Move RunnerConnection into class Runner

The old approach was to require the runner connection. This did
not work anymore with Zeitwerk in Rails 6. @sebastian.serth and I
moved the Connection class in `lib` into the ActiveRecord class
`Runner`. This will also work with future changes like specific
error classes. Furthermore the config was fixed and simplified.

Co-authored-by: Sebastian Serth <Sebastian.Serth@hpi.de>

lib/runner/connection.rb

@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+require 'faye/websocket/client'
+require 'json_schemer'
+
+class Runner::Connection
+  EVENTS = %i[start output exit stdout stderr].freeze
+  BACKEND_OUTPUT_SCHEMA = JSONSchemer.schema(JSON.parse(File.read('lib/runner/backend-output.schema.json')))
+
+  def initialize(url)
+    @socket = Faye::WebSocket::Client.new(url, [], ping: 5)
+
+    %i[open message error close].each do |event_type|
+      @socket.on(event_type) {|event| __send__(:"on_#{event_type}", event) }
+    end
+
+    EVENTS.each {|event_type| instance_variable_set(:"@#{event_type}_callback", ->(e) {}) }
+    @start_callback = -> {}
+    @exit_code = 0
+  end
+
+  def on(event, &block)
+    return unless EVENTS.include? event
+
+    instance_variable_set(:"@#{event}_callback", block)
+  end
+
+  def send(data)
+    @socket.send(encode(data))
+  end
+
+  private
+
+  def decode(event)
+    JSON.parse(event).deep_symbolize_keys
+  end
+
+  def encode(data)
+    data
+  end
+
+  def on_message(event)
+    return unless BACKEND_OUTPUT_SCHEMA.valid?(JSON.parse(event.data))
+
+    event = decode(event.data)
+    __send__("handle_#{event[:type]}", event)
+  end
+
+  def on_open(_event)
+    @start_callback.call
+  end
+
+  def on_error(event); end
+
+  def on_close(_event)
+    @exit_callback.call @exit_code
+  end
+
+  def handle_exit(event)
+    @exit_code = event[:data]
+  end
+
+  def handle_stdout(event)
+    @stdout_callback.call event[:data]
+    @output_callback.call event[:data]
+  end
+
+  def handle_stderr(event)
+    @stderr_callback.call event[:data]
+    @output_callback.call event[:data]
+  end
+
+  def handle_error(event) end
+
+  def handle_start(event) end
+
+  def handle_timeout(event)
+    # TODO: set the runner state
+  end
+end