[tracker/wip/sam/resource] Add Turtle serialisation to tracker-resource

[Sam Thursfield <sthursfield src gnome org>]

commit 613fb027cd884b3a84fcbf4f3ea44c7bccb042a9
Author: Sam Thursfield <sam afuera me uk>
Date:   Sat Apr 9 17:12:18 2016 +0100

    Add Turtle serialisation to tracker-resource

 src/libtracker-common/tracker-enums.h    |    1 +
 src/libtracker-sparql/tracker-resource.c |   85 ++++++++++++++++++++++++++++++
 src/libtracker-sparql/tracker-resource.h |    2 +
 3 files changed, 88 insertions(+), 0 deletions(-)
---
diff --git a/src/libtracker-common/tracker-enums.h b/src/libtracker-common/tracker-enums.h
index edce490..5121a72 100644
--- a/src/libtracker-common/tracker-enums.h
+++ b/src/libtracker-common/tracker-enums.h
@@ -43,6 +43,7 @@ typedef enum {
        TRACKER_SERIALIZATION_FORMAT_JSON,
        TRACKER_SERIALIZATION_FORMAT_JSON_LD,
        TRACKER_SERIALIZATION_FORMAT_SPARQL,
+       TRACKER_SERIALIZATION_FORMAT_TURTLE,
 } TrackerSerializationFormat;
 
 G_END_DECLS
diff --git a/src/libtracker-sparql/tracker-resource.c b/src/libtracker-sparql/tracker-resource.c
index 2f7c296..dd2d582 100644
--- a/src/libtracker-sparql/tracker-resource.c
+++ b/src/libtracker-sparql/tracker-resource.c
@@ -534,6 +534,91 @@ tracker_resource_compare (TrackerResource *a,
 }
 
 
+typedef struct {
+       TrackerNamespaceManager *namespaces;
+       GString *string;
+       GList *done_list;
+} GenerateTurtleData;
+
+void generate_turtle (TrackerResource *resource, GenerateTurtleData *data);
+
+void
+generate_turtle_resources_foreach (gpointer key,
+                                   gpointer value_ptr,
+                                   gpointer user_data)
+{
+       const char *property = key;
+       const GValue *value = value_ptr;
+       GenerateTurtleData *data = user_data;
+
+       if (G_VALUE_HOLDS (value, TRACKER_TYPE_RESOURCE)) {
+               TrackerResource *resource = g_value_get_object (value);
+               if (g_list_find_custom (data->done_list, resource, (GCompareFunc) tracker_resource_compare) 
== NULL) {
+                       generate_turtle (resource, data);
+                       data->done_list = g_list_prepend (data->done_list, resource);
+               }
+       }
+}
+
+void
+generate_turtle_properties_foreach (gpointer key,
+                                    gpointer value_ptr,
+                                    gpointer user_data)
+{
+       const char *property = key;
+       const GValue *value = value_ptr;
+       GenerateTurtleData *data = user_data;
+
+       /* FIXME: really crappy Turtle serializer */
+       g_string_append_printf (data->string, "  %s %s ;\n", property, g_value_dup_string (value));
+}
+
+void
+generate_turtle (TrackerResource *resource,
+                 GenerateTurtleData *data)
+{
+       TrackerResourcePrivate *priv = GET_PRIVATE (resource);
+       GString *result;
+
+       g_hash_table_foreach (priv->properties, generate_turtle_resources_foreach, data);
+
+       g_string_append_printf (data->string, "<%s> ", priv->identifier);
+
+       g_hash_table_foreach (priv->properties, generate_turtle_properties_foreach, data);
+
+       g_string_append_printf (data->string, ".\n");
+}
+
+/**
+ * tracker_resource_print_turtle:
+ * @resource: a #TrackerResource
+ * @error: address where an error can be returned
+ *
+ * Serialize all the information in @resource as a Turtle document.
+ *
+ * The generated Turtle should correspond to this standard:
+ * <https://www.w3.org/TR/2014/REC-turtle-20140225/>
+ *
+ * Returns: a newly-allocated string
+ *
+ * Since: 1.10
+ */
+char *
+tracker_resource_print_turtle(TrackerResource *self,
+                              TrackerNamespaceManager *namespaces)
+{
+       GenerateTurtleData context;
+
+       context.namespaces = namespaces;
+       context.string = g_string_new ("");
+       context.done_list = NULL;
+
+       generate_turtle (self, &context);
+
+       return g_string_free (context.string, FALSE);
+}
+
+
 static void generate_jsonld_foreach (gpointer key, gpointer value_ptr, gpointer user_data);
 
 /* FIXME: this could hit an infinite loop if there are circular resource
diff --git a/src/libtracker-sparql/tracker-resource.h b/src/libtracker-sparql/tracker-resource.h
index 260b7ca..5aea11b 100644
--- a/src/libtracker-sparql/tracker-resource.h
+++ b/src/libtracker-sparql/tracker-resource.h
@@ -69,6 +69,8 @@ const char *tracker_resource_get_first_uri (TrackerResource *self, const char *p
 const char *tracker_resource_get_identifier (TrackerResource *self);
 gint tracker_resource_identifier_compare_func (TrackerResource *resource, const char *identifier);
 
+char *tracker_resource_print_turtle(TrackerResource *self, TrackerNamespaceManager *namespaces);
+
 char *tracker_resource_print_jsonld (TrackerResource *self, GError **error);
 
 void tracker_resource_generate_sparql_update (TrackerResource *self, TrackerSparqlBuilder *builder, 
TrackerNamespaceManager *namespaces, const char *graph_id, GError **error);