cooking with kefir

packages/server/src/table.ts

@@ -0,0 +1,66 @@
+import { XOR } from "ts-xor";
+import Bus, { type Bus as TBus } from "kefir-bus";
+import { merge, Observable, Property, Stream } from "kefir";
+import { Game } from "@prisma/client";
+
+type TableInputEvent<GameAction> = { humanKey: string } & XOR<
+	{ presence: "joined" | "left" },
+	{ proposeGame: string },
+	{ startGame: true },
+	{ action: GameAction }
+>;
+
+type InMemoryTable<GameState> = {
+	playersPresent: string[];
+	gameState: GameState | null;
+};
+
+type TableOutputEvents<GameState> = {
+	playersPresent: Property<string[], never>;
+	gameState: Property<GameState | null, never>;
+};
+
+type TablePayload<GameAction, GameState> = {
+	input: TBus<TableInputEvent<GameAction>, never>;
+	outputs: TableOutputEvents<GameState>;
+};
+
+const tables: {
+	[key: string]: TablePayload<unknown, unknown>;
+} = {};
+
+export const liveTable = <GameState, GameAction>(key: string) => {
+	if (!(key in tables)) {
+		const inputEvents = Bus<TableInputEvent<GameAction>, never>();
+
+		tables[key] = {
+			input: inputEvents,
+			outputs: {
+				playersPresent: inputEvents
+					.filter((evt) => Boolean(evt.presence))
+					.scan((prev, evt) => {
+						if (evt.presence == "joined") {
+							prev.push(evt.humanKey);
+						} else if (evt.presence == "left") {
+							prev.splice(prev.indexOf(evt.humanKey), 1);
+						}
+						return prev;
+					}, [] as string[]),
+				gameState: inputEvents
+					.filter((evt) => Boolean(evt.startGame || evt.action))
+					.scan((prev, evt) => {
+						return prev;
+					}, null as GameState | null),
+			},
+		};
+
+		// cleanup
+		tables[key].outputs.playersPresent
+			.slidingWindow(2)
+			.filter(([prev, curr]) => prev.length > 0 && curr.length == 0)
+			.onValue((_) => {
+				delete tables[key];
+			});
+	}
+	return tables[key] as TablePayload<GameAction, GameState>;
+};