feat(backend): make FeedSourceProvider async (#77)

* feat(backend): make FeedSourceProvider async

Make feedSourceForUser and FeedSourceProviderFn return promises.
Use Promise.allSettled to tolerate partial provider failures.
Guard concurrent getOrCreate calls with in-flight promise dedup.
Return 503 from HTTP handlers when session creation fails.

Co-authored-by: Ona <no-reply@ona.com>

* fix(backend): handle remove() during in-flight session creation

Cancel pending getOrCreate when remove() is called mid-flight.
Destroy the resulting session to prevent it from leaking.

Co-authored-by: Ona <no-reply@ona.com>

---------

Co-authored-by: Ona <no-reply@ona.com>

apps/aelis-backend/src/session/feed-source-provider.ts

@@ -1,9 +1,9 @@
 import type { FeedSource } from "@aelis/core"
 
 export interface FeedSourceProvider {
-	feedSourceForUser(userId: string): FeedSource
+	feedSourceForUser(userId: string): Promise<FeedSource>
 }
 
-export type FeedSourceProviderFn = (userId: string) => FeedSource
+export type FeedSourceProviderFn = (userId: string) => Promise<FeedSource>
 
 export type FeedSourceProviderInput = FeedSourceProvider | FeedSourceProviderFn

apps/aelis-backend/src/session/user-session-manager.test.ts

@@ -1,7 +1,7 @@
 import type { WeatherKitClient, WeatherKitResponse } from "@aelis/source-weatherkit"
 
 import { LocationSource } from "@aelis/source-location"
-import { describe, expect, mock, test } from "bun:test"
+import { describe, expect, mock, spyOn, test } from "bun:test"
 
 import { WeatherSourceProvider } from "../weather/provider.ts"
 import { UserSessionManager } from "./user-session-manager.ts"
@@ -11,38 +11,38 @@ const mockWeatherClient: WeatherKitClient = {
 }
 
 describe("UserSessionManager", () => {
-	test("getOrCreate creates session on first call", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+	test("getOrCreate creates session on first call", async () => {
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session).toBeDefined()
 		expect(session.engine).toBeDefined()
 	})
 
-	test("getOrCreate returns same session for same user", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+	test("getOrCreate returns same session for same user", async () => {
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 
 		expect(session1).toBe(session2)
 	})
 
-	test("getOrCreate returns different sessions for different users", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+	test("getOrCreate returns different sessions for different users", async () => {
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-2")
+		const session1 = await manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-2")
 
 		expect(session1).not.toBe(session2)
 	})
 
-	test("each user gets independent source instances", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+	test("each user gets independent source instances", async () => {
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-2")
+		const session1 = await manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-2")
 
 		const source1 = session1.getSource<LocationSource>("aelis.location")
 		const source2 = session2.getSource<LocationSource>("aelis.location")
@@ -50,58 +50,58 @@ describe("UserSessionManager", () => {
 		expect(source1).not.toBe(source2)
 	})
 
-	test("remove destroys session and allows re-creation", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+	test("remove destroys session and allows re-creation", async () => {
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
 		manager.remove("user-1")
-		const session2 = manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 
 		expect(session1).not.toBe(session2)
 	})
 
 	test("remove is no-op for unknown user", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
 		expect(() => manager.remove("unknown")).not.toThrow()
 	})
 
 	test("accepts function providers", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		const result = await session.engine.refresh()
 
 		expect(result.errors).toHaveLength(0)
 	})
 
-	test("accepts object providers", () => {
+	test("accepts object providers", async () => {
 		const provider = new WeatherSourceProvider({ client: mockWeatherClient })
 		const manager = new UserSessionManager({
-			providers: [() => new LocationSource(), provider],
+			providers: [async () => new LocationSource(), provider],
 		})
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session.getSource("aelis.weather")).toBeDefined()
 	})
 
-	test("accepts mixed providers", () => {
+	test("accepts mixed providers", async () => {
 		const provider = new WeatherSourceProvider({ client: mockWeatherClient })
 		const manager = new UserSessionManager({
-			providers: [() => new LocationSource(), provider],
+			providers: [async () => new LocationSource(), provider],
 		})
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session.getSource("aelis.location")).toBeDefined()
 		expect(session.getSource("aelis.weather")).toBeDefined()
 	})
 
 	test("refresh returns feed result through session", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		const result = await session.engine.refresh()
 
 		expect(result).toHaveProperty("context")
@@ -111,9 +111,9 @@ describe("UserSessionManager", () => {
 	})
 
 	test("location update via executeAction works", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		await session.engine.executeAction("aelis.location", "update-location", {
 			lat: 51.5074,
 			lng: -0.1278,
@@ -126,10 +126,10 @@ describe("UserSessionManager", () => {
 	})
 
 	test("subscribe receives updates after location push", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 		const callback = mock()
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		session.engine.subscribe(callback)
 
 		await session.engine.executeAction("aelis.location", "update-location", {
@@ -146,16 +146,16 @@ describe("UserSessionManager", () => {
 	})
 
 	test("remove stops reactive updates", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 		const callback = mock()
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		session.engine.subscribe(callback)
 
 		manager.remove("user-1")
 
 		// Create new session and push location — old callback should not fire
-		const session2 = manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 		await session2.engine.executeAction("aelis.location", "update-location", {
 			lat: 51.5074,
 			lng: -0.1278,
@@ -167,4 +167,93 @@ describe("UserSessionManager", () => {
 
 		expect(callback).not.toHaveBeenCalled()
 	})
+
+	test("creates session with successful providers when some fail", async () => {
+		const manager = new UserSessionManager({
+			providers: [
+				async () => new LocationSource(),
+				async () => {
+					throw new Error("provider failed")
+				},
+			],
+		})
+
+		const spy = spyOn(console, "error").mockImplementation(() => {})
+
+		const session = await manager.getOrCreate("user-1")
+
+		expect(session).toBeDefined()
+		expect(session.getSource("aelis.location")).toBeDefined()
+		expect(spy).toHaveBeenCalled()
+
+		spy.mockRestore()
+	})
+
+	test("throws AggregateError when all providers fail", async () => {
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					throw new Error("first failed")
+				},
+				async () => {
+					throw new Error("second failed")
+				},
+			],
+		})
+
+		await expect(manager.getOrCreate("user-1")).rejects.toBeInstanceOf(AggregateError)
+	})
+
+	test("concurrent getOrCreate for same user returns same session", async () => {
+		let callCount = 0
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					callCount++
+					// Simulate async work to widen the race window
+					await new Promise((resolve) => setTimeout(resolve, 10))
+					return new LocationSource()
+				},
+			],
+		})
+
+		const [session1, session2] = await Promise.all([
+			manager.getOrCreate("user-1"),
+			manager.getOrCreate("user-1"),
+		])
+
+		expect(session1).toBe(session2)
+		expect(callCount).toBe(1)
+	})
+
+	test("remove during in-flight getOrCreate prevents session from being stored", async () => {
+		let resolveProvider: () => void
+		const providerGate = new Promise<void>((r) => {
+			resolveProvider = r
+		})
+
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					await providerGate
+					return new LocationSource()
+				},
+			],
+		})
+
+		const sessionPromise = manager.getOrCreate("user-1")
+
+		// remove() while provider is still resolving
+		manager.remove("user-1")
+
+		// Let the provider finish
+		resolveProvider!()
+
+		await expect(sessionPromise).rejects.toThrow("removed during creation")
+
+		// A fresh getOrCreate should produce a new session, not the cancelled one
+		const freshSession = await manager.getOrCreate("user-1")
+		expect(freshSession).toBeDefined()
+		expect(freshSession.engine).toBeDefined()
+	})
 })

apps/aelis-backend/src/session/user-session-manager.ts

@@ -1,3 +1,5 @@
+import type { FeedSource } from "@aelis/core"
+
 import type { FeedEnhancer } from "../enhancement/enhance-feed.ts"
 import type { FeedSourceProviderInput } from "./feed-source-provider.ts"
 
@@ -10,6 +12,7 @@ export interface UserSessionManagerConfig {
 
 export class UserSessionManager {
 	private sessions = new Map<string, UserSession>()
+	private pending = new Map<string, Promise<UserSession>>()
 	private readonly providers: FeedSourceProviderInput[]
 	private readonly feedEnhancer: FeedEnhancer | null
 
@@ -18,16 +21,28 @@ export class UserSessionManager {
 		this.feedEnhancer = config.feedEnhancer ?? null
 	}
 
-	getOrCreate(userId: string): UserSession {
-		let session = this.sessions.get(userId)
-		if (!session) {
-			const sources = this.providers.map((p) =>
-				typeof p === "function" ? p(userId) : p.feedSourceForUser(userId),
-			)
-			session = new UserSession(sources, this.feedEnhancer)
+	async getOrCreate(userId: string): Promise<UserSession> {
+		const existing = this.sessions.get(userId)
+		if (existing) return existing
+
+		const inflight = this.pending.get(userId)
+		if (inflight) return inflight
+
+		const promise = this.createSession(userId)
+		this.pending.set(userId, promise)
+		try {
+			const session = await promise
+			// If remove() was called while we were awaiting, it clears the
+			// pending entry. Detect that and destroy the session immediately.
+			if (!this.pending.has(userId)) {
+				session.destroy()
+				throw new Error(`Session for user ${userId} was removed during creation`)
+			}
 			this.sessions.set(userId, session)
+			return session
+		} finally {
+			this.pending.delete(userId)
 		}
-		return session
 	}
 
 	remove(userId: string): void {
@@ -36,5 +51,36 @@ export class UserSessionManager {
 			session.destroy()
 			this.sessions.delete(userId)
 		}
+		// Cancel any in-flight creation so getOrCreate won't store the session
+		this.pending.delete(userId)
+	}
+
+	private async createSession(userId: string): Promise<UserSession> {
+		const results = await Promise.allSettled(
+			this.providers.map((p) =>
+				typeof p === "function" ? p(userId) : p.feedSourceForUser(userId),
+			),
+		)
+
+		const sources: FeedSource[] = []
+		const errors: unknown[] = []
+
+		for (const result of results) {
+			if (result.status === "fulfilled") {
+				sources.push(result.value)
+			} else {
+				errors.push(result.reason)
+			}
+		}
+
+		if (sources.length === 0 && errors.length > 0) {
+			throw new AggregateError(errors, "All feed source providers failed")
+		}
+
+		for (const error of errors) {
+			console.error("[UserSessionManager] Feed source provider failed:", error)
+		}
+
+		return new UserSession(sources, this.feedEnhancer)
 	}
 }