UI: Ellipsize playbook paths from the left when it's too long

Ellipsizing from the right is not helpful since it tends to hide
the most important parts from the paths like the playbook file and the
directory it's located in.

truncatepath is taken from an implementation in ara 0.x [1].

[1]: fac4d33

Change-Id: Ia2b8121fb497490e702e244dd3b31db55031c998

ara/ui/templates/partials/playbook_card.html

@@ -1,4 +1,5 @@
 {% load datetime_formatting %}
+{% load truncatepath %}
 {% if playbook.status == "completed" %}
 <div class="pf-c-card pf-m-hoverable pf-c-alert pf-m-success pf-m-inline">
 {% elif playbook.status == "failed" %}
@@ -28,7 +29,7 @@
                     <div class="pf-c-data-list__cell pf-m-flex-4">
                         <div style="padding-top:1em;" title="{{ playbook.path }}">
                             <a href="{% if page != "index" %}../{% endif %}playbook/{{ playbook.id }}.html">
-                                {% if playbook.name is not None %}{{ playbook.name }}{% else %}{{ playbook.path | truncatechars:50 }}{% endif %}
+                                {% if playbook.name is not None %}{{ playbook.name }}{% else %}{{ playbook.path | truncatepath:50 }}{% endif %}
                             </a>
                         </div>
                     </div>

ara/ui/templatetags/truncatepath.py

@@ -0,0 +1,51 @@
+#  Copyright (c) 2020 Red Hat, Inc.
+#
+#  This file is part of ARA Records Ansible.
+#
+#  ARA is free software: you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation, either version 3 of the License, or
+#  (at your option) any later version.
+#
+#  ARA is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with ARA.  If not, see <http://www.gnu.org/licenses/>.
+
+import os
+
+from django import template
+from django.template.defaultfilters import stringfilter
+
+register = template.Library()
+
+
+@register.filter(name="truncatepath")
+@stringfilter
+def truncatepath(path, count):
+    """
+    Truncates a path to less than 'count' characters.
+    Paths are truncated on path separators.
+    We prepend an ellipsis when we return a truncated path.
+    """
+    try:
+        length = int(count)
+    except ValueError:
+        return path
+
+    # Return immediately if there's nothing to truncate
+    if len(path) < length:
+        return path
+
+    dirname, basename = os.path.split(path)
+    while dirname:
+        if len(dirname) + len(basename) < length:
+            break
+        dirlist = dirname.split("/")
+        dirlist.pop(0)
+        dirname = "/".join(dirlist)
+
+    return "..." + os.path.join(dirname, basename)