require "date"
require "fixnum"

class DateRangeFormatter
  def initialize(start_date, end_date, start_time = nil, end_time = nil)
    @start_date = Date.parse(start_date)
    @end_date = Date.parse(end_date)
    @start_time = start_time
    @end_time = end_time
  end

  def to_s
    return same_date if same_date?
    return same_month if same_month?
    return same_year if same_year?
    all_different
  end

  private

  def full_end_date
    @end_date.strftime("#{@end_date.day.ordinalize} %B %Y")
  end

  def full_start_date
    @start_date.strftime("#{@start_date.day.ordinalize} %B %Y")
  end

  def same_date?
    @start_date == @end_date
  end

  def same_month?
    @start_date.month == @end_date.month
  end

  def same_year?
    @start_date.year == @end_date.year
  end

  def same_date
    if @start_time && @end_time
      "#{full_start_date} at #{@start_time} to #{@end_time}"
    elsif @start_time
      "#{full_start_date} at #{@start_time}"
    elsif @end_time
      "#{full_start_date} until #{@end_time}"
    else
      full_start_date
    end
  end

  def same_month
    return format_with_time { @start_date.strftime("#{@start_date.day.ordinalize} - #{@end_date.day.ordinalize} %B %Y") } if same_year?
    all_different
  end

  def same_year
    format_with_time { @start_date.strftime("#{@start_date.day.ordinalize} %B - ") + full_end_date }
  end

  def all_different
    format_with_time { "#{full_start_date} - #{full_end_date}" }
  end

  def format_with_time
    if @start_time || @end_time
      format_datetime(full_start_date, @start_time) + ' - ' + format_datetime(full_end_date, @end_time)
    else
      yield
    end
  end

  def format_datetime(date, time = nil)
    return "#{date} at #{time}" if time
    date
  end
end