# DSL step for Magnetic::Normalizer.
# Translates `:input` and `:output` into VariableMapping taskWrap extensions.
def self.normalizer_step_for_input_output(ctx, *)
  options, io_config = Magnetic::Options.normalize( ctx[:options], [:input, :output] )

  return if io_config.empty?

  ctx[:options] = options # without :input and :output
  ctx[:options] = options.merge(Trailblazer::Activity::TaskWrap::VariableMapping(io_config) => true)
end


# @private
def self.filter_for(filter)
  if filter.is_a?(::Array) || filter.is_a?(::Hash)
    TaskWrap::DSL.filter_from_dsl(filter)
  else
    filter
  end
end

# Returns an Extension instance to be thrown into the `step` DSL arguments.
def self.VariableMapping(input:, output:)
  input = Input.new(
    Input::Scoped.new(
      Trailblazer::Option::KW( filter_for(input) )
    )
  )

  output = Output.new(
    Output::Unscoped.new(
      Trailblazer::Option::KW( filter_for(output) )
    )
  )

  VariableMapping.extension_for(input, output)
end

module Input
  class Scoped
    def initialize(filter)
      @filter = filter
    end

    def call(original_ctx, circuit_options)
      Trailblazer::Context( # TODO: make this interchangeable so we can work on faster contexts?
        @filter.(original_ctx, **circuit_options)
      )
    end
  end
end

module DSL
  # The returned filter compiles a new hash for Scoped/Unscoped that only contains
  # the desired i/o variables.
  def self.filter_from_dsl(map)
    hsh = DSL.hash_for(map)

    ->(incoming_ctx, kwargs) { Hash[hsh.collect { |from_name, to_name| [to_name, incoming_ctx[from_name]] }] }
  end

  def self.hash_for(ary)
    return ary if ary.instance_of?(::Hash)
    Hash[ary.collect { |name| [name, name] }]
  end
end

module Output
  # Merge the resulting {@filter.()} hash back into the original ctx.
  # DISCUSS: do we need the original_ctx as a filter argument?
  class Unscoped
    def initialize(filter)
      @filter = filter
    end

    def call(original_ctx, new_ctx, **circuit_options)
      original_ctx.merge(
        @filter.(new_ctx, **circuit_options)
      )
    end
  end
end