Ruby Wei to eth converter

wei.rb

# Example of usage: 
# result = WeiConverter.new(1890000000000000000).call
# Result contains 1.89

class WeiConverter

  UNITS = {
    wei:        1,
    kwei:       1000,
    ada:        1000,
    femtoether: 1000,
    mwei:       1000000,
    babbage:    1000000,
    picoether:  1000000,
    gwei:       1000000000,
    shannon:    1000000000,
    nanoether:  1000000000,
    nano:       1000000000,
    szabo:      1000000000000,
    microether: 1000000000000,
    micro:      1000000000000,
    finney:     1000000000000000,
    milliether: 1000000000000000,
    milli:      1000000000000000,
    ether:      1000000000000000000,
    eth:        1000000000000000000,
    kether:     1000000000000000000000,
    grand:      1000000000000000000000,
    einstein:   1000000000000000000000,
    mether:     1000000000000000000000000,
    gether:     1000000000000000000000000000,
    tether:     1000000000000000000000000000000
  }

  def initialize(amount)
    @amount = amount
  end

  def call(unit: "ether")
    return nil if @amount.nil?
    unit = UNITS[unit.to_sym]
    (BigDecimal.new(@amount, 16) / BigDecimal.new(unit, 16)).to_s rescue nil
  end
end