proper color support for labels

app/models/label.rb

@@ -1,5 +1,6 @@
 class Label < ActiveRecord::Base
   validates_presence_of :name
+  validate :color_valid
   belongs_to :role
   has_and_belongs_to_many :forums
   has_many :forumthreads
@@ -8,4 +9,33 @@ class Label < ActiveRecord::Base
     name.upcase
   end
 
+  # calculate the foreground color
+  # either black or white, based on the bg color
+  def fcolor
+    bg = color.dup
+    # convert 3 char to 6 char hex
+    bg.gsub!(/./, '\&\&') if bg.length == 3
+    [0, 2, 4].each do |i|
+      if bg[i..i+1] >= "7f"
+        return "000"
+      end
+    end
+    return "fff"
+  end
+
+  private
+
+  def color_valid
+    color.downcase!
+    unless [3, 6].include? color.length
+      errors.add(:color, "Must be 3 or 6 characters long")
+    end
+    valid_chars = ("0".."9").to_a + ("a".."f").to_a
+    color.split("").each do |c|
+      unless valid_chars.include? c
+        errors.add(:color, "Must be a valid HEX code")
+        return
+      end
+    end
+  end
 end