fix: missing problem redirects to homepage

client/hooks.tsx

@@ -39,10 +39,11 @@ type HeuristicStateUpdater<S> = StateUpdater<S>
 
 type ResourceHookFunction = <T>(
     url: string | (() => string),
-    initialValue: T
+    initialValue: T,
+    onError?: () => void
 ) => [T, RefreshFunction, HeuristicStateUpdater<T>]
 
-export const useResource: ResourceHookFunction = (url, initialValue) => {
+export const useResource: ResourceHookFunction = (url, initialValue, onError) => {
     const [value, setValue] = useState(initialValue)
 
     function refresh() {
@@ -54,6 +55,7 @@ export const useResource: ResourceHookFunction = (url, initialValue) => {
                 if (res.ok) {
                     return res.json()
                 } else {
+                    onError?.()
                     return initialValue
                 }
             })

client/pages/Problem.tsx

@@ -1,6 +1,7 @@
+import { route } from 'preact-router'
 import { useContext, useState } from 'preact/hooks'
-import { isAdministrator, Problem as ProblemModel, Solution as SolutionModel } from '../../shared/model'
+import { isAdministrator, Solution as SolutionModel } from '../../shared/model'
-import { server } from '../api'
+import { prependBaseUrl, server } from '../api'
 import { Header } from '../components/Header'
 import { MarkdownEditor } from '../components/MarkdownEditor'
 import { Problem } from '../components/Problem'
@@ -20,9 +21,15 @@ export const ProblemPage = ({ id }: RouteProps) => {
 
     const [source, setSource] = useState('')
 
-    const [{ content }] = useResource<{ content: string }>(`/api/problem/${id}`, {
+    const [{ content }] = useResource<{ content?: string }>(
-        content: '',
+        `/api/problem/${id}`,
-    })
+        {
+            content: '',
+        },
+        () => {
+            route(prependBaseUrl('/'))
+        }
+    )
 
     const [solutions, refreshSolutions, setSolutionHeuristic] = useListResource<SolutionModel>(
         `/api/solutions?problem=${id}`