gistfile1.rb

class EventController
  ...
  def index
    @month = current_month
    @year = current_year
 
    if @month == 1
      @previous_month = 12
      @previous_year = @year - 1
 
      @next_month = 2
      @next_year = @year
    elsif @month == 12
      @previous_month = 11
      @previous_year = @year
 
      @next_month = 1
      @next_year = @year + 1
    else
      @previous_month = @month - 1
      @previous_year = @year
 
      @next_month = @month + 1
      @next_year = @year
    end 
    ...
  end
  ...
end