Reimplement admin send mail to users (#903)

* Reimplement admin send mail to users as `/api/v1/users/<user_id>/email`
* Update form and related Javascript
* Write test for controller
* Closes #897

CTFd/api/v1/users.py

@@ -4,9 +4,12 @@ from CTFd.models import db, Users, Solves, Awards, Fails, Tracking, Unlocks, Sub
 from CTFd.utils.decorators import (
     authed_only,
     admins_only,
-    authed
+    authed,
+    ratelimit
 )
 from CTFd.cache import cache, clear_standings
+from CTFd.utils.config import get_mail_provider
+from CTFd.utils.email import sendmail
 from CTFd.utils.user import get_current_user, is_admin
 from CTFd.utils.decorators.visibility import check_account_visibility, check_score_visibility
 
@@ -280,3 +283,44 @@ class UserAwards(Resource):
             'success': True,
             'data': response.data
         }
+
+
+@users_namespace.route('/<int:user_id>/email')
+@users_namespace.param('user_id', "User ID")
+class UserEmails(Resource):
+    @admins_only
+    @ratelimit(method="POST", limit=10, interval=60)
+    def post(self, user_id):
+        req = request.get_json()
+        text = req.get('text', '').strip()
+        user = Users.query.filter_by(id=user_id).first_or_404()
+
+        if get_mail_provider() is None:
+            return {
+                'success': False,
+                'errors': {
+                    "": [
+                        "Email settings not configured"
+                    ]
+                }
+            }, 400
+
+        if not text:
+            return {
+                'success': False,
+                'errors': {
+                    "text": [
+                        "Email text cannot be empty"
+                    ]
+                }
+            }, 400
+
+        result, response = sendmail(
+            addr=user.email,
+            text=text
+        )
+
+        return {
+            'success': result,
+            'data': {}
+        }