From e51175c4a29b44cd32af2b6f901c0e6d8a2e850a Mon Sep 17 00:00:00 2001
From: William Phetsinorath <william.phetsinorath-open@interieur.gouv.fr>
Date: Fri, 13 Mar 2026 18:04:37 +0100
Subject: [PATCH] feat(telemetry): add decorator based tracing utils

Signed-off-by: William Phetsinorath <william.phetsinorath-open@interieur.gouv.fr>
---
 .../telemetry/telemetry.constants.ts          |  1 +
 .../telemetry/telemetry.decorator.ts          | 65 +++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.constants.ts
 create mode 100644 apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.decorator.ts

diff --git a/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.constants.ts b/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.constants.ts
new file mode 100644
index 000000000..cc4af6f36
--- /dev/null
+++ b/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.constants.ts
@@ -0,0 +1 @@
+export const TELEMETRY_TRACER_NAME = 'cloud-pi-native-console'
diff --git a/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.decorator.ts b/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.decorator.ts
new file mode 100644
index 000000000..88a81f158
--- /dev/null
+++ b/apps/server-nestjs/src/cpin-module/infrastructure/telemetry/telemetry.decorator.ts
@@ -0,0 +1,65 @@
+import { SpanStatusCode, trace } from '@opentelemetry/api'
+import type { Attributes, SpanOptions, Span as OpenTelemetrySpan } from '@opentelemetry/api'
+import { TELEMETRY_TRACER_NAME } from './telemetry.constants'
+
+export interface TelemetrySpanMetadata {
+  options?: SpanOptions
+  attributes?: Attributes
+}
+
+export function Span(name?: string, metadata: TelemetrySpanMetadata = {}): MethodDecorator {
+  return <T>(
+    _target: object,
+    propertyKey: string | symbol,
+    descriptor: TypedPropertyDescriptor<T>,
+  ): TypedPropertyDescriptor<T> => {
+    const original = descriptor.value
+    if (typeof original !== 'function') return descriptor
+
+    descriptor.value = function (this: unknown, ...args: unknown[]): unknown {
+      const tracer = trace.getTracer(TELEMETRY_TRACER_NAME)
+      const className = (this as any)?.constructor?.name ?? 'Unknown'
+      const spanName = name ?? `${className}.${String(propertyKey)}`
+
+      return tracer.startActiveSpan(spanName, metadata.options ?? {}, (span) => {
+        if (metadata.attributes) span.setAttributes(metadata.attributes)
+
+        try {
+          const result = original.apply(this, args)
+          if (result instanceof Promise) {
+            return handlePromiseResult(span, result)
+          }
+          span.end()
+          return result
+        } catch (error) {
+          recordError(span, error)
+          span.end()
+          throw error
+        }
+      })
+    } as T
+
+    return descriptor
+  }
+}
+
+async function handlePromiseResult(span: OpenTelemetrySpan, promise: Promise<unknown>): Promise<unknown> {
+  try {
+    return await promise
+  } catch (error) {
+    recordError(span, error)
+    throw error
+  } finally {
+    span.end()
+  }
+}
+
+function recordError(span: OpenTelemetrySpan, error: unknown): void {
+  // If it's an actual Error object, OpenTelemetry captures the stack trace automatically
+  if (error instanceof Error) {
+    span.recordException(error)
+  } else {
+    span.recordException(String(error))
+  }
+  span.setStatus({ code: SpanStatusCode.ERROR })
+}