# TODO: tests.

# Serialization (and deserialization) doesn't refer to IPC format.
# IPC serialization format: 'length + value'
# IPCMessage serialization: 'value'
# 'Value' is:
# - simply the message payload for UntypedMessage
# - type (u8) + payload for TypedMessage
module IPCMessage
  class UntypedMessage
    property payload : Bytes

    def initialize(string : String)
      @payload = Bytes.new string.to_unsafe, string.size
    end

    def initialize(@payload)
    end

    def self.deserialize(payload : Bytes) : UntypedMessage
      IPCMessage::UntypedMessage.new payload
    end

    def serialize
      @payload
    end
  end

  # WARNING: you can only have up to 256 types.
  class TypedMessage < UntypedMessage
    property type : UInt8? = nil

    def initialize(@type, string : String)
      super string
    end

    def initialize(@type, payload)
      super payload
    end

    def initialize(payload)
      super payload
    end

    def self.deserialize(bytes : Bytes) : TypedMessage?
      if bytes.size == 0
        nil
      else
        type = bytes[0]
        IPCMessage::TypedMessage.new type, bytes[1..]
      end
    end

    def serialize
      bytes = Bytes.new(1 + @payload.size)
      type = @type
      bytes[0] = type.nil? ? 0.to_u8 : type
      bytes[1..].copy_from @payload
      bytes
    end
  end
end

# Send both typed and untyped messages.
class IPC
  def schedule(fd : Int32, m : (IPCMessage::TypedMessage | IPCMessage::UntypedMessage))
    payload = m.serialize
    schedule fd, payload
  end

  def write(fd : Int32, m : (IPCMessage::TypedMessage | IPCMessage::UntypedMessage))
    payload = m.serialize
    write fd, payload
  end
end