/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.ml.feature

import org.apache.spark.annotation.AlphaComponent
import org.apache.spark.ml.UnaryTransformer
import org.apache.spark.ml.param.ParamMap
import org.apache.spark.sql.{DataType, StringType, ArrayType}

/**
 * :: AlphaComponent ::
 * A tokenizer that converts the input string to lowercase and then splits it by white spaces.
 */
@AlphaComponent
class Tokenizer extends UnaryTransformer[String, Seq[String], Tokenizer] {

  protected override def createTransformFunc(paramMap: ParamMap): String => Seq[String] = {
    _.toLowerCase.split("\\s")
  }

  protected override def validateInputType(inputType: DataType): Unit = {
    require(inputType == StringType, s"Input type must be string type but got $inputType.")
  }

  override protected def outputDataType: DataType = new ArrayType(StringType, false)
}
