First move toward Disk class w/ a2mg data

Finally!  The Disk class doesn't actually serve as much more than a slightly
improved Globals class at the moment holding every splitting of the source path
and filename that we use in legacy code, as well as a copy of the disk image
itself that gets used long enough to read the a2mg header.

The idea I have here is to begin building the module-based code in parallel.
Then I'll just modify the linear code to compare doing it the old way to doing
it the new.  That'll let me verify that the new code does what the old should.

When it's all done, we can just modify main to use the new modular code and
look at splitting the modular code into a package with cppo as a runner.  At
that point the code should begin being able to do things cppo cannot.  We could
continue to extend cppo at that point, but my inclination is to maintain the
cppo runner as a compatibility layer and begin building a more modern image
tool.  Essentially to begin building the CiderPress for Linux or the Java-free
AppleCommander.

cppo

@@ -37,8 +37,43 @@ import subprocess
 #import tempfile # not used, but should be for temp directory?
 import logging
 import struct
+from collections import namedtuple
 from binascii import a2b_hex, b2a_hex
 
+A2MG1_UNPACK = (
+		'<'              # use little-endian numbers
+		'4s'             # magic string '2IMG'
+		'4s'             # creator string
+		'H'              # header length
+		'H'              # 2mg version
+		'L'              # image format
+		'L'              # flags (we unpack it into "vol")
+		'L'              # number of 512 blocks
+		'L'              # image data offset
+		'L'              # image data length
+		'L'              # comment offset
+		'L'              # comment length
+		'L'              # creator private use offset
+		'L'              # creator private use length
+		'16x'            # reserved for future use
+		)
+A2MG1_ATTRS = (
+		'magic', 'creator', 'hdr_len', 'version',
+		'img_fmt', 'vol', 'num_blocks',
+		'data_offset', 'data_len',
+		'cmnt_offset', 'cmnt_len',
+		'creator_offset', 'creator_len'
+		)
+A2MG1_VOL_ATTRS = ('locked', 'dosvol')
+
+# We assume 2mg files with unknown version have these fields
+A2MG_UNK_ATTRS = ('magic', 'creator', 'hdr_len', 'version')
+
+A2mg1 = namedtuple('A2mg1', A2MG1_ATTRS)
+A2mg1Vol = namedtuple('A2mg1Vol', A2MG1_VOL_ATTRS)
+A2mgUnk = namedtuple('A2mgUnk', A2MG_UNK_ATTRS)
+
+
 class Globals:
 	pass
 
@@ -63,7 +98,6 @@ g.DIRPATH = ""
 g.target_name = None
 g.target_dir = ""
 g.appledouble_dir = None
-g.image_file = None
 g.extract_file = None
 
 # runtime options
@@ -79,12 +113,12 @@ g.dos33 = False             #      (DOS 3.3 image source, selected automatically
 
 # functions
 
-def pack_u24be(buf: bytes, offset: int, val: int):
+def pack_u24be(buf: bytearray, offset: int, val: int):
 	lo16 = val & 0xffff
 	hi8 = (val >> 16) & 0xff
 	struct.pack_into('>BH', buf, offset, hi8, lo16)
 
-def pack_u32be(buf: bytes, offset: int, val: int):
+def pack_u32be(buf: bytearray, offset: int, val: int):
 	# Currently unused, will be needed for resource fork dates later
 	struct.pack_into('>L', buf, offset, val)
 
@@ -95,6 +129,35 @@ def unpack_u24le(buf: bytes, offset: int = 0) -> int:
 	lo16, hi8 = struct.unpack_from('<HB', buf, offset)
 	return lo16 | (hi8 << 16)
 
+# FIXME: I know -> namedtuple below is _wrong_.  It's a hint, and I am doing
+# things wrong here.  I'm not 100% sure how to do this right.  If you are,
+# please submit a more pythonic fix.
+def unpack_2mg(buf: bytes, offset: int = 0) -> namedtuple:
+	try:
+		# 2017-07-01: Version 1 data is the only kind so far...
+		a2mg = A2mg1(*struct.unpack_from(A2MG1_UNPACK, buf, offset))
+		if a2mg.magic == b'2IMG':
+			if a2mg.version == 1:
+				vol = A2mg1Vol(
+					locked=bool(a2mg.vol & (1<<31)),
+					dosvol=a2mg.vol & 0xff if a2mg.vol & 0x100 else None
+					)
+				a2mg = a2mg._replace(vol=vol)
+			else:
+				log.warn(
+						"Unrecognized 2mg version {}: '{}'".format(
+							a2mg.version, name
+							)
+						)
+				a2mg = A2mgUnk(*a2mg[0:len(A2MG_UNK_ATTRS)])
+		else:
+			a2mg = None
+	except ValueError:
+		a2mg = None
+	print(a2mg)
+	return a2mg
+
+
 def date_prodos_to_unix(prodos_date: bytes) -> int:
 	"""Returns a UNIX timestamp given a raw ProDOS date"""
 	"""The ProDOS date consists of two 16-bit words stored little-
@@ -875,6 +938,22 @@ def isnumber(number):
 
 #---- end IvanX general purpose functions ----#
 
+### NEW DISK CLASSES
+
+class Disk:
+	def __init__(self, name=None):
+		if name is not None:
+			self.pathname = name
+			self.path, self.filename = os.path.split(name)
+			self.diskname, self.ext = os.path.splitext(self.filename)
+			self.ext = os.path.splitext(name)[1].lower()
+			# FIXME: Handle compressed images?
+			with open(to_sys_name(name), "rb") as f:
+				self.image = f.read()
+
+			self.a2mg = unpack_2mg(self.image)
+
+
 ### LOGGING
 # *sigh* No clean/simple way to use str.format() type log strings without
 # jumping through a few hoops
@@ -894,10 +973,11 @@ class StyleAdapter(logging.LoggerAdapter):
 	def log(self, level, msg, *args, **kwargs):
 		if self.isEnabledFor(level):
 			msg, kwargs = self.process(msg, kwargs)
-			self.logger._log(level, Message(msg, args), (), **kwargs)
+			self.logger._log(level, Message(str(msg), args), (), **kwargs)
 
 log = StyleAdapter(logging.getLogger(__name__))
 
+
 def main(args: list):
 	# Set up our logging facility
 	handler = logging.StreamHandler(sys.stdout)
@@ -959,16 +1039,14 @@ def main(args: list):
 		if len(args) not in (3, 4):
 			usage()
 
-	g.image_file = args[1]
+	try:
-	if not os.path.isfile(g.image_file):
+		disk = Disk(args[1])
-		print('Image/archive file "{}" was not found.'.format(g.image_file))
+	except IOError as e:
+		log.critical(e)
 		quit_now(2)
 
-	g.image_name = os.path.splitext(os.path.basename(g.image_file))
-	g.image_ext = g.image_name[1].lower()
-
 	# automatically set ShrinkIt mode if extension suggests it
-	if g.src_shk or g.image_ext in ('.shk', '.sdk', '.bxy'):
+	if g.src_shk or disk.ext in ('.shk', '.sdk', '.bxy'):
 		if os.name == "nt":
 			print("ShrinkIt archives cannot be extracted on Windows.")
 			quit_now(2)
@@ -984,6 +1062,7 @@ def main(args: list):
 				quit_now(2)
 
 	if len(args) == 4:
+		print(args)
 		g.extract_file = args[2]
 
 	if g.extract_file:
@@ -1009,7 +1088,7 @@ def main(args: list):
 		makedirs(unshkdir)
 		result = os.system(
 				"/bin/bash -c 'cd " + unshkdir + "; "
-				+ "result=$(nulib2 -xse " + os.path.abspath(g.image_file)
+				+ "result=$(nulib2 -xse " + os.path.abspath(disk.pathname)
 				+ ((" " + args[2].replace('/', ':'))
 					if g.extract_file else "") + " 2> /dev/null); "
 				+ "if [[ $result == \"Failed.\" ]]; then exit 3; "
@@ -1052,7 +1131,7 @@ def main(args: list):
 			volumeName = toProdosName(fileNames[0].split("#")[0])
 		else: # extract in folder based on disk image name
 			curDir = False
-			volumeName = toProdosName(os.path.basename(g.image_file))
+			volumeName = toProdosName(os.path.basename(disk.pathname))
 			if volumeName[-4:].lower() in ('.shk', '.sdk', '.bxy'):
 				volumeName = volumeName[:-4]
 		if not g.catalog_only and not curDir and not g.extract_file:
@@ -1099,10 +1178,10 @@ def main(args: list):
 
 	# end script if SHK
 
-	g.image_data = load_file(g.image_file)
+	g.image_data = load_file(disk.pathname)
 
 	# detect if image is 2mg and remove 64-byte header if so
-	if g.image_ext in ('.2mg', '.2img'):
+	if disk.ext in ('.2mg', '.2img'):
 		g.image_data = g.image_data[64:]
 
 	# handle 140k disk image
@@ -1137,7 +1216,7 @@ def main(args: list):
 		# fall back on disk extension if weird boot block (e.g. AppleCommander)
 		if not prodos_disk and not g.dos33:
 			log.debug("format and ordering unknown, checking extension")
-			if g.image_ext in ('.dsk', '.do'):
+			if disk.ext in ('.dsk', '.do'):
 				log.debug("extension indicates DO, changing to PO")
 				fix_order = True
 		if fix_order:
@@ -1156,12 +1235,14 @@ def main(args: list):
 		usage()
 
 	if g.dos33:
-		disk_name = (g.image_name[0] if g.image_ext in ('.dsk', '.do', '.po')
+		disk_name = (disk.diskname
-				else "".join(g.image_name))
+				if disk.ext in ('.dsk', '.do', '.po')
+				else disk.filename)
 		if g.prodos_names:
 			disk_name = toProdosName(disk_name)
 		if not g.catalog_only:
-			g.target_dir = (args[3] if g.extract_file
+			g.target_dir = (args[3]
+					if g.extract_file
 					else (args[2] + "/" + disk_name))
 			g.appledouble_dir = (g.target_dir + "/.AppleDouble")
 			makedirs(g.target_dir)