Seamless Infinite UITableView with double page data

SeamlessInfiniteTableViewController.swift

// Reference - Main : http://stackoverflow.com/questions/18164519/uitableview-inserting-section-at-top-while-scrolling
// Reference - Sub  : http://bharath2020.in/2012/10/01/uitableview-tricks-part-2-infinite-scrolling/

import UIKit

class SeamlessInfiniteTableViewController: UITableViewController {

    /* Variables */
    let FetchingCount = 10 //WARNING : Below 10 is not recommened and tested
    var mergedSections:[[String]] = [] //WARNING : Every section has more than 0 row
    /* */
    
    /* Private */
    var numOfBackItems = 0
    var backSections:[[String]] = []
    
    var numOfFrontItems = 0
    var frontSections:[[String]] = []
    /* */
    
    /* Debug */
    let numOfDummySections = 3
    let numOfDummyRows = 5
    /* */
    
    var page = INT_MAX{
        didSet{
            if page == oldValue {
                return
            }else if page - 1 == oldValue{
                //Next Page
                println("Next Page")
                backSections = frontSections
                numOfBackItems = numOfFrontItems
                loadFrontItems()
            }else if page + 1 == oldValue {
                // Previous Page
                println("Previous page")
                frontSections = backSections
                numOfFrontItems = numOfBackItems
                loadBackItems()
            }else{
                println("Load all pages")
                loadBackItems()
                loadFrontItems()
            }
            mergedSections = backSections + frontSections
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        page = 0

        if mergedSections.count == 0{
            return
        }
        var initialSection = backSections.count // Last index of backSections + 1
        var initialRow = 0
        
        if frontSections.count == 0 {
            initialSection = backSections.count - 1
            initialRow = backSections.last!.count - 1
        }
        var initialIndexPath = NSIndexPath(forRow: initialRow, inSection: initialSection)
        
        tableView.scrollToRowAtIndexPath(initialIndexPath, atScrollPosition: UITableViewScrollPosition.Top, animated: false)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func prefersStatusBarHidden() -> Bool {
        return true
    }

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return mergedSections.count
    }
    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return mergedSections[section].count
    }
    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        var cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! UITableViewCell!
        cell.textLabel!.text = mergedSections[indexPath.section][indexPath.row]
        return cell
    }
    override func tableView(tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return mergedSections[section][0]
    }
    override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
        
        if (tableView.contentSize.height < tableView.frame.size.height) {
            println("TableView is smaller than frame")
            return
        }
        
        var visibleIndexPaths = tableView.indexPathsForVisibleRows() as! [NSIndexPath]
        if visibleIndexPaths.count == 0{
            println("TableView has no visiable rows")
            return
        }

        var pageStepper = 0
        
        // 1. Check Top
        if indexPath.section == 0 && indexPath.row == 0{
            
            if numOfBackItems < FetchingCount{
                println("[Top] There is no previous items")
                return
            }
            println("[Top] Load previous page")
            pageStepper = -1
        }
        // 2. Check Bottom
        else if indexPath.section == (mergedSections.count - 1) && indexPath.row == (mergedSections.last!.count - 1){
            
            if numOfFrontItems < FetchingCount{
                println("[Bottom] There is no next items")
                return
            }
            println("[Bottom] Load next page")
            pageStepper = 1
        }
        
        if pageStepper == 0{
            return
        }
        
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            self.page += pageStepper
            
            var oldIndexPath = indexPath
            
            var before = self.tableView.rectForRowAtIndexPath(oldIndexPath)
            var contentOffset = self.tableView.contentOffset
            self.tableView.reloadData()
            var newIndexPath = NSIndexPath(forRow: oldIndexPath.row, inSection: oldIndexPath.section - pageStepper)
            var after = self.tableView.rectForRowAtIndexPath(newIndexPath)
            contentOffset.y += (after.origin.y - before.origin.y);
            self.tableView.contentOffset = contentOffset
        })

    }
    
    //MARK: - Private
    func loadBackItems(){
        backSections = []
        //Load dummy back items
        for s in 0..<numOfDummySections{
            var section:[String] = []
            for r in 0 ..< numOfDummyRows{
                section.append(("[Page \(page - 1)]\(s) / \(r)"))
            }
            backSections.append(section)
        }
        numOfBackItems = countItems(backSections)
    }
    func loadFrontItems(){
        frontSections = []
        //Load dummy front items
        for s in 0..<numOfDummySections{
            var section:[String] = []
            for r in 0 ..< numOfDummyRows{
                section.append(("[Page \(page)]\(s) / \(r)"))
            }
            frontSections.append(section)
        }
        numOfFrontItems = countItems(frontSections)
    }
    func countItems(twoDimensionArray:[[String]]) -> Int{
        var count = 0
        for ar in twoDimensionArray{
            count += ar.count
        }
        return count
    }
}

I recommend to use JTTableViewController