restore the announcement feature

commafeed-client/src/components/AnnouncementDialog.tsx

@@ -0,0 +1,36 @@
+import { Trans } from "@lingui/macro"
+import { Box, Dialog, Text } from "@mantine/core"
+import { useAppSelector } from "app/store"
+import { Content } from "components/content/Content"
+import { useAsync } from "react-async-hook"
+import useLocalStorage from "use-local-storage"
+
+const sha256Hex = async (input: string | undefined) => {
+    const data = new TextEncoder().encode(input)
+    const buffer = await crypto.subtle.digest("SHA-256", data)
+    const array = Array.from(new Uint8Array(buffer))
+    return array.map(b => b.toString(16).padStart(2, "0")).join("")
+}
+
+export function AnnouncementDialog() {
+    const announcement = useAppSelector(state => state.server.serverInfos?.announcement)
+    const announcementHash = useAsync(sha256Hex, [announcement]).result
+    const [localStorageHash, setLocalStorageHash] = useLocalStorage("announcement-hash", "no-hash")
+
+    const opened = !!announcementHash && announcementHash !== localStorageHash
+    const onClosed = () => setLocalStorageHash(announcementHash)
+
+    if (!announcement) return null
+    return (
+        <Dialog opened={opened} withCloseButton onClose={onClosed} size="xl" radius="md">
+            <Box>
+                <Text weight="bold">
+                    <Trans>Announcement</Trans>
+                </Text>
+            </Box>
+            <Box>
+                <Content content={announcement} />
+            </Box>
+        </Dialog>
+    )
+}