# encoding: utf-8

module RuboCop
  module Cop
    module Style
      # This cop checks whether the multiline do end blocks have a newline
      # after the start of the block. Additionally, it checks whether the block
      # arguments, if any, are on the same line as the start of the block.
      #
      # @example
      #   # bad
      #   blah do |i| foo(i)
      #     bar(i)
      #   end
      #
      #   # bad
      #   blah do
      #     |i| foo(i)
      #     bar(i)
      #   end
      #
      #   # good
      #   blah do |i|
      #     foo(i)
      #     bar(i)
      #   end
      #
      #   # bad
      #   blah { |i| foo(i)
      #     bar(i)
      #   }
      #
      #   # good
      #   blah { |i|
      #     foo(i)
      #     bar(i)
      #   }
      class MultilineBlockLayout < Cop
        MSG = 'Block body expression is on the same line as the block start.'
        ARG_MSG = 'Block argument expression is not on the same line as the ' \
                  'block start.'

        def on_block(node)
          end_loc = node.loc.end
          do_loc = node.loc.begin # Actually it's either do or {.
          return if do_loc.line == end_loc.line # One-liner, no newline needed.

          # A block node has three children: the block start,
          # the arguments, and the expression. We care if the block start
          # with arguments and the expression start on the same line.
          _block_start, args, last_expression = node.children

          unless args.children.empty?
            line = args.loc.end.nil? ? args.loc.line : args.loc.end.line
            if do_loc.line != line
              add_offense_for_expression(node, args, ARG_MSG)
            end
          end

          return unless last_expression
          expression_loc = last_expression.loc
          return unless do_loc.line == expression_loc.line
          add_offense_for_expression(node, last_expression, MSG)
        end

        def add_offense_for_expression(node, expr, msg)
          expression = expr.loc.expression
          range = Parser::Source::Range.new(expression.source_buffer,
                                            expression.begin_pos,
                                            expression.end_pos)

          add_offense(node, range, msg)
        end

        def autocorrect(node)
          lambda do |corrector|
            _method, args, block_body = *node
            unless args.children.empty? ||
                   args.loc.end.line == node.loc.begin.line
              autocorrect_arguments(corrector, node, args, block_body)
              expr_before_body = args.loc.expression.end
            end

            return unless block_body

            expr_before_body ||= node.loc.begin
            if expr_before_body.line == block_body.loc.line
              autocorrect_body(corrector, node, block_body)
            end
          end
        end

        def autocorrect_arguments(corrector, node, args, block_body)
          end_pos = if block_body
                      block_body.loc.expression.begin_pos
                    else
                      node.loc.end.begin.begin_pos - 1
                    end
          range = Parser::Source::Range.new(args.loc.expression.source_buffer,
                                            node.loc.begin.end.begin_pos,
                                            end_pos)
          corrector.replace(range, " |#{block_arg_string(args)}|")
        end

        def autocorrect_body(corrector, node, block_body)
          first_node = if block_body.type == :begin
                         block_body.children.first
                       else
                         block_body
                       end

          block_start_col = node.loc.expression.column

          corrector.insert_before(first_node.loc.expression,
                                  "\n  #{' ' * block_start_col}")
        end

        def block_arg_string(args)
          args.children.map { |a| a.loc.expression.source }.join(', ')
        end
      end
    end
  end
end