multikey_hash.rb

multikey_hash.rb

class MultikeyHash
  include Enumerable

  def initialize(initial_values = nil)
    @outer_hash = {}

    @inner_hash = {}

    @next_inner_key = 1

    if initial_values
      initial_values.each do |keys, value|
        if keys.is_a?(Array) && !keys.empty?
          keys.each do |key|
            self[key] = value
          end
        else
          self[keys] = value
        end
      end
    end
  end

  def [](outer_key)
    inner_key = @outer_hash[outer_key]

    if inner_key.nil?
      nil
    else
      @inner_hash[inner_key]
    end
  end

  def []=(outer_key, new_value)
    inner_key = @inner_hash.select { |_, existing_value| existing_value == new_value }.map { |key, _| key }.first

    if inner_key
      @outer_hash[outer_key] = inner_key
    else
      @outer_hash[outer_key] = @next_inner_key

      @inner_hash[@next_inner_key] = new_value

      @next_inner_key += 1
    end
  end

  def each(&block)
    @outer_hash.group_by { |_, inner_key| inner_key }.inject({}) { |acc, e| acc[e.last.map { |i| i.first }] = @inner_hash[e.first]; acc }.each do |key, value|
      block.call(key, value)
    end
  end

  def inspect
    "{#{self.map { |keys, value| "#{keys.inspect}=>#{value.inspect}" }.join(', ')}}"
  end

  def to_s
    inspect
  end
end