skip installation if the version is already installed (#27)

* remove ansi codes from provided version string

* add check func whether the specify version is already installed or not

* Revert "remove ansi codes from provided version string"

This reverts commit 9e5b27f942e8be94c1bffda13a254f46cbf3dece.

* apply code review(rename check function)

* run esy fmt

* move short path to the top of the switch case

* use Result.fold instead of switch case

* use Array.exists instead of List.exists

executable/Install.re

@@ -27,6 +27,7 @@ let main = (~version as versionName) => {
     };
 
   let versionName = Versions.format(versionName);
+  let%lwt _ = Versions.throwIfInstalled(versionName);
 
   Console.log(
     <Pastel>

library/Versions.re

@@ -8,6 +8,7 @@ module Local = {
 };
 
 exception Version_not_found(string);
+exception Already_installed(string);
 
 module Remote = {
   type t = {
@@ -145,3 +146,15 @@ let getRemoteVersions = () => {
      )
   |> Lwt.return;
 };
+
+let throwIfInstalled = versionName => {
+  getInstalledVersions()
+  |> Result.fold(
+       _ => Lwt.return(),
+       xs =>
+         Array.exists(x => Local.(x.name == versionName), xs)
+         |> (
+           x => x ? Lwt.fail(Already_installed(versionName)) : Lwt.return()
+         ),
+     );
+};