remote_billing_page: Deny login for server / remote realm.

If server has plan, deny login for realm.
If realm has plan, deny login for server.

Co-authored-by: Aman Agrawal <amanagr@zulip.com>
Co-authored-by: Alya Abbott <alya@zulip.com>

corporate/views/remote_billing_page.py

@@ -5,6 +5,7 @@ from urllib.parse import urlsplit, urlunsplit
 from django.conf import settings
 from django.core import signing
 from django.core.exceptions import ObjectDoesNotExist
+from django.db.models import Exists, OuterRef
 from django.http import HttpRequest, HttpResponse, HttpResponseNotAllowed, HttpResponseRedirect
 from django.shortcuts import render
 from django.urls import reverse
@@ -35,6 +36,11 @@ from corporate.lib.stripe import (
     RemoteRealmBillingSession,
     RemoteServerBillingSession,
 )
+from corporate.models import (
+    CustomerPlan,
+    get_current_plan_by_customer,
+    get_customer_by_remote_server,
+)
 from zerver.lib.exceptions import (
     JsonableError,
     MissingRemoteRealmError,
@@ -190,6 +196,19 @@ def remote_realm_billing_finalize_login(
         # pretty recently. (And we generally don't delete these at all.)
         raise AssertionError
 
+    # Redirect to error page if server is on an active plan
+    server_customer = get_customer_by_remote_server(remote_server)
+    if server_customer is not None:
+        server_plan = get_current_plan_by_customer(server_customer)
+        if server_plan is not None:
+            return render(
+                request,
+                "corporate/remote_realm_login_error_for_server_on_active_plan.html",
+                context={
+                    "server_plan_name": server_plan.name,
+                },
+            )
+
     user_dict = identity_dict["user"]
 
     user_email = user_dict["user_email"]
@@ -592,6 +611,21 @@ def remote_billing_legacy_server_confirm_login(
     )
 
 
+def has_live_plan_for_any_remote_realm_on_server(server: RemoteZulipServer) -> bool:
+    has_plan_with_status_lt_live_threshold = CustomerPlan.objects.filter(
+        customer__remote_realm__server=server,
+        status__lt=CustomerPlan.LIVE_STATUS_THRESHOLD,
+        customer__remote_realm=OuterRef("pk"),
+    )
+
+    return (
+        RemoteRealm.objects.filter(server=server)
+        .annotate(has_plan=Exists(has_plan_with_status_lt_live_threshold))
+        .filter(has_plan=True)
+        .exists()
+    )
+
+
 @self_hosting_management_endpoint
 @typed_endpoint
 def remote_billing_legacy_server_from_login_confirmation_link(
@@ -658,6 +692,12 @@ def remote_billing_legacy_server_from_login_confirmation_link(
         # don't need a pretty error.
         raise JsonableError(_("You must accept the Terms of Service to proceed."))
 
+    if has_live_plan_for_any_remote_realm_on_server(remote_server):
+        return render(
+            request,
+            "corporate/remote_server_login_error_for_any_realm_on_active_plan.html",
+        )
+
     if remote_billing_user is None:
         assert full_name is not None
         assert settings.TERMS_OF_SERVICE_VERSION is not None

templates/corporate/remote_realm_login_error_for_server_on_active_plan.html

@@ -0,0 +1,39 @@
+{% extends "zerver/portico.html" %}
+
+{% block title %}
+<title>{{ _("Plan management not available") }} | Zulip</title>
+{% endblock %}
+
+{% block portico_class_name %}error{% endblock %}
+
+{% block portico_content %}
+<div class="error_page">
+    <div class="container">
+        <div class="row-fluid">
+            <img src="{{ static('images/errors/400art.svg') }}" alt=""/>
+            <div class="errorbox">
+                <div class="errorcontent">
+                    <h1 class="lead">{{ _("Plan management not available") }}</h1>
+                    <p>
+                        {% trans %} Plan management is not available for this
+                        organization, because your Zulip server is already on a
+                        {{ server_plan_name }} plan, which covers all
+                        organizations on this server. Follow the <a
+                        href="https://zulip.com/help/self-hosted-billing#manage-billing">log
+                        in instructions</a>
+                        for <b>All older versions</b>
+                        of the Zulip server to manage your plan.
+                        {% endtrans %}
+                    </p>
+                    <p>
+                        {% trans %} To move the plan from the server to this
+                        organization, or for other questions, <a href="mailto:{{
+                        support_email }}">contact support</a>.
+                        {% endtrans %}
+                    </p>
+                </div>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}

templates/corporate/remote_server_login_error_for_any_realm_on_active_plan.html

@@ -0,0 +1,34 @@
+{% extends "zerver/portico.html" %}
+
+{% block title %}
+<title>{{ _("Plan management not available") }} | Zulip</title>
+{% endblock %}
+
+{% block portico_class_name %}error{% endblock %}
+
+{% block portico_content %}
+<div class="error_page">
+    <div class="container">
+        <div class="row-fluid">
+            <img src="{{ static('images/errors/400art.svg') }}" alt=""/>
+            <div class="errorbox">
+                <div class="errorcontent">
+                    <h1 class="lead">{{ _("Plan management not available") }}</h1>
+                    <p>
+                        {% trans %}
+                        Plan management for this server is not available because at least one organization
+                        hosted on this server already has an active plan.
+                        {% endtrans %}
+                    </p>
+                    <p>
+                        {% trans %}
+                        <a href="https://zulip.com/help/self-hosted-billing#manage-billing">Log in</a> to plan management for your
+                        organization instead, or <a href='mailto:{{ support_email }}'>contact support</a> with any questions.
+                        {% endtrans %}
+                    </p>
+                </div>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}