[web] Add delete action to A/B experiment detail page

Adds a Delete button to the experiment header.  Clicking it opens a
Bootstrap modal that requires the user to type "delete" before the
"Permanently delete" button becomes active, preventing accidental
deletions.

On confirmation, POST /abtest/<id>/delete clears the experiment's run
FKs, deletes the ABExperiment row, then deletes the associated ABRun
rows (which cascade-delete their ABSample children via the existing
ab_samples relationship).  After deletion the user is redirected to
the experiments list page.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Pull Request: #223

Author: jroelofs

lnt/server/ui/templates/v4_abtest.html

@@ -24,6 +24,11 @@
   function selectAll(source) {
     $(source).closest("table").find("input:checkbox").prop("checked", source.checked);
   }
+  function checkDeleteConfirm() {
+    var val = document.getElementById('delete-confirm-input').value;
+    var btn = document.getElementById('delete-confirm-btn');
+    btn.disabled = (val !== 'delete');
+  }
   </script>
 {% endblock %}
 
@@ -56,6 +61,37 @@ <h3>
 </form>
 <small class="text-muted" style="margin-left:8px">Keep Forever &mdash; created {{ exp.created_time }}</small>
 
+<a href="#deleteModal" role="button" class="btn btn-danger btn-small"
+   style="margin-left:1em" data-toggle="modal">Delete</a>
+
+{# ------------------------------------------------------------------ #}
+{# Delete confirmation modal                                          #}
+{# ------------------------------------------------------------------ #}
+<div id="deleteModal" class="modal hide fade" tabindex="-1" role="dialog"
+     aria-labelledby="deleteModalLabel" aria-hidden="true">
+  <div class="modal-header">
+    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
+    <h3 id="deleteModalLabel">Delete experiment?</h3>
+  </div>
+  <div class="modal-body">
+    <p>This will permanently delete experiment
+      <strong>{{ exp.name or ('Experiment #' ~ exp.id) }}</strong>
+      and all of its run data. This cannot be undone.</p>
+    <p>Type <code>delete</code> to confirm:</p>
+    <input id="delete-confirm-input" type="text" oninput="checkDeleteConfirm()"
+           placeholder="delete" autocomplete="off" style="width:100%"/>
+  </div>
+  <div class="modal-footer">
+    <button class="btn" data-dismiss="modal">Cancel</button>
+    <form method="POST"
+          action="{{ v4_url_for('.v4_abtest_delete', id=exp.id) }}"
+          style="display:inline">
+      <button id="delete-confirm-btn" type="submit"
+              class="btn btn-danger" disabled>Permanently delete</button>
+    </form>
+  </div>
+</div>
+
 <div style="margin-top:1em"></div>
 
 {% if pending %}

lnt/server/ui/views.py

@@ -2161,6 +2161,31 @@ def v4_abtest_pin(id):
     return v4_redirect(v4_url_for('.v4_abtest', id=id))
 
 
+@v4_route("/abtest/<int:id>/delete", methods=['POST'])
+def v4_abtest_delete(id):
+    """Permanently delete an A/B experiment and its associated runs/samples."""
+    session = request.session
+    ts = request.get_testsuite()
+    exp = session.query(ts.ABExperiment).filter_by(id=id).first()
+    if exp is None:
+        abort(404, "No A/B experiment with id %d." % id)
+    run_ids = [rid for rid in [exp.control_run_id, exp.variant_run_id]
+               if rid is not None]
+    # Clear the FKs first so the run rows can be deleted without a
+    # FK constraint violation, then delete the experiment itself.
+    exp.control_run_id = None
+    exp.variant_run_id = None
+    session.flush()
+    session.delete(exp)
+    session.flush()
+    for rid in run_ids:
+        run = session.query(ts.ABRun).filter_by(id=rid).first()
+        if run is not None:
+            session.delete(run)   # cascades to ABSample via ab_samples
+    session.commit()
+    return v4_redirect(v4_url_for('.v4_abtests'))
+
+
 @v4_route("/abtest/<int:id>/scurve")
 def v4_abtest_scurve(id):
     """S-curve graph for selected benchmarks in an A/B experiment."""

tests/server/ui/v4/V4Pages.py

@@ -864,6 +864,17 @@ def _post_run(exp_id, role, run_data):
     _post_run(pending_control, 'variant', _sample_run)
     check_html(client, '/db_default/v4/nts/abtest/%d' % pending_control)
 
+    # Delete: POST to delete route redirects to the list page.
+    delete_id = _post_abtest({'name': 'to-be-deleted'})
+    _post_run(delete_id, 'control', _sample_run)
+    check_html(client, '/db_default/v4/nts/abtest/%d' % delete_id)
+    r = client.post('/db_default/v4/nts/abtest/%d/delete' % delete_id)
+    assert r.status_code in (301, 302), \
+        "Delete returned %d, expected redirect" % r.status_code
+    # Confirm the experiment is gone.
+    check_code(client, '/db_default/v4/nts/abtest/%d' % delete_id,
+               expected_code=HTTP_NOT_FOUND)
+
 
 if __name__ == '__main__':
     main()