[Persisted] Fork web and native, make it synchronous on the web (#4872)

* Delete logic for legacy storage

* Delete superfluous tests

At this point these tests aren't testing anything useful, let's just get rid of them.

* Inline store.ts methods into persisted/index.ts

* Fork persisted/index.ts into index.web.ts

* Remove non-essential code and comments from both forks

* Remove async/await from web fork of persisted/index.ts

* Remove unused return

* Enforce that forked types match

1 files changed, 126 insertions, 0 deletions

diff --git a/src/state/persisted/index.web.ts b/src/state/persisted/index.web.ts
new file mode 100644
index 000000000..50f28b6b8
--- /dev/null
+++ b/src/state/persisted/index.web.ts
@@ -0,0 +1,126 @@
+import EventEmitter from 'eventemitter3'
+
+import BroadcastChannel from '#/lib/broadcast'
+import {logger} from '#/logger'
+import {defaults, Schema, schema} from '#/state/persisted/schema'
+import {PersistedApi} from './types'
+
+export type {PersistedAccount, Schema} from '#/state/persisted/schema'
+export {defaults} from '#/state/persisted/schema'
+
+const BSKY_STORAGE = 'BSKY_STORAGE'
+
+const broadcast = new BroadcastChannel('BSKY_BROADCAST_CHANNEL')
+const UPDATE_EVENT = 'BSKY_UPDATE'
+
+let _state: Schema = defaults
+const _emitter = new EventEmitter()
+
+export async function init() {
+  broadcast.onmessage = onBroadcastMessage
+
+  try {
+    const stored = readFromStorage()
+    if (!stored) {
+      writeToStorage(defaults)
+    }
+    _state = stored || defaults
+  } catch (e) {
+    logger.error('persisted state: failed to load root state from storage', {
+      message: e,
+    })
+  }
+}
+init satisfies PersistedApi['init']
+
+export function get<K extends keyof Schema>(key: K): Schema[K] {
+  return _state[key]
+}
+get satisfies PersistedApi['get']
+
+export async function write<K extends keyof Schema>(
+  key: K,
+  value: Schema[K],
+): Promise<void> {
+  try {
+    _state[key] = value
+    writeToStorage(_state)
+    // must happen on next tick, otherwise the tab will read stale storage data
+    setTimeout(() => broadcast.postMessage({event: UPDATE_EVENT}), 0)
+  } catch (e) {
+    logger.error(`persisted state: failed writing root state to storage`, {
+      message: e,
+    })
+  }
+}
+write satisfies PersistedApi['write']
+
+export function onUpdate(cb: () => void): () => void {
+  _emitter.addListener('update', cb)
+  return () => _emitter.removeListener('update', cb)
+}
+onUpdate satisfies PersistedApi['onUpdate']
+
+export async function clearStorage() {
+  try {
+    localStorage.removeItem(BSKY_STORAGE)
+  } catch (e: any) {
+    logger.error(`persisted store: failed to clear`, {message: e.toString()})
+  }
+}
+clearStorage satisfies PersistedApi['clearStorage']
+
+async function onBroadcastMessage({data}: MessageEvent) {
+  if (typeof data === 'object' && data.event === UPDATE_EVENT) {
+    try {
+      // read next state, possibly updated by another tab
+      const next = readFromStorage()
+
+      if (next) {
+        _state = next
+        _emitter.emit('update')
+      } else {
+        logger.error(
+          `persisted state: handled update update from broadcast channel, but found no data`,
+        )
+      }
+    } catch (e) {
+      logger.error(
+        `persisted state: failed handling update from broadcast channel`,
+        {
+          message: e,
+        },
+      )
+    }
+  }
+}
+
+function writeToStorage(value: Schema) {
+  schema.parse(value)
+  localStorage.setItem(BSKY_STORAGE, JSON.stringify(value))
+}
+
+function readFromStorage(): Schema | undefined {
+  const rawData = localStorage.getItem(BSKY_STORAGE)
+  const objData = rawData ? JSON.parse(rawData) : undefined
+
+  // new user
+  if (!objData) return undefined
+
+  // existing user, validate
+  const parsed = schema.safeParse(objData)
+
+  if (parsed.success) {
+    return objData
+  } else {
+    const errors =
+      parsed.error?.errors?.map(e => ({
+        code: e.code,
+        // @ts-ignore exists on some types
+        expected: e?.expected,
+        path: e.path?.join('.'),
+      })) || []
+    logger.error(`persisted store: data failed validation on read`, {errors})
+    return undefined
+  }
+}