code refactoring, backend code optimization

frontend/src/atoms/downloads.ts

@@ -1,7 +1,22 @@
-import { atom } from 'recoil'
+import * as O from 'fp-ts/Option'
+import { pipe } from 'fp-ts/lib/function'
+import { atom, selector } from 'recoil'
 import { RPCResult } from '../types'
 
-export const activeDownloadsState = atom<RPCResult[] | undefined>({
+export const downloadsState = atom<O.Option<RPCResult[]>>({
+  key: 'downloadsState',
+  default: O.none
+})
+
+export const loadingDownloadsState = selector<boolean>({
+  key: 'loadingDownloadsState',
+  get: ({ get }) => O.isNone(get(downloadsState))
+})
+
+export const activeDownloadsState = selector<RPCResult[]>({
   key: 'activeDownloadsState',
-  default: undefined
+  get: ({ get }) => pipe(
+    get(downloadsState),
+    O.getOrElse(() => new Array<RPCResult>())
+  )
 })