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package com.twitter.io

import java.nio.charset.{Charset, CharsetDecoder, CharsetEncoder, CodingErrorAction}

import scala.collection.mutable

/**
 * Provides a set of frequently used [[java.nio.charset.Charset]] instances and
 * the utilities related to them.
 */
object Charsets {

  /**
   * 16-bit UTF (UCS Transformation Format) whose byte order is identified by
   * an optional byte-order mark
   */
  val Utf16: Charset = Charset.forName("UTF-16")

  /**
   * 16-bit UTF (UCS Transformation Format) whose byte order is big-endian
   */
  val Utf16BE: Charset = Charset.forName("UTF-16BE")

  /**
   * 16-bit UTF (UCS Transformation Format) whose byte order is little-endian
   */
  val Utf16LE: Charset = Charset.forName("UTF-16LE")

  /**
   * 8-bit UTF (UCS Transformation Format)
   */
  val Utf8: Charset = Charset.forName("UTF-8")

  /**
   * ISO Latin Alphabet No. 1, as known as `ISO-LATIN-1`
   */
  val Iso8859_1: Charset = Charset.forName("ISO-8859-1")

  /**
   * 7-bit ASCII, as known as ISO646-US or the Basic Latin block of the
   * Unicode character set
   */
  val UsAscii: Charset = Charset.forName("US-ASCII")

  private[this] val encoders = new ThreadLocal[mutable.Map[Charset, CharsetEncoder]] {
    protected override def initialValue = new mutable.HashMap()
  }

  private[this] val decoders = new ThreadLocal[mutable.Map[Charset, CharsetDecoder]] {
    protected override def initialValue = new mutable.HashMap()
  }

  /**
   * Returns a cached thread-local [[java.nio.charset.CharsetEncoder]] for
   * the specified `charset`.
   */
  def encoder(charset: Charset): CharsetEncoder = {
    val e = encoders.get.getOrElseUpdate(charset, charset.newEncoder());
    e.reset
    e.onMalformedInput(CodingErrorAction.REPLACE)
    e.onUnmappableCharacter(CodingErrorAction.REPLACE)
  }

  /**
   * Returns a cached thread-local [[java.nio.charset.CharsetDecoder]] for
   * the specified `charset`.
   */
  def decoder(charset: Charset): CharsetDecoder = {
    val d = decoders.get.getOrElseUpdate(charset, charset.newDecoder())
    d.reset
    d.onMalformedInput(CodingErrorAction.REPLACE)
    d.onUnmappableCharacter(CodingErrorAction.REPLACE)
  }
}