From 62b4b53fb4085e9a21167532958e950331dbfb02 Mon Sep 17 00:00:00 2001
From: Kacper Donat <kadet1090@gmail.com>
Date: Tue, 8 Sep 2020 20:54:05 +0200
Subject: [PATCH] Add async state management

---
 src/api/edition.ts             |  3 ++
 src/helpers.ts                 |  4 +++
 src/hooks/index.ts             |  1 +
 src/hooks/useAsync.ts          | 50 ++++++++++++++++++++++++++++++++++
 src/pages/edition/register.tsx | 32 +++++++++++++---------
 5 files changed, 77 insertions(+), 13 deletions(-)
 create mode 100644 src/hooks/useAsync.ts

diff --git a/src/api/edition.ts b/src/api/edition.ts
index 966a036..bce8982 100644
--- a/src/api/edition.ts
+++ b/src/api/edition.ts
@@ -1,6 +1,7 @@
 import { axios } from "@/api/index";
 import { Edition } from "@/data/edition";
 import { sampleEdition } from "@/provider/dummy";
+import { delay } from "@/helpers";
 
 const EDITIONS_ENDPOINT = "/editions";
 const EDITION_INFO_ENDPOINT = "/editions/:key";
@@ -24,6 +25,8 @@ export async function join(key: string): Promise<boolean> {
 
 // MOCK
 export async function get(key: string): Promise<Edition | null> {
+    await delay(Math.random() * 200 + 100);
+
     if (key == "inf2020") {
         return sampleEdition;
     }
diff --git a/src/helpers.ts b/src/helpers.ts
index b24217f..ae9da92 100644
--- a/src/helpers.ts
+++ b/src/helpers.ts
@@ -8,3 +8,7 @@ export type Index = string | symbol | number;
 export interface DOMEvent<TTarget extends EventTarget> extends Event {
     target: TTarget;
 }
+
+export function delay(time: number) {
+  return new Promise(resolve => setTimeout(resolve, time));
+}
diff --git a/src/hooks/index.ts b/src/hooks/index.ts
index 9e7f847..848cfd7 100644
--- a/src/hooks/index.ts
+++ b/src/hooks/index.ts
@@ -1,2 +1,3 @@
 export * from "./useProxyState"
 export * from "./useUpdateEffect"
+export * from "./useAsync"
diff --git a/src/hooks/useAsync.ts b/src/hooks/useAsync.ts
new file mode 100644
index 0000000..91e1de2
--- /dev/null
+++ b/src/hooks/useAsync.ts
@@ -0,0 +1,50 @@
+import { useEffect, useState } from "react";
+
+export type AsyncResult<T, TError = any> = {
+    isLoading: boolean,
+    value: T | undefined,
+    error: TError | undefined
+};
+
+export type AsyncState<T, TError = any> = [AsyncResult<T, TError>, (promise: Promise<T> | undefined) => void]
+
+export function useAsync<T, TError = any>(promise: Promise<T> | undefined): AsyncResult<T, TError> {
+    const [isLoading, setLoading] = useState<boolean>(true);
+    const [error, setError] = useState<TError | undefined>(undefined);
+    const [value, setValue] = useState<T | undefined>(undefined);
+    const [semaphore] = useState<{ value: number }>({ value: 0 })
+
+    useEffect(() => {
+        setLoading(true);
+        setError(undefined);
+        setValue(undefined);
+
+        const myMagicNumber = semaphore.value + 1;
+        semaphore.value = myMagicNumber;
+
+        promise && promise.then(value => {
+            if (semaphore.value == myMagicNumber) {
+                setValue(value);
+                setLoading(false);
+            }
+        }).catch(error => {
+            if (semaphore.value == myMagicNumber) {
+                setError(error);
+                setLoading(false);
+            }
+        })
+    }, [ promise ])
+
+    return {
+        isLoading,
+        value,
+        error,
+    };
+}
+
+export function useAsyncState<T, TError = any>(initial: Promise<T> | undefined): AsyncState<T, TError> {
+    const [promise, setPromise] = useState<Promise<T> | undefined>(initial);
+    const asyncState = useAsync(promise);
+
+    return [ asyncState, setPromise ];
+}
diff --git a/src/pages/edition/register.tsx b/src/pages/edition/register.tsx
index a10a105..7c69834 100644
--- a/src/pages/edition/register.tsx
+++ b/src/pages/edition/register.tsx
@@ -1,11 +1,12 @@
 import React, { useEffect, useState } from "react";
 import { Page } from "@/pages/base";
 import { useTranslation } from "react-i18next";
-import { Button, Container, TextField, Typography } from "@material-ui/core";
+import { Box, Button, CircularProgress, Container, TextField, Typography } from "@material-ui/core";
 
 import api from "@/api";
 import { useVerticalSpacing } from "@/styles";
 import { Edition } from "@/data/edition";
+import { useAsyncState } from "@/hooks";
 import { Label, Section } from "@/components/section";
 import { Alert } from "@material-ui/lab";
 
@@ -13,12 +14,12 @@ export const RegisterEditionPage = () => {
     const { t } = useTranslation();
 
     const [key, setKey] = useState<string>("");
-    const [edition, setEdition] = useState<Edition | null>(null);
+    const [{ value: edition, isLoading }, setEdition] = useAsyncState<Edition | null>(undefined);
 
     const classes = useVerticalSpacing(3);
 
     useEffect(() => {
-        (async () => setEdition(await api.edition.get(key)))();
+        setEdition(api.edition.get(key));
     }, [ key ])
 
     const handleRegister = () => {
@@ -33,6 +34,17 @@ export const RegisterEditionPage = () => {
         setKey(ev.currentTarget.value);
     }
 
+    const Edition = () => edition
+        ? <Section>
+            <Label>{ t("forms.edition-register.edition" ) }</Label>
+            <Typography className="proposal__primary">{ edition.course.name }</Typography>
+            <Typography className="proposal__secondary">
+                { t('internship.date-range', { start: edition.startDate, end: edition.endDate }) }
+            </Typography>
+        </Section>
+        : <Alert severity="warning">{ t("forms.edition-register.edition-not-found") }</Alert>
+
+
     return <Page>
         <Page.Header maxWidth="md">
             <Page.Title>{ t("pages.edition.header") }</Page.Title>
@@ -42,16 +54,10 @@ export const RegisterEditionPage = () => {
             <TextField label={ t("forms.edition-register.fields.key") } fullWidth
                        onChange={ handleKeyChange }
                        value={ key } />
-            { edition
-                ? <Section>
-                    <Label>{ t("forms.edition-register.edition" ) }</Label>
-                    <Typography className="proposal__primary">{ edition.course.name }</Typography>
-                    <Typography className="proposal__secondary">
-                        { t('internship.date-range', { start: edition.startDate, end: edition.endDate }) }
-                    </Typography>
-                </Section>
-                : <Alert severity="warning">{ t("forms.edition-register.edition-not-found") }</Alert>
-            }
+
+            <Box>
+                { isLoading ? <CircularProgress /> : <Edition /> }
+            </Box>
 
             <Button onClick={ handleRegister } variant="contained" color="primary" disabled={ !edition }>{ t("forms.edition-register.register") }</Button>
         </Container>