Improve automatic emails with temporary urls

This MR targets the improvement for automatic emails concerning validation of new users by supervisors/re-validation of users.

Fixes #542 (closed)

Fixes #550 (closed)

beat/web/accounts/models.py

@@ -160,15 +160,24 @@ def save_user_profile(sender, instance, **kwargs):
     instance.profile.save()
 
 
+def generate_url_hash():
+    # url_hash creation
+    url_hash = "".join(
+        random.choice(string.ascii_letters + string.digits)  # nosec
+        for _ in range(TEMPORARY_URL_LENGTH)
+    )
+    return url_hash
+
+
 class TemporaryUrlManager(models.Manager):
     def create_temporary_url(self, status, supervision_track):
         # Actions that result creating the object
 
-        # url_hash creation
-        url_hash = "".join(
-            random.choice(string.ascii_letters + string.digits)  # nosec
-            for _ in range(TEMPORARY_URL_LENGTH)
-        )
+        url_hash = generate_url_hash()
+        used_hashes = [x.url_hash for x in TemporaryUrl.objects.all()]
+        while url_hash in used_hashes:
+            url_hash = generate_url_hash()
+
         now = datetime.datetime.now()
         expiration_date_delta = datetime.timedelta(
             days=settings.ACCOUNT_ACTIVATION_DAYS_FROM_SUPERVISOR