2_30.rb

class RevealingReferences
  attr_reader :wheels
  def initialize(data)
    @wheels = wheelify(data)
  end

  # first - iterate over the array
  def diameters
    wheels.collect {|wheel| diameter(wheel)}
  end

  # second - calculate diameter of ONE wheel
  def diameter(wheel)
    wheel.rim + (wheel.tire * 2)
  end

  # ... now everyone can send rim/tire to wheel
  Wheel = Struct.new(:rim, :tire)
  def wheelify(data)
    data.collect {|cell|
      Wheel.new(cell[0], cell[1])}
  end
end

@data = [[622, 20], [622, 23], [559, 30], [559, 40]]
puts "RevealingReferences diameters = #{RevealingReferences.new(@data).diameters}"

# gear_inches does too much
class Gear
  attr_reader :chainring, :cog, :rim, :tire
  def initialize(chainring, cog, rim, tire)
    @chainring = chainring
    @cog       = cog
    @rim       = rim
    @tire      = tire
  end

  def ratio
    chainring / cog.to_f
  end

  def gear_inches
      # tire goes around rim twice for diameter
    ratio * (rim + (tire * 2))
  end
end

puts "1st Gear gear_inches = #{Gear.new(54,11,622,20).gear_inches}"


# diameter method doesn't belong in Gear, notice it
# depends on rim and tire only
class Gear
  attr_reader :chainring, :cog, :rim, :tire
  def initialize(chainring, cog, rim, tire)
    @chainring = chainring
    @cog       = cog
    @rim       = rim
    @tire      = tire
  end

  def ratio
    chainring / cog.to_f
  end

  def gear_inches
    ratio * diameter
  end

  def diameter
    rim + (tire * 2)
  end
end

puts "2nd Gear gear_inches = #{Gear.new(54,11,622,20).gear_inches}"