[tracker/wip/sam/resource: 17/27] libtracker-sparql: Add TrackerNamespaceManager

[Sam Thursfield <sthursfield src gnome org>]

commit 4a6080670999c3e7482ec2ef6bb3957eb181b344
Author: Sam Thursfield <sam afuera me uk>
Date:   Fri Apr 8 17:57:46 2016 +0100

    libtracker-sparql: Add TrackerNamespaceManager
    
    This will keep track of a set of namespaces and their prefixes. Then,
    when we are serializing a resource, we can use it.
    
    This is separate from the Namespace and Ontologies classes in
    libtracker-data. They may be able to make use of it though.

 src/libtracker-sparql/Makefile.am                 |    3 +
 src/libtracker-sparql/tracker-namespace-manager.c |  310 +++++++++++++++++++++
 src/libtracker-sparql/tracker-namespace-manager.h |   49 ++++
 3 files changed, 362 insertions(+), 0 deletions(-)
---
diff --git a/src/libtracker-sparql/Makefile.am b/src/libtracker-sparql/Makefile.am
index 48ed4ad..3f6925b 100644
--- a/src/libtracker-sparql/Makefile.am
+++ b/src/libtracker-sparql/Makefile.am
@@ -22,6 +22,8 @@ libtracker_sparql_la_SOURCES =   \
        tracker-builder.vala                           \
        tracker-connection.vala                        \
        tracker-cursor.vala                            \
+       tracker-namespace-manager.c                    \
+       tracker-namespace-manager.h                    \
        tracker-utils.vala                             \
        tracker-uri.c                                  \
        tracker-ontologies.h \
@@ -48,6 +50,7 @@ tracker-sparql-$(TRACKER_API_VERSION).vapi: tracker-sparql.vapi
 
 libtracker_sparqlinclude_HEADERS =                     \
        $(vala_header)                                 \
+       tracker-namespace-manager.h                    \
        tracker-ontologies.h \
        tracker-sparql.h                               \
        tracker-version.h
diff --git a/src/libtracker-sparql/tracker-namespace-manager.c 
b/src/libtracker-sparql/tracker-namespace-manager.c
new file mode 100644
index 0000000..e2ed50e
--- /dev/null
+++ b/src/libtracker-sparql/tracker-namespace-manager.c
@@ -0,0 +1,310 @@
+/*
+ * Copyright (C) 2016, Sam Thursfield <sam afuera me uk>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA  02110-1301, USA.
+ */
+
+#include "config.h"
+
+#include <string.h>
+#include <stdlib.h>
+
+#include <glib.h>
+
+#include "tracker-namespace-manager.h"
+#include "tracker-ontologies.h"
+
+#define MAX_PREFIX_LENGTH 100
+
+struct _TrackerNamespaceManager {
+       GObject parent;
+};
+
+typedef struct {
+       GHashTable *prefix_to_namespace;
+       GHashTable *namespace_to_prefix;
+} TrackerNamespaceManagerPrivate;
+
+G_DEFINE_TYPE_WITH_PRIVATE (TrackerNamespaceManager, tracker_namespace_manager, G_TYPE_OBJECT);
+#define GET_PRIVATE(object)  (tracker_namespace_manager_get_instance_private (object))
+
+/**
+ * SECTION: tracker-namespace-manager
+ * @short_description: A set of well-known namespaces, and known abbreviations for them
+ * @title: TrackerNamespaceManager
+ * @stability: Stable
+ * @include: tracker-namespace-manager.h
+ *
+ * <para>
+ * #TrackerNamespaceManager keeps track of namespaces. It allows you to assign
+ * short prefixes for them to avoid typing full URLs all the time.
+ *
+ * The syntax used is that of Compact URIs (CURIEs) as defined here:
+ * <https://www.w3.org/TR/2010/NOTE-curie-20101216/>
+ *
+ * Usually you'll want to use the default namespace manager, as returned by
+ * tracker_namespace_manager_get_default(). This has a set of well-known
+ * prefixes predefined.
+ * </para>
+ */
+
+static void finalize     (GObject      *object);
+
+static void
+tracker_namespace_manager_class_init (TrackerNamespaceManagerClass *klass)
+{
+       GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+       object_class->finalize     = finalize;
+}
+
+static void
+tracker_namespace_manager_init (TrackerNamespaceManager *self)
+{
+       TrackerNamespaceManagerPrivate *priv = GET_PRIVATE (self);
+
+       priv->prefix_to_namespace = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, g_free);
+       priv->namespace_to_prefix = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, g_free);
+}
+
+static void
+finalize (GObject *object)
+{
+       TrackerNamespaceManagerPrivate *priv;
+
+       priv = GET_PRIVATE (TRACKER_NAMESPACE_MANAGER (object));
+
+       g_hash_table_unref (priv->prefix_to_namespace);
+       g_hash_table_unref (priv->namespace_to_prefix);
+
+       (G_OBJECT_CLASS (tracker_namespace_manager_parent_class)->finalize) (object);
+}
+
+/**
+ * tracker_namespace_manager_new:
+ *
+ * Creates a new #TrackerNamespaceManager instance.
+ *
+ * Returns: a new #TrackerNamespaceManager instance
+ *
+ * Since: 1.10
+ */
+TrackerNamespaceManager *
+tracker_namespace_manager_new ()
+{
+       TrackerNamespaceManager *namespace_manager;
+
+       namespace_manager = g_object_new (TRACKER_TYPE_NAMESPACE_MANAGER, NULL);
+
+       return namespace_manager;
+}
+
+/**
+ * tracker_namespace_manager_get_default:
+ *
+ * Returns the global #TrackerNamespaceManager that contains a set of well-known
+ * namespaces and prefixes, such as rdf:, rdfs:, nie:, tracker:, etc.
+ *
+ * Note that the list of prefixes and namespaces is hardcoded in
+ * libtracker-sparql. It may not correspond with the installed set of
+ * ontologies, if they have been modified since they were installed.
+ *
+ * Returns: a global, shared #TrackerNamespaceManager instance
+ *
+ * Since: 1.10
+ */
+TrackerNamespaceManager *
+tracker_namespace_manager_get_default ()
+{
+       static TrackerNamespaceManager * volatile default_namespace_manager__volatile = NULL;
+
+       if (g_once_init_enter (&default_namespace_manager__volatile)) {
+               TrackerNamespaceManager *manager = tracker_namespace_manager_new();
+
+               tracker_namespace_manager_add_prefix (manager, "rdf", TRACKER_PREFIX_RDF);
+               tracker_namespace_manager_add_prefix (manager, "rdfs", TRACKER_PREFIX_RDFS);
+               tracker_namespace_manager_add_prefix (manager, "xsd", TRACKER_PREFIX_XSD);
+               tracker_namespace_manager_add_prefix (manager, "tracker", TRACKER_PREFIX_TRACKER);
+               tracker_namespace_manager_add_prefix (manager, "dc", TRACKER_PREFIX_DC);
+
+               tracker_namespace_manager_add_prefix (manager, "nrl", TRACKER_PREFIX_NRL);
+               tracker_namespace_manager_add_prefix (manager, "nmo", TRACKER_PREFIX_NMO);
+               tracker_namespace_manager_add_prefix (manager, "nie", TRACKER_PREFIX_NIE);
+               tracker_namespace_manager_add_prefix (manager, "nco", TRACKER_PREFIX_NCO);
+               tracker_namespace_manager_add_prefix (manager, "nao", TRACKER_PREFIX_NAO);
+               tracker_namespace_manager_add_prefix (manager, "nid3", TRACKER_PREFIX_NID3);
+               tracker_namespace_manager_add_prefix (manager, "nfo", TRACKER_PREFIX_NFO);
+
+               tracker_namespace_manager_add_prefix (manager, "slo", TRACKER_PREFIX_SLO);
+               tracker_namespace_manager_add_prefix (manager, "nmm", TRACKER_PREFIX_NMM);
+               tracker_namespace_manager_add_prefix (manager, "mlo", TRACKER_PREFIX_MLO);
+               tracker_namespace_manager_add_prefix (manager, "mfo", TRACKER_PREFIX_MFO);
+
+               g_once_init_leave (&default_namespace_manager__volatile, manager);
+       }
+
+       return default_namespace_manager__volatile;
+}
+
+/**
+ * tracker_namespace_manager_has_prefix:
+ * @self: a #TrackerNamespaceManager
+ * @prefix: a string
+ *
+ * Returns: %TRUE if the #TrackerNamespaceManager knows about @prefix, %FALSE otherwise
+ *
+ * Since: 1.10
+ */
+gboolean
+tracker_namespace_manager_has_prefix (TrackerNamespaceManager *self,
+                                      const char *prefix)
+{
+       TrackerNamespaceManagerPrivate *priv = GET_PRIVATE (self);
+
+       return g_hash_table_contains (priv->prefix_to_namespace, prefix);
+}
+
+/**
+ * tracker_namespace_manager_lookup_prefix:
+ * @self: a #TrackerNamespaceManager
+ * @prefix: a string
+ *
+ * Looks up the namespace URI corresponding to @prefix, or %NULL if the prefix
+ * is not known.
+ *
+ * Returns: a string owned by the #TrackerNamespaceManager, or %NULL
+ *
+ * Since: 1.10
+ */
+const char *
+tracker_namespace_manager_lookup_prefix (TrackerNamespaceManager *self,
+                                         const char *prefix)
+{
+       TrackerNamespaceManagerPrivate *priv = GET_PRIVATE (self);
+
+       return g_hash_table_lookup (priv->prefix_to_namespace, prefix);
+}
+
+/**
+ * tracker_namespace_manager_add_prefix:
+ * @self: a #TrackerNamespaceManager
+ * @prefix: a short, unique prefix to identify @namespace
+ * @namespace: the URL of the given namespace
+ *
+ * Adds @prefix as the recognised abbreviaton of @namespace.
+ *
+ * Only one prefix is allowed for a given namespace, and all prefixes must
+ * be unique.
+ *
+ * Since: 1.10
+ */
+void
+tracker_namespace_manager_add_prefix (TrackerNamespaceManager *self,
+                                      const char *prefix,
+                                      const char *namespace)
+{
+       TrackerNamespaceManagerPrivate *priv;
+       const char *str;
+
+       priv = GET_PRIVATE (TRACKER_NAMESPACE_MANAGER (self));
+
+       if (strlen (prefix) > MAX_PREFIX_LENGTH) {
+               g_error ("Prefix is too long: max %i characters.", MAX_PREFIX_LENGTH);
+               return;
+       }
+
+       str = g_hash_table_lookup (priv->prefix_to_namespace, prefix);
+       if (str) {
+               g_error ("Prefix %s already points to %s", prefix, str);
+               return;
+       }
+
+       str = g_hash_table_lookup (priv->namespace_to_prefix, namespace);
+       if (str) {
+               g_error ("Namespace %s already has prefix %s", namespace, str);
+               return;
+       }
+
+       g_hash_table_insert (priv->prefix_to_namespace, g_strdup (prefix), g_strdup (namespace));
+       g_hash_table_insert (priv->namespace_to_prefix, g_strdup (namespace), g_strdup (prefix));
+}
+
+/**
+ * tracker_namespace_manager_expand_uri:
+ * @self: a #TrackerNamespaceManager
+ * @compact_uri: a URI or compact URI
+ *
+ * If @compact_uri begins with one of the prefixes known to this
+ * #TrackerNamespaceManager, then the return value will be the
+ * expanded URI. Otherwise, a copy of @compact_uri will be returned.
+ *
+ * Returns: a newly-allocated string
+ *
+ * Since: 1.10
+ */
+char *
+tracker_namespace_manager_expand_uri (TrackerNamespaceManager *self,
+                                      const char *compact_uri)
+{
+       TrackerNamespaceManagerPrivate *priv = GET_PRIVATE (self);
+
+       char prefix[MAX_PREFIX_LENGTH + 1];
+       char *colon;
+       char *namespace = NULL;
+
+       colon = strchr (compact_uri, ':');
+       if (colon != NULL) {
+               int colon_pos = colon - compact_uri;
+               if (colon_pos < MAX_PREFIX_LENGTH) {
+                       strncpy (prefix, compact_uri, colon_pos - 1);
+
+                       namespace = g_hash_table_lookup (priv->prefix_to_namespace, prefix);
+               }
+       }
+
+       if (namespace) {
+               return g_strconcat (namespace, colon, NULL);
+       } else {
+               return g_strdup (compact_uri);
+       }
+}
+
+/**
+ * tracker_namespace_manager_print_turtle:
+ * @self: a #TrackerNamespaceManager
+ *
+ * Writes out all namespaces as Turtle @prefix statements.
+ *
+ * Returns: a newly-allocated string
+ *
+ * Since: 1.10
+ */
+char *
+tracker_namespace_manager_print_turtle (TrackerNamespaceManager *self)
+{
+       TrackerNamespaceManagerPrivate *priv = GET_PRIVATE (self);
+       GString *result = g_string_new ("");
+       GHashTableIter iter;
+       const char *prefix;
+       const char *namespace;
+
+       g_hash_table_iter_init (&iter, priv->prefix_to_namespace);
+       while (g_hash_table_iter_next (&iter, (gpointer *)&prefix, (gpointer *)&namespace)) {
+               g_string_append_printf (result, "@prefix %s: <%s> .\n", prefix, namespace);
+       }
+
+       return g_string_free (result, FALSE);
+}
diff --git a/src/libtracker-sparql/tracker-namespace-manager.h 
b/src/libtracker-sparql/tracker-namespace-manager.h
new file mode 100644
index 0000000..2a6e45e
--- /dev/null
+++ b/src/libtracker-sparql/tracker-namespace-manager.h
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2016, Sam Thursfield <sam afuera me uk>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA  02110-1301, USA.
+ */
+
+#ifndef __LIBTRACKER_SPARQL_NAMESPACE_MANAGER_H__
+#define __LIBTRACKER_SPARQL_NAMESPACE_MANAGER_H__
+
+#include <glib-object.h>
+
+G_BEGIN_DECLS
+
+#if !defined (__LIBTRACKER_SPARQL_INSIDE__) && !defined (TRACKER_COMPILATION)
+#error "only <libtracker-sparql/tracker-sparql.h> must be included directly."
+#endif
+
+#define TRACKER_TYPE_NAMESPACE_MANAGER (tracker_namespace_manager_get_type())
+G_DECLARE_FINAL_TYPE (TrackerNamespaceManager, tracker_namespace_manager, TRACKER, NAMESPACE_MANAGER, 
GObject)
+
+TrackerNamespaceManager *tracker_namespace_manager_new (void);
+TrackerNamespaceManager *tracker_namespace_manager_get_default (void);
+
+char *tracker_namespace_manager_expand_uri (TrackerNamespaceManager *self, const char *compact_uri);
+
+gboolean tracker_namespace_manager_has_prefix (TrackerNamespaceManager *self, const char *prefix);
+const char *tracker_namespace_manager_lookup_prefix (TrackerNamespaceManager *self, const char *prefix);
+
+void tracker_namespace_manager_add_prefix (TrackerNamespaceManager *self, const char *prefix, const char 
*namespace);
+
+char *tracker_namespace_manager_print_turtle (TrackerNamespaceManager *self);
+
+G_END_DECLS
+
+#endif /* __LIBTRACKER_SPARQL_NAMESPACE_MANAGER_H__ */
+