class Opal::Rewriters::TargetedPatches

def on_array(node)
  children = node.children
  # Optimize large arrays produced by lexer, but mainly we are interested
  # in improving compile times, by reducing the tree for the further
  # compilation efforts (also reducing the bundle size a bit)
  #
  # This particular patch reduces compile time of the following command
  # by 12.5%:
  #
  #     OPAL_CACHE_DISABLE=true OPAL_PREFORK_DISABLE=true bin/opal \
  #         --no-source-map -ropal-parser -ropal/platform -ce \
  #         'puts ::Opal.compile($stdin.read)' > _Cnow.js
  #
  # So, in short, an array of a kind:
  #
  #     [1, 2, 3, nil, nil, :something, :abc, nil, ...]
  #
  # Becomes compiled to:
  #
  #     Opal.large_array_unpack("1,2,3,,something,abc,,...")
  if children.length > 32
    ssin_array = children.all? do |child|
      # Break for wrong types
      next false unless %i[str sym int nil].include?(child.type)
      # Break for strings that may conflict with our numbers, nils and separator
      next false if %i[str sym].include?(child.type) && child.children.first.to_s =~ /\A[0-9-]|\A\z|,/
      # Break for too numbers out of range, as there may be decoding issues
      next false if child.type == :int && !(-1_000_000..1_000_000).cover?(child.children.first)
      true
    end
    if ssin_array
      str = children.map { |i| i.children.first.to_s }.join(',')
      node.updated(:jscall, [s(:js_tmp, :Opal), :large_array_unpack, s(:sym, str)])
    else
      super
    end
  else
    super
  end
end