feat: add snjs package

packages/snjs/lib/Migrations/StorageReaders/Reader.ts

@@ -0,0 +1,31 @@
+import { ApplicationIdentifier } from '@standardnotes/common'
+import { DeviceInterface, Environment } from '@standardnotes/services'
+
+/**
+ * A storage reader reads storage via a device interface
+ * given a specific version of SNJS
+ */
+export abstract class StorageReader {
+  constructor(
+    protected deviceInterface: DeviceInterface,
+    protected identifier: ApplicationIdentifier,
+    protected environment: Environment,
+  ) {}
+
+  public static version(): string {
+    throw Error('Must override')
+  }
+
+  public abstract getAccountKeyParams(): Promise<unknown | undefined>
+
+  /**
+   * Returns true if the state of storage has account keys present
+   * in version-specific storage (either keychain or raw storage)
+   */
+  public abstract hasNonWrappedAccountKeys(): Promise<boolean>
+
+  public abstract hasPasscode(): Promise<boolean>
+
+  /** Whether this version used the keychain to store keys */
+  public abstract usesKeychain(): boolean
+}