Added feature flags system (#803)

* added feature flag system

* Update packages/web/src/core/services/featureFlags.ts

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* remove process.env

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

packages/web/src/core/hooks/useFeatureFlags.ts

@@ -0,0 +1,22 @@
+import {
+  type FlagKey,
+  type Flags,
+  featureFlags,
+} from "@core/services/featureFlags.ts";
+import * as React from "react";
+
+export function useFeatureFlags(): Flags {
+  return React.useSyncExternalStore(
+    (cb) => featureFlags.subscribe(cb),
+    () => featureFlags.all(),
+    () => featureFlags.all(),
+  );
+}
+
+export function useFeatureFlag(key: FlagKey): boolean {
+  return React.useSyncExternalStore(
+    (cb) => featureFlags.subscribe(cb),
+    () => featureFlags.get(key),
+    () => featureFlags.get(key),
+  );
+}

packages/web/src/core/services/dev-overrides.ts

@@ -0,0 +1,10 @@
+import { featureFlags } from "@core/services/featureFlags";
+
+const isDev = typeof import.meta !== "undefined" && import.meta.env?.DEV;
+console.log(`Dev mode: ${isDev}`);
+
+if (isDev) {
+  featureFlags.setOverrides({
+    persistNodeDB: true,
+  });
+}

packages/web/src/core/services/featureFlags.ts

@@ -0,0 +1,89 @@
+import { z } from "zod";
+
+/** Map feature keys -> env var names (Vite exposes only VITE_*). */
+export const FLAG_ENV = {
+  persistNodeDB: "VITE_PERSIST_NODE_DB",
+  persistMessages: "VITE_PERSIST_MESSAGES",
+} as const;
+
+export type FlagKey = keyof typeof FLAG_ENV;
+export type Flags = Record<FlagKey, boolean>;
+
+type Listener = () => void;
+
+const present = z
+  .string()
+  .optional()
+  .transform((v) => v !== undefined);
+
+const mutableShape: Record<string, z.ZodTypeAny> = {};
+for (const envName of Object.values(FLAG_ENV)) {
+  mutableShape[envName] = present;
+}
+const EnvSchema = z.object(mutableShape);
+
+class FeatureFlags {
+  private base: Flags;
+  private overrides: Partial<Flags> = {};
+  private listeners = new Set<Listener>();
+
+  constructor(base: Flags) {
+    this.base = base;
+  }
+
+  get(key: FlagKey): boolean {
+    return this.overrides[key] ?? this.base[key];
+  }
+
+  /** Get all flags */
+  all(): Flags {
+    return { ...this.base, ...this.overrides };
+  }
+
+  /** Optional dev/test override. Pass null to clear. */
+  setOverride(key: FlagKey, val: boolean | null) {
+    if (val === null) {
+      delete this.overrides[key];
+    } else {
+      this.overrides[key] = val;
+    }
+    this.emit();
+  }
+
+  /** Set many at once */
+  setOverrides(partial: Partial<Flags>) {
+    for (const [k, v] of Object.entries(partial)) {
+      this.setOverride(k as FlagKey, v as boolean);
+      if (v === null) {
+        delete this.overrides[k as FlagKey];
+      } else {
+        this.overrides[k as FlagKey] = v as boolean;
+      }
+    }
+    this.emit();
+  }
+
+  subscribe(fn: Listener) {
+    this.listeners.add(fn);
+    return () => this.listeners.delete(fn);
+  }
+
+  private emit() {
+    for (const listener of this.listeners) {
+      listener();
+    }
+  }
+}
+
+export function createFeatureFlags(env: Record<string, unknown>): FeatureFlags {
+  const parsed = EnvSchema.parse(env);
+  const base = Object.fromEntries(
+    (Object.keys(FLAG_ENV) as FlagKey[]).map((k) => [
+      k,
+      parsed[FLAG_ENV[k]] as boolean,
+    ]),
+  ) as Flags;
+  return new FeatureFlags(base);
+}
+
+export const featureFlags = createFeatureFlags(import.meta.env);