feat: add assignment service

app/services/auto_assignment/rate_limiter.rb

@@ -0,0 +1,49 @@
+class AutoAssignment::RateLimiter
+  pattr_initialize [:inbox!, :agent!]
+
+  def within_limit?
+    return true unless enabled?
+
+    current_count < limit
+  end
+
+  def track_assignment(conversation)
+    return unless enabled?
+
+    assignment_key = build_assignment_key(conversation.id)
+    Redis::Alfred.set(assignment_key, conversation.id.to_s, ex: window)
+  end
+
+  def current_count
+    return 0 unless enabled?
+
+    pattern = assignment_key_pattern
+    Redis::Alfred.keys_count(pattern)
+  end
+
+  private
+
+  def enabled?
+    limit.present? && limit.positive?
+  end
+
+  def limit
+    config['fair_distribution_limit']&.to_i
+  end
+
+  def window
+    config['fair_distribution_window']&.to_i || 3600
+  end
+
+  def config
+    @config ||= inbox.auto_assignment_config || {}
+  end
+
+  def assignment_key_pattern
+    "assignment:#{inbox.id}:agent:#{agent.id}:*"
+  end
+
+  def build_assignment_key(conversation_id)
+    "assignment:#{inbox.id}:agent:#{agent.id}:conversation:#{conversation_id}"
+  end
+end