Magic signum

signum.rb

  def self.percent_by_prices(previous_price, current_price)
    return 0 if previous_price.nil? || previous_price.zero?
    res = (((current_price.to_f/previous_price.to_f) - 1) * 100).round
    res = self.signum(current_price - previous_price) if res.zero?
    res
  end

  def self.signum(number)
    case
      when number > 0
        1
      when number < 0
        -1
      when number == 0
        0
    end
  end

# Specs on signum functionality

  context "go to 1" do

    it 'should return 1 percent if 0 < result < 1 ' do
      described_class.percent_by_prices(1000, 1001).should == 1
    end

    it 'should return -1 percent if -1 < result < 0 ' do
      described_class.percent_by_prices(1000, 999).should == -1
    end

  end