Feature flags

1import { col, createDatabase } from "yatta/db";2import { createCache } from "yatta/cache";3 4export const FLAG_KEYS = [5  "new-checkout",6  "ai-summaries",7  "dark-mode",8  "usage-billing",9] as const;10 11export type FlagKey = (typeof FLAG_KEYS)[number];12export type FlagValue = boolean | number | string;13 14export const schema = {15  flags: {16    key: col.text().primaryKey(),17    value: col.text(),18    description: col.text().nullable(),19    updatedAt: col.createdAt(),20  },21 22  // Per-user overrides, so you can enable a flag for yourself before rolling23  // it out to everyone.24  flagOverrides: {25    id: col.uuid(),26    flagKey: col.text(),27    userId: col.text(),28    value: col.text(),29    expiresAt: col.date().nullable(),30  },31};32 33export const db = createDatabase({ url: process.env.DATABASE_URL, schema });34export const cache = createCache({ maxSize: 500 });

1import { z } from "zod";2 3const CACHE_TTL = "30s";4 5function parse(raw: string): FlagValue {6  if (raw === "true") return true;7  if (raw === "false") return false;8  const n = Number(raw);9  return Number.isNaN(n) ? raw : n;10}11 12/**13 * Resolve one flag: override, then cache, then database.14 */15export async function getFlag(key: FlagKey, userId?: string): Promise<FlagValue> {16  if (userId) {17    const override = await db.flagOverrides18      .where((f) => and(19        f.flagKey.isEqualTo(key),20        f.userId.isEqualTo(userId),21      ))22      .first();23 24    if (override && (!override.expiresAt || override.expiresAt > new Date())) {25      return parse(override.value);26    }27  }28 29  return cache.remember(30    `flag:${key}`,31    async () => {32      const row = await db.flags.where((f) => f.key.isEqualTo(key)).first();33      return row ? parse(row.value) : false;34    },35    { ttl: CACHE_TTL, tags: ["flags"] },36  );37}38 39/** Evaluate many flags in one round trip. */40export async function evaluate(userId?: string): Promise<Record<FlagKey, FlagValue>> {41  const entries = await Promise.all(42    FLAG_KEYS.map(async (k) => [k, await getFlag(k, userId)] as const),43  );44  return Object.fromEntries(entries) as Record<FlagKey, FlagValue>;45}

1import { realtime } from "./realtime";2 3export async function setFlag(4  key: FlagKey,5  value: FlagValue,6): Promise<void> {7  await db.flags8    .where((f) => f.key.isEqualTo(key))9    .update({ value: String(value), updatedAt: new Date() });10 11  // One tag invalidates every read for this key, in L1 and L2.12  await cache.invalidateTags("flags");13 14  // Open browsers apply it without a refresh.15  realtime.to("flags").send("flag.updated", { key, value });16}17 18/** Give one user a temporary override, e.g. to debug a rollout. */19export async function overrideFor(20  key: FlagKey,21  userId: string,22  value: FlagValue,23  hours = 24,24): Promise<void> {25  await db.flagOverrides.insert({26    flagKey: key,27    userId,28    value: String(value),29    expiresAt: new Date(Date.now() + hours * 3_600_000),30  });31}

1const store = {};2 3// One socket, not one per flag.4const ws = new WebSocket(`ws://${location.host}/ws`);5 6ws.addEventListener("message", (e) => {7  const { event, data } = JSON.parse(e.data);8  if (event !== "flag.updated") return;9 10  store[data.key] = data.value;11 12  // Re-render whatever subscribed to this flag.13  window.dispatchEvent(14    new CustomEvent("yatta:flag", { detail: data }),15  );16});17 18window.flags = {19  get: (key) => store[key] ?? false,20  on: (key, fn) => {21    const handler = (e) => {22      if (e.detail.key === key) fn(e.detail.value);23    };24    window.addEventListener("yatta:flag", handler);25    return () => window.removeEventListener("yatta:flag", handler);26  },27};28 29// Hydrate from the server on first paint so there is no flash of default.30const res = await fetch("/api/flags");31const initial = await res.json();32Object.assign(store, initial);