module Roda::RodaPlugins::Sessions::RequestMethods

def _deserialize_rack_session(data)
  opts = roda_class.opts[:sessions]
  key = opts[:upgrade_from_rack_session_cookie_key]
  secret = opts[:upgrade_from_rack_session_cookie_secret]
  data, digest = data.split("--", 2)
  unless digest
    return _session_serialization_error("Not decoding Rack::Session::Cookie session: invalid format")
  end
  unless Rack::Utils.secure_compare(digest, OpenSSL::HMAC.hexdigest(OpenSSL::Digest::SHA1.new, opts[:upgrade_from_rack_session_cookie_secret], data))
    return _session_serialization_error("Not decoding Rack::Session::Cookie session: HMAC invalid")
  end
  begin
    session = Marshal.load(data.unpack('m').first)
  rescue
    return _session_serialization_error("Error decoding Rack::Session::Cookie session: not base64 encoded marshal dump")
  end
  # Mark rack session cookie for deletion on success
  env[SESSION_DELETE_RACK_COOKIE] = true
  # Convert the rack session by roundtripping it through
  # the parser and serializer, so that you would get the
  # same result as you would if the session was handled
  # by this plugin.
  env[SESSION_SERIALIZED] = data = opts[:serializer].call(session)
  env[SESSION_CREATED_AT] = Time.now.to_i
  opts[:parser].call(data)
end

def _deserialize_session(data)
  opts = roda_class.opts[:sessions]
  begin
    data = Base64.urlsafe_decode64(data)
  rescue ArgumentError
    return _session_serialization_error("Unable to decode session: invalid base64")
  end
  length = data.bytesize
  if data.length < 61
    # minimum length (1+16+12+32) (version+cipher_iv+minimum session+hmac)
    # 1 : version
    # 16 : cipher_iv
    # 12 : minimum_session
    #      2 : bitmap for gzip + padding info
    #      4 : creation time
    #      4 : update time
    #      2 : data
    # 32 : HMAC-SHA-256
    return _session_serialization_error("Unable to decode session: data too short")
  end
  unless data.getbyte(0) == 0
    # version marker
    return _session_serialization_error("Unable to decode session: version marker unsupported")
  end
  encrypted_data = data.slice!(0, length-32)
  unless Rack::Utils.secure_compare(data, OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:hmac_secret], encrypted_data+opts[:key]))
    if opts[:old_hmac_secret] && Rack::Utils.secure_compare(data, OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:old_hmac_secret], encrypted_data+opts[:key]))
      use_old_cipher_secret = true
    else
      return _session_serialization_error("Not decoding session: HMAC invalid")
    end
  end
  encrypted_data.slice!(0)
  cipher = OpenSSL::Cipher.new("aes-256-ctr")
  # Not rescuing cipher errors.  If there is an error in the decryption, that's
  # either a bug in the plugin that needs to be fixed, or an attacker is already
  # able to forge a valid HMAC, in which case the error should be raised to
  # alert the application owner about the problem.
  cipher.decrypt
  cipher.key = opts[use_old_cipher_secret ? :old_cipher_secret : :cipher_secret]
  cipher_iv = cipher.iv = encrypted_data.slice!(0, 16)
  data = cipher.update(encrypted_data) << cipher.final
  bitmap, created_at, updated_at = data.unpack('vVV')
  padding_bytes = bitmap & PADDING_MASK
  if (max = opts[:max_seconds]) && Time.now.to_i > created_at + max
    return _session_serialization_error("Not returning session: maximum session time expired")
  end
  if (max = opts[:max_idle_seconds]) && Time.now.to_i > updated_at + max
    return _session_serialization_error("Not returning session: maximum session idle time expired")
  end
  data = data.slice(10+padding_bytes, data.bytesize)
  if bitmap & DEFLATE_BIT > 0
    data = Zlib::Inflate.inflate(data)
  end
  env = @env
  env[SESSION_CREATED_AT] = created_at
  env[SESSION_UPDATED_AT] = updated_at
  env[SESSION_SERIALIZED] = data
  opts[:parser].call(data)
end

def _load_session
  opts = roda_class.opts[:sessions]
  cs = cookies
  if data = cs[opts[:key]]
    _deserialize_session(data)
  elsif (key = opts[:upgrade_from_rack_session_cookie_key]) && (data = cs[key])
    _deserialize_rack_session(data)
  end || {}
end

def _serialize_session(session)
  opts = roda_class.opts[:sessions]
  env = @env
  now = Time.now.to_i
  json_data = opts[:serializer].call(session).force_encoding('BINARY')
  if (serialized_session = env[SESSION_SERIALIZED]) &&
     (updated_at = env[SESSION_UPDATED_AT]) &&
     (now - updated_at < opts[:skip_within]) &&
     (serialized_session == json_data)
    return
  end
  bitmap = 0
  json_length = json_data.bytesize
  gzip_over = opts[:gzip_over]
  if gzip_over && json_length > gzip_over
    json_data = Zlib.deflate(json_data)
    json_length = json_data.bytesize
    bitmap |= DEFLATE_BIT
  end
  # When calculating padding bytes to use, include 10 bytes for bitmap and
  # session create/update times, so total size of encrypted data is a
  # multiple of pad_size.
  if (pad_size = opts[:pad_size]) && (padding_bytes = (json_length+10) % pad_size) != 0
    padding_bytes = pad_size - padding_bytes
    bitmap |= padding_bytes
    padding_data = SecureRandom.random_bytes(padding_bytes)
  end
  session_create_time = env[SESSION_CREATED_AT]
  serialized_data = [bitmap, session_create_time||now, now].pack('vVV')
  serialized_data << padding_data if padding_data
  serialized_data << json_data
  cipher = OpenSSL::Cipher.new("aes-256-ctr")
  cipher.encrypt
  cipher.key = opts[:cipher_secret]
  cipher_iv = cipher.random_iv
  encrypted_data = cipher.update(serialized_data) << cipher.final
  data = String.new
  data << "\0" # version marker
  data << cipher_iv
  data << encrypted_data
  data << OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:hmac_secret], data+opts[:key])
  data = Base64.urlsafe_encode64(data)
  if data.bytesize >= 4096
    raise CookieTooLarge, "attempted to create cookie larger than 4096 bytes"
  end
  data
end

def _session_serialization_error(msg)
  return unless error_stream = @env['rack.errors']
  error_stream.puts(msg)
  nil
end

def persist_session(headers, session)
  opts = roda_class.opts[:sessions]
  if session.empty?
    if env[SESSION_SERIALIZED]
      # If session was submitted and is now empty, remove the cookie
      Rack::Utils.delete_cookie_header!(headers, opts[:key])
    # else
      # If no session was submitted, and the session is empty
      # then there is no need to do anything
    end
  elsif cookie_value = _serialize_session(session)
    cookie = Hash[opts[:cookie_options]]
    cookie[:value] = cookie_value
    cookie[:secure] = true if !cookie.has_key?(:secure) && ssl?
    Rack::Utils.set_cookie_header!(headers, opts[:key], cookie)
  end
  
  if env[SESSION_DELETE_RACK_COOKIE]
    Rack::Utils.delete_cookie_header!(headers, opts[:upgrade_from_rack_session_cookie_key], opts[:upgrade_from_rack_session_cookie_options])
  end
  nil
end

def session
  @env['rack.session'] ||= _load_session
end