availability_checker.rb

class AvailabilityChecker
  def initialize(reservation)
    @reservation = reservation
  end

  def available?
    if @reservation.new_record?
      new_record_available?
    elsif @reservation.unit_id_changed?
      update_unit_available?
    elsif @reservation.arrive_changed? or @reservation.depart_changed?
      update_record_available?
    else
      true
    end
  end

  def new_record_available?
    dates_available?(@reservation.arrive...@reservation.depart, @reservation.unit_id)
  end

  def update_unit_available?
    dates_available?(@reservation.arrive...@reservation.depart, @reservation.unit_id)
  end

  def update_record_available?
    new_dates = @reservation.arrive...@reservation.depart
    old_dates = @reservation.arrive_was...@reservation.depart_was

    check_range = new_dates.to_a - old_dates.to_a

    dates_available?(check_range, @reservation.unit_id)
  end

  def dates_available?(date_range, unit_id)
    capacity = Unit.find(unit_id).capacity

    date_range.to_a.all? do |date|
      pitch_count(date, unit_id) < capacity
    end
  end

  def pitch_count(date, unit_id)
    Pitch.find_or_create_by(date: date, unit_id: unit_id).count
  end
end