/*  Title:      Pure/library.scala

    Author:     Makarius

Basic library.

*/

package isabelle

import java.lang.System

object Library

{

  /* reverse CharSequence */

  class Reverse(text: CharSequence, start: Int, end: Int) extends CharSequence

  {

    require(0 <= start && start <= end && end <= text.length)

    def this(text: CharSequence) = this(text, 0, text.length)

    def length: Int = end - start

    def charAt(i: Int): Char = text.charAt(end - i - 1)

    def subSequence(i: Int, j: Int): CharSequence =

      if (0 <= i && i <= j && j <= length) new Reverse(text, end - j, end - i)

      else throw new IndexOutOfBoundsException

    override def toString: String =

    {

      val buf = new StringBuilder(length)

      for (i <- 0 until length)

        buf.append(charAt(i))

      buf.toString

    }

  }

  /* permissive UTF-8 decoding */

  // see also http://en.wikipedia.org/wiki/UTF-8#Description

  def decode_permissive_utf8(text: CharSequence): String =

  {

    val buf = new java.lang.StringBuilder(text.length)

    var code = -1

    var rest = 0

    def flush()

    {

      if (code != -1) {

        if (rest == 0 && Character.isValidCodePoint(code))

          buf.appendCodePoint(code)

        else buf.append('\uFFFD')

        code = -1

        rest = 0

      }

    }

    def init(x: Int, n: Int)

    {

      flush()

      code = x

      rest = n

    }

    def push(x: Int)

    {

      if (rest <= 0) init(x, -1)

      else {

        code <<= 6

        code += x

        rest -= 1

      }

    }

    for (i <- 0 until text.length) {

      val c = text.charAt(i)

      if (c < 128) { flush(); buf.append(c) }

      else if ((c & 0xC0) == 0x80) push(c & 0x3F)

      else if ((c & 0xE0) == 0xC0) init(c & 0x1F, 1)

      else if ((c & 0xF0) == 0xE0) init(c & 0x0F, 2)

      else if ((c & 0xF8) == 0xF0) init(c & 0x07, 3)

    }

    flush()

    buf.toString

  }

  /* timing */

  def timeit[A](e: => A) =

  {

    val start = System.currentTimeMillis()

    val result = Exn.capture(e)

    val stop = System.currentTimeMillis()

    System.err.println((stop - start) + "ms elapsed time")

    Exn.release(result)

  }

}