Import and export library from/to a file (#1940)

Co-authored-by: dwelle <luzar.david@gmail.com>

src/data/library.ts

@@ -0,0 +1,43 @@
+import { loadLibraryFromBlob } from "./blob";
+import { LibraryItems, LibraryItem } from "../types";
+import { loadLibrary, saveLibrary } from "./localStorage";
+
+export class Library {
+  /** imports library (currently merges, removing duplicates) */
+  static async importLibrary(blob: any) {
+    const libraryFile = await loadLibraryFromBlob(blob);
+    if (!libraryFile || !libraryFile.library) {
+      return;
+    }
+
+    /**
+     * checks if library item does not exist already in current library
+     */
+    const isUniqueitem = (
+      existingLibraryItems: LibraryItems,
+      targetLibraryItem: LibraryItem,
+    ) => {
+      return !existingLibraryItems.find((libraryItem) => {
+        if (libraryItem.length !== targetLibraryItem.length) {
+          return false;
+        }
+
+        // detect z-index difference by checking the excalidraw elements
+        //  are in order
+        return libraryItem.every((libItemExcalidrawItem, idx) => {
+          return (
+            libItemExcalidrawItem.id === targetLibraryItem[idx].id &&
+            libItemExcalidrawItem.versionNonce ===
+              targetLibraryItem[idx].versionNonce
+          );
+        });
+      });
+    };
+
+    const existingLibraryItems = await loadLibrary();
+    const filtered = libraryFile.library!.filter((libraryItem) =>
+      isUniqueitem(existingLibraryItems, libraryItem),
+    );
+    saveLibrary([...existingLibraryItems, ...filtered]);
+  }
+}