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package com.twitter.io

import com.twitter.util.{Future, Return, Try, Throw}

/**
 * Construct a Reader from a Buf.
 */
private[io] class BufReader(buf: Buf) extends Reader {
  @volatile private[this] var state: Try[Buf] = Return(buf)

  def read(n: Int) = synchronized {
    state match {
      case Return(buf) =>
        if (buf.isEmpty) Future.None else {
          val f = Future.value(Some(buf.slice(0, n)))
          state = Return(buf.slice(n, Int.MaxValue))
          f
        }
      case Throw(exc) => Future.exception(exc)
    }
  }

  def discard() = synchronized {
    state = Throw(new Reader.ReaderDiscarded)
  }
}

object BufReader {
  def apply(buf: Buf): Reader =
    if (buf.isEmpty) Reader.Null else new BufReader(buf)
}