package com.rockymadden.stringmetric.similarity

import com.rockymadden.stringmetric.Metric.StringMetric

final case class WeightedLevenshteinMetric(delete: BigDecimal, insert: BigDecimal, substitute: BigDecimal)
	extends StringMetric[Double] {

	import com.rockymadden.stringmetric.CompareTuple

	override def compare(a: Array[Char], b: Array[Char]): Option[Double] =
		if (a.length == 0 || b.length == 0) None
		else if (a.sameElements(b)) Some(0d)
		else Some(weightedLevenshtein((a, b), (delete, insert, substitute)).toDouble)

	override def compare(a: String, b: String): Option[Double] = compare(a.toCharArray, b.toCharArray)

	private val weightedLevenshtein: ((CompareTuple[Char], (BigDecimal, BigDecimal, BigDecimal)) => BigDecimal) =
		(ct, w) => {
			val m = Array.ofDim[BigDecimal](ct._1.length + 1, ct._2.length + 1)

			for (r <- 0 to ct._1.length) m(r)(0) = w._1 * r
			for (c <- 0 to ct._2.length) m(0)(c) = w._2 * c

			for (r <- 1 to ct._1.length; c <- 1 to ct._2.length) {
				m(r)(c) =
					if (ct._1(r - 1) == ct._2(c - 1)) m(r - 1)(c - 1)
					else (m(r - 1)(c) + w._1).min( // Delete (left).
						(m(r)(c - 1) + w._2).min( // Insert (up).
							m(r - 1)(c - 1) + w._3 // Substitute (left-up).
						)
					)
			}

			m(ct._1.length)(ct._2.length)
		}
}