# frozen_string_literal: true module RuboCop module Cop module Style # This cop is used to identify usages of `shuffle.first`, # `shuffle.last`, and `shuffle[]` and change them to use # `sample` instead. # # @example # # bad # [1, 2, 3].shuffle.first # [1, 2, 3].shuffle.first(2) # [1, 2, 3].shuffle.last # [2, 1, 3].shuffle.at(0) # [2, 1, 3].shuffle.slice(0) # [1, 2, 3].shuffle[2] # [1, 2, 3].shuffle[0, 2] # sample(2) will do the same # [1, 2, 3].shuffle[0..2] # sample(3) will do the same # [1, 2, 3].shuffle(random: Random.new).first # # # good # [1, 2, 3].shuffle # [1, 2, 3].sample # [1, 2, 3].sample(3) # [1, 2, 3].shuffle[1, 3] # sample(3) might return a longer Array # [1, 2, 3].shuffle[1..3] # sample(3) might return a longer Array # [1, 2, 3].shuffle[foo, bar] # [1, 2, 3].shuffle(random: Random.new) class Sample < Base extend AutoCorrector MSG = 'Use `%s` instead of `%s`.' RESTRICT_ON_SEND = %i[first last [] at slice].freeze def_node_matcher :sample_candidate?, <<~PATTERN (send $(send _ :shuffle $...) ${:#{RESTRICT_ON_SEND.join(' :')}} $...) PATTERN def on_send(node) sample_candidate?(node) do |shuffle_node, shuffle_arg, method, method_args| return unless offensive?(method, method_args) range = source_range(shuffle_node, node) message = message(shuffle_arg, method, method_args, range) add_offense(range, message: message) do |corrector| corrector.replace( source_range(shuffle_node, node), correction(shuffle_arg, method, method_args) ) end end end private def offensive?(method, method_args) case method when :first, :last true when :[], :at, :slice sample_size(method_args) != :unknown else false end end def sample_size(method_args) case method_args.size when 1 sample_size_for_one_arg(method_args.first) when 2 sample_size_for_two_args(*method_args) end end def sample_size_for_one_arg(arg) if arg.range_type? range_size(arg) elsif arg.int_type? [0, -1].include?(arg.to_a.first) ? nil : :unknown else :unknown end end def sample_size_for_two_args(first, second) return :unknown unless first.int_type? && first.to_a.first.zero? second.int_type? ? second.to_a.first : :unknown end def range_size(range_node) # rubocop:todo Metrics/CyclomaticComplexity vals = range_node.to_a return :unknown unless vals.all?(&:int_type?) low, high = vals.map { |val| val.children[0] } return :unknown unless low.zero? && high >= 0 case range_node.type when :erange (low...high).size when :irange (low..high).size end end def source_range(shuffle_node, node) Parser::Source::Range.new(shuffle_node.source_range.source_buffer, shuffle_node.loc.selector.begin_pos, node.source_range.end_pos) end def message(shuffle_arg, method, method_args, range) format(MSG, correct: correction(shuffle_arg, method, method_args), incorrect: range.source) end def correction(shuffle_arg, method, method_args) shuffle_arg = extract_source(shuffle_arg) sample_arg = sample_arg(method, method_args) args = [sample_arg, shuffle_arg].compact.join(', ') args.empty? ? 'sample' : "sample(#{args})" end def sample_arg(method, method_args) case method when :first, :last extract_source(method_args) when :[], :slice sample_size(method_args) end end def extract_source(args) args.empty? ? nil : args.first.source end end end end end