//
//  ScrollableViewController.swift
//

import UIKit

class ScrollableViewController: UIViewController, UIScrollViewDelegate {
    
    private let scrollView = UIScrollView()
    private var controllers: Array<ViewController> = [
        ViewController(color: UIColor.yellowColor()),
        ViewController(color: UIColor.redColor()),
        ViewController(color: UIColor.blueColor()),
        ViewController(color: UIColor.yellowColor()),
        ViewController(color: UIColor.redColor()),
        ViewController(color: UIColor.blueColor())]
    
    private var isDragging = false
    
    override func loadView() {
        self.automaticallyAdjustsScrollViewInsets = false
        scrollView.delegate = self
        scrollView.backgroundColor = UIColor.whiteColor()
        scrollView.showsHorizontalScrollIndicator = true
        scrollView.decelerationRate = UIScrollViewDecelerationRateFast
        self.view = scrollView
        
        self.navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Scroll", style: UIBarButtonItemStyle.Plain, target: self, action: "didTapBarButton")
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        let width: CGFloat = CGFloat(controllers.count) * self.view.bounds.size.width
        scrollView.contentSize = CGSizeMake(width, self.view.bounds.size.height)
        layoutViewController(0, toIndex: 0)
    }
    
    func scrollViewDidScroll(scrollView: UIScrollView) {
        let fromIndex = floor(scrollView.bounds.origin.x  / scrollView.bounds.size.width)
        let toIndex = floor((CGRectGetMaxX(scrollView.bounds) - 1) / scrollView.bounds.size.width)
        
        layoutViewController(Int(fromIndex), toIndex: Int(toIndex))
    }
    
    func scrollViewWillBeginDragging(scrollView: UIScrollView) {
        isDragging = true
    }
    
    func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let offset = round(targetContentOffset.memory.x / self.view.bounds.size.width) * self.view.bounds.size.width
        targetContentOffset.memory.x = offset
        isDragging = false
    }
    
    
    func didTapBarButton() {
        // Scroll mid-view
        scrollView.setContentOffset(CGPointMake(2.5 * self.view.bounds.size.width, 0), animated: true)
    }
    
    
    private func layoutViewController(fromIndex: Int, toIndex: Int) {
        
        for var i = 0; i < controllers.count; i++ {
            // Remove views that should not be visible anymore
            if (controllers[i].view.superview != nil && (i < fromIndex || i > toIndex)) {
                println(NSString(format: "Hiding view controller at index: %i", i))
                controllers[i].willMoveToParentViewController(nil)
                controllers[i].view.removeFromSuperview()
                controllers[i].removeFromParentViewController()
            }
            
            // Add views that are now visible
            if (controllers[i].view.superview == nil && (i >= fromIndex && i <= toIndex)) {
                println(NSString(format: "Showing view controller at index: %i", i))
                var viewFrame = self.view.bounds
                viewFrame.origin.x = CGFloat(i) * self.view.bounds.size.width
                controllers[i].view.frame = viewFrame
                self.addChildViewController(controllers[i])
                scrollView.addSubview(controllers[i].view)
                controllers[i].didMoveToParentViewController(self)
            }
        }
    }
}