new framework

lib/service/chat_service.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+# Tiny in-memory chat hub. Each session subscribes to receive broadcast
+# messages from other sessions. Backed by a per-session Queue so the
+# Application's idle tick can drain pending messages.
+class ChatService
+  ChatLine = Struct.new(:timestamp, :username, :text)
+
+  def initialize
+    @subs = {}
+    @mu   = Mutex.new
+    @history = []
+    @history_limit = 200
+  end
+
+  def subscribe(session_id)
+    @mu.synchronize do
+      @subs[session_id] = Queue.new
+      @history.last(50).each { |line| @subs[session_id] << line }
+    end
+  end
+
+  def unsubscribe(session_id)
+    @mu.synchronize { @subs.delete(session_id) }
+  end
+
+  def broadcast(username, text)
+    line = ChatLine.new(Time.now.strftime('%H:%M:%S'), username, text)
+    @mu.synchronize do
+      @history << line
+      @history.shift while @history.size > @history_limit
+      @subs.each_value { |q| q << line }
+    end
+    line
+  end
+
+  # Returns Array<ChatLine> of pending messages for the given session.
+  def drain(session_id)
+    queue = @mu.synchronize { @subs[session_id] }
+    return [] unless queue
+    pending = []
+    pending << queue.pop(true) while !queue.empty?
+    pending
+  rescue ThreadError
+    pending
+  end
+
+  def history(n = 50)
+    @mu.synchronize { @history.last(n).dup }
+  end
+
+  def subscriber_count
+    @mu.synchronize { @subs.size }
+  end
+end