feat(frontend): add instance registry to handle singletons (#52)

Author: gregory-j-baker

frontend/app/.server/redis.ts

@@ -1,41 +1,33 @@
 import { Duration, Redacted } from 'effect';
+import type { RedisOptions } from 'ioredis';
 import Redis from 'ioredis';
 
 import { serverEnvironment } from '~/.server/environment';
 import { LogFactory } from '~/.server/logging';
+import { singleton } from '~/.server/utils/instance-registry';
 
 const log = LogFactory.getLogger(import.meta.url);
 
-/**
- * A holder for our singleton redis client instance.
- */
-const clientHolder: { client?: Redis } = {};
-
 /**
  * Retrieves the application's redis client instance.
  * If the client does not exist, it initializes a new one.
  */
-export function getRedisClient() {
-  return (clientHolder.client ??= createRedisClient());
-}
-
-/**
- * Creates a new Redis client and sets up logging for connection and error events.
- */
-function createRedisClient(): Redis {
-  log.info('Creating new redis client');
+export function getRedisClient(): Redis {
+  return singleton('redisClient', () => {
+    log.info('Creating new redis client');
 
-  const { REDIS_CONNECTION_TYPE, REDIS_HOST, REDIS_PORT } = serverEnvironment;
+    const { REDIS_CONNECTION_TYPE, REDIS_HOST, REDIS_PORT } = serverEnvironment;
 
-  return new Redis(getRedisConfig())
-    .on('connect', () => log.info('Connected to %s://%s:%s/', REDIS_CONNECTION_TYPE, REDIS_HOST, REDIS_PORT))
-    .on('error', (error) => log.error('Redis client error: %s', error.message));
+    return new Redis(getRedisConfig())
+      .on('connect', () => log.info('Connected to %s://%s:%s/', REDIS_CONNECTION_TYPE, REDIS_HOST, REDIS_PORT))
+      .on('error', (error) => log.error('Redis client error: %s', error.message));
+  });
 }
 
 /**
  * Constructs the configuration object for the Redis client based on the server environment.
  */
-function getRedisConfig() {
+function getRedisConfig(): RedisOptions {
   const {
     REDIS_COMMAND_TIMEOUT_SECONDS, //
     REDIS_HOST,

frontend/app/.server/utils/instance-registry.ts

@@ -0,0 +1,27 @@
+import { AppError } from '~/errors/app-error';
+import { ErrorCodes } from '~/errors/error-codes';
+
+/* eslint-disable @typescript-eslint/no-unnecessary-condition */
+
+export const instanceNames = ['redisClient'] as const;
+
+export type InstanceName = (typeof instanceNames)[number];
+
+/**
+ * Retrieves a singleton instance. If the instance does not exist, it is created using the provided factory function.
+ *
+ * @throws {AppError} If the instance is not found and no factory function is provided.
+ */
+export function singleton<T>(instanceName: InstanceName, factory?: () => T): T {
+  globalThis.__instanceRegistry ??= new Map<InstanceName, unknown>();
+
+  if (!globalThis.__instanceRegistry.has(instanceName)) {
+    if (!factory) {
+      throw new AppError(`Instance [${instanceName}] not found and factory not provided`, ErrorCodes.NO_FACTORY_PROVIDED);
+    }
+
+    globalThis.__instanceRegistry.set(instanceName, factory());
+  }
+
+  return globalThis.__instanceRegistry.get(instanceName) as T;
+}

frontend/app/@types/global.d.ts

@@ -1,6 +1,7 @@
 import type { RouteModules } from 'react-router';
 
 import type { ClientEnvironment } from '~/.server/environment';
+import type { InstanceName } from '~/.server/utils/instance-registry';
 
 /* eslint-disable no-var */
 
@@ -20,6 +21,11 @@ declare global {
    */
   var __appEnvironment: ClientEnvironment;
 
+  /**
+   * A holder for any application-scoped singletons.
+   */
+  var __instanceRegistry: Map<InstanceName, unknown>;
+
   /**
    * React Router adds the route modules to global
    * scope, but doesn't declare them anywhere.

frontend/app/errors/error-codes.ts

@@ -13,6 +13,9 @@ export const ErrorCodes = {
   // i18n error codes
   NO_LANGUAGE_FOUND: 'I18N-0001',
 
+  // instance error codes
+  NO_FACTORY_PROVIDED: 'INST-0001',
+
   // route error codes
   ROUTE_NOT_FOUND: 'RTE-0001',