Make invitation and show on user management page

src/registrar/models/domain.py

@@ -281,3 +281,6 @@ class Domain(TimeStampedModel):
 
     # ManyToManyField on User creates a "users" member for all of the
     # users who have some role on this domain
+
+    # ForeignKey on DomainInvitation creates an "invitations" member for
+    # all of the invitations that have been sent for this domain

src/registrar/models/domain_invitation.py

@@ -22,6 +22,7 @@ class DomainInvitation(TimeStampedModel):
         "registrar.Domain",
         on_delete=models.CASCADE,  # delete domain, then get rid of invitations
         null=False,
+        related_name="invitations",
     )
 
     status = FSMField(

src/registrar/templates/domain_users.html

@@ -25,7 +25,7 @@
       <tbody>
         {% for permission in domain.permissions.all %}
         <tr>
-          <th scope="row" role="rowheader" data-sort-value="{{ user.email }}" data-label="Domain name">
+          <th scope="row" role="rowheader" data-sort-value="{{ user.email }}" data-label="Email">
             {{ permission.user.email }}
           </th>
           <td data-label="Role">{{ permission.role|title }}</td>
@@ -45,4 +45,29 @@
     </svg><span class="margin-left-05">Add another user</span>
   </a>
 
+  {% if domain.invitations.all %}
+  <h2>Invitations</h2>
+  <table class="usa-table usa-table--borderless usa-table--stacked dotgov-table--stacked dotgov-table">
+      <caption class="sr-only">Domain invitations</caption>
+      <thead>
+        <tr>
+          <th data-sortable scope="col" role="columnheader">Email</th>
+          <th data-sortable scope="col" role="columnheader">Date created</th>
+          <th data-sortable scope="col" role="columnheader">Status</th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for invitation in domain.invitations.all %}
+        <tr>
+          <th scope="row" role="rowheader" data-sort-value="{{ user.email }}" data-label="Email">
+            {{ invitation.email }}
+          </th>
+          <td data-sort-value="{{ invitation.created_at|date:"U" }}" data-label="Date created">{{ invitation.created_at|date }} </td>
+          <td data-label="Status">{{ invitation.status|title }}</td>
+        </tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  {% endif %}
+
 {% endblock %}  {# domain_content #}

src/registrar/views/domain.py

@@ -8,7 +8,7 @@ from django.urls import reverse
 from django.views.generic import DetailView
 from django.views.generic.edit import FormMixin
 
-from registrar.models import Domain, User, UserDomainRole
+from registrar.models import Domain, DomainInvitation, User, UserDomainRole
 
 from .utility import DomainPermission
 
@@ -31,15 +31,6 @@ class DomainAddUserForm(DomainPermission, forms.Form):
 
     email = forms.EmailField(label="Email")
 
-    def clean_email(self):
-        requested_email = self.cleaned_data["email"]
-        try:
-            User.objects.get(email=requested_email)
-        except User.DoesNotExist:
-            # TODO: send an invitation email to a non-existent user
-            raise forms.ValidationError("That user does not exist in this system.")
-        return requested_email
-
 
 class DomainAddUserView(DomainPermission, FormMixin, DetailView):
     template_name = "domain_add_user.html"
@@ -53,16 +44,30 @@ class DomainAddUserView(DomainPermission, FormMixin, DetailView):
         self.object = self.get_object()
         form = self.get_form()
         if form.is_valid():
+            # there is a valid email address in the form
             return self.form_valid(form)
         else:
             return self.form_invalid(form)
 
+    def _make_invitation(self, email_address):
+        """Make a Domain invitation for this email and redirect with a message."""
+        invitation, created = DomainInvitation.objects.get_or_create(email=email_address, domain=self.object)
+        if not created:
+            # that invitation already existed
+            messages.warning(self.request, f"{email_address} has already been invited to this domain.")
+        else:
+            messages.success(self.request, f"Invited {email_address} to this domain.")
+        return redirect(self.get_success_url())
+
     def form_valid(self, form):
         """Add the specified user on this domain."""
         requested_email = form.cleaned_data["email"]
         # look up a user with that email
-        # they should exist because we checked in clean_email
-        requested_user = User.objects.get(email=requested_email)
+        try:
+            requested_user = User.objects.get(email=requested_email)
+        except User.DoesNotExist:
+            # no matching user, go make an invitation
+            return self._make_invitation(requested_email)
 
         try:
             UserDomainRole.objects.create(