[PATCH] Name thread based on matching msgs instead of first msg.

[Jesse Rosenthal <jrosenthal@jhu.edu>]

At the moment all threads are named based on the name of the first message
in the thread. However, this can cause problems if people either start
new threads by replying-all (as unfortunately, many out there do) or
change the subject of their mails to reflect a shift in a thread on a
list.

This patch names threads based on matches for the query, and the search
order. If the search order is oldest-first (as in the default inbox) it
chooses the oldest matching message as the subject. If the search order is
newest-first it chooses the newest one.

Reply prefixes ("Re: ", "Aw: ", "Sv: ", "Vs: ") are ignored
(case-insensitively) so a Re: won't change the subject.

Note that this adds a "sort" argument to _notmuch_thread_create and
_thread_add_matched_message, so that when constructing the thread we can
be aware of the sort order.
---
 lib/notmuch-private.h |    3 ++-
 lib/query.cc          |    3 ++-
 lib/thread.cc         |   30 +++++++++++++++++++++++++++---
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index d52d84d..94cce1b 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -205,7 +205,8 @@ notmuch_thread_t *
 _notmuch_thread_create (void *ctx,
 			notmuch_database_t *notmuch,
 			const char *thread_id,
-			const char *query_string);
+			const char *query_string,
+			notmuch_sort_t sort);
 
 /* message.cc */
 
diff --git a/lib/query.cc b/lib/query.cc
index 9266d35..946f367 100644
--- a/lib/query.cc
+++ b/lib/query.cc
@@ -297,7 +297,8 @@ notmuch_threads_get (notmuch_threads_t *threads)
     return _notmuch_thread_create (threads->query,
 				   threads->query->notmuch,
 				   threads->thread_id,
-				   threads->query->query_string);
+				   threads->query->query_string,
+				   threads->query->sort);
 }
 
 void
diff --git a/lib/thread.cc b/lib/thread.cc
index ec80f85..9ba7b70 100644
--- a/lib/thread.cc
+++ b/lib/thread.cc
@@ -129,7 +129,8 @@ _thread_add_message (notmuch_thread_t *thread,
 
 static void
 _thread_add_matched_message (notmuch_thread_t *thread,
-			     notmuch_message_t *message)
+			     notmuch_message_t *message,
+			     notmuch_sort_t sort)
 {
     time_t date;
     notmuch_message_t *hashed_message;
@@ -142,6 +143,28 @@ _thread_add_matched_message (notmuch_thread_t *thread,
     if (date > thread->newest || ! thread->matched_messages)
 	thread->newest = date;
 
+    const char *subject;
+    const char *cleaned_subject;
+
+    subject = notmuch_message_get_header (message, "subject");
+
+    if ((strncasecmp (subject, "Re: ", 4) == 0) ||
+	(strncasecmp (subject, "Aw: ", 4) == 0) ||
+	(strncasecmp (subject, "Vs: ", 4) == 0) ||
+	(strncasecmp (subject, "Sv: ", 4) == 0)) {
+
+	cleaned_subject = talloc_strndup (thread,
+					  subject + 4,
+					  strlen(subject) - 4);
+    } else {
+	cleaned_subject = talloc_strdup (thread, subject);
+    }
+
+    if ((sort == NOTMUCH_SORT_OLDEST_FIRST && date <= thread->newest) ||
+	(sort != NOTMUCH_SORT_OLDEST_FIRST && date == thread->newest)) {
+	thread->subject = talloc_strdup (thread, cleaned_subject);
+    }
+
     thread->matched_messages++;
 
     if (g_hash_table_lookup_extended (thread->message_hash,
@@ -209,7 +232,8 @@ notmuch_thread_t *
 _notmuch_thread_create (void *ctx,
 			notmuch_database_t *notmuch,
 			const char *thread_id,
-			const char *query_string)
+			const char *query_string,
+			notmuch_sort_t sort)
 {
     notmuch_thread_t *thread;
     const char *thread_id_query_string, *matched_query_string;
@@ -284,7 +308,7 @@ _notmuch_thread_create (void *ctx,
 	 notmuch_messages_move_to_next (messages))
     {
 	message = notmuch_messages_get (messages);
-	_thread_add_matched_message (thread, message);
+	_thread_add_matched_message (thread, message, sort);
 	_notmuch_message_close (message);
     }
 
-- 
1.6.3.3