Contents

class Measured::ConversionTableBuilder
  attr_reader :units

  def initialize(units)
    @units = units
  end

  def to_h
    table = {}

    units.map{|u| u.name}.each do |to_unit|
      to_table = {to_unit => Rational(1, 1)}

      table.each do |from_unit, from_table|
        conversion = find_conversion(to: from_unit, from: to_unit)
        to_table[from_unit] = conversion
        from_table[to_unit] = 1 / conversion
      end

      table[to_unit] = to_table
    end

    table
  end

  private

  def find_conversion(to:, from:)
    conversion = find_direct_conversion_cached(to: to, from: from) || find_tree_traversal_conversion(to: to, from: from)

    raise Measured::UnitError, "Cannot find conversion path from #{ from } to #{ to }." unless conversion

    conversion
  end

  def find_direct_conversion_cached(to:, from:)
    @cache ||= {}
    @cache[to] ||= {}

    if @cache[to].key?(from)
       @cache[to][from]
    else
      @cache[to][from] = find_direct_conversion(to: to, from: from)
    end
  end

  def find_direct_conversion(to:, from:)
    units.each do |unit|
      return unit.conversion_amount if unit.name == from && unit.conversion_unit == to
      return unit.inverse_conversion_amount if unit.name == to && unit.conversion_unit == from
    end

    nil
  end

  def find_tree_traversal_conversion(to:, from:)
    traverse(from: from, to: to, units_remaining: units.map(&:name), amount: 1)
  end

  def traverse(from:, to:, units_remaining:, amount:)
    units_remaining = units_remaining - [from]

    units_remaining.each do |name|
      conversion = find_direct_conversion_cached(from: from, to: name)

      if conversion
        new_amount = amount * conversion
        if name == to
          return new_amount
        else
          result = traverse(from: name, to: to, units_remaining: units_remaining, amount: new_amount)
          return result if result
        end
      end
    end

    nil
  end

end

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
measured-2.4.0	lib/measured/conversion_table_builder.rb