Add digest to theme images to not keep rebuilding them

The digest is based on the colors of theme, so will change when the colors change

lib/screenshot.rb

@@ -5,7 +5,7 @@ require 'mini_magick'
 
 class Screenshot
   include Capybara::DSL
-  attr_accessor :theme, :theme_name
+  attr_accessor :theme
 
   def self.prepare
     Capybara.register_driver :poltergeist do |app|
@@ -19,30 +19,42 @@ class Screenshot
     end
   end
 
-  def initialize(theme_name)
-    @theme_name = theme_name
-    @theme = theme_name.parameterize.underscore
+  def initialize(theme)
+    @theme = OpenStruct.new(theme.merge(
+      slug: theme[:name].parameterize.underscore,
+      digest: Digest::MD5.new.hexdigest(theme[:colors])
+    ))
   end
 
   def generate_theme_image
-    puts "Generating image for theme #{theme_name}"
+    if File.exist? target_file
+      puts "Image for theme #{theme.name} already exists"
+      return
+    end
+
+    puts "Generating image for theme #{theme.name}"
     visit '/'
-    within ".theme_#{theme}" do
+    within ".theme_#{theme.slug}" do
       choose 'sidebar_theme_rd'
     end
     sleep 1
-    file = Tempfile.new([theme, ".png"])
+
+    file = Tempfile.new([theme.slug, ".png"])
     begin
       page.save_screenshot(file.path, full: true)
 
       MiniMagick::Tool::Convert.new do |convert|
         convert << file.path
         convert.crop '220x220+0+0'
-        convert << "source/images/theme/#{theme}.png"
+        convert << target_file
       end
     ensure
       file.close
       file.unlink
     end
   end
+
+  def target_file
+    "source/images/theme/#{theme.slug}-#{theme.digest}.png"
+  end
 end