diff calculator

diffs.swift

// swift 1.2

/**
:param: old array of items
:param: new array of items

:return: a tuple where with the following components:

  - `newIndexesAdded` indexes in new, for elements that did not exist in old
  - `oldIndexesDeleted` indexes in old, for elements not in new
  - `indexesOfMovedItems` array of (oldIndex,newIndex) pairs, indicating the change in index of an item that exists in old and in new and has a different index in old than in new


*/
func diffs<T:Hashable>(old: [T], new: [T]) ->
   (newIndexesAdded:[Int],oldIndexesDeleted:[Int],indexesOfMovedItems:[(Int,Int)])
{
  let newMinusOld = Array(Set(new).subtract(Set(old)))
  let oldMinusNew = Array(Set(old).subtract(Set(new)))
  let oldIntersectNew = Array(Set(new).intersect(Set(old)))
  
  
  let newIndexesAdded = newMinusOld.map { find(new,$0)! }
  let oldIndexesDeleted = oldMinusNew.map { find(old,$0)! }
  
  let moved = oldIntersectNew
    
  let moves:[(Int,Int)] = moved.map({ (find(old,$0)!,find(new,$0)!)}).filter({$0 != $1})
  
  return (
    newIndexesAdded:newIndexesAdded,
    oldIndexesDeleted:oldIndexesDeleted,
    indexesOfMovedItems:moves
  )
}