allocate.rb

# from https://github.com/drKreso/guerrilla_patch
class Allocate
  attr_accessor :amount
  attr_accessor :ratios

  def self.evenly(amount, number_of_slices)
    Allocate.new.tap do |a|
      a.amount = amount
      a.ratios = (1..number_of_slices).map { 1.to_d/number_of_slices }
    end.divided
  end

  def initialize(amount = 0 , ratios = [])
    @amount = amount
    @ratios = ratios
  end

  def divided
    divided_ratios = @ratios.map { |ratio| ratio.to_d/ array_sum(ratios).to_d }
    rates = divided_ratios.map { |ratio| ((@amount * ratio).round(2)) }
    compensate_last_slice(rates)
  end

  def compensate_last_slice(rates)
    rates.tap do |rates|
      max_rate = rates.max.abs
      rates[-1] = (rates[-1] + (amount - array_sum(rates))).round(2)
      if  rates[-1].abs > (2 * max_rate.abs )
        raise "Number is too small to be allocated on that number of slices(#@amount on #{@ratios.size} slices)."
      end
    end
  end

  def array_sum(array)
    array.reduce(0, :+)
  end
end