require "json"

# IPC::JSON is the root class for all exchanged messages (using JSON).
# IPC::JSON inherited classes have a common 'type' class attribute,
# which enables to find the right IPC::JSON+ class given a TypedMessage's type.

# All transfered messages are typed messages.
# TypedMessage = u8 type (= IPC::JSON+ class type) + JSON content.
# 'JSON content' being a serialized IPC::JSON+ class.

# Conventionally, IPC::JSON+ classes have a 'handle' method to process incoming messages.
class IPC::JSON
  include ::JSON::Serializable

  class_property type = -1
  property id : ::JSON::Any?

  def type
    @@type
  end

  macro message(id, type, &block)
    class {{id}} < ::IPC::JSON
      include ::JSON::Serializable

      @@type = {{type}}

      {{yield}}
    end
  end
end

class IPC
  # Schedule messages contained into IPC::JSON+.
  def schedule(fd : Int32, message : IPC::JSON)
    typed_msg = IPCMessage::TypedMessage.new message.type.to_u8, message.to_json
    schedule fd, typed_msg
  end

  def write(fd : Int32, message : IPC::JSON)
    typed_msg = IPCMessage::TypedMessage.new message.type.to_u8, message.to_json
    write fd, typed_msg
  end
end

# CAUTION: only use this method on an Array(IPC::JSON.class).
class Array(T)
  def parse_ipc_json(message : IPCMessage::TypedMessage) : IPC::JSON?
    message_type = find &.type.==(message.type)

    payload = String.new message.payload

    if message_type.nil?
      raise "invalid message type (#{message.type})"
    end

    message_type.from_json payload
  end
end