implemented namespaced config

src/config.module.ts

@@ -23,6 +23,8 @@
  *   - Validation runs BEFORE any other provider resolves.
  *   - If validation fails, ConfigValidationError is thrown and the app
  *     never finishes booting.
+ *   - A shared namespace registry (Set<string>) is exported so that
+ *     NamespacedConfig.asProvider() can detect duplicate namespaces.
  *
  *   Contents:
  *   - ConfigModuleAsyncOptions — interface for registerAsync options
@@ -33,9 +35,9 @@ import { DynamicModule, Global, Module } from "@nestjs/common";
 import type { Provider } from "@nestjs/common";
 import type { z } from "zod";
 
-import { CONFIG_VALUES_TOKEN } from "@/constants";
-import type { ConfigDefinition } from "@/define-config";
 import { ConfigService } from "@/config.service";
+import { CONFIG_VALUES_TOKEN, NAMESPACE_REGISTRY_TOKEN } from "@/constants";
+import type { ConfigDefinition } from "@/define-config";
 
 // ─────────────────────────────────────────────────────────────────────────────
 // Internal type helpers
@@ -82,9 +84,7 @@ export interface ConfigModuleAsyncOptions<T extends AnyZodObject = AnyZodObject>
    * Factory function that returns the ConfigDefinition to validate.
    * May be synchronous or async.
    */
-  useFactory: (
-    ...args: unknown[]
-  ) => Promise<ConfigDefinition<T>> | ConfigDefinition<T>;
+  useFactory: (...args: unknown[]) => Promise<ConfigDefinition<T>> | ConfigDefinition<T>;
 }
 
 // ─────────────────────────────────────────────────────────────────────────────
@@ -145,14 +145,24 @@ export class ConfigModule {
       useValue: parsedConfig,
     };
 
+    // Namespace registry — a shared Set<string> that NamespacedConfig.asProvider()
+    // injects to detect duplicate namespace registrations at module init time.
+    // A fresh Set is created per ConfigModule instance.
+    const namespaceRegistryProvider: Provider = {
+      provide: NAMESPACE_REGISTRY_TOKEN,
+      useValue: new Set<string>(),
+    };
+
     return {
       module: ConfigModule,
       providers: [
-        configValuesProvider, // must be listed before ConfigService (which depends on it)
+        configValuesProvider, // parsed config values — must come before ConfigService
+        namespaceRegistryProvider, // registry for namespace duplicate detection
         ConfigService,
       ],
-      // Export ConfigService so the importing module can inject it
-      exports: [ConfigService],
+      // Export both ConfigService and the registry so feature modules' asProvider()
+      // can inject NAMESPACE_REGISTRY_TOKEN
+      exports: [ConfigService, NAMESPACE_REGISTRY_TOKEN],
       // Non-global: only available in the importing module unless re-exported
       global: false,
     };
@@ -201,12 +211,18 @@ export class ConfigModule {
       inject: (options.inject ?? []) as never[],
     };
 
+    // Namespace registry shared with feature modules' asProvider() factories
+    const namespaceRegistryProvider: Provider = {
+      provide: NAMESPACE_REGISTRY_TOKEN,
+      useValue: new Set<string>(),
+    };
+
     return {
       module: ConfigModule,
       // Make the imported modules available so the factory can resolve them
       imports: options.imports ?? [],
-      providers: [configValuesProvider, ConfigService],
-      exports: [ConfigService],
+      providers: [configValuesProvider, namespaceRegistryProvider, ConfigService],
+      exports: [ConfigService, NAMESPACE_REGISTRY_TOKEN],
       global: false,
     };
   }

src/constants.ts

@@ -6,22 +6,62 @@
  *   These tokens are the "glue" between ConfigModule providers and the
  *   services that consume them.  They are NOT part of the public API —
  *   consumers should never inject these tokens directly; they should use
- *   ConfigService instead.
+ *   ConfigService or @InjectConfig() instead.
  *
  *   Contents:
- *   - CONFIG_VALUES_TOKEN — token for the parsed, frozen config object
+ *   - CONFIG_VALUES_TOKEN        — token for the root parsed config object
+ *   - getNamespaceToken()        — generates a unique DI token per namespace
+ *   - NAMESPACE_REGISTRY_TOKEN   — token for the set of registered namespace names
  */
 
 // ─────────────────────────────────────────────────────────────────────────────
-// DI Tokens
+// Root config token
 // ─────────────────────────────────────────────────────────────────────────────
 
 /**
- * Injection token for the parsed and validated config object.
+ * Injection token for the parsed and validated root config object.
  *
  * ConfigModule registers the result of `definition.parse(process.env)` under
  * this token.  ConfigService then injects it to serve typed `get()` calls.
  *
  * Consumers should never inject this token directly — always use ConfigService.
  */
 export const CONFIG_VALUES_TOKEN = "CONFIG_KIT_VALUES" as const;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Namespace tokens
+// ─────────────────────────────────────────────────────────────────────────────
+
+/**
+ * Generates a unique, stable DI token for a given namespace string.
+ *
+ * Each namespace gets its own token so that NestJS can inject the correct
+ * validated config slice into each feature module independently.
+ *
+ * The token is a plain string prefixed with `CONFIG_KIT_NS:` to avoid any
+ * accidental collision with other DI tokens in the consuming app.
+ *
+ * @param namespace - The namespace name passed to `defineNamespace()`.
+ * @returns A unique DI token string for that namespace.
+ *
+ * @example
+ * ```typescript
+ * getNamespaceToken('database') // → 'CONFIG_KIT_NS:database'
+ * getNamespaceToken('auth')     // → 'CONFIG_KIT_NS:auth'
+ * ```
+ */
+export function getNamespaceToken(namespace: string): string {
+  return `CONFIG_KIT_NS:${namespace}`;
+}
+
+/**
+ * Injection token for the namespace registry.
+ *
+ * ConfigModule stores a `Set<string>` of all registered namespace names under
+ * this token at startup.  When a new NamespacedConfig is added, it checks this
+ * registry and throws if the namespace has already been registered — preventing
+ * silent duplicate registrations that would produce unpredictable behavior.
+ *
+ * This token is internal; consumers never interact with it directly.
+ */
+export const NAMESPACE_REGISTRY_TOKEN = "CONFIG_KIT_NS_REGISTRY" as const;

src/decorators/inject-config.decorator.ts

@@ -0,0 +1,72 @@
+/**
+ * @file inject-config.decorator.ts
+ * @description
+ *   Parameter decorator for injecting a typed namespace config slice into
+ *   NestJS constructors.
+ *
+ *   Usage:
+ *   ```typescript
+ *   constructor(
+ *     @InjectConfig('auth') private cfg: z.output<typeof authConfig.definition.schema>
+ *   ) {}
+ *   ```
+ *
+ *   Under the hood it is just `@Inject(getNamespaceToken(namespace))` — a thin
+ *   wrapper so consumers never have to know about the internal token format.
+ *
+ *   Contents:
+ *   - InjectConfig() — parameter decorator factory
+ */
+
+import { Inject } from "@nestjs/common";
+
+import { getNamespaceToken } from "@/constants";
+
+// ─────────────────────────────────────────────────────────────────────────────
+// @InjectConfig
+// ─────────────────────────────────────────────────────────────────────────────
+
+/**
+ * Parameter decorator that injects the validated config slice for a namespace.
+ *
+ * Must be used in constructors of NestJS providers (services, controllers, etc.)
+ * inside a module that has imported ConfigModule and added the corresponding
+ * `NamespacedConfig.asProvider()` to its `providers` array.
+ *
+ * The injected value is a frozen, fully-typed object — the Zod output of the
+ * schema passed to `defineNamespace()`.  No `string | undefined` values.
+ *
+ * @param namespace - The namespace name used in `defineNamespace(namespace, schema)`.
+ *                   Must match exactly (case-sensitive).
+ * @returns A NestJS `@Inject()` parameter decorator bound to the namespace token.
+ *
+ * @example
+ * ```typescript
+ * // auth/auth.config.ts
+ * export const authConfig = defineNamespace('auth', z.object({
+ *   JWT_SECRET:     z.string().min(32),
+ *   JWT_EXPIRES_IN: z.string().default('7d'),
+ * }));
+ *
+ * // auth/auth.module.ts
+ * @Module({ providers: [authConfig.asProvider(), AuthService] })
+ * export class AuthModule {}
+ *
+ * // auth/auth.service.ts
+ * @Injectable()
+ * export class AuthService {
+ *   constructor(
+ *     // Injects the validated { JWT_SECRET: string, JWT_EXPIRES_IN: string } object
+ *     @InjectConfig('auth') private cfg: z.output<typeof authConfig.definition.schema>
+ *   ) {}
+ *
+ *   getSecret(): string {
+ *     return this.cfg.JWT_SECRET; // string — never undefined
+ *   }
+ * }
+ * ```
+ */
+export function InjectConfig(namespace: string): ParameterDecorator {
+  // Resolve the namespace to its unique DI token and delegate to NestJS @Inject
+  return Inject(getNamespaceToken(namespace));
+}