refactor!: Improve Mappings helper function(s) (#387)

BREAKING CHANGE: The `setStageDependentValue` and `getStageDependentValue` helper functions have been removed. In order to reduce boilerplate, the same functionality is now provided via a single function (`withStageDependentValue`).
guardian · Apr 7, 2021 · e001123 · e001123
1 parent 25d9da5
commit e001123
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Showing 2 changed files with 25 additions and 26 deletions.
diff --git a/src/constructs/autoscaling/asg.ts b/src/constructs/autoscaling/asg.ts
@@ -4,7 +4,7 @@ import type { ISecurityGroup, MachineImage, MachineImageConfig } from "@aws-cdk/
 import { InstanceType, OperatingSystemType, UserData } from "@aws-cdk/aws-ec2";
 import type { ApplicationTargetGroup } from "@aws-cdk/aws-elasticloadbalancingv2";
 import { Stage } from "../../constants";
-import type { GuStack, GuStageDependentValue } from "../core";
+import type { GuStack } from "../core";
 import { GuAmiParameter, GuInstanceTypeParameter } from "../core";
 import type { AppIdentity } from "../core/identity";
 import { GuHttpsEgressSecurityGroup } from "../ec2";
@@ -59,27 +59,21 @@ interface AwsAsgCapacityProps {
 }
 
 function wireStageDependentProps(stack: GuStack, stageDependentProps: GuStageDependentAsgProps): AwsAsgCapacityProps {
-  const minInstancesKey = "minInstances";
-  const maxInstancesKey = "maxInstances";
-  const minInstances: GuStageDependentValue<number> = {
-    variableName: minInstancesKey,
-    stageValues: {
-      [Stage.CODE]: stageDependentProps.CODE.minimumInstances,
-      [Stage.PROD]: stageDependentProps.PROD.minimumInstances,
-    },
-  };
-  const maxInstances: GuStageDependentValue<number> = {
-    variableName: maxInstancesKey,
-    stageValues: {
-      [Stage.CODE]: stageDependentProps.CODE.maximumInstances ?? stageDependentProps.CODE.minimumInstances * 2,
-      [Stage.PROD]: stageDependentProps.PROD.maximumInstances ?? stageDependentProps.PROD.minimumInstances * 2,
-    },
-  };
-  stack.setStageDependentValue(minInstances);
-  stack.setStageDependentValue(maxInstances);
   return {
-    minCapacity: stack.getStageDependentValue(minInstancesKey),
-    maxCapacity: stack.getStageDependentValue(maxInstancesKey),
+    minCapacity: stack.withStageDependentValue({
+      variableName: "minInstances",
+      stageValues: {
+        [Stage.CODE]: stageDependentProps.CODE.minimumInstances,
+        [Stage.PROD]: stageDependentProps.PROD.minimumInstances,
+      },
+    }),
+    maxCapacity: stack.withStageDependentValue({
+      variableName: "maxInstances",
+      stageValues: {
+        [Stage.CODE]: stageDependentProps.CODE.maximumInstances ?? stageDependentProps.CODE.minimumInstances * 2,
+        [Stage.PROD]: stageDependentProps.PROD.maximumInstances ?? stageDependentProps.PROD.minimumInstances * 2,
+      },
+    }),
   };
 }
 

diff --git a/src/constructs/core/stack.ts b/src/constructs/core/stack.ts
@@ -62,13 +62,18 @@ export class GuStack extends Stack implements StackStageIdentity {
     return this._mappings ?? (this._mappings = new GuStageMapping(this));
   }
 
-  setStageDependentValue<T extends string | number | boolean>(stageDependentValue: GuStageDependentValue<T>): void {
+  /**
+   * A helper function to switch between different values depending on the Stage being CloudFormed (e.g.
+   * use 1 in `CODE` or 3 in `PROD`).
+   *
+   * Note: Standard conditional logic which references a CloudFormation Parameter's value will not work
+   * as Parameters are not resolved at synth-time. This helper function creates CloudFormation
+   * Mappings to work around this limitation.
+   */
+  withStageDependentValue<T extends string | number | boolean>(stageDependentValue: GuStageDependentValue<T>): T {
     this.mappings.setValue(Stage.CODE, stageDependentValue.variableName, stageDependentValue.stageValues.CODE);
     this.mappings.setValue(Stage.PROD, stageDependentValue.variableName, stageDependentValue.stageValues.PROD);
-  }
-
-  getStageDependentValue<T>(key: string): T {
-    return (this.mappings.findInMap(this.stage, key) as unknown) as T;
+    return (this.mappings.findInMap(this.stage, stageDependentValue.variableName) as unknown) as T;
   }
 
   /**