feat: initial mini simple event sourcing for pending application updates

domain/AppProjections.ts

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+import ApplicationUpdates from "./projections/ApplicationUpdates";
+
+export default class AppProjections {
+  public readonly ApplicationUpdates = new ApplicationUpdates();
+
+  getAll(): DomainProjection[] {
+    return [this.ApplicationUpdates];
+  }
+}

domain/AppQueries.ts

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+import AppProjections from "./AppProjections";
+import { UpdateDefinition } from "./projections/ApplicationUpdates";
+
+export default class AppQueries {
+  constructor(private readonly projections: AppProjections) {}
+
+  pendingApplicationUpdates(appName?: string): UpdateDefinition[] {
+    // TODO: Implement filtering by appName
+    return this.projections.ApplicationUpdates.getPendingUpdates();
+  }
+}

domain/DomainEvent.ts

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+interface DomainEvent<T> {
+  readonly type: string;
+  readonly createdAt: Date;
+  readonly payload: T;
+}

domain/DomainProjection.ts

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+interface DomainProjection {
+  handle(event: DomainEvent<any>): void;
+}

domain/EventStore.ts

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+export default interface EventStore {
+  append(event: DomainEvent<any>): void;
+  subscribe(projection: DomainProjection): void;
+  replay(): Promise<void>;
+}

domain/events/ApplicationUpdateStarted.ts

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+type ApplicationUpdateStartedPayload = {
+  id: string;
+  newVersion: string;
+};
+
+export class ApplicationUpdateStarted
+  implements DomainEvent<ApplicationUpdateStartedPayload>
+{
+  readonly type = "ApplicationUpdateStarted" as const;
+  constructor(
+    public readonly payload: ApplicationUpdateStartedPayload,
+    public readonly createdAt: Date
+  ) {}
+}

domain/projections/ApplicationUpdates.ts

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+export type UpdateDefinition = {
+  id: string;
+  newVersion: string;
+};
+
+export default class ApplicationUpdates implements DomainProjection {
+  private readonly pendingUpdates: UpdateDefinition[] = [];
+  handle(event: DomainEvent<any>): void {
+    if (event.type === "ApplicationUpdateStarted") {
+      console.log("ApplicationUpdateStarted", event.payload);
+      this.pendingUpdates.push(event.payload);
+    }
+  }
+
+  getPendingUpdates(): UpdateDefinition[] {
+    return this.pendingUpdates;
+  }
+}