v0.1.0 initial commit

tui/scroll_state.go

@@ -0,0 +1,115 @@
+package tui
+
+// ScrollState tracks scroll position for a scrollable container
+type ScrollState struct {
+	Offset    int // First visible item index
+	Total     int // Total item count
+	Visible   int // Visible item count (viewport height)
+	Selection int // Currently selected item, -1 if none
+}
+
+// NewScrollState creates initialized scroll state
+func NewScrollState(total, visible int) *ScrollState {
+	return &ScrollState{
+		Total:     total,
+		Visible:   visible,
+		Selection: -1,
+	}
+}
+
+// --- Scroll manipulation ---
+
+// ScrollBy adjusts offset by delta, clamping to valid range
+func (s *ScrollState) ScrollBy(delta int) {
+	s.Offset += delta
+	s.Clamp()
+}
+
+// ScrollTo sets offset to specific position
+func (s *ScrollState) ScrollTo(pos int) {
+	s.Offset = pos
+	s.Clamp()
+}
+
+// EnsureVisible adjusts offset to make item at pos visible
+func (s *ScrollState) EnsureVisible(pos int) {
+	if pos < s.Offset {
+		s.Offset = pos
+	} else if pos >= s.Offset+s.Visible {
+		s.Offset = pos - s.Visible + 1
+	}
+	s.Clamp()
+}
+
+// Clamp ensures offset is within valid range
+func (s *ScrollState) Clamp() {
+	s.Offset = ClampScroll(s.Offset, s.Visible, s.Total)
+}
+
+// --- Page navigation ---
+
+// PageUp scrolls up by half visible height
+func (s *ScrollState) PageUp() {
+	s.ScrollBy(-PageDelta(s.Visible))
+}
+
+// PageDown scrolls down by half visible height
+func (s *ScrollState) PageDown() {
+	s.ScrollBy(PageDelta(s.Visible))
+}
+
+// --- State updates ---
+
+// SetTotal updates total count and reclamps
+func (s *ScrollState) SetTotal(total int) {
+	s.Total = total
+	s.Clamp()
+	if s.Selection >= total {
+		s.Selection = total - 1
+	}
+}
+
+// SetVisible updates visible count and reclamps
+func (s *ScrollState) SetVisible(visible int) {
+	s.Visible = visible
+	s.Clamp()
+}
+
+// --- Positions queries ---
+
+// AtTop returns true if scrolled to top
+func (s *ScrollState) AtTop() bool {
+	return s.Offset == 0
+}
+
+// AtBottom returns true if scrolled to bottom
+func (s *ScrollState) AtBottom() bool {
+	if s.Total <= s.Visible {
+		return true
+	}
+	return s.Offset >= s.Total-s.Visible
+}
+
+// --- Selection management ---
+
+// Select sets selection and ensures it's visible
+func (s *ScrollState) Select(idx int) {
+	s.Selection = ClampCursor(idx, s.Total)
+	s.EnsureVisible(s.Selection)
+}
+
+// SelectNext moves selection down
+func (s *ScrollState) SelectNext() {
+	if s.Selection < s.Total-1 {
+		s.Selection++
+		s.EnsureVisible(s.Selection)
+	}
+}
+
+// SelectPrev moves selection up
+func (s *ScrollState) SelectPrev() {
+	if s.Selection > 0 {
+		s.Selection--
+		s.EnsureVisible(s.Selection)
+	}
+}