Free Architecture - sgml/signature GitHub Wiki

                          +---------------------+
                          |      Publisher      |
                          |     (Subject)       |
                          +---------------------+
                                     |
                                     |  notify(event)
                                     v
                          +---------------------+
                          |     Interceptor     |
                          | (InterceptingFilter)|
                          +---------------------+
                                     |
                                     |  forward(event)
                                     v
                          +---------------------+
                          |      Subscriber     |
                          |      (Observer)     |
                          +---------------------+

Legend:
- Observer Pattern: Publisher → Subscriber
- Interceptor Pattern: Interceptor inserted between Publisher and Subscriber
- Interceptor can:
    • Inspect or modify the event
    • Block or short-circuit the dispatch
    • Log, transform, or enrich the message

          +--------------------+
          |     Observer       |
          |  (reacts to event) |
          +--------------------+
                   /\
                  /  \
                 /    \
                /      \
               /        \
              /          \
             /            \
            /              \
           /                \
+--------------------+     +----------------------+
|   Interceptor      |<--->|   Shared Concerns    |
| (filters event)    |     |  - Message awareness |
+--------------------+     |  - Decoupled wiring  |
                           |  - Cross-cutting     |
                           |    behavior          |
                           +----------------------+