commands: add align

Add a new :align command that aligns the selected message vertically at
the top, center, or bottom of the message list.

The command requires a position argument that can either be: "top",
"center", or "bottom".

Create the following default keybinds:
	zz = :align center<Enter>
	zt = :align top<Enter>
	zb = :align bottom<Enter>

Changelog-added: Add new `:align` command to align the selected
 message at the top, center, or bottom of the message list.
Suggested-by: Ángel Castañeda <angel@acsq.me>
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Jason Cox <me@jasoncarloscox.com>
Acked-by: Robin Jarry <robin@jarry.cc>

2 files changed, 41 insertions, 0 deletions

diff --git a/app/msglist.go b/app/msglist.go
index a5e5fbb6..38970123 100644
--- a/app/msglist.go
+++ b/app/msglist.go
@@ -51,6 +51,23 @@ type messageRowParams struct {
 	headers      *mail.Header
 }
 
+// AlignMessage aligns the selected message to position pos.
+func (ml *MessageList) AlignMessage(pos AlignPosition) {
+	store := ml.Store()
+	if store == nil {
+		return
+	}
+	idx := 0
+	iter := store.UidsIterator()
+	for i := 0; iter.Next(); i++ {
+		if store.SelectedUid() == iter.Value().(uint32) {
+			idx = i
+			break
+		}
+	}
+	ml.Align(idx, pos)
+}
+
 func (ml *MessageList) Draw(ctx *ui.Context) {
 	ml.height = ctx.Height()
 	ml.width = ctx.Width()
diff --git a/app/scrollable.go b/app/scrollable.go
index 3a0555fe..04436375 100644
--- a/app/scrollable.go
+++ b/app/scrollable.go
@@ -62,6 +62,10 @@ func (s *Scrollable) EnsureScroll(idx int) {
 		s.scroll = idx + s.offset - s.height + 1
 	}
 
+	s.checkBounds()
+}
+
+func (s *Scrollable) checkBounds() {
 	maxScroll := s.elems - s.height
 	if maxScroll < 0 {
 		maxScroll = 0
@@ -75,3 +79,23 @@ func (s *Scrollable) EnsureScroll(idx int) {
 		s.scroll = 0
 	}
 }
+
+type AlignPosition uint
+
+const (
+	AlignTop AlignPosition = iota
+	AlignCenter
+	AlignBottom
+)
+
+func (s *Scrollable) Align(idx int, pos AlignPosition) {
+	switch pos {
+	case AlignTop:
+		s.scroll = idx
+	case AlignCenter:
+		s.scroll = idx - s.height/2
+	case AlignBottom:
+		s.scroll = idx - s.height + 1
+	}
+	s.checkBounds()
+}