analytics: Add python api to get relation path

A new api `Mtd.relation_path()` is added to get relation chain
between two Mtd in RelationMeta.

Usage:
```
for i in mtd1.relation_path(mtd2, max_span=4, relation_type=...):
  pass
```

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8556>

subprojects/gst-python/gi/overrides/GstAnalytics.py

@@ -50,6 +50,9 @@ class Mtd(GstAnalytics.Mtd):
         return _gi_gst_analytics.AnalyticsMtdDirectRelatedIterator(
             sys.modules[__name__], self, relation, mtd_type)
 
+    def relation_path(self, mtd, max_span = 0, reltype = GstAnalytics.RelTypes.ANY):
+        return _gi_gst_analytics.AnalyticsMtdRelationPath(
+            sys.modules[__name__], self, mtd.get_id(), max_span, reltype);
 
 __all__.append('Mtd')
 

subprojects/gst-python/gi/overrides/gstanalyticsmodule.c

@@ -219,7 +219,43 @@ _gst_analytics_relation_meta_iterator_next (_GstAnalyticsRelationMetaIterator *
   return py_result;
 }
 
+static PyObject *
+_gi_gst_analytics_mtd_relation_path (PyObject * self, PyObject * args)
+{
+  PyObject *py_module = NULL;
+  PyObject *py_mtd;
+  guint id;
+  guint max_span;
+  GstAnalyticsRelTypes reltype;
+  GArray *relation_path;
+  GstAnalyticsMtd *mtd;
+  PyObject *pathList;
+
+  if (!PyArg_ParseTuple (args, "OOIII", &py_module, &py_mtd, &id, &max_span,
+          &reltype)) {
+    return NULL;
+  }
+
+  relation_path = g_array_new (FALSE, FALSE, sizeof (guint));
+  mtd = (GstAnalyticsMtd *) pygobject_get (py_mtd);
+  gst_analytics_relation_meta_exist (mtd->meta, mtd->id, id,
+      max_span, reltype, &relation_path);
+
+  pathList = PyList_New (relation_path->len);
+  for (guint i = 0; i < relation_path->len; i++) {
+    guint id = g_array_index (relation_path, guint, i);
+    PyList_SetItem (pathList, i, PyLong_FromUnsignedLong (id));
+  }
+  g_array_free (relation_path, TRUE);
+
+  return pathList;
+}
+
 static PyMethodDef _gi_gst_analytics_functions[] = {
+  {"AnalyticsMtdRelationPath",
+        (PyCFunction) _gi_gst_analytics_mtd_relation_path,
+        METH_VARARGS,
+      "Returns the relation path between two Mtd"},
   {NULL, NULL, 0, NULL}
 };
 

subprojects/gst-python/testsuite/test_analytics.py

@@ -325,3 +325,13 @@ class TestAnalyticsRelationMetaIterator(TestCase):
 
         assert(count == 2)
 
+        # Create a relation path as od_mtd -> cls_mtd -> trk_mtd -> seg_mtd
+        rmeta.set_relation(GstAnalytics.RelTypes.NONE, od_mtd.id, trk_mtd.id) # clear relation
+        rmeta.set_relation(GstAnalytics.RelTypes.RELATE_TO, cls_mtd.id, trk_mtd.id)
+        rmeta.set_relation(GstAnalytics.RelTypes.RELATE_TO, trk_mtd.id, seg_mtd.id)
+        count = 0
+        expected_rel_ids = [od_mtd.id, cls_mtd.id, trk_mtd.id, seg_mtd.id]
+        for i in od_mtd.relation_path(seg_mtd, max_span=4):
+            assert i == expected_rel_ids[count]
+            count += 1
+        assert(count == 4)