/*
  Monster - an advanced game scripting language
  Copyright (C) 2007-2009  Nicolay Korslund
  Email: <korslund@gmail.com>
  WWW: http://monster.snaptoad.com/

  This file (codestream.d) is part of the Monster script language
  package.

  Monster is distributed as free software: you can redistribute it
  and/or modify it under the terms of the GNU General Public License
  version 3, as published by the Free Software Foundation.

  This program is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License for more details.

  You should have received a copy of the GNU General Public License
  version 3 along with this program. If not, see
  http://www.gnu.org/licenses/ .

 */

module monster.vm.codestream;

import std.string;
import std.stdio;
import monster.vm.error;

// CodeStream is a simple utility structure for reading data
// sequentially. It holds a piece of byte compiled code, and keeps
// track of the position within the code.
struct CodeStream
{
  private:
  ubyte[] data;
  int len;
  ubyte *pos;

  public:

  void setData(ubyte[] data)
  {
    this.data = data;
    len = data.length;
    pos = data.ptr;
  }

  // Called when the end of the stream was unexpectedly encountered
  void eos(char[] func)
  {
    char[] res = format("Premature end of input: %s() missing %s byte(s)",
			func, -len);
    fail(res);
  }

  // Jump to given position
  void jump(int newPos)
  {
    if(newPos<0 || newPos>=data.length)
      fail("Jump out of range");
    len = data.length - newPos;
    pos = &data[newPos];
  }

  // Get the current position
  int getPos()
  {
    return pos-data.ptr;
  }

  ubyte get()
  {
    if(len--) return *(pos++);
    eos("get");
  }

  int getInt()
  {
    len -= 4;
    if(len < 0) eos("getInt");
    int i = *(cast(int*)pos);
    pos+=4;
    return i;
  }

  // Get a slice of the 'size' next ints
  int[] getIntArray(uint size)
  {
    size *=4; // Convert size to bytes
    len -= size;
    if(len < 0) eos("getArray");
    int[] res = cast(int[])pos[0..size];
    pos += size;
    return res;
  }
}