module Eco
  module Data
    class Mapper

      # it expects [[v1a, v1b], [v2a, v2b] ...]
      def initialize (array_of_arrays = [], internal: :last)
        @source = array_of_arrays

        if @source
          # internal should be always last in @source
          @source = @source.map { |a| a.reverse } unless internal == :last

          # first declarations take priority
          @by_external = @source.reverse.to_h
          @by_internal = @source.reverse.map do |pair|
            pair.reverse
          end.to_h
        end
      end

      def list(type = :internal)
        return [] if !@source
        @source.map do |pair|
          type == :internal ? pair.last : pair.first
        end.uniq
      end

      def internal?(value)
        return true if !@source
        @by_internal.key?(value)
      end

      def external?(value)
        return true if !@source
        @by_external.key?(value)
      end

      def include?(value)
        return true if !@source
        internal?(value) || external?(value)
      end

      def to_internal(value)
        return value if !@source
        @by_external[value]
      end

      def to_external(value)
        return value if !@source
        @by_internal[value]
      end

    end
  end
end