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import Foundation
class VisibilityViewManager {
static let shared = VisibilityViewManager()
private let views = NSHashTable<VisibilityView>(options: .weakMemory)
private var currentlyActiveView: VisibilityView?
private var screenHeight: CGFloat = UIScreen.main.bounds.height
private var prevCount = 0
func addView(_ view: VisibilityView) {
self.views.add(view)
if self.prevCount == 0 {
self.updateActiveView()
}
self.prevCount = self.views.count
}
func removeView(_ view: VisibilityView) {
self.views.remove(view)
self.prevCount = self.views.count
}
func updateActiveView() {
DispatchQueue.main.async {
var activeView: VisibilityView?
if self.views.count == 1 {
let view = self.views.allObjects[0]
if view.isViewableEnough() {
activeView = view
}
} else if self.views.count > 1 {
let views = self.views.allObjects
var mostVisibleView: VisibilityView?
var mostVisiblePosition: CGRect?
views.forEach { view in
if !view.isViewableEnough() {
return
}
guard let position = view.getPositionOnScreen() else {
return
}
if position.minY >= 150 {
if mostVisiblePosition == nil {
mostVisiblePosition = position
}
if let unwrapped = mostVisiblePosition,
position.minY <= unwrapped.minY {
mostVisibleView = view
mostVisiblePosition = position
}
}
}
activeView = mostVisibleView
}
if activeView == self.currentlyActiveView {
return
}
self.clearActiveView()
if let view = activeView {
self.setActiveView(view)
}
}
}
private func clearActiveView() {
if let currentlyActiveView = self.currentlyActiveView {
currentlyActiveView.setIsCurrentlyActive(isActive: false)
self.currentlyActiveView = nil
}
}
private func setActiveView(_ view: VisibilityView) {
view.setIsCurrentlyActive(isActive: true)
self.currentlyActiveView = view
}
}
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