#!/usr/bin/perl
# 
# Copyright © 2015-2020 by Vincent Slyngstad
# 
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS LISTED ABOVE BE LIABLE
# FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
# CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
# 
# Except as contained in this notice, the names of the authors above
# shall not be used in advertising or otherwise to promote the sale, use
# or other dealings in this Software without prior written authorization
# from those authors.

#
# OK, time for a bigger hammer.
# DUMPRX01 has generated a bytewise dump of the media, 
# in hardware sector/track order. Problem is, there 
# are several schemes, involving 8 or 12 bit mode, 
# for encoding the interesting 12 bit words on the 
# media.  Here, we look at every single sector, with 
# known encodings, trying to find things that look 
# like they might be the OS/8 directory segment 
# headers.
# This does assume that every OS/8 block starts on 
# a sector boundary, which ought to be the case.

# Check if this might be a directory segment, report if so.
sub isdirseg {
  local($fmt, $nseg, $sblk, $link, $flag, $aiw) = @_;
  # Number of entrees this segment should be negative.
  $nseg -=  010000 unless $nseg == 0; # Form two's complement
# return unless $nseg >= -40; # ...but not more than 40 files/segment.
  $aiw -=  010000 unless $aiw == 0; # Form two's complement
  return unless $aiw <= 0; # Expect a negative or zero aiw.
  return unless $aiw > -2; # Expect 0 or -1.
#return unless $link == 2;
  return unless ($sblk == 0070) || ($sblk == 0007);
  printf "$f: sector 0%06o is plausible ($nseg, %04o, $aiw, $fmt)\n", $sec, $sblk;
}

# The main loop just feeds sectors to the subroutines.
foreach $f (@ARGV) {
  open(INPUT, $f) || die "$f: $!";
  binmode(INPUT);
  $size = 0200 * 2; # 128 words
  for ($sec = 0; ; $sec++) {
    $spos = $sec * $size;
    seek(INPUT, $spos, 0) || die "seek($f): $!";
    $count = read(INPUT, $buf, $size);
    last unless $count;
    die "read($f): $!" if $count < 0;
    @buf = unpack("S*", $buf);
    $fmt = "os8";
    $nseg = $buf[0];
    $sblk = $buf[1];
    $link = $buf[2];
    $flag = $buf[3];
    $aiw  = $buf[4];
    &isdirseg($fmt, $nseg, $sblk, $link, $flag, $aiw);
  }
}

exit 0;