast_message.rb

@@ -20,6 +20,9 @@ class BroadcastMessage < ActiveRecord::Base
   validates :starts_at, presence: true
   validates :ends_at, presence: true
+  validates :color, format: { with: /\A\#[0-9A-Fa-f]{6}+\Z/ }, allow_blank: true
+  validates :font,  format: { with: /\A\#[0-9A-Fa-f]{6}+\Z/ }, allow_blank: true
+
   def self.current
     where("ends_at > :now AND starts_at < :now", now: Time.zone.now).last
   end

app/views/admin/broadcast_messages/index.html.haml

@@ -21,11 +21,13 @@
   .control-group.js-toggle-colors-container.hide
     = f.label :color, "Background Color"
     .controls
-      = f.text_field :color
+      = f.text_field :color, placeholder: "#AA33EE"
+      .light Hex values as 3 double digit numbers, starting with a # sign.
   .control-group.js-toggle-colors-container.hide
     = f.label :font, "Font Color"
     .controls
-      = f.text_field :font
+      = f.text_field :font, placeholder: "#224466"
+      .light Hex values as 3 double digit numbers, starting with a # sign.
   .control-group
     = f.label :starts_at
     .controls.datetime-controls