Validate date ranges for legislation process

Only validates start and end dates for the whole process or a phase, not overlap between phases, as they are permitted, at least for now.

app/models/legislation/process.rb

@@ -18,6 +18,7 @@ class Legislation::Process < ActiveRecord::Base
   validates :allegations_start_date, presence: true
   validates :allegations_end_date, presence: true
   validates :final_publication_date, presence: true
+  validate :valid_date_ranges
 
   scope :open, -> { where("start_date <= ? and end_date >= ?", Date.current, Date.current).order('id DESC') }
   scope :next, -> { where("start_date > ?", Date.current).order('id DESC') }
@@ -57,4 +58,13 @@ class Legislation::Process < ActiveRecord::Base
   def total_comments
     questions.map(&:comments_count).sum
   end
+
+  private
+
+    def valid_date_ranges
+      errors.add(:end_date, :invalid_date_range) if end_date < start_date
+      errors.add(:debate_end_date, :invalid_date_range) if debate_end_date < debate_start_date
+      errors.add(:allegations_end_date, :invalid_date_range) if allegations_end_date < allegations_start_date
+    end
+
 end