AnsiFilterStream.scala

package tut

import java.io.{ OutputStream, FilterOutputStream }

// FilterOutputStream that removes ANSI escapes. This should be fairly efficient, I guess, since
// it's all case switches on constants. Can inline more if needed but it seems fine. For the
// record, the format is ESC '[' digits (';' digits)* terminal
case class AnsiFilterStream(os: OutputStream) extends FilterOutputStream(os) {

  case class State(apply: Int => State)

  val S: State = State {
    case 27 => I0
    case _  => F
  }

  val F: State = State(_ => F)

  val T: State = State(_ => T)

  val I0: State = State {
    case '[' => I1
    case _   => F
  }

  val I1: State = State {
    case '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' 
             => I2
    case _   => F 
  }

  val I2: State = State { 
    case '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' 
             => I2
    case ';' => I1
    case '@' | 'A' | 'B' | 'C' | 'D' | 'E' | 'F' | 'G' | 'H' | 'I' | 'J' | 'K' | 'L' | 'M' | 'N' | 
         'O' | 'P' | 'Q' | 'R' | 'S' | 'T' | 'U' | 'V' | 'W' | 'X' | 'Y' | 'Z' | '[' | '\\'| ']' | 
         '^' | '_' | '`' | 'a' | 'b' | 'c' | 'd' | 'e' | 'f' | 'g' | 'h' | 'i' | 'j' | 'k' | 'l' | 
         'm' | 'n' | 'o' | 'p' | 'q' | 'r' | 's' | 't' | 'u' | 'v' | 'w' | 'x' | 'y' | 'z' | '{' | 
         '|' | '}' | '~'
             => T // end of ANSI escape
    case _   => F
  }

  // Strategy is, accumulate values as long as we're in a non-terminal state, then either discard 
  // them if we reach T (which means we accumulated an ANSI escape sequence) or print them out if 
  // we reach F. 

  private var stack: List[Int] = Nil
  private var state: State     = S // Start

  override def write(n: Int): Unit = 
    state.apply(n) match {

      case F => 
        stack.foldRight(())((c, _) => super.write(c))
        super.write(n)
        stack = Nil
        state = S
      
      case T =>
        stack = Nil
        state = S

      case s =>
        stack = n :: stack
        state = s

    }

}

from https://github.com/tpolecat/tut/blob/master/core/src/main/scala/tut/AnsiFilterStream.scala