From 684bb147a21a3a9566722018c04bb11a889605bf Mon Sep 17 00:00:00 2001
From: Thorsten Vitt <thorsten.vitt@uni-wuerzburg.de>
Date: Wed, 19 Aug 2020 22:46:47 +0200
Subject: [PATCH] gvfa: mproved error reporting

---
 src/graphviewer/gvfa.py             |  6 ++++--
 src/graphviewer/templates/form.html | 17 +++++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/graphviewer/gvfa.py b/src/graphviewer/gvfa.py
index 89f42cc..1369e80 100644
--- a/src/graphviewer/gvfa.py
+++ b/src/graphviewer/gvfa.py
@@ -187,8 +187,10 @@ def agraph(nodeinfo: NodeInput = Depends(),
             reduction = nx.transitive_reduction(g)
             g = g.edge_subgraph([(u, v, k) for u, v, k, _ in expand_edges(g, reduction.edges)])
         else:
-            raise ValueError(
-                    'Cannot produce transitive reduction – the subgraph is not acyclic after removing conflict edges!')
+            raise HTTPException(500, dict(
+                    error="not-acyclic",
+                    msg='Cannot produce transitive reduction – the subgraph is not acyclic after removing conflict edges!',
+                    dot=write_dot(g, target=None, highlight=nodes).to_string()))
 
     g = simplify_timeline(g)
 
diff --git a/src/graphviewer/templates/form.html b/src/graphviewer/templates/form.html
index 94820b5..71a5cfb 100644
--- a/src/graphviewer/templates/form.html
+++ b/src/graphviewer/templates/form.html
@@ -207,8 +207,21 @@
                 })
             //.then(() => message())
             .catch(reason => {
-                addLongMessage(`<pre>${reason}</pre>`, "danger")
-                console.error(reason)
+                try {
+                    const details = JSON.parse(reason).detail;
+                    console.error(details);
+                    if (details.msg) {
+                        addLongMessage(details.msg, 'danger')
+                    } else {
+                        addLongMessage(`<pre>${details}</pre>`, "danger")
+                    }
+                    if (details.dot) {
+                        graphviz.transition(transitionFactory).renderDot(details.dot);
+                    }
+                } catch (e) {
+                    addLongMessage(`<pre>${reason}</pre>`, "danger")
+                    console.error(reason)
+                }
             });
             updateURLs(formdata);
             if (formdata.get('dir').includes('B')) { // vertical layout