# MessageEncoders are registered with the Ably client library and are responsible
# for encoding & decoding messages.
#
# For example, if a message body is detected as JSON, it is encoded as a String and the encoding attribute
# of the message is defined as 'json'.
# Encrypted messages are encoded & decoded by the Cipher encoder.
#
module Ably::Models::MessageEncoders
  extend Ably::Modules::Conversions

  # Base interface for an Ably Encoder
  #
  class Base
    attr_reader :client

    def initialize(client)
      @client = client
    end

    # #encode is called once before a message is sent to Ably
    #
    # It is the responsibility of the #encode method to detect the intended encoding and modify the :data & :encoding properties of the message object.
    #
    # @param [Hash] message          the message as a Hash object received directly from Ably.
    #                                The message contains properties :name, :data, :encoding, :timestamp, and optionally :id and :client_id.
    #                                This #encode method should modify the message Hash if any encoding action is to be taken
    # @param [Hash] channel_options  the options used to initialize the channel that this message was received on
    #
    # @return [void]
    def encode(message, channel_options)
      raise "Not yet implemented"
    end

    # #decode is called once for every encoding step
    # i.e. if message encoding arrives with 'utf-8/cipher+aes-128-cbc/base64'
    #      the decoder will call #decode once for each encoding part such as 'base64', then 'cipher+aes-128-cbc', and finally 'utf-8'
    #
    # It is the responsibility of the #decode method to detect the current encoding part and modify the :data & :encoding properties of the message object.
    #
    # @param [Hash] message          the message as a Hash object received directly from Ably.
    #                                The message contains properties :name, :data, :encoding, :timestamp, and optionally :id and :client_id.
    #                                This #encode method should modify the message Hash if any decoding action is to be taken
    # @param [Hash] channel_options  the options used to initialize the channel that this message was received on
    #
    # @return [void]
    def decode(message, channel_options)
      raise "Not yet implemented"
    end

    # Add encoding to the message Hash.
    # Ensures that encoding delimeter is used where required i.e utf-8/cipher+aes-128-cbc/base64
    #
    # @param [Hash]   message   the message as a Hash object received directly from Ably.
    # @param [String] encoding  encoding to add to the current encoding
    #
    # @return [void]
    def add_encoding_to_message(encoding, message)
      message[:encoding] = [message[:encoding], encoding].compact.join('/')
    end

    # Returns the right most encoding form a meessage encoding, and nil if none exists
    # i.e. current_encoding_part('utf-8/cipher+aes-128-cbc/base64') => 'base64'
    #
    # @return [String,nil]
    def current_encoding_part(message)
      if message[:encoding]
        message[:encoding].split('/')[-1]
      end
    end

    # Strip the current encoding part within the message Hash.
    #
    # For example, calling this method on an :encoding value of 'utf-8/cipher+aes-128-cbc/base64' would update the attribute
    # :encoding to 'utf-8/cipher+aes-128-cbc'
    #
    # @param [Hash]   message   the message as a Hash object received directly from Ably.
    #
    # @return [void]
    def strip_current_encoding_part(message)
      raise "Cannot strip encoding when there is no encoding for this message" unless message[:encoding]
      message[:encoding] = message[:encoding].split('/')[0...-1].join('/')
      message[:encoding] = nil if message[:encoding].empty?
    end

    # True of the message data payload is empty
    #
    # @param [Hash]   message   the message as a Hash object received directly from Ably.
    #
    # @return [Boolean]
    def is_empty?(message)
      message[:data].nil? || message[:data] == ''
    end
  end

  def self.register_default_encoders(client)
    Dir.glob(File.expand_path("*.rb", File.dirname(__FILE__))).each do |file|
      next if __FILE__ == file
      require file
    end

    client.register_encoder Ably::Models::MessageEncoders::Utf8
    client.register_encoder Ably::Models::MessageEncoders::Json
    client.register_encoder Ably::Models::MessageEncoders::Cipher
    client.register_encoder Ably::Models::MessageEncoders::Base64
  end
end