path: root/ios/MullvadVPN/Presentation controllers/FormsheetPresentationController.swift

//
//  FormSheetPresentationController.swift
//  MullvadVPN
//
//  Created by pronebird on 18/02/2023.
//  Copyright © 2025 Mullvad VPN AB. All rights reserved.
//

import MullvadTypes
import UIKit

struct FormSheetPresentationOptions {
    /**
     Indicates whether the presentation controller should use a fullscreen presentation when in a compact width environment
     */
    var useFullScreenPresentationInCompactWidth = false

    /**
     Indicates whether the presentation controller should handle keyboard notifications
     */
    var adjustViewWhenKeyboardAppears = false
}

/**
 Custom implementation of a formsheet presentation controller.
 */
class FormSheetPresentationController: UIPresentationController {
    /**
     Name of notification posted when fullscreen presentation changes, including during initial presentation.
     */
    static let willChangeFullScreenPresentation =
        Notification
        .Name(rawValue: "FormSheetPresentationControllerWillChangeFullScreenPresentation")

    /**
     User info key passed along with `willChangeFullScreenPresentation` notification that contains boolean value that
     indicates if presentation controller is using fullscreen presentation.
     */
    static let isFullScreenUserInfoKey = "isFullScreen"

    /**
     Last known presentation style used to prevent emitting duplicate `willChangeFullScreenPresentation` notifications.
     */
    private var lastKnownIsInFullScreen: Bool?

    /**
     Change the position of `presentedView` if `FormSheetPresentationOptions.adjustViewWhenKeyboardAppears` is `true`
     */
    private var keyboardResponder: AutomaticKeyboardResponder?

    private let dimmingView: UIView = {
        let dimmingView = UIView()
        dimmingView.backgroundColor = UIMetrics.DimmingView.backgroundColor
        return dimmingView
    }()

    override var shouldRemovePresentersView: Bool {
        false
    }

    /**
     Returns `true` if presentation controller is in fullscreen presentation.
     */
    var isInFullScreenPresentation: Bool {
        options.useFullScreenPresentationInCompactWidth && traitCollection.horizontalSizeClass == .compact
    }

    private let options: FormSheetPresentationOptions

    init(
        presentedViewController: UIViewController,
        presenting presentingViewController: UIViewController?,
        options: FormSheetPresentationOptions
    ) {
        self.options = options
        super.init(presentedViewController: presentedViewController, presenting: presentingViewController)
        addKeyboardResponderIfNeeded()
    }

    override var frameOfPresentedViewInContainerView: CGRect {
        guard let containerView else {
            return super.frameOfPresentedViewInContainerView
        }

        if isInFullScreenPresentation {
            return containerView.bounds
        }

        let preferredContentSize = presentedViewController.preferredContentSize

        assert(preferredContentSize.width > 0 && preferredContentSize.height > 0)

        return CGRect(
            origin: CGPoint(
                x: containerView.bounds.midX - preferredContentSize.width * 0.5,
                y: containerView.bounds.midY - preferredContentSize.height * 0.5
            ),
            size: preferredContentSize
        )
    }

    override func containerViewWillLayoutSubviews() {
        dimmingView.frame = containerView?.bounds ?? .zero
        presentedView?.frame = frameOfPresentedViewInContainerView
    }

    override func presentationTransitionWillBegin() {
        dimmingView.alpha = 0
        containerView?.addSubview(dimmingView)

        presentedView?.layer.cornerRadius = UIMetrics.DimmingView.cornerRadius
        presentedView?.clipsToBounds = true

        let revealDimmingView = {
            self.dimmingView.alpha = UIMetrics.DimmingView.opacity
        }

        if let transitionCoordinator = presentingViewController.transitionCoordinator {
            transitionCoordinator.animate { _ in
                revealDimmingView()
            }
        } else {
            revealDimmingView()
        }

        postFullscreenPresentationWillChangeIfNeeded()
    }

    override func presentationTransitionDidEnd(_ completed: Bool) {
        if !completed {
            dimmingView.removeFromSuperview()
        }
    }

    override func dismissalTransitionWillBegin() {
        let fadeDimmingView = {
            self.dimmingView.alpha = 0
        }

        if let transitionCoordinator = presentingViewController.transitionCoordinator {
            transitionCoordinator.animate { _ in
                fadeDimmingView()
            }
        } else {
            fadeDimmingView()
        }
    }

    override func dismissalTransitionDidEnd(_ completed: Bool) {
        if completed {
            dimmingView.removeFromSuperview()
        }
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        postFullscreenPresentationWillChangeIfNeeded()
    }

    private func postFullscreenPresentationWillChangeIfNeeded() {
        let currentIsInFullScreen = isInFullScreenPresentation

        guard lastKnownIsInFullScreen != currentIsInFullScreen else { return }

        lastKnownIsInFullScreen = currentIsInFullScreen

        NotificationCenter.default.post(
            name: Self.willChangeFullScreenPresentation,
            object: presentedViewController,
            userInfo: [Self.isFullScreenUserInfoKey: NSNumber(value: currentIsInFullScreen)]
        )
    }

    private func addKeyboardResponderIfNeeded() {
        guard options.adjustViewWhenKeyboardAppears,
            let presentedView
        else { return }
        keyboardResponder = AutomaticKeyboardResponder(
            targetView: presentedView,
            handler: { [weak self] view, adjustment in
                guard let self,
                    let containerView,
                    !isInFullScreenPresentation
                else { return }
                let frame = view.frame
                let bottomMarginFromKeyboard = adjustment > 0 ? UIMetrics.TableView.sectionSpacing : 0
                view.frame = CGRect(
                    origin: CGPoint(
                        x: frame.origin.x,
                        y: containerView.bounds.midY - presentedViewController.preferredContentSize
                            .height * 0.5 - adjustment - bottomMarginFromKeyboard
                    ),
                    size: frame.size
                )
                view.layoutIfNeeded()
            }
        )
    }
}

class FormSheetTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
    let options: FormSheetPresentationOptions

    init(options: FormSheetPresentationOptions = FormSheetPresentationOptions()) {
        self.options = options
    }

    func animationController(
        forPresented presented: UIViewController,
        presenting: UIViewController,
        source: UIViewController
    ) -> UIViewControllerAnimatedTransitioning? {
        FormSheetPresentationAnimator()
    }

    func animationController(forDismissed dismissed: UIViewController)
        -> UIViewControllerAnimatedTransitioning?
    {
        FormSheetPresentationAnimator()
    }

    func presentationController(
        forPresented presented: UIViewController,
        presenting: UIViewController?,
        source: UIViewController
    ) -> UIPresentationController? {
        FormSheetPresentationController(
            presentedViewController: presented,
            presenting: source,
            options: options
        )
    }
}

class FormSheetPresentationAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?)
        -> TimeInterval
    {
        (transitionContext?.isAnimated ?? true) ? UIMetrics.FormSheetTransition.duration.timeInterval : 0
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let destination = transitionContext.viewController(forKey: .to)

        if destination?.isBeingPresented ?? false {
            animatePresentation(transitionContext)
        } else {
            animateDismissal(transitionContext)
        }
    }

    private func animatePresentation(_ transitionContext: UIViewControllerContextTransitioning) {
        let duration = transitionDuration(using: transitionContext)
        let containerView = transitionContext.containerView
        let destinationView = transitionContext.view(forKey: .to)!
        let destinationController = transitionContext.viewController(forKey: .to)!

        containerView.addSubview(destinationView)

        var initialFrame = transitionContext.finalFrame(for: destinationController)
        initialFrame.origin.y = containerView.bounds.maxY
        destinationView.frame = initialFrame

        if transitionContext.isAnimated {
            UIView.animate(
                withDuration: duration,
                delay: UIMetrics.FormSheetTransition.delay.timeInterval,
                options: UIMetrics.FormSheetTransition.animationOptions,
                animations: {
                    destinationView.frame = transitionContext.finalFrame(for: destinationController)
                },
                completion: { _ in
                    transitionContext.completeTransition(true)
                }
            )
        } else {
            destinationView.frame = transitionContext.finalFrame(for: destinationController)
        }
    }

    private func animateDismissal(_ transitionContext: UIViewControllerContextTransitioning) {
        let duration = transitionDuration(using: transitionContext)
        let containerView = transitionContext.containerView
        let sourceView = transitionContext.view(forKey: .from)!
        let sourceController = transitionContext.viewController(forKey: .from)!

        var initialFrame = transitionContext.finalFrame(for: sourceController)
        initialFrame.origin.y = containerView.bounds.maxY

        if transitionContext.isAnimated {
            UIView.animate(
                withDuration: duration,
                delay: UIMetrics.FormSheetTransition.delay.timeInterval,
                options: UIMetrics.FormSheetTransition.animationOptions,
                animations: {
                    sourceView.frame = initialFrame
                },
                completion: { _ in
                    transitionContext.completeTransition(true)
                }
            )
        } else {
            sourceView.frame = initialFrame
            transitionContext.completeTransition(true)
        }
    }
}