[Patch v3 3/3] emacs: show: make `seen' mean user viewed whole message

[Mark Walters]

This changes `seen' to mean that the user viewed `enough' of the whole
message: more precisely, a message is deemed seen if the top of the
message and either the bottom of the message or a point at least some
customisable number of lines into the message have each been visible
in the buffer at some point.

This is placed into the post-command-hook infrastructure introduced in
the previous patch.
---
 emacs/notmuch-show.el |   63 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 61 insertions(+), 2 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 1a7de85..1abf24b 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -211,6 +211,20 @@ (defcustom notmuch-show-mark-read-tags '("-unread")
   :type '(repeat string)
   :group 'notmuch-show)
 
+(defcustom notmuch-show-seen-lines-needed 0.75
+  "Control which messages get marked seen.
+
+A message is marked seen if both the top of the message and a
+point far \"enough\" down in the message have each been visible
+in the buffer at some point. This parameter controls the
+definition of enough.
+
+Enough means either the bottom of the message or a point in the
+message more than LINES-NEEDED lines into the message, where
+LINES-NEEDED is this variable if this variable is an integer and
+this variable times the current window height if it is a float."
+  :type 'number
+  :group 'notmuch-show)
 
 (defmacro with-current-notmuch-show-message (&rest body)
   "Evaluate body with current buffer set to the text of current message"
@@ -1532,9 +1546,54 @@ (defun notmuch-show-mark-read (&optional unread)
     (apply 'notmuch-show-tag-message
 	   (notmuch-tag-change-list notmuch-show-mark-read-tags unread))))
 
+(defun notmuch-show-update-seen (top-or-bottom)
+  "Update seen status of current message
+
+Mark that we have seen the TOP-OR-BOTTOM of current message."
+  (let ((current (notmuch-show-get-prop :seen)))
+    (unless (or (eq current 'both) (eq current top-or-bottom))
+      (if (not current)
+	  (notmuch-show-set-prop :seen top-or-bottom)
+	(notmuch-show-set-prop :seen 'both)
+	(notmuch-show-mark-read)))))
+
+(defun notmuch-show-do-message-seen (start end)
+  "Update seen status for the current message.
+
+A message is seen if both the top and enough of the rest of the
+message have been visible in the buffer.  See the
+`notmuch-show-seen-lines-needed' for the definition of `enough'."
+  (let* ((lines-needed (if (integerp notmuch-show-seen-lines-needed)
+			   notmuch-show-seen-lines-needed
+			 (truncate (* notmuch-show-seen-lines-needed (window-body-height)))))
+	 (top (notmuch-show-message-top))
+	 (bottom (notmuch-show-message-bottom)))
+    (when (notmuch-show-message-visible-p)
+      (when (>= top start)
+	(notmuch-show-update-seen 'top))
+      (when (or (<= bottom end)
+		(> (count-screen-lines top end) lines-needed))
+	(notmuch-show-update-seen 'bottom)))))
+
 (defun notmuch-show-do-seen (start end)
-  "Update seen status for all messages between start and end."
-  )
+  "Update seen status for all messages between start and end.
+
+We mark the top (bottom) of a message seen if the top (enough of
+the rest of the message) respectively have been visible in the
+buffer. See the `notmuch-show-seen-lines-needed' for the
+definition of `enough'. When both the top and bottom have been
+seen we mark the message read."
+  (save-excursion
+    (goto-char start)
+    (notmuch-show-do-message-seen start end)
+    (while (and (< (notmuch-show-message-bottom) end)
+		(notmuch-show-goto-message-next))
+      (notmuch-show-do-message-seen start end))
+    ;; This is a work around because emacs gives weird answers for
+    ;; window-end if the buffer ends with invisible text.
+    (when (and (pos-visible-in-window-p (point-max))
+	       (notmuch-show-message-visible-p))
+      (notmuch-show-update-seen 'bottom))))
 
 (defun notmuch-show-command-hook ()
   (when (eq major-mode 'notmuch-show-mode)
-- 
1.7.10.4