Add monitor daemon

.gitignore

@@ -4,3 +4,5 @@
 Gemfile.lock
 # Ignore .idea
 .idea
+# Ignore log files
+log/*.log

bin/scout_apm_logging_monitor

@@ -0,0 +1,5 @@
+#!/usr/bin/env ruby
+
+require_relative "../lib/scout_apm/logging/monitor/monitor.rb"
+
+ScoutApm::Logging::Monitor.new.run

lib/scout_apm/logging/monitor/monitor.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+##
+# Launched as a daemon process by the monitor manager and Rails startup.
+##
+
+module ScoutApm
+  module Logging
+    class Monitor
+      def run
+        loop do
+          sleep 1
+          puts "Running..."
+        end
+      end
+    end
+  end
+end

lib/scout_apm/logging/monitor_manager.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module ScoutApm
+  module Logging
+    class MonitorManager
+      PID_FILE = '/tmp/scout_apm_log_monitor.pid'
+
+      @instance = nil
+
+      # TODO: Is this necessary?
+      def self.instance
+        @instance ||= new
+      end
+
+      def self.setup!
+        instance.create_process
+      end
+
+      def create_process
+        return if File.exist? PID_FILE
+
+        gem_directory = File.expand_path('../../..', __dir__)
+        monitor_daemon = Process.spawn("ruby #{gem_directory}/bin/scout_apm_logging_monitor &")
+
+        # TODO: Why are we off by one?
+        File.write(PID_FILE, monitor_daemon + 1)
+
+        # TODO: Add exit handlers?
+      end
+    end
+  end
+end

lib/scout_apm_logging.rb

@@ -2,12 +2,15 @@
 
 require 'scout_apm'
 
+require 'scout_apm/logging/monitor_manager'
+
 module ScoutApm
   module Logging
-    # Temporary class for testing hierarchy.
-    class Hello
-      def self.world
-        puts 'Hello World.'
+    if defined?(Rails) && defined?(Rails::Railtie)
+      class RailTie < ::Rails::Railtie
+        initializer "scout_apm_logging.monitor" do
+          ScoutApm::Logging::MonitorManager.setup!
+        end
       end
     end
   end

spec/scout_apm_logging_spec.rb

@@ -2,13 +2,28 @@
 
 require 'spec_helper'
 
+require 'rails'
+
 describe ScoutApm::Logging do
-  let(:hello_world) do
-    Class.new(ScoutApm::Logging::Hello)
+  before(:all) do
+    # Run the Railtie initializers to trigger the daemon spawning
+    make_basic_app
+  end
+
+  it "spawns the daemon process" do
+    # Check if the PID file exists
+    expect(File.exist?(ScoutApm::Logging::MonitorManager::PID_FILE)).to be_truthy
+
+    # Read the PID from the PID file
+    pid = File.read(ScoutApm::Logging::MonitorManager::PID_FILE).to_i
+
+    # Check if the process with the stored PID is running
+    expect(Process.kill(0, pid)).to be_truthy
   end
 
-  it 'writes hello world' do
-    allow($stdout).to receive(:puts)
-    expect { hello_world.world }.to output("Hello World.\n").to_stdout
+  after(:all) do
+    process = File.read(ScoutApm::Logging::MonitorManager::PID_FILE).to_i
+    Process.kill('TERM', process)
+    File.delete(ScoutApm::Logging::MonitorManager::PID_FILE)
   end
 end

spec/spec_helper.rb

@@ -1,4 +1,34 @@
 # frozen_string_literal: true
 
 require 'scout_apm'
-require 'scout_apm_logging'
+
+# Taken from:
+# https://github.com/rails/rails/blob/v7.1.3.2/railties/test/isolation/abstract_unit.rb#L252
+def make_basic_app
+  require "rails"
+  require "action_controller/railtie"
+  require "action_view/railtie"
+
+  # Require after rails, to ensure the railtie is loaded
+  require 'scout_apm_logging'
+
+  @app = Class.new(Rails::Application) do
+    def self.name; "RailtiesTestApp"; end
+  end
+  @app.config.hosts << proc { true }
+  @app.config.eager_load = false
+  @app.config.session_store :cookie_store, key: "_myapp_session"
+  @app.config.active_support.deprecation = :log
+  @app.config.log_level = :info
+  @app.config.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
+
+  yield @app if block_given?
+  @app.initialize!
+
+  @app.routes.draw do
+    get "/" => "omg#index"
+  end
+
+  require "rack/test"
+  extend ::Rack::Test::Methods
+end