LeadKit/TITransitions/Sources/PanelTransition/Driver/TransitionDriver.swift

//
//  Copyright (c) 2020 Touch Instinct
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the Software), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED AS IS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import UIKit

open class TransitionDriver: UIPercentDrivenInteractiveTransition {
    private weak var presentedController: UIViewController?
    
    private var panRecognizer: UIPanGestureRecognizer?
    
    public var direction: TransitionDirection = .present
    
    // MARK: - Linking
    public func link(to controller: UIViewController) {
        presentedController = controller
        
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handleGesture))
        
        panRecognizer = panGesture
        presentedController?.view.addGestureRecognizer(panGesture)
    }
    
    // MARK: - Override
    override open var wantsInteractiveStart: Bool {
        get {
            switch direction {
            case .present:
                return false
            case .dismiss:
                return panRecognizer?.state == .began
            }
        }
        
        set {}
    }
    
    @objc private func handleGesture(recognizer: UIPanGestureRecognizer) {
        switch direction {
        case .present:
            handlePresentation(recognizer: recognizer)
        case .dismiss:
            handleDismiss(recognizer: recognizer)
        }
    }
}

// MARK: - Gesture Handling
private extension TransitionDriver {
    var maxTranslation: CGFloat {
        presentedController?.view.frame.height ?? 0
    }
    
    /// `pause()` before call `isRunning`
    var isRunning: Bool {
        percentComplete != 0
    }
    
    func handlePresentation(recognizer: UIPanGestureRecognizer) {
        switch recognizer.state {
        case .began:
            pause()
        case .changed:
            update(percentComplete - recognizer.incrementToBottom(maxTranslation: maxTranslation))
            
        case .ended, .cancelled:
            if recognizer.isProjectedToDownHalf(maxTranslation: maxTranslation) {
                cancel()
            } else {
                finish()
            }
            
        case .failed:
            cancel()
            
        default:
            break
        }
    }
    
    func handleDismiss(recognizer: UIPanGestureRecognizer) {
        switch recognizer.state {
        case .began:
            pause() // Pause allows to detect isRunning
            
            if !isRunning {
                presentedController?.dismiss(animated: true) // Start the new one
            }
        
        case .changed:
            update(percentComplete + recognizer.incrementToBottom(maxTranslation: maxTranslation))
            
        case .ended, .cancelled:
            if recognizer.isProjectedToDownHalf(maxTranslation: maxTranslation) {
                finish()
            } else {
                cancel()
            }

        case .failed:
            cancel()
            
        default:
            break
        }
    }
}

private extension UIPanGestureRecognizer {
    func isProjectedToDownHalf(maxTranslation: CGFloat) -> Bool {
        let endLocation = projectedLocation(decelerationRate: .fast)
        let isPresentationCompleted = endLocation.y > maxTranslation / 2
        
        return isPresentationCompleted
    }
    
    func incrementToBottom(maxTranslation: CGFloat) -> CGFloat {
        let translation = self.translation(in: view).y
        setTranslation(.zero, in: nil)
        
        let percentIncrement = translation / maxTranslation
        return percentIncrement
    }
}