[PATCH 2/5] lib: Add a MTIME value to every mail document

[Thomas Jost <schnouki@schnouki.net>]

This is a time_t value, similar to the message date (TIMESTAMP). It is first set
when the message is added to the database, and is then updated every time a tag
is added or removed. It can thus be used for doing incremental dumps of the
database or for synchronizing it between several computers.

This value can be read freely (with notmuch_message_get_mtime()) but for now it
can't be set to an arbitrary value: it can only be set to "now" when updated.
There's no specific reason for this except that I don't really see a real use
case for setting it to an arbitrary value.
---
 lib/database.cc       |    7 ++++++-
 lib/message.cc        |   32 ++++++++++++++++++++++++++++++++
 lib/notmuch-private.h |    6 +++++-
 lib/notmuch.h         |    4 ++++
 4 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/lib/database.cc b/lib/database.cc
index 2025189..6dc6f73 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -81,7 +81,7 @@ typedef struct {
  *		        STRING is the name of a file within that
  *		        directory for this mail message.
  *
- *    A mail document also has four values:
+ *    A mail document also has five values:
  *
  *	TIMESTAMP:	The time_t value corresponding to the message's
  *			Date header.
@@ -92,6 +92,9 @@ typedef struct {
  *
  *	SUBJECT:	The value of the "Subject" header
  *
+ *	MTIME:		The time_t value corresponding to the last time
+ *			a tag was added or removed on the message.
+ *
  * In addition, terms from the content of the message are added with
  * "from", "to", "attachment", and "subject" prefixes for use by the
  * user in searching. Similarly, terms from the path of the mail
@@ -1735,6 +1738,8 @@ notmuch_database_add_message (notmuch_database_t *notmuch,
 	    date = notmuch_message_file_get_header (message_file, "date");
 	    _notmuch_message_set_header_values (message, date, from, subject);
 
+            _notmuch_message_update_mtime (message);
+
 	    _notmuch_message_index_file (message, filename);
 	} else {
 	    ret = NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID;
diff --git a/lib/message.cc b/lib/message.cc
index 0075425..0c98589 100644
--- a/lib/message.cc
+++ b/lib/message.cc
@@ -830,6 +830,34 @@ _notmuch_message_set_header_values (notmuch_message_t *message,
     message->doc.add_value (NOTMUCH_VALUE_SUBJECT, subject);
 }
 
+/* Get the message mtime, i.e. when it was added or the last time a tag was
+ * added/removed. */
+time_t
+notmuch_message_get_mtime (notmuch_message_t *message)
+{
+    std::string value;
+
+    try {
+	value = message->doc.get_value (NOTMUCH_VALUE_MTIME);
+    } catch (Xapian::Error &error) {
+	INTERNAL_ERROR ("Failed to read mtime value from document.");
+	return 0;
+    }
+
+    return Xapian::sortable_unserialise (value);
+}
+
+/* Set the message mtime to "now". */
+void
+_notmuch_message_update_mtime (notmuch_message_t *message)
+{
+    time_t time_value;
+
+    time_value = time (NULL);
+    message->doc.add_value (NOTMUCH_VALUE_MTIME,
+                            Xapian::sortable_serialise (time_value));
+}
+
 /* Synchronize changes made to message->doc out into the database. */
 void
 _notmuch_message_sync (notmuch_message_t *message)
@@ -994,6 +1022,8 @@ notmuch_message_add_tag (notmuch_message_t *message, const char *tag)
 			private_status);
     }
 
+    _notmuch_message_update_mtime (message);
+
     if (! message->frozen)
 	_notmuch_message_sync (message);
 
@@ -1022,6 +1052,8 @@ notmuch_message_remove_tag (notmuch_message_t *message, const char *tag)
 			private_status);
     }
 
+    _notmuch_message_update_mtime (message);
+
     if (! message->frozen)
 	_notmuch_message_sync (message);
 
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 60a932f..9859872 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -95,7 +95,8 @@ typedef enum {
     NOTMUCH_VALUE_TIMESTAMP = 0,
     NOTMUCH_VALUE_MESSAGE_ID,
     NOTMUCH_VALUE_FROM,
-    NOTMUCH_VALUE_SUBJECT
+    NOTMUCH_VALUE_SUBJECT,
+    NOTMUCH_VALUE_MTIME
 } notmuch_value_t;
 
 /* Xapian (with flint backend) complains if we provide a term longer
@@ -276,6 +277,9 @@ _notmuch_message_set_header_values (notmuch_message_t *message,
 				    const char *from,
 				    const char *subject);
 void
+_notmuch_message_update_mtime (notmuch_message_t *message);
+
+void
 _notmuch_message_sync (notmuch_message_t *message);
 
 notmuch_status_t
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 9f23a10..643ebce 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -910,6 +910,10 @@ notmuch_message_set_flag (notmuch_message_t *message,
 time_t
 notmuch_message_get_date  (notmuch_message_t *message);
 
+/* Get the mtime of 'message' as a time_t value. */
+time_t
+notmuch_message_get_mtime (notmuch_message_t *message);
+
 /* Get the value of the specified header from 'message'.
  *
  * The value will be read from the actual message file, not from the
-- 
1.7.8