Refactors the api (#113)

* Refactor api.

* Try fix ci.

* Fix test.

* Address review comments.

.github/workflows/rust.yml

@@ -16,8 +16,7 @@ jobs:
 
     - name: setup
       run: |
-        rustup install nightly
-        rustup component add rustfmt --toolchain nightly
+        rustup install nightly --profile default
 
     - name: fmt
       run: cargo +nightly fmt --all -- --check