refactor: real-time system (#2228)

Co-authored-by: Andrew Bastin <andrewbastin.k@gmail.com>
Co-authored-by: liyasthomas <liyascthomas@gmail.com>

packages/hoppscotch-app/helpers/realtime/SSEConnection.ts

@@ -0,0 +1,86 @@
+import { BehaviorSubject, Subject } from "rxjs"
+import { logHoppRequestRunToAnalytics } from "../fb/analytics"
+
+export type SSEEvent = { time: number } & (
+  | { type: "STARTING" }
+  | { type: "STARTED" }
+  | { type: "MESSAGE_RECEIVED"; message: string }
+  | { type: "STOPPED"; manual: boolean }
+  | { type: "ERROR"; error: Event | null }
+)
+
+export type ConnectionState = "STARTING" | "STARTED" | "STOPPED"
+
+export class SSEConnection {
+  connectionState$: BehaviorSubject<ConnectionState>
+  event$: Subject<SSEEvent> = new Subject()
+  sse: EventSource | undefined
+  constructor() {
+    this.connectionState$ = new BehaviorSubject<ConnectionState>("STOPPED")
+  }
+
+  private addEvent(event: SSEEvent) {
+    this.event$.next(event)
+  }
+
+  start(url: string, eventType: string) {
+    this.connectionState$.next("STARTING")
+    this.addEvent({
+      time: Date.now(),
+      type: "STARTING",
+    })
+    if (typeof EventSource !== "undefined") {
+      try {
+        this.sse = new EventSource(url)
+        this.sse.onopen = () => {
+          this.connectionState$.next("STARTED")
+          this.addEvent({
+            type: "STARTED",
+            time: Date.now(),
+          })
+        }
+        this.sse.onerror = this.handleError
+        this.sse.addEventListener(eventType, ({ data }) => {
+          this.addEvent({
+            type: "MESSAGE_RECEIVED",
+            message: data,
+            time: Date.now(),
+          })
+        })
+      } catch (error) {
+        // A generic event type returned if anything goes wrong or browser doesn't support SSE
+        // https://developer.mozilla.org/en-US/docs/Web/API/EventSource/error_event#event_type
+        this.handleError(error as Event)
+      }
+    } else {
+      this.addEvent({
+        type: "ERROR",
+        time: Date.now(),
+        error: null,
+      })
+    }
+
+    logHoppRequestRunToAnalytics({
+      platform: "sse",
+    })
+  }
+
+  private handleError(error: Event) {
+    this.stop()
+    this.addEvent({
+      time: Date.now(),
+      type: "ERROR",
+      error,
+    })
+  }
+
+  stop() {
+    this.sse?.close()
+    this.connectionState$.next("STOPPED")
+    this.addEvent({
+      type: "STOPPED",
+      time: Date.now(),
+      manual: true,
+    })
+  }
+}