Add addNewAccountForKeyring method

packages/keyring-controller/src/KeyringController.test.ts

@@ -147,6 +147,106 @@ describe('KeyringController', () => {
     });
   });
 
+  describe('addNewAccountForKeyring', () => {
+    describe('when accountCount is not provided', () => {
+      it('should add new account', async () => {
+        await withController(
+          async ({ controller, initialState, preferences }) => {
+            const [primaryKeyring] = controller.getKeyringsByType(
+              KeyringTypes.hd,
+            ) as Keyring<Json>[];
+            const addedAccountAddress =
+              await controller.addNewAccountForKeyring(primaryKeyring);
+            expect(initialState.keyrings).toHaveLength(1);
+            expect(initialState.keyrings[0].accounts).not.toStrictEqual(
+              controller.state.keyrings[0].accounts,
+            );
+            expect(controller.state.keyrings[0].accounts).toHaveLength(2);
+            expect(initialState.keyrings[0].accounts).not.toContain(
+              addedAccountAddress,
+            );
+            expect(addedAccountAddress).toBe(
+              controller.state.keyrings[0].accounts[1],
+            );
+            expect(
+              preferences.updateIdentities.calledWith(
+                controller.state.keyrings[0].accounts,
+              ),
+            ).toBe(true);
+            expect(preferences.setSelectedAddress.called).toBe(false);
+          },
+        );
+      });
+    });
+
+    describe('when accountCount is provided', () => {
+      it('should add new account if accountCount is in sequence', async () => {
+        await withController(
+          async ({ controller, initialState, preferences }) => {
+            const [primaryKeyring] = controller.getKeyringsByType(
+              KeyringTypes.hd,
+            ) as Keyring<Json>[];
+            const addedAccountAddress =
+              await controller.addNewAccountForKeyring(primaryKeyring);
+            expect(initialState.keyrings).toHaveLength(1);
+            expect(initialState.keyrings[0].accounts).not.toStrictEqual(
+              controller.state.keyrings[0].accounts,
+            );
+            expect(controller.state.keyrings[0].accounts).toHaveLength(2);
+            expect(initialState.keyrings[0].accounts).not.toContain(
+              addedAccountAddress,
+            );
+            expect(addedAccountAddress).toBe(
+              controller.state.keyrings[0].accounts[1],
+            );
+            expect(
+              preferences.updateIdentities.calledWith(
+                controller.state.keyrings[0].accounts,
+              ),
+            ).toBe(true);
+            expect(preferences.setSelectedAddress.called).toBe(false);
+          },
+        );
+      });
+
+      it('should throw an error if passed accountCount param is out of sequence', async () => {
+        await withController(async ({ controller, initialState }) => {
+          const [primaryKeyring] = controller.getKeyringsByType(
+            KeyringTypes.hd,
+          ) as Keyring<Json>[];
+          const accountCount = initialState.keyrings[0].accounts.length;
+          await expect(
+            controller.addNewAccountForKeyring(
+              primaryKeyring,
+              accountCount + 1,
+            ),
+          ).rejects.toThrow('Account out of sequence');
+        });
+      });
+
+      it('should not add a new account if called twice with the same accountCount param', async () => {
+        await withController(async ({ controller, initialState }) => {
+          const accountCount = initialState.keyrings[0].accounts.length;
+          const [primaryKeyring] = controller.getKeyringsByType(
+            KeyringTypes.hd,
+          ) as Keyring<Json>[];
+          const firstAccountAdded = await controller.addNewAccountForKeyring(
+            primaryKeyring,
+            accountCount,
+          );
+          const secondAccountAdded = await controller.addNewAccountForKeyring(
+            primaryKeyring,
+            accountCount,
+          );
+          expect(firstAccountAdded).toBe(secondAccountAdded);
+          expect(controller.state.keyrings[0].accounts).toHaveLength(
+            accountCount + 1,
+          );
+        });
+      });
+    });
+  });
+
   describe('addNewAccountWithoutUpdate', () => {
     it('should add new account without updating', async () => {
       await withController(

packages/keyring-controller/src/KeyringController.ts

@@ -311,6 +311,37 @@ export class KeyringController extends BaseControllerV2<
     };
   }
 
+  /**
+   * Adds a new account to the specified keyring.
+   *
+   * @param keyring - Keyring to add the account to.
+   * @param accountCount - Number of accounts before adding a new one, used to make the method idempotent.
+   * @returns Promise resolving to keyring current state and added account
+   */
+  async addNewAccountForKeyring(
+    keyring: Keyring<Json>,
+    accountCount?: number,
+  ): Promise<Hex> {
+    const oldAccounts = await keyring.getAccounts();
+
+    if (accountCount && oldAccounts.length !== accountCount) {
+      if (accountCount > oldAccounts.length) {
+        throw new Error('Account out of sequence');
+      }
+      return oldAccounts[accountCount];
+    }
+
+    await this.#keyring.addNewAccount(keyring);
+    const addedAccountAddress = (await keyring.getAccounts()).find(
+      (selectedAddress) => !oldAccounts.includes(selectedAddress),
+    );
+    assertIsStrictHexString(addedAccountAddress);
+
+    this.updateIdentities(await this.#keyring.getAccounts());
+
+    return addedAccountAddress;
+  }
+
   /**
    * Adds a new account to the default (first) HD seed phrase keyring without updating identities in preferences.
    *