init: pristine aerc 0.20.0 source

app/scrollable.go

@@ -0,0 +1,101 @@
+package app
+
+// Scrollable implements vertical scrolling
+type Scrollable struct {
+	scroll int
+	offset int
+	height int
+	elems  int
+}
+
+func (s *Scrollable) Scroll() int {
+	return s.scroll
+}
+
+func (s *Scrollable) SetOffset(offset int) {
+	s.offset = offset
+}
+
+func (s *Scrollable) ScrollOffset() int {
+	return s.offset
+}
+
+func (s *Scrollable) PercentVisible() float64 {
+	if s.elems <= 0 {
+		return 1.0
+	}
+	return float64(s.height) / float64(s.elems)
+}
+
+func (s *Scrollable) PercentScrolled() float64 {
+	if s.elems <= 0 {
+		return 1.0
+	}
+	return float64(s.scroll) / float64(s.elems)
+}
+
+func (s *Scrollable) NeedScrollbar() bool {
+	needScrollbar := true
+	if s.PercentVisible() >= 1.0 {
+		needScrollbar = false
+	}
+	return needScrollbar
+}
+
+func (s *Scrollable) UpdateScroller(height, elems int) {
+	s.height = height
+	s.elems = elems
+}
+
+func (s *Scrollable) EnsureScroll(idx int) {
+	if idx < 0 {
+		return
+	}
+
+	middle := s.height / 2
+	switch {
+	case s.offset > middle:
+		s.scroll = idx - middle
+	case idx < s.scroll+s.offset:
+		s.scroll = idx - s.offset
+	case idx >= s.scroll-s.offset+s.height:
+		s.scroll = idx + s.offset - s.height + 1
+	}
+
+	s.checkBounds()
+}
+
+func (s *Scrollable) checkBounds() {
+	maxScroll := s.elems - s.height
+	if maxScroll < 0 {
+		maxScroll = 0
+	}
+
+	if s.scroll > maxScroll {
+		s.scroll = maxScroll
+	}
+
+	if s.scroll < 0 {
+		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()
+}