feat(source-location): add LocationSource for push-based location context

Implements FeedSource interface. Accepts external location pushes,
provides context to downstream sources, does not produce feed items.

Supports configurable history size.

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

packages/aris-source-location/src/location-source.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, mock, test } from "bun:test"
+
+import { LocationKey, LocationSource, type Location } from "./location-source.ts"
+
+function createLocation(overrides: Partial<Location> = {}): Location {
+	return {
+		lat: 37.7749,
+		lng: -122.4194,
+		accuracy: 10,
+		timestamp: new Date(),
+		...overrides,
+	}
+}
+
+describe("LocationSource", () => {
+	describe("FeedSource interface", () => {
+		test("has correct id", () => {
+			const source = new LocationSource()
+			expect(source.id).toBe("location")
+		})
+
+		test("fetchItems always returns empty array", async () => {
+			const source = new LocationSource()
+			source.pushLocation(createLocation())
+
+			const items = await source.fetchItems()
+			expect(items).toEqual([])
+		})
+
+		test("fetchContext returns empty when no location", async () => {
+			const source = new LocationSource()
+
+			const context = await source.fetchContext()
+			expect(context).toEqual({})
+		})
+
+		test("fetchContext returns location when available", async () => {
+			const source = new LocationSource()
+			const location = createLocation()
+			source.pushLocation(location)
+
+			const context = await source.fetchContext()
+			expect(context).toEqual({ [LocationKey]: location })
+		})
+	})
+
+	describe("pushLocation", () => {
+		test("updates lastLocation", () => {
+			const source = new LocationSource()
+			expect(source.lastLocation).toBeNull()
+
+			const location = createLocation()
+			source.pushLocation(location)
+
+			expect(source.lastLocation).toEqual(location)
+		})
+
+		test("notifies listeners", () => {
+			const source = new LocationSource()
+			const listener = mock()
+
+			source.onContextUpdate(listener)
+
+			const location = createLocation()
+			source.pushLocation(location)
+
+			expect(listener).toHaveBeenCalledTimes(1)
+			expect(listener).toHaveBeenCalledWith({ [LocationKey]: location })
+		})
+	})
+
+	describe("history", () => {
+		test("default historySize is 1", () => {
+			const source = new LocationSource()
+
+			source.pushLocation(createLocation({ lat: 1 }))
+			source.pushLocation(createLocation({ lat: 2 }))
+
+			expect(source.locationHistory).toHaveLength(1)
+			expect(source.lastLocation?.lat).toBe(2)
+		})
+
+		test("respects configured historySize", () => {
+			const source = new LocationSource({ historySize: 3 })
+
+			const loc1 = createLocation({ lat: 1 })
+			const loc2 = createLocation({ lat: 2 })
+			const loc3 = createLocation({ lat: 3 })
+
+			source.pushLocation(loc1)
+			source.pushLocation(loc2)
+			source.pushLocation(loc3)
+
+			expect(source.locationHistory).toEqual([loc1, loc2, loc3])
+		})
+
+		test("evicts oldest when exceeding historySize", () => {
+			const source = new LocationSource({ historySize: 2 })
+
+			const loc1 = createLocation({ lat: 1 })
+			const loc2 = createLocation({ lat: 2 })
+			const loc3 = createLocation({ lat: 3 })
+
+			source.pushLocation(loc1)
+			source.pushLocation(loc2)
+			source.pushLocation(loc3)
+
+			expect(source.locationHistory).toEqual([loc2, loc3])
+		})
+
+		test("locationHistory is readonly", () => {
+			const source = new LocationSource({ historySize: 3 })
+			source.pushLocation(createLocation())
+
+			const history = source.locationHistory
+			expect(Array.isArray(history)).toBe(true)
+		})
+	})
+
+	describe("onContextUpdate", () => {
+		test("returns cleanup function", () => {
+			const source = new LocationSource()
+			const listener = mock()
+
+			const cleanup = source.onContextUpdate(listener)
+
+			source.pushLocation(createLocation({ lat: 1 }))
+			expect(listener).toHaveBeenCalledTimes(1)
+
+			cleanup()
+
+			source.pushLocation(createLocation({ lat: 2 }))
+			expect(listener).toHaveBeenCalledTimes(1)
+		})
+
+		test("supports multiple listeners", () => {
+			const source = new LocationSource()
+			const listener1 = mock()
+			const listener2 = mock()
+
+			source.onContextUpdate(listener1)
+			source.onContextUpdate(listener2)
+
+			source.pushLocation(createLocation())
+
+			expect(listener1).toHaveBeenCalledTimes(1)
+			expect(listener2).toHaveBeenCalledTimes(1)
+		})
+	})
+})