From 209ffa55bfd3532b2771e3bfb03ef771d1a05eed Mon Sep 17 00:00:00 2001
From: Jacob Bolda <me@jacobbolda.com>
Date: Wed, 28 Aug 2024 12:30:04 -0500
Subject: [PATCH 1/2] foundation simulator delay response API

---
 .changes/foundation-delay.md                |  5 ++
 packages/foundation/src/index.ts            |  4 ++
 packages/foundation/src/middleware/delay.ts | 61 +++++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 .changes/foundation-delay.md
 create mode 100644 packages/foundation/src/middleware/delay.ts

diff --git a/.changes/foundation-delay.md b/.changes/foundation-delay.md
new file mode 100644
index 00000000..48f324f9
--- /dev/null
+++ b/.changes/foundation-delay.md
@@ -0,0 +1,5 @@
+---
+"@simulacrum/foundation-simulator": minor:enhance
+---
+
+Add API to configure a delay of all responses with a set interval. Using this in a simulator would enable a feel closer to a real external endpoint.
diff --git a/packages/foundation/src/index.ts b/packages/foundation/src/index.ts
index aa2febda..5ef77cd7 100644
--- a/packages/foundation/src/index.ts
+++ b/packages/foundation/src/index.ts
@@ -28,6 +28,7 @@ import type {
   ExtendSimulationSchema,
 } from "./store/schema";
 import type { RecursivePartial } from "./store/types";
+import { delayMiddleware } from "./middleware/delay";
 
 type SimulationHandlerFunctions = (
   context: OpenAPIBackendContext,
@@ -50,12 +51,14 @@ export function createFoundationSimulationServer<
   ExtendedSimulationSelectors
 >({
   port = 9000,
+  delayResponses,
   serveJsonFiles,
   openapi,
   extendStore,
   extendRouter,
 }: {
   port: number;
+  delayResponses?: number | { minimum: number; maximum: number };
   serveJsonFiles?: string;
   openapi?: {
     document: Document | (Document | RecursivePartial<Document>)[];
@@ -93,6 +96,7 @@ export function createFoundationSimulationServer<
     let app = express();
     app.use(express.json());
     let simulationStore = createSimulationStore(extendStore);
+    app.use(delayMiddleware(delayResponses));
 
     if (serveJsonFiles) {
       const jsonFiles = new fdir()
diff --git a/packages/foundation/src/middleware/delay.ts b/packages/foundation/src/middleware/delay.ts
new file mode 100644
index 00000000..519d0834
--- /dev/null
+++ b/packages/foundation/src/middleware/delay.ts
@@ -0,0 +1,61 @@
+import type { Request, Response, NextFunction } from "express";
+
+export function delayMiddleware(
+  delayResponses?: number | { minimum: number; maximum: number }
+) {
+  const delayMin =
+    typeof delayResponses === "number"
+      ? delayResponses
+      : delayResponses?.minimum;
+  const delayMax =
+    typeof delayResponses === "number" ? undefined : delayResponses?.maximum;
+
+  const minFromProcess = process.env.SIM_RESPONSE_DELAY_MIN
+    ? process.env.SIM_RESPONSE_DELAY_MIN
+    : process.env.SIM_RESPONSE_DELAY;
+  const min = minFromProcess ? parseInt(minFromProcess, 10) : delayMin;
+
+  const maxFromProcess = process.env.SIM_RESPONSE_DELAY_MAX;
+  const max = maxFromProcess ? parseInt(maxFromProcess, 10) : delayMax;
+
+  return async function delayHandler(
+    request: Request,
+    response: Response,
+    next: NextFunction
+  ) {
+    if (min || max) {
+      let timeoutDuration = calculateTimeoutDuration(min, max);
+      await new Promise<void>((resolve) => {
+        let timeoutHandle: NodeJS.Timeout | undefined = undefined;
+
+        const done = () => {
+          if (timeoutHandle) {
+            clearTimeout(timeoutHandle);
+          }
+          resolve();
+        };
+
+        timeoutHandle = setTimeout(done, timeoutDuration);
+      });
+    }
+    next();
+  };
+}
+
+function calculateTimeoutDuration(
+  min: number | undefined,
+  max: number | undefined
+): number {
+  if (max && !min) {
+    // sets the timeout at +/- 20% of configured max
+    return max * 0.8 + max * 0.4 * Math.random();
+  } else if (min && !max) {
+    // sets the timeout at +/- 20% of configured max
+    return min * 0.8 + min * 0.4 * Math.random();
+  } else if (max && min) {
+    const timeoutRange = max - min;
+    return min + timeoutRange * Math.random();
+  }
+
+  return 0;
+}

From 1254deeddf49d2b16beab283bc8b9f165c3519ff Mon Sep 17 00:00:00 2001
From: Jacob Bolda <me@jacobbolda.com>
Date: Thu, 12 Sep 2024 14:55:26 -0500
Subject: [PATCH 2/2] remove process

---
 packages/foundation/src/middleware/delay.ts | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/packages/foundation/src/middleware/delay.ts b/packages/foundation/src/middleware/delay.ts
index 519d0834..29e9fb1c 100644
--- a/packages/foundation/src/middleware/delay.ts
+++ b/packages/foundation/src/middleware/delay.ts
@@ -10,21 +10,13 @@ export function delayMiddleware(
   const delayMax =
     typeof delayResponses === "number" ? undefined : delayResponses?.maximum;
 
-  const minFromProcess = process.env.SIM_RESPONSE_DELAY_MIN
-    ? process.env.SIM_RESPONSE_DELAY_MIN
-    : process.env.SIM_RESPONSE_DELAY;
-  const min = minFromProcess ? parseInt(minFromProcess, 10) : delayMin;
-
-  const maxFromProcess = process.env.SIM_RESPONSE_DELAY_MAX;
-  const max = maxFromProcess ? parseInt(maxFromProcess, 10) : delayMax;
-
   return async function delayHandler(
     request: Request,
     response: Response,
     next: NextFunction
   ) {
-    if (min || max) {
-      let timeoutDuration = calculateTimeoutDuration(min, max);
+    if (delayMin || delayMax) {
+      let timeoutDuration = calculateTimeoutDuration(delayMin, delayMax);
       await new Promise<void>((resolve) => {
         let timeoutHandle: NodeJS.Timeout | undefined = undefined;