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/*
 * Copyright (C) 2015 - 2016 Juergen Pfundt
 *
 * Licensed 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.chelona

import java.nio.ByteBuffer
import java.nio.charset.StandardCharsets

object URIDecoder {
  def apply(s: String) = {
    val decoder = new URIDecoder()
    decoder.decode(s)
  }
}

/*
 * Utility class for URI decoding.
 *
 * The conversion process is the reverse of that used by the URIEncoder class.
 *
 * The rules of the RFC3986 URIParser assure the correctness of the syntax for hex-encoded characters passed as
 * arguments to the decode function of this class. The input string contains only legal characters and correctly formed
 * pct-encoded characters (pct-encoded = "%" HEXDIG HEXDIG). Therefore no validation or sanity checks are part of
 * the decode function.
 */

class URIDecoder {

  def decode(s: String): String = {

    @inline
    def PCTEncodedOctetToNibble(c: Char) = if (c <= '9') c - '0' else if (c <= 'F') c - '7' else c - 'W'

    val byteBuffer: ByteBuffer = ByteBuffer.allocate(s.length << 2)

    val iterator = s.iterator

    while (iterator.hasNext) {
      val c: Char = iterator.next()

      if (c != '%') {
        if (!c.isSurrogate) byteBuffer.put(c.toString.getBytes)
        else byteBuffer.put((c.toString + iterator.next().toString).getBytes)
      } else {
        byteBuffer.put(((PCTEncodedOctetToNibble(iterator.next()) << 4) | PCTEncodedOctetToNibble(iterator.next())).toByte)
      }
    }
    byteBuffer.flip()

    StandardCharsets.UTF_8.decode(byteBuffer).toString
  }
}