//
//  SheetContainerViewController.swift
//  SheetImagePicker
//
//  Created by Shadowfacts on 9/23/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit

public class SheetContainerViewController: UIViewController {

    let content: UIViewController
    
    public var detents: [Detent] = [.bottom, .middle, .top] {
        didSet {
            
        }
    }

    var topConstraint: NSLayoutConstraint!
    lazy var initialConstant: CGFloat = view.bounds.height / 2
    
    public init(content: UIViewController) {
        self.content = content
        
        super.init(nibName: nil, bundle: nil)
    }
    
    required public init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override public func viewDidLoad() {
        super.viewDidLoad()
        
        addChild(content)
        content.didMove(toParent: self)
        view.addSubview(content.view)
        topConstraint = content.view.topAnchor.constraint(equalTo: view.topAnchor, constant: initialConstant)
        NSLayoutConstraint.activate([
            content.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            content.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            topConstraint,
            content.view.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
        
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognized(_:)))
        content.view.addGestureRecognizer(panGesture)
    }
    
    @objc func panGestureRecognized(_ recognizer: UIPanGestureRecognizer) {
        switch recognizer.state {
        case .began:
            initialConstant = topConstraint.constant
            
        case .changed:
            let translation = recognizer.translation(in: content.view)
            var realOffset = initialConstant + translation.y
            if realOffset < view.safeAreaInsets.top {
                print(realOffset)
                realOffset = view.safeAreaInsets.top - realOffset / pow(CGFloat(M_E), realOffset / view.safeAreaInsets.top)
            }
            topConstraint.constant = realOffset
            
        case .ended:
            if let offset = nearestDetentOffset(offset: topConstraint.constant) {
                let distance = abs(topConstraint.constant - offset)
                self.topConstraint.constant = offset
                let velocity = recognizer.velocity(in: view)
                let springVelocity = velocity.y / distance
                UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: springVelocity, animations: {
                    self.view.layoutIfNeeded()
                })
            }
            
        default:
            return
        }
    }
    
    func nearestDetentOffset(offset: CGFloat) -> CGFloat? {
        return detents.map { $0.offset(in: view) }.min { (a, b) -> Bool in
            return abs(offset - a) < abs(offset - b)
        }
    }
    
}