feat(billing): outbound webhook engine (HMAC + retry/backoff)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fusion_centralize_billing/models/webhook.py

@@ -1,7 +1,19 @@
 # -*- coding: utf-8 -*-
 # Copyright 2026 Nexa Systems Inc.
 # License OPL-1
-from odoo import fields, models
+import hashlib
+import hmac
+import json
+import logging
+from datetime import timedelta
+
+import requests
+
+from odoo import api, fields, models
+
+_logger = logging.getLogger(__name__)
+
+MAX_ATTEMPTS = 8
 
 
 class FusionBillingWebhook(models.Model):
@@ -40,3 +52,50 @@ class FusionBillingWebhook(models.Model):
     next_retry_at = fields.Datetime()
     signature = fields.Char(help="HMAC-SHA256 of the payload using the service webhook_secret.")
     last_error = fields.Text()
+
+    @api.model
+    def _sign(self, secret, body):
+        return hmac.new((secret or '').encode(), body.encode(), hashlib.sha256).hexdigest()
+
+    @api.model
+    def _enqueue(self, service, event_type, payload):
+        body = json.dumps(payload, sort_keys=True, separators=(',', ':'))
+        return self.create({
+            'service_id': service.id,
+            'event_type': event_type,
+            'payload': payload,
+            'signature': self._sign(service.webhook_secret, body),
+            'state': 'pending',
+            'next_retry_at': fields.Datetime.now(),
+        })
+
+    @api.model
+    def _cron_dispatch(self):
+        now = fields.Datetime.now()
+        due = self.search([
+            ('state', 'in', ('pending', 'failed')),
+            ('next_retry_at', '<=', now),
+        ], limit=100)
+        for wh in due:
+            body = json.dumps(wh.payload, sort_keys=True, separators=(',', ':'))
+            try:
+                resp = requests.post(
+                    wh.service_id.webhook_url,
+                    data=body,
+                    headers={'Content-Type': 'application/json',
+                             'X-Fusion-Signature': wh.signature,
+                             'X-Fusion-Event': wh.event_type},
+                    timeout=10,
+                )
+                ok = 200 <= resp.status_code < 300
+            except Exception as e:  # noqa: BLE001 - record and retry
+                ok = False
+                wh.last_error = str(e)[:500]
+            wh.attempts += 1
+            if ok:
+                wh.state = 'sent'
+            elif wh.attempts >= MAX_ATTEMPTS:
+                wh.state = 'dead'
+            else:
+                wh.state = 'failed'
+                wh.next_retry_at = now + timedelta(minutes=2 ** wh.attempts)