class FFI::Generator

def initialize(ffi_name, rb_name, options = {})
  @ffi_name = ffi_name
  @rb_name = rb_name
  @options = options
  @name = File.basename rb_name, '.rb'
  file = File.read @ffi_name
  new_file = file.gsub(/^( *)@@@(.*?)@@@/m) do
    @constants = []
    @structs = []
    indent = $1
    original_lines = $2.count "\n"
    instance_eval $2, @ffi_name, $`.count("\n")
    new_lines = []
    @constants.each { |c| new_lines << c.to_ruby }
    @structs.each { |s| new_lines << s.generate_layout }
    new_lines = new_lines.join("\n").split "\n" # expand multiline blocks
    new_lines = new_lines.map { |line| indent + line }
    padding = original_lines - new_lines.length
    new_lines += [nil] * padding if padding >= 0
    new_lines.join "\n"
  end
  open @rb_name, 'w' do |f|
    f.puts "# This file is generated from `#{@ffi_name}'. Do not edit."
    f.puts
    f.puts new_file
  end
end