feat: stronger types for SSM getParameter

Author: dreamorosi

packages/parameters/src/ssm/SSMProvider.ts

@@ -16,7 +16,9 @@ import type {
 import type {
   SSMProviderOptions,
   SSMGetMultipleOptionsInterface,
-  SSMGetOptionsInterface,
+  SSMGetOptions,
+  SSMGetOptionsUnion,
+  SSMGetOutput,
   SSMGetParametersByNameOutputInterface,
   SSMGetParametersByNameOptionsInterface,
   SSMSplitBatchAndDecryptParametersOutputType,
@@ -315,11 +317,11 @@ class SSMProvider extends BaseProvider {
    * @param {SSMGetOptionsInterface} options - Options to configure the provider
    * @see https://awslabs.github.io/aws-lambda-powertools-typescript/latest/utilities/parameters/
    */
-  public async get(
+  public async get<O extends SSMGetOptionsUnion | undefined = undefined>(
     name: string,
-    options?: SSMGetOptionsInterface | undefined
-  ): Promise<string | Record<string, unknown> | undefined> {
-    return super.get(name, options) as Promise<string | Record<string, unknown> | undefined>;
+    options?: O & SSMGetOptions
+  ): Promise<SSMGetOutput<O> | undefined> {
+    return super.get(name, options) as Promise<SSMGetOutput<O> | undefined>;
   }
 
   /**
@@ -471,7 +473,7 @@ class SSMProvider extends BaseProvider {
    */
   protected async _get(
     name: string,
-    options?: SSMGetOptionsInterface
+    options?: SSMGetOptions
   ): Promise<string | undefined> {
     const sdkOptions: GetParameterCommandInput = {
       ...(options?.sdkOptions || {}),

packages/parameters/src/ssm/getParameter.ts

@@ -1,5 +1,9 @@
 import { SSMProvider, DEFAULT_PROVIDERS } from './SSMProvider';
-import type { SSMGetOptionsInterface } from '../types/SSMProvider';
+import type {
+  SSMGetOptions,
+  SSMGetOptionsUnion,
+  SSMGetOutput,
+} from '../types/SSMProvider';
 
 /**
  * ## Intro
@@ -136,15 +140,15 @@ import type { SSMGetOptionsInterface } from '../types/SSMProvider';
  * @param {SSMGetOptionsInterface} options - Options to configure the provider
  * @see https://awslabs.github.io/aws-lambda-powertools-typescript/latest/utilities/parameters/
  */
-const getParameter = (
+const getParameter = <O extends SSMGetOptionsUnion | undefined = undefined>(
   name: string,
-  options?: SSMGetOptionsInterface
-): Promise<undefined | string | Record<string, unknown>> => {
+  options?: O & SSMGetOptions
+): Promise<SSMGetOutput<O> | undefined> => {
   if (!DEFAULT_PROVIDERS.hasOwnProperty('ssm')) {
     DEFAULT_PROVIDERS.ssm = new SSMProvider();
   }
 
-  return (DEFAULT_PROVIDERS.ssm as SSMProvider).get(name, options);
+  return (DEFAULT_PROVIDERS.ssm as SSMProvider).get(name, options) as Promise<SSMGetOutput<O> | undefined>;
 };
 
 export {

packages/parameters/src/types/SSMProvider.ts

@@ -54,11 +54,32 @@ type SSMProviderOptions = SSMProviderOptionsWithClientConfig | SSMProviderOption
  * @property {TransformOptions} transform - Transform to be applied, can be 'json' or 'binary'.
  * @property {boolean} decrypt - If true, the parameter will be decrypted.
  */
-interface SSMGetOptionsInterface extends GetOptionsInterface {
+interface SSMGetOptions extends GetOptionsInterface {
   decrypt?: boolean
   sdkOptions?: Partial<GetParameterCommandInput>
 }
 
+interface SSMGetOptionsTransformJson extends SSMGetOptions {
+  transform: 'json'
+}
+
+interface SSMGetOptionsTransformBinary extends SSMGetOptions {
+  transform: 'binary'
+}
+
+interface SSMGetOptionsTransformNone extends SSMGetOptions {
+  transform?: never
+}
+
+type SSMGetOptionsUnion = SSMGetOptionsTransformJson | SSMGetOptionsTransformBinary | SSMGetOptionsTransformNone | undefined;
+
+type SSMGetOutput<O = undefined> =
+    undefined extends O ? string :
+      O extends SSMGetOptionsTransformNone | SSMGetOptionsTransformBinary ? string :
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        O extends SSMGetOptionsTransformJson ? Record<string, any> :
+          never;
+
 /**
  * Options for the SSMProvider getMultiple method.
  *
@@ -121,7 +142,9 @@ type SSMGetParametersByNameFromCacheOutputType = {
 
 export type {
   SSMProviderOptions,
-  SSMGetOptionsInterface,
+  SSMGetOptions,
+  SSMGetOptionsUnion,
+  SSMGetOutput,
   SSMGetMultipleOptionsInterface,
   SSMGetParametersByNameOptionsInterface,
   SSMSplitBatchAndDecryptParametersOutputType,