Tools/infrastructure/FileEventStore.ts

import { appendFile } from "node:fs/promises";
import EventStore from "../domain/EventStore";
import { ApplicationUpdateStarted } from "../domain/events/ApplicationUpdateStarted";
import DomainEvent from "../domain/DomainEvent";
import DomainProjection from "../domain/DomainProjection";

export default class FileEventStore implements EventStore {
  private handlers: DomainProjection[] = [];
  constructor(private readonly filePath: string) {}

  append(event: DomainEvent<any>): void {
    appendFile(this.filePath, this.serialize(event) + "\n");
    this.emit(event);
  }

  subscribe(projection: DomainProjection) {
    this.handlers.push(projection);
  }

  async replay() {
    // TODO Improve this with streaming
    console.log("Replaying events from", this.filePath);
    const file = Bun.file(this.filePath);
    const content = await file.text();
    const lines = content.split("\n");
    for (const line of lines) {
      if (!line) {
        continue;
      }
      console.log("Deserializing", line);
      const event = this.deserialize(line);
      this.emit(event);
    }
    console.log("Replaying done");
  }

  private emit(event: DomainEvent<any>) {
    for (const handler of this.handlers) {
      handler.handle(event);
    }
  }

  private serialize(event: DomainEvent<any>) {
    return JSON.stringify(event);
  }

  private deserialize(line: string) {
    const event = JSON.parse(line);
    switch (event.type) {
      case "ApplicationUpdateStarted":
        return new ApplicationUpdateStarted(
          {
            id: event.payload.id,
            newVersion: event.payload.newVersion,
          },
          new Date(event.createdAt)
        );
      default:
        throw new Error("Unknown event type" + event.type);
    }
  }
}