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# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# This cop identifies places where `reverse.first(n)` and `reverse.first`
# can be replaced by `last(n).reverse` and `last`.
#
# @example
#
# # bad
# array.reverse.first(5)
# array.reverse.first
#
# # good
# array.last(5).reverse
# array.last
#
class ReverseFirst < Cop
include RangeHelp
MSG = 'Use `%<good_method>s` instead of `%<bad_method>s`.'
def_node_matcher :reverse_first_candidate?, <<~PATTERN
(send $(send _ :reverse) :first (int _)?)
PATTERN
def on_send(node)
reverse_first_candidate?(node) do |receiver|
range = correction_range(receiver, node)
message = build_message(node)
add_offense(node, location: range, message: message)
end
end
def autocorrect(node)
reverse_first_candidate?(node) do |receiver|
range = correction_range(receiver, node)
replacement = build_good_method(node)
lambda do |corrector|
corrector.replace(range, replacement)
end
end
end
private
def correction_range(receiver, node)
range_between(receiver.loc.selector.begin_pos, node.loc.expression.end_pos)
end
def build_message(node)
good_method = build_good_method(node)
bad_method = build_bad_method(node)
format(MSG, good_method: good_method, bad_method: bad_method)
end
def build_good_method(node)
if node.arguments?
"last(#{node.arguments.first.source}).reverse"
else
'last'
end
end
def build_bad_method(node)
if node.arguments?
"reverse.first(#{node.arguments.first.source})"
else
'reverse.first'
end
end
end
end
end
end
|
