# frozen_string_literal: true

module RuboCop
  module Cop
    module Rails
      # Prefer the use of uniq (or distinct), before pluck instead of after.
      #
      # The use of uniq before pluck is preferred because it executes within
      # the database.
      #
      # @example
      #   # bad
      #   Model.pluck(:id).uniq
      #
      #   # good
      #   Model.uniq.pluck(:id)
      #
      # This cop has two different enforcement modes. When the EnforcedMode
      # is conservative (the default) then only calls to pluck on a constant
      # (i.e. a model class) before uniq are added as offenses.
      #
      # When the EnforcedMode is aggressive then all calls to pluck before
      # uniq are added as offenses. This may lead to false positives as the cop
      # cannot distinguish between calls to pluck on an ActiveRecord::Relation
      # vs a call to pluck on an ActiveRecord::Associations::CollectionProxy.
      #
      # @example
      #   # this will return a Relation that pluck is called on
      #   Model.where(...).pluck(:id).uniq
      #
      #   # an association on an instance will return a CollectionProxy
      #   instance.assoc.pluck(:id).uniq
      #
      # Autocorrect is disabled by default for this cop since it may generate
      # false positives.
      #
      class UniqBeforePluck < RuboCop::Cop::Cop
        MSG = 'Use `%s` before `pluck`.'.freeze
        NEWLINE = "\n".freeze
        PATTERN = '[!^block (send (send %s :pluck ...) ${:uniq :distinct} ...)]'
                  .freeze

        def_node_matcher :conservative_node_match,
                         format(PATTERN, 'const')

        def_node_matcher :aggressive_node_match,
                         format(PATTERN, '_')

        def on_send(node)
          method = if mode == :conservative
                     conservative_node_match(node)
                   else
                     aggressive_node_match(node)
                   end

          add_offense(node, :selector, format(MSG, method)) if method
        end

        def autocorrect(node)
          send_pluck, method, *_args = *node
          lambda do |corrector|
            corrector.remove(dot_method_with_whitespace(method, node))
            corrector.insert_before(send_pluck.loc.dot.begin, ".#{method}")
          end
        end

        private

        def mode
          @mode ||= cop_config['EnforcedMode'].to_sym
        end

        def dot_method_with_whitespace(method, node)
          range_between(dot_method_begin_pos(method, node),
                        node.loc.selector.end_pos)
        end

        def dot_method_begin_pos(method, node)
          lines = node.source.split(NEWLINE)

          if lines.last.strip == ".#{method}"
            node.source.rindex(NEWLINE)
          else
            node.loc.dot.begin_pos
          end
        end
      end
    end
  end
end