# frozen_string_literal: true

module RuboCop
  module Cop
    module UsageData
      # Allows counts only for selected tables' foreign keys for `distinct_count` method.
      #
      # Because distinct_counts over large tables' foreign keys will take a long time
      #
      # @example
      #
      #   # bad because pipeline_id points to a large table
      #   distinct_count(Ci::Build, :commit_id)
      #
      class DistinctCountByLargeForeignKey < RuboCop::Cop::Cop
        MSG = 'Avoid doing `%s` on foreign keys for large tables having above 100 million rows.'.freeze

        def_node_matcher :distinct_count?, <<-PATTERN
          (send _ $:distinct_count $...)
        PATTERN

        def on_send(node)
          distinct_count?(node) do |method_name, method_arguments|
            next unless method_arguments && method_arguments.length >= 2
            next if allowed_foreign_key?(method_arguments[1])

            add_offense(node, location: :selector, message: format(MSG, method_name))
          end
        end

        private

        def allowed_foreign_key?(key)
          [:sym, :str].include?(key.type) && allowed_foreign_keys.include?(key.value.to_sym)
        end

        def allowed_foreign_keys
          cop_config['AllowedForeignKeys'] || []
        end
      end
    end
  end
end
