add parameter helper functions on GuStack

Helper functions to get/set parameters on the GuStack. An `Error` is thrown when getting a parameter that hasn't been set; this is to catch the error at compile time.

src/constructs/core/parameters.ts

@@ -10,11 +10,16 @@ export interface GuParameterProps extends CfnParameterProps {
 export type GuNoTypeParameterProps = Omit<GuParameterProps, "type">;
 
 export class GuParameter extends CfnParameter {
+  public readonly id: string;
+
   constructor(scope: GuStack, id: string, props: GuParameterProps) {
     super(scope, id, {
       ...props,
       type: props.fromSSM ? `AWS::SSM::Parameter::Value<${props.type ?? "String"}>` : props.type,
     });
+
+    this.id = id;
+    scope.setParam(this);
   }
 }
 

src/constructs/core/stack.test.ts

@@ -7,6 +7,7 @@ import { alphabeticalTags, simpleGuStackForTesting } from "../../../test/utils";
 import type { SynthedStack } from "../../../test/utils";
 import { Stage, Stages } from "../../constants";
 import { TrackingTag } from "../../constants/library-info";
+import { GuParameter } from "./parameters";
 import { GuStack } from "./stack";
 
 describe("The GuStack construct", () => {
@@ -63,4 +64,21 @@ describe("The GuStack construct", () => {
 
     expect(stack.app).toBe("MyApp");
   });
+
+  it("should return a parameter that exists", () => {
+    const stack = new GuStack(new App(), "Test", { app: "MyApp", stack: "test" });
+    const testParam = new GuParameter(stack, "MyTestParam", {});
+    stack.setParam(testParam);
+
+    const actual = stack.getParam<GuParameter>("MyTestParam");
+    expect(actual).toBe(testParam);
+  });
+
+  it("should throw on attempt to get a parameter that doesn't exist", () => {
+    const stack = new GuStack(new App(), "Test", { app: "MyApp", stack: "test" });
+
+    expect(() => stack.getParam<GuParameter>("i-do-not-exist")).toThrowError(
+      "Attempting to read parameter i-do-not-exist which does not exist"
+    );
+  });
 });

src/constructs/core/stack.ts

@@ -1,6 +1,7 @@
 import type { App, StackProps } from "@aws-cdk/core";
 import { Stack, Tags } from "@aws-cdk/core";
 import { TrackingTag } from "../../constants/library-info";
+import type { GuParameter } from "./parameters";
 import { GuStageParameter } from "./parameters";
 
 export interface GuStackProps extends StackProps {
@@ -43,6 +44,8 @@ export class GuStack extends Stack {
   private readonly _stack: string;
   private readonly _app: string;
 
+  private params: Map<string, GuParameter>;
+
   public readonly migratedFromCloudFormation: boolean;
 
   get stage(): string {
@@ -73,12 +76,26 @@ export class GuStack extends Stack {
     Tags.of(this).add(key, value, { applyToLaunchedInstances });
   }
 
+  setParam(value: GuParameter): void {
+    this.params.set(value.id, value);
+  }
+
+  getParam<T extends GuParameter>(key: string): T {
+    if (!this.params.has(key)) {
+      throw new Error(`Attempting to read parameter ${key} which does not exist`);
+    }
+
+    return this.params.get(key) as T;
+  }
+
   // eslint-disable-next-line custom-rules/valid-constructors -- GuStack is the exception as it must take an App
   constructor(app: App, id: string, props: GuStackProps) {
     super(app, id, props);
 
     this.migratedFromCloudFormation = !!props.migratedFromCloudFormation;
 
+    this.params = new Map<string, GuParameter>();
+
     this._stage = new GuStageParameter(this);
     this._stack = props.stack;
     this._app = props.app;