class RuboCop::Cop::Performance::UnneededSort

[].max_by(&:length)
[].min
# good<br><br>[].sort_by(&:length).last<br>.sort.first
# bad
@example
only the first or last element.
This cop is used to identify instances of sorting and then taking

def accessor_start(node)

(e.g. `.first`) or doesn't (e.g. `[0]`)
This gets the start of the accessor whether it has a dot 
def accessor_start(node)
  if node.loc.dot
    node.loc.dot.begin_pos
  else
    node.loc.selector.begin_pos
  end
end

def arg_node(node) 

def arg_node(node)
  node.arguments.first
end

def arg_value(node) 

def arg_value(node)
  arg_node(node).nil? ? nil : arg_node(node).node_parts.first
end

def autocorrect(node) 

def autocorrect(node)
  sort_node, sorter, accessor = unneeded_sort?(node)
  lambda do |corrector|
    # Remove accessor, e.g. `first` or `[-1]`.
    corrector.remove(
      range_between(
        accessor_start(node),
        node.loc.expression.end_pos
      )
    )
    # Replace "sort" or "sort_by" with the appropriate min/max method.
    corrector.replace(
      sort_node.loc.selector,
      suggestion(sorter, accessor, arg_value(node))
    )
  end
end

def base(accessor, arg) 

def base(accessor, arg)
  if accessor == :first || (arg && arg.zero?)
    'min'
  elsif accessor == :last || arg == -1
    'max'
  end
end

def message(node, sorter, accessor) 

def message(node, sorter, accessor)
  accessor_source = range_between(
    node.loc.selector.begin_pos,
    node.loc.expression.end_pos
  ).source
  format(MSG,
         suggestion: suggestion(sorter,
                                accessor,
                                arg_value(node)),
         sorter: sorter,
         accessor_source: accessor_source)
end

def on_send(node) 

def on_send(node)
  unneeded_sort?(node) do |sort_node, sorter, accessor|
    range = range_between(
      sort_node.loc.selector.begin_pos,
      node.loc.expression.end_pos
    )
    add_offense(node,
                location: range,
                message: message(node,
                                 sorter,
                                 accessor))
  end
end

def suffix(sorter) 

def suffix(sorter)
  if sorter == :sort
    ''
  elsif sorter == :sort_by
    '_by'
  end
end

def suggestion(sorter, accessor, arg) 

def suggestion(sorter, accessor, arg)
  base(accessor, arg) + suffix(sorter)
end