package browser

// HandleScroll updates the browser scroll index by the given delta (in entries).
// Clamps to valid bounds and triggers prefetch/eviction as needed.
func HandleScroll(s *BrowserState, delta int) {
	deltaPx := int(float64(delta) * s.EntryHeight)
	HandlePixelScroll(s, deltaPx)
}

// HandlePixelScroll updates the browser scroll offset by the given delta (in pixels).
// Clamps to valid bounds and triggers eviction as needed.
func HandlePixelScroll(s *BrowserState, delta int) {
	s.ScrollOffset += float64(delta)

	// Clamp to valid bounds
	clampScrollOffset(s)

	// Trigger eviction of distant pages
	s.EvictPages()
}

// clampScrollOffset ensures the scroll offset stays within valid bounds.
func clampScrollOffset(s *BrowserState) {
	if s.ScrollOffset < 0 {
		s.ScrollOffset = 0
	}

	// If there's no scrollable area (entries fit in viewport), clamp to 0
	if s.TotalEntries <= s.VisibleCount {
		s.ScrollOffset = 0
		return
	}

	maxScroll := float64(s.TotalEntries-s.VisibleCount) * s.EntryHeight
	if s.ScrollOffset > maxScroll {
		s.ScrollOffset = maxScroll
	}
}