require 'singleton'

class Scheduler
  include Singleton

  WEEKLY = [ 7 ]
  DAILY  = [ 1 ]

  def skip_to_dow(date, dow)
    if dow.is_a? String
      dow = Date::DAYNAMES.collect { |d| d.downcase }.index(dow.downcase)
    end

    if dow.is_a? Fixnum
      while date.wday != dow
        date += 1
      end
    end
    date
  end

  def ok_to_add(date, index, prior, breaks)
    ok = true
    breaks.each do |i|
      if i['from'] && i['to']
        if (i['from'] <= date) && (i['to'] >= date)
          ok = false
        end
      end

      if i['at_index'] && i['for_days'] && prior
        if i['at_index'] == index
          ok = (date > (prior + i['for_days']))
        end
      end
    end
    ok
  end

  def schedule(parameters, to_produce)
    dates = []

    if parameters['start']
      current = parameters['start']
      prior = nil

      breaks = parameters['breaks'] || []

      index = 0
      while dates.length < to_produce
        interval = parameters['interval'].shift

        case interval.class.to_s
          when 'String'
            current = skip_to_dow(current, interval)

            if ok_to_add(current, index, prior, breaks)
              dates << current
              prior = current
              index += 1
            end

            current += 1
          when 'Fixnum'
            if ok_to_add(current, index, prior, breaks)
              dates << current
              prior = current
              index += 1
            end

            current += interval
        end

        parameters['interval'] << interval
      end
    end

    dates
  end
end