Add puma plugin

Author: npezza93

Diff for: README.md

@@ -171,6 +171,13 @@ The inline version also works:
 <section class="bg-[url('image.svg')]">Has the image as it's background</section>
 ```
 
+## Puma plugin
+We provide a Puma plugin if you want to run the Tailwind watcher together with Puma and have Puma monitor and manage it. You just need to add
+```ruby
+plugin :tailwindcss
+```
+to your `puma.rb` configuration.
+
 ## License
 
 Tailwind for Rails is released under the [MIT License](https://opensource.org/licenses/MIT).

Diff for: lib/puma/plugin/tailwindcss.rb

@@ -0,0 +1,65 @@
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :tailwind_pid, :log_writer
+
+  def start(launcher)
+    return unless Rails.env.development?
+
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @tailwind_pid = fork do
+      Thread.new { monitor_puma }
+      system(*Tailwindcss::Commands.watch_command)
+    end
+
+    launcher.events.on_stopped { stop_solid_queue }
+
+    in_background do
+      monitor_tailwind
+    end
+  end
+
+  private
+    def stop_solid_queue
+      Process.waitpid(tailwind_pid, Process::WNOHANG)
+      log "Stopping tailwind..."
+      Process.kill(:INT, tailwind_pid) if tailwind_pid
+      Process.wait(tailwind_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping tailwind...")
+    end
+
+    def monitor_tailwind
+      monitor(:tailwind_dead?, "Detected tailwind has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def tailwind_dead?
+      Process.waitpid(tailwind_pid, Process::WNOHANG)
+      false
+    rescue Errno::ECHILD, Errno::ESRCH
+      true
+    end
+
+    def puma_dead?
+      Process.ppid != puma_pid
+    end
+
+    def log(...)
+      log_writer.log(...)
+    end
+end