core/src/main/scala/com/rockymadden/stringmetric/Tokenize.scala


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package com.rockymadden.stringmetric

object Tokenize {
	sealed trait Tokenizer[A] {
		def tokenize(a: A): Option[Array[A]]
	}


	sealed trait StringTokenizer extends Tokenizer[Array[Char]] {
		def tokenize(a: String): Option[Array[String]]
	}


	object StringTokenizer {
		val NGram = NGramTokenizer

		def tokenizeWithNGram(n: Int)(charArray: Array[Char]) = NGram(n).tokenize(charArray)
	}


	final case class NGramTokenizer(n: Int) extends StringTokenizer {
		override def tokenize(a: Array[Char]): Option[Array[Array[Char]]] =
			if (n <= 0 || a.length < n) None
			else Some(sequence(a, Array.empty[Array[Char]], n))

		override def tokenize(a: String): Option[Array[String]] = tokenize(a.toCharArray).map(_.map(_.mkString))

		@annotation.tailrec
		private val sequence: ((Array[Char], Array[Array[Char]], Int) => Array[Array[Char]]) = (i, o, n) =>
			if (i.length <= n) o :+ i
			else sequence(i.tail, o :+ i.take(n), n)
	}
}