#!/usr/bin/perl
# 
# Copyright © 2015-2022 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.

# Unpack every 3 M43 bytes into 2 words.  Similar to "3to4" except the
# bit order is different.

# Each block lives at 33 + (unit*06300+block) * (384+33)
# The interesting bit is 384 bytes long.
# The block number is at offset 28.

# Note: The media is 06300 blocks per half, not 06260.  Only the 06260
# are used by OS/8 (which gives warnings in os8xplode).

$prefix = 33; # bytes == 22 words
$suffix = 0;

foreach $f (@ARGV) {
  open(INPUT, $f) || die "$f: $!";
  binmode(INPUT);

  $o = $f; $o =~ s/.m43$//i; $o .= ".dsk";
  open(OUTPUT, ">$o") || die "$o: $!";
  binmode(OUTPUT);

  while (1) {
    # Skip the prefix, if any
    read(INPUT, $buf, $prefix) if $prefix;
    # Copy out a block
    for ($i = 0; $i < 0400; $i += 2) {
      if (read(INPUT, $buf, 3) == 3) {
        ($b1, $b2, $b3) = unpack("CCC", $buf);
        $b1 = ($b1 << 4) + ($b2 >> 4);
        $b2 = 07777 & (($b2 << 8) + $b3);
        print OUTPUT pack("SS", $b1, $b2);
      } else {
        exit 0; # Lame way to break while (1).
      }
    }
    # Skip the suffix, if any
    read(INPUT, $buf, $suffix) if $suffix;
  }
}