Add utility to check for non migrated legacy db (#4055)

* Add utility to check for non migrated legacy db

* code review changes

* add unit tests for existsAndIsNotMigrated

* ensure indexeddb is clean for each state

spec/unit/crypto/store/IndexedDBCryptoStore.spec.ts

@@ -0,0 +1,73 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import "fake-indexeddb/auto";
+import { IndexedDBCryptoStore } from "../../../../src";
+import { MigrationState } from "../../../../src/crypto/store/base";
+
+describe("IndexedDBCryptoStore", () => {
+    describe("Test `existsAndIsNotMigrated`", () => {
+        beforeEach(async () => {
+            // eslint-disable-next-line no-global-assign
+            indexedDB = new IDBFactory();
+        });
+
+        it("Should be true if there is a legacy database", async () => {
+            // should detect a store that is not migrated
+            const store = new IndexedDBCryptoStore(global.indexedDB, "tests");
+            await store.startup();
+
+            const result = await IndexedDBCryptoStore.existsAndIsNotMigrated(global.indexedDB, "tests");
+
+            expect(result).toBe(true);
+        });
+
+        it("Should be true if there is a legacy database in non migrated state", async () => {
+            // should detect a store that is not migrated
+            const store = new IndexedDBCryptoStore(global.indexedDB, "tests");
+            await store.startup();
+            await store.setMigrationState(MigrationState.NOT_STARTED);
+
+            const result = await IndexedDBCryptoStore.existsAndIsNotMigrated(global.indexedDB, "tests");
+
+            expect(result).toBe(true);
+        });
+
+        describe.each([
+            MigrationState.INITIAL_DATA_MIGRATED,
+            MigrationState.OLM_SESSIONS_MIGRATED,
+            MigrationState.MEGOLM_SESSIONS_MIGRATED,
+            MigrationState.ROOM_SETTINGS_MIGRATED,
+        ])("Exists and Migration state is %s", (migrationState) => {
+            it("Should be false if migration has started", async () => {
+                // should detect a store that is not migrated
+                const store = new IndexedDBCryptoStore(global.indexedDB, "tests");
+                await store.startup();
+                await store.setMigrationState(migrationState);
+
+                const result = await IndexedDBCryptoStore.existsAndIsNotMigrated(global.indexedDB, "tests");
+
+                expect(result).toBe(false);
+            });
+        });
+
+        it("Should be false if there is no legacy database", async () => {
+            const result = await IndexedDBCryptoStore.existsAndIsNotMigrated(global.indexedDB, "tests");
+
+            expect(result).toBe(false);
+        });
+    });
+});