Edit Distance Correctness test

object WeightedWagnerFischerTest extends App {
  
  /* currently tests for the default weights */
  
  val externalLibraryImpl = new info.debatty.java.stringsimilarity.Levenshtein
  val random = new scala.util.Random(333) // pin down random seed
  def randomString(length: Int) = random.alphanumeric.take(length).mkString  
  def randomPair(length: Int, maxTouches: Int): (String, String) = {
    val string1 = randomString(length).toCharArray 
    var string2 = string1.clone
    
    val touches = random.nextInt(maxTouches)
    
    for (touch <- 0 to touches) {
      val touchPoint = random.nextInt(string2.length)
      string2 = random.nextInt(3) match {
        case touchKind: Int if touchKind == 0 => // substitution        
          string2(touchPoint) = random.alphanumeric.take(1).toString.head
          string2
        case touchKind: Int if touchKind == 1 => // addition
          val (head, tail) = string1.splitAt(touchPoint)
          head ++ random.alphanumeric.take(1).mkString ++ tail
        case touchKind: Int if touchKind == 2 => // deletion
          val (head, tail) = string1.splitAt(touchPoint)
          head ++ tail.drop(1)
      }
    }
    
    (string1.mkString, string2.mkString)
  }
    
  def assertedEditDistance(pair: (String, String)) = {
    val externalLibraryResult = externalLibraryImpl.distance(pair._1, pair._2)
    val weightedWagnerFischer = new WeightedWagnerFischer(DefaultCosts)
    val computed = weightedWagnerFischer.distance(pair._1, pair._2)
    assert(
      computed == externalLibraryImpl.distance(pair._1, pair._2),
      s"Computed Levenshtein distance is: $computed, but should be $externalLibraryResult according to external library, for $pair"
    )
    computed
  }
  
  val testPairs = Seq.fill(100)(randomPair(10,5))
  
  testPairs map (pair => Seq(pair._1, pair._2, assertedEditDistance(pair)))
  
}