store: improve cursor position

Improve cursor re-positioning while filtering with and without threads.
Reposition cursor in client-side threading mode with a callback that is
set during store.NextPrev(). Run callback when the threads are
constructed in order to reposition the cursor correctly. The callback is
deactivated when store.Select() is called.

Steps to reproduce two issues:

* Reproduce issue 1:

1. Activate client-side threading
2. Apply a filter, e.g. :filter -f Koni
3. Move cursor around so that a message is highlighted
4. clear filter with :clear
5. The cursor is expected to remain on the selected message but is
   actually not

* Reproduce issue 2:

1. Activate client-side threading
2. Go the end of the message list
2. Apply a filter, e.g. :filter -f Koni
5. The cursor is now at the end of the filtered results instead of at
   the beginning

This patch fixes both of those issues. Tested in regular and threaded
view according to the following check list (expected behavior in
parenthesis):

1. Apply filter from a message that remains in the filter (cursor on message,
   message selected)
2. Apply filter from a message that will not remain (cursor at the top,
   no message selected)
3. Clear filter (cursor remains on message, message selected)
4. Scroll line-by-line (threads: cursor remains on line, does not "jump"
   with message)
5. Search (cursor on first result)

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Tim Culverhouse <tim@timculverhouse.com>

lib/msgstore.go

@@ -53,7 +53,9 @@ type MessageStore struct {
 
 	threadBuilderDebounce *time.Timer
 	threadBuilderDelay    time.Duration
+	threadCallback        func()
 
+	// threads mutex protects the store.threads and store.threadCallback
 	threadsMutex sync.Mutex
 }
 
@@ -343,6 +345,8 @@ func (store *MessageStore) SetThreadedView(thread bool) {
 	if store.buildThreads {
 		if store.threadedView {
 			store.runThreadBuilder()
+		} else if store.threadBuilderDebounce != nil {
+			store.threadBuilderDebounce.Stop()
 		}
 		return
 	}
@@ -376,35 +380,19 @@ func (store *MessageStore) runThreadBuilder() {
 		}
 	}
 	store.threadBuilderDebounce = time.AfterFunc(store.threadBuilderDelay, func() {
-		// temporarily deactiviate the selector in the message list by
-		// setting SelectedUid to the MagicUid
-		oldUid := store.SelectedUid()
-		store.Select(MagicUid)
-
-		// Get the current index (we want to stay at that position in
-		// the updated uid list to provide a similar scrolling
-		// experience to the user as in the regular view
-		idx := store.FindIndexByUid(oldUid)
-
 		// build new threads
 		th := store.builder.Threads(store.uids)
 
-		// try to select the same index in the updated uid list; if
-		// index is out of bound, stay at the selected message
-		rebuildUids := store.builder.Uids()
-		if idx >= 0 && idx < len(rebuildUids) {
-			store.Select(rebuildUids[idx])
-		} else {
-			store.Select(oldUid)
-		}
-
-		// save local threads to the message store variable
+		// save local threads to the message store variable and
+		// run callback if defined (callback should reposition cursor)
 		store.threadsMutex.Lock()
 		store.threads = th
+		if store.threadCallback != nil {
+			store.threadCallback()
+		}
 		store.threadsMutex.Unlock()
 
-		// invalidate message list so that it is redrawn with the new
-		// threads and selected message
+		// invalidate message list
 		if store.onUpdate != nil {
 			store.onUpdate(store)
 		}
@@ -543,6 +531,11 @@ func (store *MessageStore) SelectedUid() uint32 {
 }
 
 func (store *MessageStore) Select(uid uint32) {
+	store.threadsMutex.Lock()
+	if store.threadCallback != nil {
+		store.threadCallback = nil
+	}
+	store.threadsMutex.Unlock()
 	store.selectedUid = uid
 	if store.marker != nil {
 		store.marker.UpdateVisualMark()
@@ -572,6 +565,16 @@ func (store *MessageStore) NextPrev(delta int) {
 
 	store.Select(uids[newIdx])
 
+	if store.BuildThreads() && store.ThreadedView() {
+		store.threadsMutex.Lock()
+		store.threadCallback = func() {
+			if uids := store.Uids(); len(uids) > newIdx {
+				store.selectedUid = uids[newIdx]
+			}
+		}
+		store.threadsMutex.Unlock()
+	}
+
 	if store.marker != nil {
 		store.marker.UpdateVisualMark()
 	}
@@ -672,6 +675,7 @@ func (store *MessageStore) Sort(criteria []*types.SortCriterion, cb func(types.W
 	store.Sorting = true
 
 	handle_return := func(msg types.WorkerMessage) {
+		store.Select(store.SelectedUid())
 		store.Sorting = false
 		if cb != nil {
 			cb(msg)

widgets/msglist.go

@@ -70,9 +70,11 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 
 	ml.UpdateScroller(ml.height, len(store.Uids()))
 	if store := ml.Store(); store != nil && len(store.Uids()) > 0 {
-		if idx := store.FindIndexByUid(store.SelectedUid()); idx >= 0 {
-			ml.EnsureScroll(len(store.Uids()) - idx - 1)
+		idx := store.FindIndexByUid(store.SelectedUid())
+		if idx < 0 {
+			idx = len(store.Uids()) - 1
 		}
+		ml.EnsureScroll(len(store.Uids()) - idx - 1)
 	}
 
 	textWidth := ctx.Width()