class RuboCop::Cop::Performance::FlatMap

1, 2, 3, 4].collect { |e| [e, e

}.flatten
[1, 2, 3, 4].map { |e| [e, e] }.flatten
[1, 2, 3, 4].flat_map { |e| [e, e] }
# good
[1, 2, 3, 4].collect { |e| [e, e] }.flatten(1)
[1, 2, 3, 4].map { |e| [e, e] }.flatten(1)
# bad
@example
change them to use ‘flat_map { … }` instead.
Identifies usages of `map { … }.flatten` and

def autocorrect(corrector, node) 

def autocorrect(corrector, node)
  map_node, _first_method, _flatten, params = flat_map_candidate?(node)
  flatten_level, = *params.first
  return unless flatten_level
  map_send_node = map_node.block_type? ? map_node.send_node : map_node
  range = range_between(map_node.source_range.end_pos, node.source_range.end_pos)
  corrector.remove(range)
  corrector.replace(map_send_node.loc.selector, 'flat_map')
end

def offense_for_levels(node, map_node, first_method, flatten) 

def offense_for_levels(node, map_node, first_method, flatten)
  message = MSG + FLATTEN_MULTIPLE_LEVELS
  register_offense(node, map_node, first_method, flatten, message)
end

def offense_for_method(node, map_node, first_method, flatten) 

def offense_for_method(node, map_node, first_method, flatten)
  register_offense(node, map_node, first_method, flatten, MSG)
end

def on_send(node) 

def on_send(node)
  flat_map_candidate?(node) do |map_node, first_method, flatten, params|
    flatten_level, = *params.first
    if cop_config['EnabledForFlattenWithoutParams'] && !flatten_level
      offense_for_levels(node, map_node, first_method, flatten)
    elsif flatten_level == 1
      offense_for_method(node, map_node, first_method, flatten)
    end
  end
end

def register_offense(node, map_node, first_method, flatten, message) 

def register_offense(node, map_node, first_method, flatten, message)
  map_send_node = map_node.block_type? ? map_node.send_node : map_node
  range = range_between(map_send_node.loc.selector.begin_pos, node.source_range.end_pos)
  message = format(message, method: first_method, flatten: flatten)
  add_offense(range, message: message) do |corrector|
    autocorrect(corrector, node)
  end
end