Add android fallback for background push notifications (#102)

src/app/util/push/adapters/android.ts

@@ -0,0 +1,92 @@
+import {throttle} from "throttle-debounce"
+import {App} from "@capacitor/app"
+import {registerPlugin} from "@capacitor/core"
+import {pubkey, getSession} from "@welshman/app"
+import type {Session} from "@welshman/app"
+import {maybe, now} from "@welshman/lib"
+import type {Filter} from "@welshman/util"
+import {pushState} from "@app/core/state"
+import type {IPushAdapter} from "@app/util/push/adapters/common"
+import {requestPermissions, syncRelaySubscriptions} from "@app/util/push/adapters/common"
+
+type AndroidFallbackSubscription = {
+  relay: string
+  key: string
+  filters: Array<Filter>
+  ignore: Array<Filter>
+}
+
+type AndroidPushFallbackState = {
+  session?: Session
+  activeSince?: number
+  subscriptions?: Array<AndroidFallbackSubscription>
+}
+
+type AndroidPushFallbackPlugin = {
+  syncState: (args: {state: AndroidPushFallbackState}) => Promise<void>
+}
+
+const AndroidPushFallback = registerPlugin<AndroidPushFallbackPlugin>("AndroidPushFallback")
+
+export class AndroidFallbackNotifications implements IPushAdapter {
+  _controller = maybe<AbortController>()
+  _subscriptions = new Map<string, AndroidFallbackSubscription>()
+  _activeSince = now()
+
+  async request() {
+    return requestPermissions()
+  }
+
+  async enable() {
+    if (!this._controller) {
+      this._controller = new AbortController()
+
+      const doSync = throttle(1000, () => {
+        AndroidPushFallback.syncState({
+          state: {
+            session: pubkey.get() ? getSession(pubkey.get()!) : undefined,
+            activeSince: this._activeSince,
+            subscriptions: Array.from(this._subscriptions.values()),
+          },
+        })
+      })
+
+      let appStateListener: Awaited<ReturnType<typeof App.addListener>> | undefined
+
+      App.addListener("appStateChange", ({isActive}) => {
+        if (!isActive) {
+          this._activeSince = now()
+          doSync()
+        }
+      }).then(handle => {
+        appStateListener = handle
+      })
+
+      this._controller.signal.addEventListener("abort", () => {
+        appStateListener?.remove()
+      })
+
+      syncRelaySubscriptions(this._controller.signal, async (relay, key, filters, ignore) => {
+        if (filters.length > 0) {
+          this._subscriptions.set(`${relay}:${key}`, {relay, key, filters, ignore})
+        } else {
+          this._subscriptions.delete(`${relay}:${key}`)
+        }
+
+        doSync()
+      })
+
+      pushState.set({useFallback: true})
+    }
+  }
+
+  async disable() {
+    this._controller?.abort()
+    this._controller = undefined
+    this._subscriptions.clear()
+
+    await AndroidPushFallback.syncState({state: {}})
+
+    pushState.set({})
+  }
+}