module ActiveSupport::SecureRandom

def self.base64(n=nil)
  [random_bytes(n)].pack("m*").delete("\n")
end

def self.hex(n=nil)
  random_bytes(n).unpack("H*")[0]
end

def self.lastWin32ErrorMessage # :nodoc:
  get_last_error = Win32API.new("kernel32", "GetLastError", '', 'L')
  format_message = Win32API.new("kernel32", "FormatMessageA", 'LPLLPLPPPPPPPP', 'L')
  format_message_ignore_inserts = 0x00000200
  format_message_from_system    = 0x00001000
  code = get_last_error.call
  msg = "\0" * 1024
  len = format_message.call(format_message_ignore_inserts + format_message_from_system, 0, code, 0, msg, 1024, nil, nil, nil, nil, nil, nil, nil, nil)
  msg[0, len].tr("\r", '').chomp
end

def self.random_bytes(n=nil)
  n ||= 16
  unless defined? OpenSSL
    begin
      require 'openssl'
    rescue LoadError
    end
  end
  if defined? OpenSSL::Random
    return OpenSSL::Random.random_bytes(n)
  end
  if !defined?(@has_urandom) || @has_urandom
    flags = File::RDONLY
    flags |= File::NONBLOCK if defined? File::NONBLOCK
    flags |= File::NOCTTY if defined? File::NOCTTY
    flags |= File::NOFOLLOW if defined? File::NOFOLLOW
    begin
      File.open("/dev/urandom", flags) {|f|
        unless f.stat.chardev?
          raise Errno::ENOENT
        end
        @has_urandom = true
        ret = f.readpartial(n)
        if ret.length != n
          raise NotImplementedError, "Unexpected partial read from random device"
        end
        return ret
      }
    rescue Errno::ENOENT
      @has_urandom = false
    end
  end
  if !defined?(@has_win32)
    begin
      require 'Win32API'
      crypt_acquire_context = Win32API.new("advapi32", "CryptAcquireContext", 'PPPII', 'L')
      @crypt_gen_random = Win32API.new("advapi32", "CryptGenRandom", 'LIP', 'L')
      hProvStr = " " * 4
      prov_rsa_full = 1
      crypt_verifycontext = 0xF0000000
      if crypt_acquire_context.call(hProvStr, nil, nil, prov_rsa_full, crypt_verifycontext) == 0
        raise SystemCallError, "CryptAcquireContext failed: #{lastWin32ErrorMessage}"
      end
      @hProv, = hProvStr.unpack('L')
      @has_win32 = true
    rescue LoadError
      @has_win32 = false
    end
  end
  if @has_win32
    bytes = " " * n
    if @crypt_gen_random.call(@hProv, bytes.size, bytes) == 0
      raise SystemCallError, "CryptGenRandom failed: #{lastWin32ErrorMessage}"
    end
    return bytes
  end
  raise NotImplementedError, "No random device"
end

def self.random_number(n=0)
  if 0 < n
    hex = n.to_s(16)
    hex = '0' + hex if (hex.length & 1) == 1
    bin = [hex].pack("H*")
    mask = bin[0]
    mask |= mask >> 1
    mask |= mask >> 2
    mask |= mask >> 4
    begin
      rnd = SecureRandom.random_bytes(bin.length)
      rnd[0] = rnd[0] & mask
    end until rnd < bin
    rnd.unpack("H*")[0].hex
  else
    # assumption: Float::MANT_DIG <= 64
    i64 = SecureRandom.random_bytes(8).unpack("Q")[0]
    Math.ldexp(i64 >> (64-Float::MANT_DIG), -Float::MANT_DIG)
  end
end