add mattermost webhook function

tracker.py

@@ -43,10 +43,21 @@ def build_entry(vm: dict) -> dict:
     }
 
 
+def notify_mattermost(webhook_url: str, expiring_soon: list[dict], days: int) -> None:
+    lines = [f"#### {len(expiring_soon)} VM(s) expiring within the next {days} days"]
+    for vm in expiring_soon:
+        lines.append(
+            f"- [{vm['name']}]({vm['netbox_url']}) ({vm['tenant']}) — expires {vm['expire_date']}"
+        )
+    resp = requests.post(webhook_url, json={"text": "\n".join(lines)}, timeout=30)
+    resp.raise_for_status()
+
+
 def main() -> None:
     token = os.environ["NETBOX_TOKEN"]
     netbox_url = os.environ.get("NETBOX_URL", "https://netbox.ethquokkaops.io").rstrip("/")
     expiring_soon_days = int(os.environ.get("EXPIRING_SOON_DAYS", "7"))
+    mm_webhook_url = os.environ.get("MM_WEBHOOK_URL")
 
     today = datetime.now(timezone.utc).date()
     try:
@@ -94,6 +105,14 @@ def main() -> None:
         "no_expiry": no_expiry,
     }, indent=2))
 
+    if mm_webhook_url and expiring_soon:
+        try:
+            notify_mattermost(mm_webhook_url, expiring_soon, expiring_soon_days)
+        except requests.exceptions.RequestException as e:
+            log.error(f"Mattermost webhook request failed: {e}")
+            raise SystemExit(1)
+        log.info(f"Notified Mattermost about {len(expiring_soon)} expiring VM(s)")
+
 
 if __name__ == "__main__":
     main()