[PATCH 2/5] Added backwards iterator to messages

[Ruben Pollan <meskio@sindominio.net>]

Added the functions notmuch_messages_move_to_prevoius,
notmuch_messages_move_to_last and  notmuch_messages_move_to_first to
notmuch library. With them is possible to iterate backwards on messages.

* notmuch_messages_move_to_prevoius do the opposite than
  notmuch_messages_move_to_next, getting the messages iterator one
  position backwards.

* notmuch_messages_move_to_last move the iterator to the first last
  message.

* notmuch_messages_move_to_first move the iterator to the first valid
  message.
---
 lib/messages.c        |   31 +++++++++++++++++++++++++++++
 lib/notmuch-private.h |   10 +++++++++
 lib/notmuch.h         |   28 ++++++++++++++++++++++++++
 lib/query.cc          |   52 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 121 insertions(+), 0 deletions(-)

diff --git a/lib/messages.c b/lib/messages.c
index 2a85774..975e4b1 100644
--- a/lib/messages.c
+++ b/lib/messages.c
@@ -90,6 +90,7 @@ _notmuch_messages_create (notmuch_message_list_t *list)
 
     messages->is_of_list_type = TRUE;
     messages->iterator = list->head;
+    messages->list = list;
 
     return messages;
 }
@@ -134,6 +135,15 @@ notmuch_messages_get (notmuch_messages_t *messages)
 }
 
 void
+notmuch_messages_move_to_first (notmuch_messages_t *messages)
+{
+    if (! messages->is_of_list_type)
+	return _notmuch_mset_messages_move_to_first (messages);
+
+    messages->iterator = messages->list->head;
+}
+
+void
 notmuch_messages_move_to_next (notmuch_messages_t *messages)
 {
     if (! messages->is_of_list_type)
@@ -146,6 +156,27 @@ notmuch_messages_move_to_next (notmuch_messages_t *messages)
 }
 
 void
+notmuch_messages_move_to_last (notmuch_messages_t *messages)
+{
+    if (! messages->is_of_list_type)
+	return _notmuch_mset_messages_move_to_last (messages);
+
+    messages->iterator = messages->list->tail;
+}
+
+void
+notmuch_messages_move_to_previous (notmuch_messages_t *messages)
+{
+    if (! messages->is_of_list_type)
+	return _notmuch_mset_messages_move_to_previous (messages);
+
+    if (messages->iterator == NULL)
+	return;
+
+    messages->iterator = messages->iterator->prev;
+}
+
+void
 notmuch_messages_destroy (notmuch_messages_t *messages)
 {
     talloc_free (messages);
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 3b3f0eb..2269d2b 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -364,6 +364,7 @@ typedef struct _notmuch_message_list {
 struct _notmuch_messages {
     notmuch_bool_t is_of_list_type;
     notmuch_message_node_t *iterator;
+    notmuch_message_list_t *list;
 };
 
 notmuch_message_list_t *
@@ -389,8 +390,17 @@ notmuch_message_t *
 _notmuch_mset_messages_get (notmuch_messages_t *messages);
 
 void
+_notmuch_mset_messages_move_to_first (notmuch_messages_t *messages);
+
+void
 _notmuch_mset_messages_move_to_next (notmuch_messages_t *messages);
 
+void
+_notmuch_mset_messages_move_to_last (notmuch_messages_t *messages);
+
+void
+_notmuch_mset_messages_move_to_previous (notmuch_messages_t *messages);
+
 /* message.cc */
 
 void
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 0d9cb0f..753f3bb 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -645,6 +645,15 @@ notmuch_messages_valid (notmuch_messages_t *messages);
 notmuch_message_t *
 notmuch_messages_get (notmuch_messages_t *messages);
 
+/* Move the 'messages' iterator to the first message.
+ *
+ * After that the 'messages' iterator will be set to the first valid 
+ * message, so it can be use to iterate with 
+ * notmuch_messages_move_to_next.
+ */
+void
+notmuch_messages_move_to_first (notmuch_messages_t *messages);
+
 /* Move the 'messages' iterator to the next message.
  *
  * If 'messages' is already pointing at the last message then the
@@ -658,6 +667,25 @@ notmuch_messages_get (notmuch_messages_t *messages);
 void
 notmuch_messages_move_to_next (notmuch_messages_t *messages);
 
+/* Move the 'messages' iterator to the last message.
+ *
+ * After that the 'messages' iterator will be set to the last valid 
+ * message, so it can be use to iterate with 
+ * notmuch_messages_move_to_previous.
+ */
+void
+notmuch_messages_move_to_last (notmuch_messages_t *messages);
+
+/* Move the 'messages' iterator to the previous message.
+ *
+ * If 'messages' is already pointing at the first message then the
+ * iterator will be moved to a point just beyond that first message,
+ * (where notmuch_messages_valid will return FALSE and
+ * notmuch_messages_get will return NULL).
+ */
+void
+notmuch_messages_move_to_previous (notmuch_messages_t *messages);
+
 /* Destroy a notmuch_messages_t object.
  *
  * It's not strictly necessary to call this function. All memory from
diff --git a/lib/query.cc b/lib/query.cc
index 9266d35..970c35a 100644
--- a/lib/query.cc
+++ b/lib/query.cc
@@ -35,6 +35,7 @@ typedef struct _notmuch_mset_messages {
     notmuch_messages_t base;
     notmuch_database_t *notmuch;
     Xapian::MSetIterator iterator;
+    Xapian::MSetIterator iterator_begin;
     Xapian::MSetIterator iterator_end;
 } notmuch_mset_messages_t;
 
@@ -86,6 +87,7 @@ static int
 _notmuch_messages_destructor (notmuch_mset_messages_t *messages)
 {
     messages->iterator.~MSetIterator ();
+    messages->iterator_begin.~MSetIterator ();
     messages->iterator_end.~MSetIterator ();
 
     return 0;
@@ -108,6 +110,7 @@ notmuch_query_search_messages (notmuch_query_t *query)
 	messages->base.iterator = NULL;
 	messages->notmuch = notmuch;
 	new (&messages->iterator) Xapian::MSetIterator ();
+	new (&messages->iterator_begin) Xapian::MSetIterator ();
 	new (&messages->iterator_end) Xapian::MSetIterator ();
 
 	talloc_set_destructor (messages, _notmuch_messages_destructor);
@@ -157,6 +160,7 @@ notmuch_query_search_messages (notmuch_query_t *query)
 	mset = enquire.get_mset (0, notmuch->xapian_db->get_doccount ());
 
 	messages->iterator = mset.begin ();
+	messages->iterator_begin = mset.begin ();
 	messages->iterator_end = mset.end ();
 
     } catch (const Xapian::Error &error) {
@@ -208,6 +212,16 @@ _notmuch_mset_messages_get (notmuch_messages_t *messages)
 }
 
 void
+_notmuch_mset_messages_move_to_first (notmuch_messages_t *messages)
+{
+    notmuch_mset_messages_t *mset_messages;
+
+    mset_messages = (notmuch_mset_messages_t *) messages;
+
+    mset_messages->iterator = mset_messages->iterator_begin;
+}
+
+void
 _notmuch_mset_messages_move_to_next (notmuch_messages_t *messages)
 {
     notmuch_mset_messages_t *mset_messages;
@@ -217,6 +231,44 @@ _notmuch_mset_messages_move_to_next (notmuch_messages_t *messages)
     mset_messages->iterator++;
 }
 
+void
+_notmuch_mset_messages_move_to_last (notmuch_messages_t *messages)
+{
+    notmuch_mset_messages_t *mset_messages;
+
+    mset_messages = (notmuch_mset_messages_t *) messages;
+
+    mset_messages->iterator = mset_messages->iterator_end;
+    mset_messages->iterator--;
+}
+
+void
+_notmuch_mset_messages_move_to_previous (notmuch_messages_t *messages)
+{
+    notmuch_mset_messages_t *mset_messages;
+
+    mset_messages = (notmuch_mset_messages_t *) messages;
+
+    if (mset_messages->iterator == mset_messages->iterator_begin)
+    {
+        /*
+         * Xapian iterators can not be beyond the first element, so we
+         * assign the iterator_end to mark the iterator as invalid in case
+         * of move_to_previous with the iterator at the beginning
+         */
+        mset_messages->iterator = mset_messages->iterator_end;
+    }
+    else if (_notmuch_mset_messages_valid (messages))
+    {
+        /*
+         * If is valid move the iterator. To emulate the same behavior 
+         * than notmuch_messages_t the iterator won't be updated if is 
+         * not valid
+         */
+        mset_messages->iterator--;
+    }
+}
+
 /* Glib objects force use to use a talloc destructor as well, (but not
  * nearly as ugly as the for messages due to C++ objects). At
  * this point, I'd really like to have some talloc-friendly
-- 
1.7.0