module I18n::Backend::InterpolationCompiler::Compiler

def compile_if_an_interpolation(string)
  if interpolated_str?(string)
    string.instance_eval <<-RUBY_EVAL, __FILE__, __LINE__
      def i18n_interpolate(v = {})
        "#{compiled_interpolation_body(string)}"
      end
    RUBY_EVAL
  end
  string
end

def compile_interpolation_token(key)
  "\#{#{interpolate_or_raise_missing(key)}}"
end

def compiled_interpolation_body(str)
  tokenize(str).map do |token|
    token.match(TOKENIZER) ? handle_interpolation_token(token) : escape_plain_str(token)
  end.join
end

def direct_key(key)
  "((t = v[#{key}]) && t.respond_to?(:call) ? t.call : t)"
end

def escape_key_sym(key)
  # rely on Ruby to do all the hard work :)
  key.to_sym.inspect
end

def escape_plain_str(str)
  str.gsub(/"|\\|#/) {|x| "\\#{x}"}
end

def handle_interpolation_token(token)
  token.start_with?('%%') ? token[1..] : compile_interpolation_token(token[2..-2])
end

def interpolate_key(key)
  [direct_key(key), nil_key(key), missing_key(key)].join('||')
end

def interpolate_or_raise_missing(key)
  escaped_key = escape_key_sym(key)
  RESERVED_KEYS.include?(key) ? reserved_key(escaped_key) : interpolate_key(escaped_key)
end

def interpolated_str?(str)
  str.kind_of?(::String) && str =~ TOKENIZER
end

def missing_key(key)
  "I18n.config.missing_interpolation_argument_handler.call(#{key}, v, self)"
end

def nil_key(key)
  "(v.has_key?(#{key}) && '')"
end

def reserved_key(key)
  "raise(ReservedInterpolationKey.new(#{key}, self))"
end

def tokenize(str)
  str.split(TOKENIZER)
end