# Add Downs

require 'activerecord'

module BackwardsString
  def <<(str)
    replace(str + "\n" + self)
  end
end

class ActiveRecord::Migration
  def self.inherited(c)
    class << c
      attr_reader :text
      
      def create_table(table_name, *options)
        @text << "    drop_table :#{table_name}"
      end

      def rename_table(old_name, new_name)
        @text << "    rename_table :#{new_name}, :#{old_name}"
      end

      def add_column(table_name, column_name, *args)
        @text << "    remove_column :#{table_name}, :#{column_name}"
      end

      def rename_column(table_name, old_name, new_name)
        @text << "    rename_column :#{table_name}, :#{new_name}, :#{old_name}"
      end

      def change_column(table_name, column_name, *args)
        @text << "    change_column :#{table_name}, :#{column_name}, UNKNOWN COLUMN TYPE!"
      end

      def remove_column(table_name, column_name)
        @text << "    add_column :#{table_name}, :#{column_name}, UNKNOWN COLUMN TYPE!"
      end

      def add_index(table_name, column_names, options = {})
        index_name = options[:name]
        if index_name
          @text << "    remove_index :#{table_name}, :name => :#{index_name}"
        else
          @text << "    remove_index :#{table_name}, :column => #{column_names.inspect}"
        end
      end

      def singleton_method_added(m)
        if m == :down
          @text = "".extend(BackwardsString)
          up
          @text = "  def down\n" + @text + "  end\nend\n"
        end
      end
    end
  end
end

class DownAdder
  def self.tempfile(file)
    RAILS_ROOT + "/tmp/migrations/" + File.basename(file)
  end

  def self.create_tmp_dir
    Dir.mkdir(RAILS_ROOT + "/tmp/migrations/") rescue Errno::EEXIST
  end

  def self.add_down(migration)
    create_tmp_dir
    File.open(tempfile(migration),"w") do |temp|
      File.open(migration) do |fh|
        while line = fh.gets
          if line =~ /def self\.down/
            load migration
            b = File.basename(migration)[4..-4]
            c = Object.const_get(b.camelize)
            temp.puts(c.text)
            break
          else
            temp.puts(line)
          end
        end
      end
    end
  end
end