Changing the text color of tracks

app/helpers/application_helper.rb

@@ -286,4 +286,16 @@ module ApplicationHelper
   def unread_notifications(user)
     Comment.accessible_by(current_ability).find_since_last_login(user)
   end
+
+  # Returns black or white deppending on what of them contrast more with the
+  # given color. Useful to print text in a coloured background.
+  # hexcolor is a hex color of 7 characters, being the first one '#'.
+  # Reference: https://24ways.org/2010/calculating-color-contrast
+  def contrast_color(hexcolor)
+    r = hexcolor[1..2].to_i(16)
+    g = hexcolor[3..4].to_i(16)
+    b = hexcolor[5..6].to_i(16)
+    yiq = ((r * 299) + (g * 587) + (b * 114)) / 1000
+    (yiq >= 128) ? 'black' : 'white'
+  end
 end

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

@@ -22,7 +22,7 @@
               %p
                 = truncate(track.description)
             %td
-              %span.label{style: "background-color: #{track.color};"}
+              %span.label{style: "background-color: #{track.color}; color: #{ contrast_color(track.color) }"}
                 = track.color
             %td
               .btn-group{role: "group"}
@@ -34,4 +34,3 @@
 .row
   .col-md-12.text-right
     = link_to 'New Track', new_admin_conference_program_track_path(@conference.short_title), class: 'btn btn-success'
-

app/views/proposal/show.html.haml

@@ -70,7 +70,7 @@
             %dt Track:
             %dd
               - if @event.track
-                %span.label{:style =>"background-color: #{@event.track.color};"}
+                %span.label{:style =>"background-color: #{@event.track.color}; color: #{ contrast_color(@event.track.color) }"}
                   = @event.track.name
           .col-md-12
             %dt Difficulty: