UITableView+PerformUpdates.swift

//
//  UITableViewExtensions.swift
//
//  Created by Daniel Tartaglia on 7/21/17.
//  Copyright © 2017 MIT License.
//

import UIKit


extension UITableView {

    /// handles animating the updates to a table view.
    /// - parameter oldData: The array that the collection is currently using in its data source.
    /// - parameter newData: The new array that the collection should be using.
    /// - parameter adaptor: A closure that can turn an item into something that is Hashable. If the item is already hasable, pass in { $0 }
    /// - parameter assignment: assign your new array into your old array in this closure.
    func performUpdates<Item, ID: Hashable>(oldData: [Item], newData: [Item], adaptor: (Item) -> ID, assignment: @escaping () -> Void) {
        if oldData.isEmpty {
            assignment()
            reloadData()
        }
        else {
            let oldIDs = oldData.map(adaptor)
            let newIDs = newData.map(adaptor)
            self.beginUpdates()
            let (insertions, deletions) = findDifferences(old: oldIDs, new: newIDs, moveBlock: { (from, to) in
                self.moveRow(at: IndexPath(row: from, section: 0), to: IndexPath(row: to, section: 0))
            })
            self.insertRows(at: insertions.map { IndexPath(row: $0, section: 0) }, with: .automatic)
            self.deleteRows(at: deletions.map { IndexPath(row: $0, section: 0) }, with: .automatic)
            assignment()
            self.endUpdates()
        }
    }
    
}