Add utility function to create paginated messages

backend/src/utils/createPaginatedMessage.ts

@@ -0,0 +1,91 @@
+import { Client, Emoji, MemberPartial, Message, MessageContent, TextableChannel } from "eris";
+import { Awaitable } from "knub/dist/utils";
+import { MINUTES, noop } from "../utils";
+import Timeout = NodeJS.Timeout;
+
+export type LoadPageFn = (page: number) => Awaitable<MessageContent>;
+
+export interface PaginateMessageOpts {
+  timeout: number;
+  limitToUserId: string | null;
+}
+
+const defaultOpts: PaginateMessageOpts = {
+  timeout: 5 * MINUTES,
+  limitToUserId: null,
+};
+
+export async function createPaginatedMessage(
+  client: Client,
+  channel: TextableChannel,
+  totalPages: number,
+  loadPageFn: LoadPageFn,
+  opts: Partial<PaginateMessageOpts> = {},
+): Promise<Message> {
+  const fullOpts = { ...defaultOpts, ...opts } as PaginateMessageOpts;
+  const firstPageContent = await loadPageFn(1);
+  const message = await channel.createMessage(firstPageContent);
+
+  let page = 1;
+  let pageLoadId = 0; // Used to avoid race conditions when rapidly switching pages
+  const reactionListener = async (reactionMessage: Message, emoji: Emoji, reactor: MemberPartial) => {
+    if (reactionMessage.id !== message.id) {
+      return;
+    }
+
+    if (fullOpts.limitToUserId && reactor.id !== fullOpts.limitToUserId) {
+      return;
+    }
+
+    if (reactor.id === client.user.id) {
+      return;
+    }
+
+    let pageDelta = 0;
+    if (emoji.name === "⬅️") {
+      pageDelta = -1;
+    } else if (emoji.name === "➡️") {
+      pageDelta = 1;
+    }
+
+    if (!pageDelta) {
+      return;
+    }
+
+    const newPage = Math.max(Math.min(page + pageDelta, totalPages), 1);
+    if (newPage === page) {
+      return;
+    }
+
+    page = newPage;
+    const thisPageLoadId = ++pageLoadId;
+    const newPageContent = await loadPageFn(page);
+    if (thisPageLoadId !== pageLoadId) {
+      return;
+    }
+
+    message.edit(newPageContent).catch(noop);
+    message.removeReaction(emoji.name, reactor.id);
+    refreshTimeout();
+  };
+  client.on("messageReactionAdd", reactionListener);
+
+  // The timeout after which reactions are removed and the pagination stops working
+  // is refreshed each time the page is changed
+  let timeout: Timeout;
+  const refreshTimeout = () => {
+    clearTimeout(timeout);
+    timeout = setTimeout(() => {
+      message.removeReactions().catch(noop);
+      client.off("messageReactionAdd", reactionListener);
+    }, fullOpts.timeout);
+  };
+
+  refreshTimeout();
+
+  // Add reactions
+  message.addReaction("⬅️").catch(noop);
+  message.addReaction("➡️").catch(noop);
+
+  return message;
+}