# frozen_string_literal: true

module RuboCop
  module Cop
    module Lint
      # This cop checks for a rescued exception that get shadowed by a
      # less specific exception being rescued before a more specific
      # exception is rescued.
      #
      # @example
      #
      #   # bad
      #
      #   begin
      #     something
      #   rescue Exception
      #     handle_exception
      #   rescue StandardError
      #     handle_standard_error
      #   end
      #
      #   # good
      #
      #   begin
      #     something
      #   rescue StandardError
      #     handle_standard_error
      #   rescue Exception
      #     handle_exception
      #   end
      #
      #   # good, however depending on runtime environment.
      #   #
      #   # This is a special case for system call errors.
      #   # System dependent error code depends on runtime environment.
      #   # For example, whether `Errno::EAGAIN` and `Errno::EWOULDBLOCK` are
      #   # the same error code or different error code depends on environment.
      #   # This good case is for `Errno::EAGAIN` and `Errno::EWOULDBLOCK` with
      #   # the same error code.
      #   begin
      #     something
      #   rescue Errno::EAGAIN, Errno::EWOULDBLOCK
      #     handle_standard_error
      #   end
      #
      class ShadowedException < Cop
        include RescueNode
        include RangeHelp

        MSG = 'Do not shadow rescued Exceptions.'.freeze

        def on_rescue(node)
          return if rescue_modifier?(node)

          _body, *rescues, _else = *node
          rescued_groups = rescued_groups_for(rescues)

          rescue_group_rescues_multiple_levels = rescued_groups.any? do |group|
            contains_multiple_levels_of_exceptions?(group)
          end

          return if !rescue_group_rescues_multiple_levels &&
                    sorted?(rescued_groups)

          add_offense(node, location: offense_range(rescues))
        end

        private

        def offense_range(rescues)
          shadowing_rescue = find_shadowing_rescue(rescues)
          expression = shadowing_rescue.loc.expression
          range_between(expression.begin_pos, expression.end_pos)
        end

        def rescued_groups_for(rescues)
          rescues.map do |group|
            rescue_group, = *group
            evaluate_exceptions(rescue_group)
          end
        end

        def contains_multiple_levels_of_exceptions?(group)
          # Always treat `Exception` as the highest level exception.
          return true if group.size > 1 && group.include?(Exception)

          group.combination(2).any? do |a, b|
            compare_exceptions(a, b)
          end
        end

        def compare_exceptions(exception, other_exception)
          if system_call_err?(exception) && system_call_err?(other_exception)
            # This condition logic is for special case.
            # System dependent error code depends on runtime environment.
            # For example, whether `Errno::EAGAIN` and `Errno::EWOULDBLOCK` are
            # the same error code or different error code depends on runtime
            # environment. This checks the error code for that.
            exception.const_get(:Errno) != other_exception.const_get(:Errno) &&
              exception <=> other_exception
          else
            exception && other_exception && exception <=> other_exception
          end
        end

        def system_call_err?(error)
          error && error.ancestors[1] == SystemCallError
        end

        def silence_warnings
          # Replaces Kernel::silence_warnings since it hides any warnings,
          # including the RuboCop ones
          old_verbose = $VERBOSE
          $VERBOSE = nil
          yield
        ensure
          $VERBOSE = old_verbose
        end

        def evaluate_exceptions(rescue_group)
          if rescue_group
            rescued_exceptions = rescued_exceptions(rescue_group)
            rescued_exceptions.each_with_object([]) do |exception, converted|
              begin
                silence_warnings do
                  # Avoid printing deprecation warnings about constants
                  converted << Kernel.const_get(exception)
                end
              rescue NameError
                converted << nil
              end
            end
          else
            # treat an empty `rescue` as `rescue StandardError`
            [StandardError]
          end
        end

        def sorted?(rescued_groups)
          rescued_groups.each_cons(2).all? do |x, y|
            if x.include?(Exception)
              false
            elsif y.include?(Exception)
              true
            elsif x.none? || y.none?
              # consider sorted if a group is empty or only contains
              # `nil`s
              true
            else
              (x <=> y || 0) <= 0
            end
          end
        end

        # @param [RuboCop::AST::Node] rescue_group is a node of array_type
        def rescued_exceptions(rescue_group)
          klasses = *rescue_group
          klasses.map do |klass|
            next unless klass.const_type?

            klass.source
          end.compact
        end

        def find_shadowing_rescue(rescues)
          rescued_groups = rescued_groups_for(rescues)
          rescued_groups.zip(rescues).each do |group, res|
            return res if contains_multiple_levels_of_exceptions?(group)
          end

          rescued_groups.each_cons(2).with_index do |group_pair, i|
            return rescues[i] unless sorted?(group_pair)
          end
        end
      end
    end
  end
end