feat: add snjs package

packages/snjs/lib/Application/LiveItem.ts

@@ -0,0 +1,34 @@
+import { DecryptedItemInterface } from '@standardnotes/models'
+import { SNApplication } from './Application'
+
+/** Keeps an item reference up to date with changes */
+export class LiveItem<T extends DecryptedItemInterface> {
+  public item: T
+  private removeObserver: () => void
+
+  constructor(uuid: string, application: SNApplication, onChange?: (item: T) => void) {
+    this.item = application.items.findSureItem(uuid)
+
+    onChange && onChange(this.item)
+
+    this.removeObserver = application.streamItems(this.item.content_type, ({ changed, inserted }) => {
+      const matchingItem = [...changed, ...inserted].find((item) => {
+        return item.uuid === uuid
+      })
+
+      if (matchingItem) {
+        this.item = matchingItem as T
+        onChange && onChange(this.item)
+      }
+    })
+  }
+
+  public deinit() {
+    if (!this.removeObserver) {
+      console.error('A LiveItem is attempting to be deinited more than once.')
+    } else {
+      this.removeObserver()
+      ;(this.removeObserver as unknown) = undefined
+    }
+  }
+}