Implement animated scroll tab alternating

Sources/SearchFeature/Controllers/SearchContainerController.swift

 import UIKit
 import Theme
 import Shared
+import Combine
 import DependencyInjection
 
 public final class SearchContainerController: UIViewController {
@@ -8,8 +9,16 @@ public final class SearchContainerController: UIViewController {
 
     lazy private var screenView = SearchContainerView()
 
+    private var cancellables = Set<AnyCancellable>()
+    private let qrController = SearchQRController()
+    private let emailController = SearchEmailController()
+    private let phoneController = SearchPhoneController()
+    private let usernameController = SearchUsernameController()
+
     public override func loadView() {
         view = screenView
+        screenView.scrollView.delegate = self
+        embedControllers()
     }
 
     public override func viewWillAppear(_ animated: Bool) {
@@ -24,6 +33,7 @@ public final class SearchContainerController: UIViewController {
     public override func viewDidLoad() {
         super.viewDidLoad()
         setupNavigationBar()
+        setupBindings()
     }
 
     private func setupNavigationBar() {
@@ -42,7 +52,107 @@ public final class SearchContainerController: UIViewController {
         )
     }
 
+    private func setupBindings() {
+        screenView.segmentedControl
+            .actionPublisher
+            .receive(on: DispatchQueue.main)
+            .sink { [unowned self] in
+                let page = CGFloat($0.rawValue)
+                let point: CGPoint = CGPoint(x: screenView.frame.width * page, y: 0.0)
+                screenView.scrollView.setContentOffset(point, animated: true)
+            }.store(in: &cancellables)
+    }
+
     @objc private func didTapBack() {
         navigationController?.popViewController(animated: true)
     }
+
+    private func embedControllers() {
+        addChild(qrController)
+        addChild(emailController)
+        addChild(phoneController)
+        addChild(usernameController)
+
+        screenView.scrollView.addSubview(qrController.view)
+        screenView.scrollView.addSubview(emailController.view)
+        screenView.scrollView.addSubview(phoneController.view)
+        screenView.scrollView.addSubview(usernameController.view)
+
+        usernameController.view.snp.makeConstraints {
+            $0.top.equalTo(screenView.segmentedControl.snp.bottom)
+            $0.width.equalTo(screenView)
+            $0.bottom.equalTo(screenView)
+            $0.left.equalToSuperview()
+            $0.right.equalTo(emailController.view.snp.left)
+        }
+
+        emailController.view.snp.makeConstraints {
+            $0.top.equalTo(screenView.segmentedControl.snp.bottom)
+            $0.width.equalTo(screenView)
+            $0.bottom.equalTo(screenView)
+            $0.right.equalTo(phoneController.view.snp.left)
+        }
+
+        phoneController.view.snp.makeConstraints {
+            $0.top.equalTo(screenView.segmentedControl.snp.bottom)
+            $0.width.equalTo(screenView)
+            $0.bottom.equalTo(screenView)
+            $0.right.equalTo(qrController.view.snp.left)
+        }
+
+        qrController.view.snp.makeConstraints {
+            $0.top.equalTo(screenView.segmentedControl.snp.bottom)
+            $0.width.equalTo(screenView)
+            $0.bottom.equalTo(screenView)
+        }
+
+        qrController.didMove(toParent: self)
+        emailController.didMove(toParent: self)
+        phoneController.didMove(toParent: self)
+        usernameController.didMove(toParent: self)
+    }
+}
+
+extension SearchContainerController: UIScrollViewDelegate {
+    public func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        let pageOffset = scrollView.contentOffset.x / view.frame.width
+        scrollSegmentedControlTrack(using: pageOffset)
+        updateSegmentedControlButtonsColor(using: pageOffset)
+    }
+
+    private func scrollSegmentedControlTrack(using pageOffset: CGFloat) {
+        let amountOfTabs = 4.0
+        let tabWidth = screenView.bounds.width / amountOfTabs
+
+        if let leftConstraint = screenView.segmentedControl.leftConstraint {
+            leftConstraint.update(offset: pageOffset * tabWidth)
+        }
+    }
+
+    private func updateSegmentedControlButtonsColor(using pageOffset: CGFloat) {
+        let qrRate = highlightRateFor(page: 3, offset: pageOffset)
+        let emailRate = highlightRateFor(page: 1, offset: pageOffset)
+        let phoneRate = highlightRateFor(page: 2, offset: pageOffset)
+        let usernameRate = highlightRateFor(page: 0, offset: pageOffset)
+
+        screenView.segmentedControl.qrCodeButton.updateHighlighting(rate: qrRate)
+        screenView.segmentedControl.emailButton.updateHighlighting(rate: emailRate)
+        screenView.segmentedControl.phoneButton.updateHighlighting(rate: phoneRate)
+        screenView.segmentedControl.usernameButton.updateHighlighting(rate: usernameRate)
+    }
+
+    private func highlightRateFor(page: CGFloat, offset: CGFloat) -> CGFloat {
+        let lowerBound = page - 1
+        let upperBound = page + 1
+
+        if offset > lowerBound && offset < upperBound {
+            if (offset - lowerBound) > 1 {
+                return 1 - (offset - page)
+            } else {
+                return offset - lowerBound
+            }
+        } else {
+            return 0
+        }
+    }
 }