lib/rubocop/cop/layout/case_indentation.rb


# frozen_string_literal: true

module RuboCop
  module Cop
    module Layout
      # This cop checks how the *when*s of a *case* expression
      # are indented in relation to its *case* or *end* keyword.
      #
      # It will register a separate offense for each misaligned *when*.
      #
      # @example
      #   # If Layout/EndAlignment is set to keyword style (default)
      #   # *case* and *end* should always be aligned to same depth,
      #   # and therefore *when* should always be aligned to both -
      #   # regardless of configuration.
      #
      #   # bad for all styles
      #   case n
      #     when 0
      #       x * 2
      #     else
      #       y / 3
      #   end
      #
      #   # good for all styles
      #   case n
      #   when 0
      #     x * 2
      #   else
      #     y / 3
      #   end
      #
      # @example EnforcedStyle: case (default)
      #   # if EndAlignment is set to other style such as
      #   # start_of_line (as shown below), then *when* alignment
      #   # configuration does have an effect.
      #
      #   # bad
      #   a = case n
      #   when 0
      #     x * 2
      #   else
      #     y / 3
      #   end
      #
      #   # good
      #   a = case n
      #       when 0
      #         x * 2
      #       else
      #         y / 3
      #   end
      #
      # @example EnforcedStyle: end
      #   # bad
      #   a = case n
      #       when 0
      #         x * 2
      #       else
      #         y / 3
      #   end
      #
      #   # good
      #   a = case n
      #   when 0
      #     x * 2
      #   else
      #     y / 3
      #   end
      class CaseIndentation < Cop
        include Alignment
        include ConfigurableEnforcedStyle
        include RangeHelp

        MSG = 'Indent `when` %<depth>s `%<base>s`.'.freeze

        def on_case(case_node)
          return if case_node.single_line?

          case_node.each_when do |when_node|
            check_when(when_node)
          end
        end

        def autocorrect(node)
          whitespace = whitespace_range(node)

          return false unless whitespace.source.strip.empty?

          lambda do |corrector|
            corrector.replace(whitespace, replacement(node))
          end
        end

        private

        def check_when(when_node)
          when_column = when_node.loc.keyword.column
          base_column = base_column(when_node.parent, style)

          if when_column == base_column + indentation_width
            correct_style_detected
          else
            incorrect_style(when_node)
          end
        end

        def indent_one_step?
          cop_config['IndentOneStep']
        end

        def indentation_width
          indent_one_step? ? configured_indentation_width : 0
        end

        def incorrect_style(when_node)
          when_column = when_node.loc.keyword.column
          base_column = base_column(when_node.parent, alternative_style)

          add_offense(when_node, location: :keyword, message: message(style)) do
            if when_column == base_column
              opposite_style_detected
            else
              unrecognized_style_detected
            end
          end
        end

        def message(base)
          depth = indent_one_step? ? 'one step more than' : 'as deep as'

          format(MSG, depth: depth, base: base)
        end

        def base_column(case_node, base)
          case base
          when :case then case_node.location.keyword.column
          when :end  then case_node.location.end.column
          end
        end

        def whitespace_range(node)
          when_column = node.location.keyword.column
          begin_pos = node.loc.keyword.begin_pos

          range_between(begin_pos - when_column, begin_pos)
        end

        def replacement(node)
          case_node = node.each_ancestor(:case).first
          base_type = cop_config[style_parameter_name] == 'end' ? :end : :case

          column = base_column(case_node, base_type)
          column += indentation_width

          ' ' * column
        end
      end
    end
  end
end