class RuboCop::Cop::Style::TrailingUnderscoreVariable

def allow_named_underscore_variables
  @allow_named_underscore_variables ||=
    cop_config['AllowNamedUnderscoreVariables']
end

def autocorrect(node)
  range = unneeded_range(node)
  lambda do |corrector|
    corrector.remove(range) if range
  end
end

def find_first_offense(variables)
  first_offense = find_first_possible_offense(variables.reverse)
  return unless first_offense
  return if splat_variable_before?(first_offense, variables)
  first_offense
end

def find_first_possible_offense(variables)
  variables.reduce(nil) do |offense, variable|
    var, = *variable
    var, = *var
    if allow_named_underscore_variables
      break offense unless var == :_
    else
      break offense unless var.to_s.start_with?(UNDERSCORE)
    end
    variable
  end
end

def on_masgn(node)
  range = unneeded_range(node)
  return unless range
  good_code = node.source
  offset = range.begin_pos - node.source_range.begin_pos
  good_code[offset, range.size] = ''
  add_offense(node, range, format(MSG, good_code))
end

def reverse_index(collection, item)
  collection.size - 1 - collection.reverse.index(item)
end

def splat_variable_before?(first_offense, variables)
  # Account for cases like `_, *rest, _`, where we would otherwise get
  # the index of the first underscore.
  first_offense_index = reverse_index(variables, first_offense)
  variables[0...first_offense_index].any?(&:splat_type?)
end

def unneeded_range(node)
  left, right = *node
  variables = *left
  first_offense = find_first_offense(variables)
  return unless first_offense
  end_position =
    if first_offense.source_range == variables.first.source_range
      right.source_range.begin_pos
    else
      node.loc.operator.begin_pos
    end
  range = range_between(first_offense.source_range.begin_pos,
                        end_position)
  range_with_surrounding_space(range, :right)
end