move metrics to internal folder

Author: Vlasis-Perdikidis

internal/helpers/package.json

@@ -1,5 +1,6 @@
 {
   "dependencies": {
+    "aws-embedded-metrics": "^4.2.1",
     "pino": "^10.3.0",
     "zod": "^4.1.11"
   },

internal/helpers/src/index.ts

@@ -8,3 +8,4 @@ export * from "./version";
 export { default as $Environment } from "./environment";
 export * from "./id-ref";
 export * from "./logger";
+export * from "./metrics";

internal/helpers/src/metrics.ts

@@ -0,0 +1,55 @@
+import { MetricsLogger, Unit } from "aws-embedded-metrics";
+
+export function emitForSingleSupplier(
+  metrics: MetricsLogger,
+  functionName: string,
+  supplierId: string,
+  count: number,
+  message: string,
+  dimensions?: Record<string, string>,
+) {
+  metrics.setNamespace(process.env.AWS_LAMBDA_FUNCTION_NAME || functionName);
+  metrics.putDimensions({
+    ...dimensions,
+    Supplier: supplierId,
+  });
+  metrics.putMetric(message, count, Unit.Count);
+}
+
+export enum MetricStatus {
+  Success = "success",
+  Failure = "failure",
+}
+
+export interface MetricEntry {
+  key: string;
+  value: number;
+  unit: Unit;
+}
+
+// build EMF object
+export function buildEMFObject(
+  functionName: string,
+  dimensions: Record<string, string>,
+  metric: MetricEntry,
+) {
+  const namespace = process.env.AWS_LAMBDA_FUNCTION_NAME || functionName;
+  return {
+    LogGroup: namespace,
+    ServiceName: namespace,
+    ...dimensions,
+    _aws: {
+      Timestamp: Date.now(),
+      CloudWatchMetrics: [
+        {
+          Namespace: namespace,
+          Dimensions: [[...Object.keys(dimensions), "ServiceName", "LogGroup"]],
+          Metrics: [
+            { Name: metric.key, Value: metric.value, Unit: metric.unit },
+          ],
+        },
+      ],
+    },
+    [metric.key]: metric.value,
+  };
+}

lambdas/api-handler/src/handlers/post-letters.ts

@@ -1,6 +1,7 @@
 import { APIGatewayProxyHandler } from "aws-lambda";
 import { Unit } from "aws-embedded-metrics";
 import pino from "pino";
+import { MetricEntry, MetricStatus, buildEMFObject } from "@internal/helpers";
 import type { Deps } from "../config/deps";
 import { ApiErrorDetail } from "../contracts/errors";
 import {
@@ -14,7 +15,6 @@ import { mapToUpdateCommands } from "../mappers/letter-mapper";
 import { enqueueLetterUpdateRequests } from "../services/letter-operations";
 import { extractCommonIds } from "../utils/common-ids";
 import { assertNotEmpty, requireEnvVar } from "../utils/validation";
-import { MetricEntry, MetricStatus, buildEMFObject } from "../utils/metrics";
 
 function duplicateIdsExist(postLettersRequest: PostLettersRequest) {
   const ids = postLettersRequest.data.map((item) => item.id);