From ecc3df96dddd543da0055f26c5c7a87391ce0d82 Mon Sep 17 00:00:00 2001
From: YYang30 <yangy30@uci.edu>
Date: Mon, 27 Nov 2023 16:05:19 -0800
Subject: [PATCH] Add support for CFN function -- AccountIdFromAlias (fix for
 issue #27642)

---
 packages/aws-cdk-lib/core/lib/cfn-fn.ts       | 27 ++++++++++++++++++-
 .../core/lib/helpers-internal/cfn-parse.ts    |  4 +++
 packages/aws-cdk-lib/core/test/fn.test.ts     | 10 +++++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/packages/aws-cdk-lib/core/lib/cfn-fn.ts b/packages/aws-cdk-lib/core/lib/cfn-fn.ts
index 06344e90b5bd6..eab5dd93dba17 100644
--- a/packages/aws-cdk-lib/core/lib/cfn-fn.ts
+++ b/packages/aws-cdk-lib/core/lib/cfn-fn.ts
@@ -177,6 +177,16 @@ export class Fn {
     return Token.asList(new FnCidr(ipBlock, count, sizeMask));
   }
 
+  /**
+   * The intrinsic function ``Fn::AccountIdfromAlias`` returns the AWS account ID that
+   * corresponds to the provided AWS account alias.
+   * @param alias The user-provided AWS account alias string.
+   * @returns a token represented as a string
+   */
+  public static accountIdFromAlias(alias: string): string {
+    return Token.asString(new FnAccountIdFromAlias(alias));
+  }
+
   /**
    * Given an url, parse the domain name
    * @param url the url to parse
@@ -437,7 +447,7 @@ export class Fn {
 
   /**
    * The intrinsic function `Fn::Length` returns the number of elements within an array
-   * or an intrinsic function that returns an array.
+   * or an intrinsic function that returns an array
    *
    * @param array The array you want to return the number of elements from
    */
@@ -675,6 +685,21 @@ class FnCidr extends FnBase {
   }
 }
 
+/**
+ * The intrinsic function ``Fn::AccountIdFromAlias`` which resolves an AWS account
+ * alias to its account id. This function is typically used to to reference another
+ * account within your template.
+ */
+class FnAccountIdFromAlias extends FnBase {
+  /**
+   * Creates an ``FnAccountIdFromAlias`` function.
+   * @param alias The user-provided account alias string.
+   */
+  constructor(alias: string) {
+    super('Fn::AccountIdFromAlias', alias);
+  }
+}
+
 class FnConditionBase extends Intrinsic implements ICfnRuleConditionExpression {
   readonly disambiguator = true;
   constructor(type: string, value: any) {
diff --git a/packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts b/packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts
index 4b7fd0cbb30a4..90be702e64eff 100644
--- a/packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts
+++ b/packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts
@@ -657,6 +657,10 @@ export class CfnParser {
         }
         return { Condition: condition.logicalId };
       }
+      case 'Fn::AccountIdFromAlias': {
+        const value = this.parseValue(object[key]);
+        return Fn.accountIdFromAlias(value);
+      }
       default:
         if (this.options.context === CfnParsingContext.RULES) {
           return this.handleRulesIntrinsic(key, object);
diff --git a/packages/aws-cdk-lib/core/test/fn.test.ts b/packages/aws-cdk-lib/core/test/fn.test.ts
index a69b71f27a4fc..876a51b85eaa0 100644
--- a/packages/aws-cdk-lib/core/test/fn.test.ts
+++ b/packages/aws-cdk-lib/core/test/fn.test.ts
@@ -303,6 +303,16 @@ test('Fn.len with resolved value', () => {
   expect(Fn.len(Fn.split('|', 'a|b|c'))).toBe(3);
 });
 
+test('Fn.AccountIdFromAlias', () => {
+  const stack = new Stack();
+  const token = Fn.accountIdFromAlias('test-aws-account-alias');
+
+  expect(stack.resolve(token)).toEqual({
+    'Fn::AccountIdFromAlias':
+      'test-aws-account-alias',
+  });
+});
+
 function stringListToken(o: any): string[] {
   return Token.asList(new Intrinsic(o));
 }