[tracker/wip/carlosg/sparql1.1: 30/113] libtracker-data: Add support for DESCRIBE

[Carlos Garnacho <carlosg src gnome org>]

commit 2923777127027294784d77da78f9cc47cc7fef3e
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Jul 7 22:50:30 2019 +0200

    libtracker-data: Add support for DESCRIBE

 src/libtracker-data/tracker-sparql.c | 124 ++++++++++++++++++++++++++++++++++-
 1 file changed, 123 insertions(+), 1 deletion(-)
---
diff --git a/src/libtracker-data/tracker-sparql.c b/src/libtracker-data/tracker-sparql.c
index f4d807f0a..a91e56bfd 100644
--- a/src/libtracker-data/tracker-sparql.c
+++ b/src/libtracker-data/tracker-sparql.c
@@ -1969,7 +1969,129 @@ static gboolean
 translate_DescribeQuery (TrackerSparql  *sparql,
                          GError        **error)
 {
-       _unimplemented ("DESCRIBE");
+       TrackerStringBuilder *where_str = NULL;
+       TrackerVariable *variable;
+       TrackerBinding *binding;
+       GList *resources = NULL, *l;
+       gboolean glob = FALSE;
+
+       /* DescribeQuery ::= 'DESCRIBE' ( VarOrIri+ | '*' ) DatasetClause* WhereClause? SolutionModifier
+        */
+       sparql->context = g_object_ref_sink (tracker_select_context_new ());
+       sparql->current_state.select_context = sparql->context;
+       tracker_sparql_push_context (sparql, sparql->context);
+
+       _expect (sparql, RULE_TYPE_LITERAL, LITERAL_DESCRIBE);
+       _append_string (sparql,
+                       "SELECT "
+                       "  (SELECT Uri FROM Resource WHERE ID = subject),"
+                       "  (SELECT Uri FROM Resource WHERE ID = predicate),"
+                       "  object "
+                       "FROM tracker_triples "
+                       "WHERE object IS NOT NULL AND subject IN (");
+
+       if (_accept (sparql, RULE_TYPE_LITERAL, LITERAL_GLOB)) {
+               glob = TRUE;
+       } else {
+               TrackerContext *context;
+
+               context = tracker_triple_context_new ();
+               tracker_sparql_push_context (sparql, context);
+
+               while (_check_in_rule (sparql, NAMED_RULE_VarOrIri)) {
+                       TrackerBinding *binding;
+                       TrackerToken resource;
+
+                       _call_rule (sparql, NAMED_RULE_VarOrIri, error);
+                       _init_token (&resource, sparql->current_state.prev_node, sparql);
+
+                       if (tracker_token_get_literal (&resource)) {
+                               binding = tracker_literal_binding_new (tracker_token_get_literal (&resource),
+                                                                      NULL);
+                       } else {
+                               TrackerVariable *variable;
+
+                               variable = tracker_token_get_variable (&resource);
+                               binding = tracker_variable_binding_new (variable, NULL, NULL);
+                       }
+
+                       tracker_binding_set_data_type (binding, TRACKER_PROPERTY_TYPE_RESOURCE);
+                       resources = g_list_prepend (resources, binding);
+                       tracker_token_unset (&resource);
+               }
+
+               tracker_sparql_pop_context (sparql, FALSE);
+       }
+
+       while (_check_in_rule (sparql, NAMED_RULE_DatasetClause))
+               _call_rule (sparql, NAMED_RULE_DatasetClause, error);
+
+       if (_check_in_rule (sparql, NAMED_RULE_WhereClause)) {
+               TrackerParserNode *where_clause;
+
+               where_str = tracker_string_builder_new ();
+               where_clause = _skip_rule (sparql, NAMED_RULE_WhereClause);
+
+               if (!_postprocess_rule (sparql, where_clause, where_str, error)) {
+                       g_list_free_full (resources, g_object_unref);
+                       tracker_string_builder_free (where_str);
+                       return FALSE;
+               }
+       }
+
+       if (glob && TRACKER_SELECT_CONTEXT (sparql->context)->variables) {
+               GHashTableIter iter;
+
+               g_hash_table_iter_init (&iter, TRACKER_SELECT_CONTEXT (sparql->context)->variables);
+
+               while (g_hash_table_iter_next (&iter, NULL, (gpointer *) &variable)) {
+                       binding = tracker_variable_binding_new (variable, NULL, NULL);
+                       resources = g_list_prepend (resources, binding);
+               }
+       }
+
+       if (resources == NULL) {
+               g_clear_pointer (&where_str, tracker_string_builder_free);
+               _raise (PARSE, "Use of unprojected variables", "DescribeQuery");
+       }
+
+       for (l = resources; l; l = l->next) {
+               binding = l->data;
+
+               if (l != resources)
+                       _append_string (sparql, "UNION ALL ");
+
+               if (TRACKER_IS_LITERAL_BINDING (binding)) {
+                       tracker_select_context_add_literal_binding (TRACKER_SELECT_CONTEXT (sparql->context),
+                                                                   TRACKER_LITERAL_BINDING (binding));
+                       _append_string (sparql, "SELECT ");
+                       _append_literal_sql (sparql, TRACKER_LITERAL_BINDING (binding));
+               } else if (TRACKER_IS_VARIABLE_BINDING (binding)) {
+                       gchar *str;
+
+                       variable = TRACKER_VARIABLE_BINDING (binding)->variable;
+
+                       if (!where_str) {
+                               g_list_free_full (resources, g_object_unref);
+                               _raise (PARSE, "Use of unprojected variable in Describe", variable->name);
+                       }
+
+                       _append_string (sparql, "SELECT ");
+                       _append_variable_sql (sparql, variable);
+
+                       str = tracker_string_builder_to_string (where_str);
+                       _append_string_printf (sparql, "%s", str);
+                       g_free (str);
+               }
+       }
+
+       _call_rule (sparql, NAMED_RULE_SolutionModifier, error);
+       tracker_sparql_pop_context (sparql, FALSE);
+       _append_string (sparql, ") ");
+       g_list_free_full (resources, g_object_unref);
+       g_clear_pointer (&where_str, tracker_string_builder_free);
+
+       return TRUE;
 }
 
 static gboolean