Added full implementation of the Workflow pattern as described by @yr…

…eynhout

Updated the example of group checkout to use it.

samples/hotelManagement/src/core/command.ts

@@ -5,7 +5,7 @@ export type Command<
   CommandData extends Record<string, unknown> = Record<string, unknown>,
 > = Flavour<
   Readonly<{
-    type: Readonly<CommandType>;
+    type: CommandType;
     data: Readonly<CommandData>;
   }>,
   'Command'

samples/hotelManagement/src/core/event.ts

@@ -5,7 +5,7 @@ export type Event<
   EventData extends Record<string, unknown> = Record<string, unknown>,
 > = Flavour<
   Readonly<{
-    type: Readonly<EventType>;
+    type: EventType;
     data: Readonly<EventData>;
   }>,
   'Event'

samples/hotelManagement/src/core/workflow.ts

@@ -3,17 +3,108 @@ import { Event } from './event';
 
 /// Inspired by https://blog.bittacklr.be/the-workflow-pattern.html
 
-export type WorkflowEvent<Output extends Command | Event> = Extract<
-  Output,
-  { __brand?: 'Event' }
->;
-
 export type Workflow<
   Input extends Event | Command,
   State,
   Output extends Event | Command,
 > = {
-  decide: (command: Input, state: State) => Output[];
+  decide: (command: Input, state: State) => WorkflowOutput<Output>[];
   evolve: (currentState: State, event: WorkflowEvent<Output>) => State;
   getInitialState: () => State;
 };
+
+export type WorkflowEvent<Output extends Command | Event> = Extract<
+  Output,
+  { __brand?: 'Event' }
+>;
+
+export type WorkflowCommand<Output extends Command | Event> = Extract<
+  Output,
+  { __brand?: 'Command' }
+>;
+
+export type Reply = Command | Event;
+
+export type WorkflowOutput<TOutput extends Command | Event> =
+  | { kind: 'Reply'; message: TOutput }
+  | { kind: 'Send'; message: WorkflowCommand<TOutput> }
+  | { kind: 'Publish'; message: WorkflowEvent<TOutput> }
+  | {
+      kind: 'Schedule';
+      message: TOutput;
+      when: { afterInMs: number } | { at: Date };
+    }
+  | { kind: 'Complete' }
+  | { kind: 'Accept' }
+  | { kind: 'Ignore'; reason: string }
+  | { kind: 'Error'; reason: string };
+
+export const reply = <TOutput extends Command | Event>(
+  message: TOutput,
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Reply',
+    message,
+  };
+};
+
+export const send = <TOutput extends Command | Event>(
+  message: WorkflowCommand<TOutput>,
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Send',
+    message,
+  };
+};
+
+export const publish = <TOutput extends Command | Event>(
+  message: WorkflowEvent<TOutput>,
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Publish',
+    message,
+  };
+};
+
+export const schedule = <TOutput extends Command | Event>(
+  message: TOutput,
+  when: { afterInMs: number } | { at: Date },
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Schedule',
+    message,
+    when,
+  };
+};
+
+export const complete = <
+  TOutput extends Command | Event,
+>(): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Complete',
+  };
+};
+
+export const ignore = <TOutput extends Command | Event>(
+  reason: string,
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Ignore',
+    reason,
+  };
+};
+
+export const error = <TOutput extends Command | Event>(
+  reason: string,
+): WorkflowOutput<TOutput> => {
+  return {
+    kind: 'Error',
+    reason,
+  };
+};
+
+export const accept = <
+  TOutput extends Command | Event,
+>(): WorkflowOutput<TOutput> => {
+  return { kind: 'Accept' };
+};