SideMenu/Pod/Classes/SideMenuPresentationController.swift

//
//  BasePresentationController.swift
//  SideMenu
//
//  Created by Jon Kent on 10/20/18.
//

import UIKit

internal protocol PresentationModel {
    /// Draws `presentStyle.backgroundColor` behind the status bar. Default is 1.
    var statusBarEndAlpha: CGFloat { get }
    /// Enable or disable interaction with the presenting view controller while the menu is displayed. Enabling may make it difficult to dismiss the menu or cause exceptions if the user tries to present and already presented menu. `presentingViewControllerUseSnapshot` must also set to false. Default is false.
    var presentingViewControllerUserInteractionEnabled: Bool { get }
    /// Use a snapshot for the presenting vierw controller while the menu is displayed. Useful when layout changes occur during transitions. Not recommended for apps that support rotation. Default is false.
    var presentingViewControllerUseSnapshot: Bool { get }
    /// The presentation style of the menu.
    var presentationStyle: SideMenuPresentationStyle { get }
    /// Width of the menu when presented on screen, showing the existing view controller in the remaining space. Default is zero.
    var menuWidth: CGFloat { get }
}

internal protocol SideMenuPresentationControllerDelegate: class {
    func sideMenuPresentationControllerDidTap(_ presentationController: SideMenuPresentationController)
    func sideMenuPresentationController(_ presentationController: SideMenuPresentationController, didPanWith gesture: UIPanGestureRecognizer)
}

internal final class SideMenuPresentationController {

    private let config: PresentationModel
    private unowned var containerView: UIView
    private var interactivePopGestureRecognizerEnabled: Bool?
    private let leftSide: Bool
    private weak var originalSuperview: UIView?
    private unowned var presentedViewController: UIViewController
    private unowned var presentingViewController: UIViewController

    private lazy var snapshotView: UIView? = {
        guard config.presentingViewControllerUseSnapshot,
            let view = presentingViewController.view.snapshotView(afterScreenUpdates: true) else {
                return nil
        }

        view.autoresizingMask = [.flexibleHeight, .flexibleWidth]
        return view
    }()

    private lazy var statusBarView: UIView? = {
        guard config.statusBarEndAlpha != 0 else { return nil }

        return UIView {
            $0.backgroundColor = config.presentationStyle.backgroundColor
            $0.autoresizingMask = [.flexibleHeight, .flexibleWidth]
            $0.isUserInteractionEnabled = false
        }
    }()

    required init(config: PresentationModel, leftSide: Bool, presentedViewController: UIViewController, presentingViewController: UIViewController, containerView: UIView) {
        self.config = config
        self.containerView = containerView
        self.leftSide = leftSide
        self.presentedViewController = presentedViewController
        self.presentingViewController = presentingViewController
    }

    deinit {
        guard !presentedViewController.isHidden else { return }

        // Presentations must be reversed to preserve user experience
        dismissalTransitionWillBegin()
        dismissalTransition()
        dismissalTransitionDidEnd(true)
    }
    
    var frameOfPresentedViewInContainerView: CGRect {
        var rect = containerView.frame
        rect.origin.x = leftSide ? 0 : rect.width - config.menuWidth
        rect.size.width = config.menuWidth
        return rect
    }
    
    func containerViewWillLayoutSubviews() {
        presentedViewController.view.untransform {
            presentedViewController.view.frame = frameOfPresentedViewInContainerView
        }
        presentingViewController.view.untransform {
            presentingViewController.view.frame = containerView.frame
            snapshotView?.frame = containerView.frame
        }

        guard let statusBarView = statusBarView else { return }
        let statusBarOffset = containerView.frame.size.height - presentedViewController.view.bounds.height
        var statusBarFrame = UIApplication.shared.statusBarFrame

        // For in-call status bar, height is normally 40, which overlaps view. Instead, calculate height difference
        // of view and set height to fill in remaining space.
        if statusBarOffset >= CGFloat.ulpOfOne {
            statusBarFrame.size.height = statusBarOffset
        }

        statusBarView.frame = statusBarFrame
    }
    
    func presentationTransitionWillBegin() {
        if let snapshotView = snapshotView {
            presentingViewController.view.addSubview(snapshotView)
        }

        presentingViewController.view.isUserInteractionEnabled = config.presentingViewControllerUserInteractionEnabled
        containerView.backgroundColor = config.presentationStyle.backgroundColor

        originalSuperview = presentingViewController.view.superview
        containerView.addSubview(presentingViewController.view)
        containerView.addSubview(presentedViewController.view)
        
        layerViews()

        if let statusBarView = statusBarView {
            containerView.addSubview(statusBarView)
        }
        
        dismissalTransition()
        config.presentationStyle.presentationTransitionWillBegin(to: presentedViewController, from: presentingViewController)
    }

    func presentationTransition() {
        transition(
            to: presentedViewController,
            from: presentingViewController,
            alpha: config.presentationStyle.presentingEndAlpha,
            statusBarAlpha: config.statusBarEndAlpha,
            scale: config.presentationStyle.presentingScaleFactor,
            translate: config.presentationStyle.presentingTranslateFactor
        )

        config.presentationStyle.presentationTransition(to: presentedViewController, from: presentingViewController)
    }
    
    func presentationTransitionDidEnd(_ completed: Bool) {
        guard completed else {
            snapshotView?.removeFromSuperview()
            dismissalTransitionDidEnd(!completed)
            return
        }

        addParallax(to: presentingViewController.view)
        
        if let topNavigationController = presentingViewController as? UINavigationController {
            interactivePopGestureRecognizerEnabled = topNavigationController.interactivePopGestureRecognizer?.isEnabled
            topNavigationController.interactivePopGestureRecognizer?.isEnabled = false
        }

        containerViewWillLayoutSubviews()
        config.presentationStyle.presentationTransitionDidEnd(to: presentedViewController, from: presentingViewController, completed)
    }

    func dismissalTransitionWillBegin() {
        snapshotView?.removeFromSuperview()
        presentationTransition()
        config.presentationStyle.dismissalTransitionWillBegin(to: presentedViewController, from: presentingViewController)
    }

    func dismissalTransition() {
        transition(
            to: presentingViewController,
            from: presentedViewController,
            alpha: config.presentationStyle.menuStartAlpha,
            statusBarAlpha: 0,
            scale: config.presentationStyle.menuScaleFactor,
            translate: config.presentationStyle.menuTranslateFactor
        )

        config.presentationStyle.dismissalTransition(to: presentedViewController, from: presentingViewController)
    }

    func dismissalTransitionDidEnd(_ completed: Bool) {
        guard completed else {
            if let snapshotView = snapshotView {
                presentingViewController.view.addSubview(snapshotView)
            }
            presentationTransitionDidEnd(!completed)
            return
        }

        statusBarView?.removeFromSuperview()
        presentedViewController.view.removeFromSuperview()

        presentingViewController.view.motionEffects.removeAll()
        presentingViewController.view.layer.shadowOpacity = 0
        presentedViewController.view.layer.shadowOpacity = 0
        
        if let interactivePopGestureRecognizerEnabled = interactivePopGestureRecognizerEnabled,
            let topNavigationController = presentingViewController as? UINavigationController {
            topNavigationController.interactivePopGestureRecognizer?.isEnabled = interactivePopGestureRecognizerEnabled
        }

        originalSuperview?.addSubview(presentingViewController.view)
        presentingViewController.view.isUserInteractionEnabled = true
        config.presentationStyle.dismissalTransitionDidEnd(to: presentedViewController, from: presentingViewController, completed)
    }
}

private extension SideMenuPresentationController {

    func transition(to: UIViewController, from: UIViewController, alpha: CGFloat, statusBarAlpha: CGFloat, scale: CGFloat, translate: CGFloat) {
        containerViewWillLayoutSubviews()
        
        to.view.transform = .identity
        to.view.alpha = 1

        let x = (leftSide ? 1 : -1) * config.menuWidth * translate
        from.view.alpha = alpha
        from.view.transform = CGAffineTransform
            .identity
            .translatedBy(x: x, y: 0)
            .scaledBy(x: scale, y: scale)

        statusBarView?.alpha = statusBarAlpha
    }

    func layerViews() {
        statusBarView?.layer.zPosition = 2

        if config.presentationStyle.menuOnTop {
            addShadow(to: presentedViewController.view)
            presentedViewController.view.layer.zPosition = 1
        } else {
            addShadow(to: presentingViewController.view)
            presentedViewController.view.layer.zPosition = -1
        }
    }

    func addShadow(to view: UIView) {
        view.layer.shadowColor = config.presentationStyle.onTopShadowColor.cgColor
        view.layer.shadowRadius = config.presentationStyle.onTopShadowRadius
        view.layer.shadowOpacity = config.presentationStyle.onTopShadowOpacity
        view.layer.shadowOffset = config.presentationStyle.onTopShadowOffset
    }

    func addParallax(to view: UIView) {
        var effects: [UIInterpolatingMotionEffect] = []

        let x = config.presentationStyle.presentingParallaxStrength.width
        if x > 0 {
            let horizontal = UIInterpolatingMotionEffect(keyPath: "center.x", type: .tiltAlongHorizontalAxis)
            horizontal.minimumRelativeValue = -x
            horizontal.maximumRelativeValue = x
            effects.append(horizontal)
        }

        let y = config.presentationStyle.presentingParallaxStrength.height
        if y > 0 {
            let vertical = UIInterpolatingMotionEffect(keyPath: "center.y", type: .tiltAlongVerticalAxis)
            vertical.minimumRelativeValue = -y
            vertical.maximumRelativeValue = y
            effects.append(vertical)
        }

        if effects.count > 0 {
            let group = UIMotionEffectGroup()
            group.motionEffects = effects
            view.motionEffects.removeAll()
            view.addMotionEffect(group)
        }
    }
}