docs: add basic command bus page

docs/.vitepress/config.mts

@@ -23,6 +23,10 @@ export default defineConfig({
                 text: 'Components',
                 items: [
                     { text: 'Aggregate repo', link: '/aggregate-repo' },
+                    {
+                        text: 'Command bus',
+                        link: '/command-bus',
+                    },
                 ],
             },
         ],

docs/command-bus.md

@@ -0,0 +1,96 @@
+# Command bus
+
+## Intro
+
+A command bus is a fundamental architectural pattern used in software development, particularly in the context of
+building applications following the Command Query Responsibility Segregation (CQRS) paradigm.
+
+Acting as a mediator between the application's components, the command bus receives commands to perform from
+various parts of the system and routes them to the appropriate handlers or command handlers responsible for executing
+the requested operations. This abstraction simplifies the communication flow within the application, decoupling the
+sender of the command from its execution logic. By centralizing command processing, the command bus promotes a cleaner
+and more maintainable codebase, enhancing modularity and scalability in complex software systems.
+
+## Local Command Bus
+
+Ddd toolkit provides a simple in-memory implementation of a command bus.
+
+- `register`: register a command handler for a specific command.
+- `send`: executes a command. Resolves immediately, without waiting for the effective execution of the command.
+- `sendSync`: executes a command. Resolves when the effective execution of the command is completed.
+
+::: info
+The `send` method implements a retry mechanism by default. This means that if the command handler throws an error, the
+command bus will retry to execute the command handler until the maximum number of retries is reached.
+:::
+
+::: warning PRAGMATIC ALERT 📣
+As mentioned above, the greatest benefit of using a command bus over direct method calls is to centralise and
+standardise.
+We wanted to include the send method (in addition to sendSync) because in some contexts there is a risk of coupling to
+synchronous commands. Send allows us to develop our application without assuming that commands are local (and thus can
+return data / can be synchronous).
+
+In general, when asynchronicity is introduced into a system, complexity explodes.
+
+:::
+
+## Basic usage
+
+Define CommandBus
+
+```typescript
+import { LocalCommandBus } from '@fizzbuds/ddd-toolkit';
+
+
+export class CommandBus extends LocalCommandBus {
+    constructor() {
+        super(new Logger(CommandBus.name));
+    }
+}
+```
+
+Define a command
+
+```typescript
+type DeleteMemberCommandPayload = { memberId: string };
+
+class DeleteMemberCommand extends Command<DeleteMemberCommandPayload> {
+    constructor(public readonly payload: DeleteMemberCommandPayload) {
+        super(payload);
+    }
+}
+
+```
+
+Define a command handler
+
+```typescript
+import { LocalCommandBus } from '@fizzbuds/ddd-toolkit';
+
+
+export class DeleteCommandHandler implements ICommandHandler<DeleteMemberCommand> {
+    async handle({ payload }: DeleteMemberCommand) {
+        // Delete member logic
+    }
+}
+```
+
+Try it out
+
+```typescript
+const commandBus = new CommandBus();
+
+commandBus.registerHandler(DeleteMemberCommand, new DeleteCommandHandler())
+
+
+await commandBus.send(new DeleteMemberCommand({ memberId: '123' }));
+
+```
+
+
+
+
+
+
+