ttLib/tables/otBase.py

from fontTools.config import OPTIONS
from fontTools.misc.textTools import Tag, bytesjoin
from .DefaultTable import DefaultTable
from enum import IntEnum
import sys
import array
import struct
import logging
from functools import lru_cache
from typing import Iterator, NamedTuple, Optional, Tuple

log = logging.getLogger(__name__)

have_uharfbuzz = False
try:
	import uharfbuzz as hb
	# repack method added in uharfbuzz >= 0.23; if uharfbuzz *can* be
	# imported but repack method is missing, behave as if uharfbuzz
	# is not available (fallback to the slower Python implementation)
	have_uharfbuzz = callable(getattr(hb, "repack", None))
except ImportError:
	pass

USE_HARFBUZZ_REPACKER = OPTIONS[f"{__name__}:USE_HARFBUZZ_REPACKER"]

class OverflowErrorRecord(object):
	def __init__(self, overflowTuple):
		self.tableType = overflowTuple[0]
		self.LookupListIndex = overflowTuple[1]
		self.SubTableIndex = overflowTuple[2]
		self.itemName = overflowTuple[3]
		self.itemIndex = overflowTuple[4]

	def __repr__(self):
		return str((self.tableType, "LookupIndex:", self.LookupListIndex, "SubTableIndex:", self.SubTableIndex, "ItemName:", self.itemName, "ItemIndex:", self.itemIndex))

class OTLOffsetOverflowError(Exception):
	def __init__(self, overflowErrorRecord):
		self.value = overflowErrorRecord

	def __str__(self):
		return repr(self.value)

class RepackerState(IntEnum):
	# Repacking control flow is implemnted using a state machine. The state machine table:
	#
	# State       | Packing Success | Packing Failed | Exception Raised |
	# ------------+-----------------+----------------+------------------+
	# PURE_FT     | Return result   | PURE_FT        | Return failure   |
	# HB_FT       | Return result   | HB_FT          | FT_FALLBACK      |
	# FT_FALLBACK | HB_FT           | FT_FALLBACK    | Return failure   |

	# Pack only with fontTools, don't allow sharing between extensions.
	PURE_FT = 1

	# Attempt to pack with harfbuzz (allowing sharing between extensions)
	# use fontTools to attempt overflow resolution.
	HB_FT = 2

	# Fallback if HB/FT packing gets stuck. Pack only with fontTools, don't allow sharing between
	# extensions.
	FT_FALLBACK = 3

class BaseTTXConverter(DefaultTable):

	"""Generic base class for TTX table converters. It functions as an
	adapter between the TTX (ttLib actually) table model and the model
	we use for OpenType tables, which is necessarily subtly different.
	"""

	def decompile(self, data, font):
		"""Create an object from the binary data. Called automatically on access."""
		from . import otTables
		reader = OTTableReader(data, tableTag=self.tableTag)
		tableClass = getattr(otTables, self.tableTag)
		self.table = tableClass()
		self.table.decompile(reader, font)

	def compile(self, font):
		"""Compiles the table into binary. Called automatically on save."""

		# General outline:
		# Create a top-level OTTableWriter for the GPOS/GSUB table.
		# 	Call the compile method for the the table
		# 		for each 'converter' record in the table converter list
		# 			call converter's write method for each item in the value.
		# 				- For simple items, the write method adds a string to the
		# 				writer's self.items list.
		# 				- For Struct/Table/Subtable items, it add first adds new writer to the
		# 				to the writer's self.items, then calls the item's compile method.
		# 				This creates a tree of writers, rooted at the GUSB/GPOS writer, with
		# 				each writer representing a table, and the writer.items list containing
		# 				the child data strings and writers.
		# 	call the getAllData method
		# 		call _doneWriting, which removes duplicates
		# 		call _gatherTables. This traverses the tables, adding unique occurences to a flat list of tables
		# 		Traverse the flat list of tables, calling getDataLength on each to update their position
		# 		Traverse the flat list of tables again, calling getData each get the data in the table, now that
		# 		pos's and offset are known.

		# 		If a lookup subtable overflows an offset, we have to start all over.
		overflowRecord = None
		# this is 3-state option: default (None) means automatically use hb.repack or
		# silently fall back if it fails; True, use it and raise error if not possible
		# or it errors out; False, don't use it, even if you can.
		use_hb_repack = font.cfg[USE_HARFBUZZ_REPACKER]
		if self.tableTag in ("GSUB", "GPOS"):
			if use_hb_repack is False:
				log.debug(
					"hb.repack disabled, compiling '%s' with pure-python serializer",
					self.tableTag,
				)
			elif not have_uharfbuzz:
				if use_hb_repack is True:
					raise ImportError("No module named 'uharfbuzz'")
				else:
					assert use_hb_repack is None
					log.debug(
						"uharfbuzz not found, compiling '%s' with pure-python serializer",
						self.tableTag,
					)

		if (use_hb_repack in (None, True)
				and have_uharfbuzz
				and self.tableTag in ("GSUB", "GPOS")):
			state = RepackerState.HB_FT
		else:
			state = RepackerState.PURE_FT

		hb_first_error_logged = False
		lastOverflowRecord = None
		while True:
			try:
				writer = OTTableWriter(tableTag=self.tableTag)
				self.table.compile(writer, font)
				if state == RepackerState.HB_FT:
					return self.tryPackingHarfbuzz(writer, hb_first_error_logged)
				elif state == RepackerState.PURE_FT:
					return self.tryPackingFontTools(writer)
				elif state == RepackerState.FT_FALLBACK:
					# Run packing with FontTools only, but don't return the result as it will
					# not be optimally packed. Once a successful packing has been found, state is
					# changed back to harfbuzz packing to produce the final, optimal, packing.
					self.tryPackingFontTools(writer)
					log.debug("Re-enabling sharing between extensions and switching back to "
										"harfbuzz+fontTools packing.")
					state = RepackerState.HB_FT

			except OTLOffsetOverflowError as e:
				hb_first_error_logged = True
				ok = self.tryResolveOverflow(font, e, lastOverflowRecord)
				lastOverflowRecord = e.value

				if ok:
					continue

				if state is RepackerState.HB_FT:
					log.debug("Harfbuzz packing out of resolutions, disabling sharing between extensions and "
									 "switching to fontTools only packing.")
					state = RepackerState.FT_FALLBACK
				else:
					raise

	def tryPackingHarfbuzz(self, writer, hb_first_error_logged):
		try:
			log.debug("serializing '%s' with hb.repack", self.tableTag)
			return writer.getAllDataUsingHarfbuzz(self.tableTag)
		except (ValueError, MemoryError, hb.RepackerError) as e:
			# Only log hb repacker errors the first time they occur in
			# the offset-overflow resolution loop, they are just noisy.
			# Maybe we can revisit this if/when uharfbuzz actually gives
			# us more info as to why hb.repack failed...
			if not hb_first_error_logged:
				error_msg = f"{type(e).__name__}"
				if str(e) != "":
					error_msg += f": {e}"
				log.warning(
						"hb.repack failed to serialize '%s', attempting fonttools resolutions "
						"; the error message was: %s",
						self.tableTag,
						error_msg,
				)
				hb_first_error_logged = True
			return writer.getAllData(remove_duplicate=False)


	def tryPackingFontTools(self, writer):
		return writer.getAllData()


	def tryResolveOverflow(self, font, e, lastOverflowRecord):
		ok = 0
		if lastOverflowRecord == e.value:
			# Oh well...
			return ok

		overflowRecord = e.value
		log.info("Attempting to fix OTLOffsetOverflowError %s", e)

		if overflowRecord.itemName is None:
			from .otTables import fixLookupOverFlows
			ok = fixLookupOverFlows(font, overflowRecord)
		else:
			from .otTables import fixSubTableOverFlows
			ok = fixSubTableOverFlows(font, overflowRecord)

		if ok:
			return ok

		# Try upgrading lookup to Extension and hope
		# that cross-lookup sharing not happening would
		# fix overflow...
		from .otTables import fixLookupOverFlows
		return fixLookupOverFlows(font, overflowRecord)

	def toXML(self, writer, font):
		self.table.toXML2(writer, font)

	def fromXML(self, name, attrs, content, font):
		from . import otTables
		if not hasattr(self, "table"):
			tableClass = getattr(otTables, self.tableTag)
			self.table = tableClass()
		self.table.fromXML(name, attrs, content, font)
		self.table.populateDefaults()

	def ensureDecompiled(self, recurse=True):
		self.table.ensureDecompiled(recurse=recurse)


# https://github.com/fonttools/fonttools/pull/2285#issuecomment-834652928
assert len(struct.pack('i', 0)) == 4
assert array.array('i').itemsize == 4, "Oops, file a bug against fonttools."

class OTTableReader(object):

	"""Helper class to retrieve data from an OpenType table."""

	__slots__ = ('data', 'offset', 'pos', 'localState', 'tableTag')

	def __init__(self, data, localState=None, offset=0, tableTag=None):
		self.data = data
		self.offset = offset
		self.pos = offset
		self.localState = localState
		self.tableTag = tableTag

	def advance(self, count):
		self.pos += count

	def seek(self, pos):
		self.pos = pos

	def copy(self):
		other = self.__class__(self.data, self.localState, self.offset, self.tableTag)
		other.pos = self.pos
		return other

	def getSubReader(self, offset):
		offset = self.offset + offset
		return self.__class__(self.data, self.localState, offset, self.tableTag)

	def readValue(self, typecode, staticSize):
		pos = self.pos
		newpos = pos + staticSize
		value, = struct.unpack(f">{typecode}", self.data[pos:newpos])
		self.pos = newpos
		return value
	def readArray(self, typecode, staticSize, count):
		pos = self.pos
		newpos = pos + count * staticSize
		value = array.array(typecode, self.data[pos:newpos])
		if sys.byteorder != "big": value.byteswap()
		self.pos = newpos
		return value.tolist()

	def readInt8(self):
		return self.readValue("b", staticSize=1)
	def readInt8Array(self, count):
		return self.readArray("b", staticSize=1, count=count)

	def readShort(self):
		return self.readValue("h", staticSize=2)
	def readShortArray(self, count):
		return self.readArray("h", staticSize=2, count=count)

	def readLong(self):
		return self.readValue("i", staticSize=4)
	def readLongArray(self, count):
		return self.readArray("i", staticSize=4, count=count)

	def readUInt8(self):
		return self.readValue("B", staticSize=1)
	def readUInt8Array(self, count):
		return self.readArray("B", staticSize=1, count=count)

	def readUShort(self):
		return self.readValue("H", staticSize=2)
	def readUShortArray(self, count):
		return self.readArray("H", staticSize=2, count=count)

	def readULong(self):
		return self.readValue("I", staticSize=4)
	def readULongArray(self, count):
		return self.readArray("I", staticSize=4, count=count)

	def readUInt24(self):
		pos = self.pos
		newpos = pos + 3
		value, = struct.unpack(">l", b'\0'+self.data[pos:newpos])
		self.pos = newpos
		return value
	def readUInt24Array(self, count):
		return [self.readUInt24() for _ in range(count)]

	def readTag(self):
		pos = self.pos
		newpos = pos + 4
		value = Tag(self.data[pos:newpos])
		assert len(value) == 4, value
		self.pos = newpos
		return value

	def readData(self, count):
		pos = self.pos
		newpos = pos + count
		value = self.data[pos:newpos]
		self.pos = newpos
		return value

	def __setitem__(self, name, value):
		state = self.localState.copy() if self.localState else dict()
		state[name] = value
		self.localState = state

	def __getitem__(self, name):
		return self.localState and self.localState[name]

	def __contains__(self, name):
		return self.localState and name in self.localState


class OTTableWriter(object):

	"""Helper class to gather and assemble data for OpenType tables."""

	def __init__(self, localState=None, tableTag=None, offsetSize=2):
		self.items = []
		self.pos = None
		self.localState = localState
		self.tableTag = tableTag
		self.offsetSize = offsetSize
		self.parent = None

	# DEPRECATED: 'longOffset' is kept as a property for backward compat with old code.
	# You should use 'offsetSize' instead (2, 3 or 4 bytes).
	@property
	def longOffset(self):
		return self.offsetSize == 4

	@longOffset.setter
	def longOffset(self, value):
		self.offsetSize = 4 if value else 2

	def __setitem__(self, name, value):
		state = self.localState.copy() if self.localState else dict()
		state[name] = value
		self.localState = state

	def __getitem__(self, name):
		return self.localState[name]

	def __delitem__(self, name):
		del self.localState[name]

	# assembler interface

	def getDataLength(self):
		"""Return the length of this table in bytes, without subtables."""
		l = 0
		for item in self.items:
			if hasattr(item, "getCountData"):
				l += item.size
			elif hasattr(item, "getData"):
				l += item.offsetSize
			else:
				l = l + len(item)
		return l

	def getData(self):
		"""Assemble the data for this writer/table, without subtables."""
		items = list(self.items)  # make a shallow copy
		pos = self.pos
		numItems = len(items)
		for i in range(numItems):
			item = items[i]

			if hasattr(item, "getData"):
				if item.offsetSize == 4:
					items[i] = packULong(item.pos - pos)
				elif item.offsetSize == 2:
					try:
						items[i] = packUShort(item.pos - pos)
					except struct.error:
						# provide data to fix overflow problem.
						overflowErrorRecord = self.getOverflowErrorRecord(item)

						raise OTLOffsetOverflowError(overflowErrorRecord)
				elif item.offsetSize == 3:
					items[i] = packUInt24(item.pos - pos)
				else:
					raise ValueError(item.offsetSize)

		return bytesjoin(items)

	def getDataForHarfbuzz(self):
		"""Assemble the data for this writer/table with all offset field set to 0"""
		items = list(self.items)
		packFuncs = {2: packUShort, 3: packUInt24, 4: packULong}
		for i, item in enumerate(items):
			if hasattr(item, "getData"):
				# Offset value is not needed in harfbuzz repacker, so setting offset to 0 to avoid overflow here
				if item.offsetSize in packFuncs:
					items[i] = packFuncs[item.offsetSize](0)
				else:
					raise ValueError(item.offsetSize)

		return bytesjoin(items)

	def __hash__(self):
		# only works after self._doneWriting() has been called
		return hash(self.items)

	def __ne__(self, other):
		result = self.__eq__(other)
		return result if result is NotImplemented else not result

	def __eq__(self, other):
		if type(self) != type(other):
			return NotImplemented
		return self.offsetSize == other.offsetSize and self.items == other.items

	def _doneWriting(self, internedTables, shareExtension=False):
		# Convert CountData references to data string items
		# collapse duplicate table references to a unique entry
		# "tables" are OTTableWriter objects.

		# For Extension Lookup types, we can
		# eliminate duplicates only within the tree under the Extension Lookup,
		# as offsets may exceed 64K even between Extension LookupTable subtables.
		isExtension = hasattr(self, "Extension")

		# Certain versions of Uniscribe reject the font if the GSUB/GPOS top-level
		# arrays (ScriptList, FeatureList, LookupList) point to the same, possibly
		# empty, array.  So, we don't share those.
		# See: https://github.com/fonttools/fonttools/issues/518
		dontShare = hasattr(self, 'DontShare')

		if isExtension and not shareExtension:
			internedTables = {}

		items = self.items
		for i in range(len(items)):
			item = items[i]
			if hasattr(item, "getCountData"):
				items[i] = item.getCountData()
			elif hasattr(item, "getData"):
				item._doneWriting(internedTables, shareExtension=shareExtension)
				# At this point, all subwriters are hashable based on their items.
				# (See hash and comparison magic methods above.) So the ``setdefault``
				# call here will return the first writer object we've seen with
				# equal content, or store it in the dictionary if it's not been
				# seen yet. We therefore replace the subwriter object with an equivalent
				# object, which deduplicates the tree.
				if not dontShare:
					items[i] = item = internedTables.setdefault(item, item)
		self.items = tuple(items)

	def _gatherTables(self, tables, extTables, done):
		# Convert table references in self.items tree to a flat
		# list of tables in depth-first traversal order.
		# "tables" are OTTableWriter objects.
		# We do the traversal in reverse order at each level, in order to
		# resolve duplicate references to be the last reference in the list of tables.
		# For extension lookups, duplicate references can be merged only within the
		# writer tree under the  extension lookup.

		done[id(self)] = True

		numItems = len(self.items)
		iRange = list(range(numItems))
		iRange.reverse()

		isExtension = hasattr(self, "Extension")

		selfTables = tables

		if isExtension:
			assert extTables is not None, "Program or XML editing error. Extension subtables cannot contain extensions subtables"
			tables, extTables, done = extTables, None, {}

		# add Coverage table if it is sorted last.
		sortCoverageLast = False
		if hasattr(self, "sortCoverageLast"):
			# Find coverage table
			for i in range(numItems):
				item = self.items[i]
				if getattr(item, 'name', None) == "Coverage":
					sortCoverageLast = True
					break
			if id(item) not in done:
				item._gatherTables(tables, extTables, done)
			else:
				# We're a new parent of item
				pass

		for i in iRange:
			item = self.items[i]
			if not hasattr(item, "getData"):
				continue

			if sortCoverageLast and (i==1) and getattr(item, 'name', None) == 'Coverage':
				# we've already 'gathered' it above
				continue

			if id(item) not in done:
				item._gatherTables(tables, extTables, done)
			else:
				# Item is already written out by other parent
				pass

		selfTables.append(self)

	def _gatherGraphForHarfbuzz(self, tables, obj_list, done, objidx, virtual_edges):
		real_links = []
		virtual_links = []
		item_idx = objidx

		# Merge virtual_links from parent
		for idx in virtual_edges:
			virtual_links.append((0, 0, idx))

		sortCoverageLast = False
		coverage_idx = 0
		if hasattr(self, "sortCoverageLast"):
			# Find coverage table
			for i, item in enumerate(self.items):
				if getattr(item, 'name', None) == "Coverage":
					sortCoverageLast = True
					if id(item) not in done:
						coverage_idx = item_idx = item._gatherGraphForHarfbuzz(tables, obj_list, done, item_idx, virtual_edges)
					else:
						coverage_idx = done[id(item)]
					virtual_edges.append(coverage_idx)
					break

		child_idx = 0
		offset_pos = 0
		for i, item in enumerate(self.items):
			if hasattr(item, "getData"):
				pos = offset_pos
			elif hasattr(item, "getCountData"):
				offset_pos += item.size
				continue
			else:
				offset_pos = offset_pos + len(item)
				continue

			if id(item) not in done:
				child_idx = item_idx = item._gatherGraphForHarfbuzz(tables, obj_list, done, item_idx, virtual_edges)
			else:
				child_idx = done[id(item)]

			real_edge = (pos, item.offsetSize, child_idx)
			real_links.append(real_edge)
			offset_pos += item.offsetSize

		tables.append(self)
		obj_list.append((real_links,virtual_links))
		item_idx += 1
		done[id(self)] = item_idx
		if sortCoverageLast:
			virtual_edges.pop()

		return item_idx

	def getAllDataUsingHarfbuzz(self, tableTag):
		"""The Whole table is represented as a Graph.
                Assemble graph data and call Harfbuzz repacker to pack the table.
                Harfbuzz repacker is faster and retain as much sub-table sharing as possible, see also:
                https://github.com/harfbuzz/harfbuzz/blob/main/docs/repacker.md
                The input format for hb.repack() method is explained here:
                https://github.com/harfbuzz/uharfbuzz/blob/main/src/uharfbuzz/_harfbuzz.pyx#L1149
                """
		internedTables = {}
		self._doneWriting(internedTables, shareExtension=True)
		tables = []
		obj_list = []
		done = {}
		objidx = 0
		virtual_edges = []
		self._gatherGraphForHarfbuzz(tables, obj_list, done, objidx, virtual_edges)
		# Gather all data in two passes: the absolute positions of all
		# subtable are needed before the actual data can be assembled.
		pos = 0
		for table in tables:
			table.pos = pos
			pos = pos + table.getDataLength()

		data = []
		for table in tables:
			tableData = table.getDataForHarfbuzz()
			data.append(tableData)

		if hasattr(hb, "repack_with_tag"):
			return hb.repack_with_tag(str(tableTag), data, obj_list)
		else:
			return hb.repack(data, obj_list)

	def getAllData(self, remove_duplicate=True):
		"""Assemble all data, including all subtables."""
		if remove_duplicate:
			internedTables = {}
			self._doneWriting(internedTables)
		tables = []
		extTables = []
		done = {}
		self._gatherTables(tables, extTables, done)
		tables.reverse()
		extTables.reverse()
		# Gather all data in two passes: the absolute positions of all
		# subtable are needed before the actual data can be assembled.
		pos = 0
		for table in tables:
			table.pos = pos
			pos = pos + table.getDataLength()

		for table in extTables:
			table.pos = pos
			pos = pos + table.getDataLength()

		data = []
		for table in tables:
			tableData = table.getData()
			data.append(tableData)

		for table in extTables:
			tableData = table.getData()
			data.append(tableData)

		return bytesjoin(data)

	# interface for gathering data, as used by table.compile()

	def getSubWriter(self, offsetSize=2):
		subwriter = self.__class__(self.localState, self.tableTag, offsetSize=offsetSize)
		subwriter.parent = self # because some subtables have idential values, we discard
					# the duplicates under the getAllData method. Hence some
					# subtable writers can have more than one parent writer.
					# But we just care about first one right now.
		return subwriter

	def writeValue(self, typecode, value):
		self.items.append(struct.pack(f">{typecode}", value))
	def writeArray(self, typecode, values):
		a = array.array(typecode, values)
		if sys.byteorder != "big": a.byteswap()
		self.items.append(a.tobytes())

	def writeInt8(self, value):
		assert -128 <= value < 128, value
		self.items.append(struct.pack(">b", value))
	def writeInt8Array(self, values):
		self.writeArray('b', values)

	def writeShort(self, value):
		assert -32768 <= value < 32768, value
		self.items.append(struct.pack(">h", value))
	def writeShortArray(self, values):
		self.writeArray('h', values)

	def writeLong(self, value):
		self.items.append(struct.pack(">i", value))
	def writeLongArray(self, values):
		self.writeArray('i', values)

	def writeUInt8(self, value):
		assert 0 <= value < 256, value
		self.items.append(struct.pack(">B", value))
	def writeUInt8Array(self, values):
		self.writeArray('B', values)

	def writeUShort(self, value):
		assert 0 <= value < 0x10000, value
		self.items.append(struct.pack(">H", value))
	def writeUShortArray(self, values):
		self.writeArray('H', values)

	def writeULong(self, value):
		self.items.append(struct.pack(">I", value))
	def writeULongArray(self, values):
		self.writeArray('I', values)

	def writeUInt24(self, value):
		assert 0 <= value < 0x1000000, value
		b = struct.pack(">L", value)
		self.items.append(b[1:])
	def writeUInt24Array(self, values):
		for value in values:
			self.writeUInt24(value)

	def writeTag(self, tag):
		tag = Tag(tag).tobytes()
		assert len(tag) == 4, tag
		self.items.append(tag)

	def writeSubTable(self, subWriter):
		self.items.append(subWriter)

	def writeCountReference(self, table, name, size=2, value=None):
		ref = CountReference(table, name, size=size, value=value)
		self.items.append(ref)
		return ref

	def writeStruct(self, format, values):
		data = struct.pack(*(format,) + values)
		self.items.append(data)

	def writeData(self, data):
		self.items.append(data)

	def getOverflowErrorRecord(self, item):
		LookupListIndex = SubTableIndex = itemName = itemIndex = None
		if self.name == 'LookupList':
			LookupListIndex = item.repeatIndex
		elif self.name == 'Lookup':
			LookupListIndex = self.repeatIndex
			SubTableIndex = item.repeatIndex
		else:
			itemName = getattr(item, 'name', '<none>')
			if hasattr(item, 'repeatIndex'):
				itemIndex = item.repeatIndex
			if self.name == 'SubTable':
				LookupListIndex = self.parent.repeatIndex
				SubTableIndex = self.repeatIndex
			elif self.name == 'ExtSubTable':
				LookupListIndex = self.parent.parent.repeatIndex
				SubTableIndex = self.parent.repeatIndex
			else: # who knows how far below the SubTable level we are! Climb back up to the nearest subtable.
				itemName = ".".join([self.name, itemName])
				p1 = self.parent
				while p1 and p1.name not in ['ExtSubTable', 'SubTable']:
					itemName = ".".join([p1.name, itemName])
					p1 = p1.parent
				if p1:
					if p1.name == 'ExtSubTable':
						LookupListIndex = p1.parent.parent.repeatIndex
						SubTableIndex = p1.parent.repeatIndex
					else:
						LookupListIndex = p1.parent.repeatIndex
						SubTableIndex = p1.repeatIndex

		return OverflowErrorRecord( (self.tableTag, LookupListIndex, SubTableIndex, itemName, itemIndex) )


class CountReference(object):
	"""A reference to a Count value, not a count of references."""
	def __init__(self, table, name, size=None, value=None):
		self.table = table
		self.name = name
		self.size = size
		if value is not None:
			self.setValue(value)
	def setValue(self, value):
		table = self.table
		name = self.name
		if table[name] is None:
			table[name] = value
		else:
			assert table[name] == value, (name, table[name], value)
	def getValue(self):
		return self.table[self.name]
	def getCountData(self):
		v = self.table[self.name]
		if v is None: v = 0
		return {1:packUInt8, 2:packUShort, 4:packULong}[self.size](v)


def packUInt8 (value):
	return struct.pack(">B", value)

def packUShort(value):
	return struct.pack(">H", value)

def packULong(value):
	assert 0 <= value < 0x100000000, value
	return struct.pack(">I", value)

def packUInt24(value):
	assert 0 <= value < 0x1000000, value
	return struct.pack(">I", value)[1:]


class BaseTable(object):

	"""Generic base class for all OpenType (sub)tables."""

	def __getattr__(self, attr):
		reader = self.__dict__.get("reader")
		if reader:
			del self.reader
			font = self.font
			del self.font
			self.decompile(reader, font)
			return getattr(self, attr)

		raise AttributeError(attr)

	def ensureDecompiled(self, recurse=False):
		reader = self.__dict__.get("reader")
		if reader:
			del self.reader
			font = self.font
			del self.font
			self.decompile(reader, font)
		if recurse:
			for subtable in self.iterSubTables():
				subtable.value.ensureDecompiled(recurse)

	@classmethod
	def getRecordSize(cls, reader):
		totalSize = 0
		for conv in cls.converters:
			size = conv.getRecordSize(reader)
			if size is NotImplemented: return NotImplemented
			countValue = 1
			if conv.repeat:
				if conv.repeat in reader:
					countValue = reader[conv.repeat] + conv.aux
				else:
					return NotImplemented
			totalSize += size * countValue
		return totalSize

	def getConverters(self):
		return self.converters

	def getConverterByName(self, name):
		return self.convertersByName[name]

	def populateDefaults(self, propagator=None):
		for conv in self.getConverters():
			if conv.repeat:
				if not hasattr(self, conv.name):
					setattr(self, conv.name, [])
				countValue = len(getattr(self, conv.name)) - conv.aux
				try:
					count_conv = self.getConverterByName(conv.repeat)
					setattr(self, conv.repeat, countValue)
				except KeyError:
					# conv.repeat is a propagated count
					if propagator and conv.repeat in propagator:
						propagator[conv.repeat].setValue(countValue)
			else:
				if conv.aux and not eval(conv.aux, None, self.__dict__):
					continue
				if hasattr(self, conv.name):
					continue # Warn if it should NOT be present?!
				if hasattr(conv, 'writeNullOffset'):
					setattr(self, conv.name, None) # Warn?
				#elif not conv.isCount:
				#	# Warn?
				#	pass
				if hasattr(conv, "DEFAULT"):
					# OptionalValue converters (e.g. VarIndex)
					setattr(self, conv.name, conv.DEFAULT)

	def decompile(self, reader, font):
		self.readFormat(reader)
		table = {}
		self.__rawTable = table  # for debugging
		for conv in self.getConverters():
			if conv.name == "SubTable":
				conv = conv.getConverter(reader.tableTag,
						table["LookupType"])
			if conv.name == "ExtSubTable":
				conv = conv.getConverter(reader.tableTag,
						table["ExtensionLookupType"])
			if conv.name == "FeatureParams":
				conv = conv.getConverter(reader["FeatureTag"])
			if conv.name == "SubStruct":
				conv = conv.getConverter(reader.tableTag,
				                         table["MorphType"])
			try:
				if conv.repeat:
					if isinstance(conv.repeat, int):
						countValue = conv.repeat
					elif conv.repeat in table:
						countValue = table[conv.repeat]
					else:
						# conv.repeat is a propagated count
						countValue = reader[conv.repeat]
					countValue += conv.aux
					table[conv.name] = conv.readArray(reader, font, table, countValue)
				else:
					if conv.aux and not eval(conv.aux, None, table):
						continue
					table[conv.name] = conv.read(reader, font, table)
					if conv.isPropagated:
						reader[conv.name] = table[conv.name]
			except Exception as e:
				name = conv.name
				e.args = e.args + (name,)
				raise

		if hasattr(self, 'postRead'):
			self.postRead(table, font)
		else:
			self.__dict__.update(table)

		del self.__rawTable  # succeeded, get rid of debugging info

	def compile(self, writer, font):
		self.ensureDecompiled()
		# TODO Following hack to be removed by rewriting how FormatSwitching tables
		# are handled.
		# https://github.com/fonttools/fonttools/pull/2238#issuecomment-805192631
		if hasattr(self, 'preWrite'):
			deleteFormat = not hasattr(self, 'Format')
			table = self.preWrite(font)
			deleteFormat = deleteFormat and hasattr(self, 'Format')
		else:
			deleteFormat = False
			table = self.__dict__.copy()

		# some count references may have been initialized in a custom preWrite; we set
		# these in the writer's state beforehand (instead of sequentially) so they will
		# be propagated to all nested subtables even if the count appears in the current
		# table only *after* the offset to the subtable that it is counting.
		for conv in self.getConverters():
			if conv.isCount and conv.isPropagated:
				value = table.get(conv.name)
				if isinstance(value, CountReference):
					writer[conv.name] = value

		if hasattr(self, 'sortCoverageLast'):
			writer.sortCoverageLast = 1

		if hasattr(self, 'DontShare'):
			writer.DontShare = True

		if hasattr(self.__class__, 'LookupType'):
			writer['LookupType'].setValue(self.__class__.LookupType)

		self.writeFormat(writer)
		for conv in self.getConverters():
			value = table.get(conv.name) # TODO Handle defaults instead of defaulting to None!
			if conv.repeat:
				if value is None:
					value = []
				countValue = len(value) - conv.aux
				if isinstance(conv.repeat, int):
					assert len(value) == conv.repeat, 'expected %d values, got %d' % (conv.repeat, len(value))
				elif conv.repeat in table:
					CountReference(table, conv.repeat, value=countValue)
				else:
					# conv.repeat is a propagated count
					writer[conv.repeat].setValue(countValue)
				try:
					conv.writeArray(writer, font, table, value)
				except Exception as e:
					e.args = e.args + (conv.name+'[]',)
					raise
			elif conv.isCount:
				# Special-case Count values.
				# Assumption: a Count field will *always* precede
				# the actual array(s).
				# We need a default value, as it may be set later by a nested
				# table. We will later store it here.
				# We add a reference: by the time the data is assembled
				# the Count value will be filled in.
				# We ignore the current count value since it will be recomputed,
				# unless it's a CountReference that was already initialized in a custom preWrite.
				if isinstance(value, CountReference):
					ref = value
					ref.size = conv.staticSize
					writer.writeData(ref)
					table[conv.name] = ref.getValue()
				else:
					ref = writer.writeCountReference(table, conv.name, conv.staticSize)
					table[conv.name] = None
				if conv.isPropagated:
					writer[conv.name] = ref
			elif conv.isLookupType:
				# We make sure that subtables have the same lookup type,
				# and that the type is the same as the one set on the
				# Lookup object, if any is set.
				if conv.name not in table:
					table[conv.name] = None
				ref = writer.writeCountReference(table, conv.name, conv.staticSize, table[conv.name])
				writer['LookupType'] = ref
			else:
				if conv.aux and not eval(conv.aux, None, table):
					continue
				try:
					conv.write(writer, font, table, value)
				except Exception as e:
					name = value.__class__.__name__ if value is not None else conv.name
					e.args = e.args + (name,)
					raise
				if conv.isPropagated:
					writer[conv.name] = value

		if deleteFormat:
			del self.Format

	def readFormat(self, reader):
		pass

	def writeFormat(self, writer):
		pass

	def toXML(self, xmlWriter, font, attrs=None, name=None):
		tableName = name if name else self.__class__.__name__
		if attrs is None:
			attrs = []
		if hasattr(self, "Format"):
			attrs = attrs + [("Format", self.Format)]
		xmlWriter.begintag(tableName, attrs)
		xmlWriter.newline()
		self.toXML2(xmlWriter, font)
		xmlWriter.endtag(tableName)
		xmlWriter.newline()

	def toXML2(self, xmlWriter, font):
		# Simpler variant of toXML, *only* for the top level tables (like GPOS, GSUB).
		# This is because in TTX our parent writes our main tag, and in otBase.py we
		# do it ourselves. I think I'm getting schizophrenic...
		for conv in self.getConverters():
			if conv.repeat:
				value = getattr(self, conv.name, [])
				for i in range(len(value)):
					item = value[i]
					conv.xmlWrite(xmlWriter, font, item, conv.name,
							[("index", i)])
			else:
				if conv.aux and not eval(conv.aux, None, vars(self)):
					continue
				value = getattr(self, conv.name, None) # TODO Handle defaults instead of defaulting to None!
				conv.xmlWrite(xmlWriter, font, value, conv.name, [])

	def fromXML(self, name, attrs, content, font):
		try:
			conv = self.getConverterByName(name)
		except KeyError:
			raise    # XXX on KeyError, raise nice error
		value = conv.xmlRead(attrs, content, font)
		if conv.repeat:
			seq = getattr(self, conv.name, None)
			if seq is None:
				seq = []
				setattr(self, conv.name, seq)
			seq.append(value)
		else:
			setattr(self, conv.name, value)

	def __ne__(self, other):
		result = self.__eq__(other)
		return result if result is NotImplemented else not result

	def __eq__(self, other):
		if type(self) != type(other):
			return NotImplemented

		self.ensureDecompiled()
		other.ensureDecompiled()

		return self.__dict__ == other.__dict__

	class SubTableEntry(NamedTuple):
		"""See BaseTable.iterSubTables()"""
		name: str
		value: "BaseTable"
		index: Optional[int] = None  # index into given array, None for single values

	def iterSubTables(self) -> Iterator[SubTableEntry]:
		"""Yield (name, value, index) namedtuples for all subtables of current table.

		A sub-table is an instance of BaseTable (or subclass thereof) that is a child
		of self, the current parent table.
		The tuples also contain the attribute name (str) of the of parent table to get
		a subtable, and optionally, for lists of subtables (i.e. attributes associated
		with a converter that has a 'repeat'), an index into the list containing the
		given subtable value.
		This method can be useful to traverse trees of otTables.
		"""
		for conv in self.getConverters():
			name = conv.name
			value = getattr(self, name, None)
			if value is None:
				continue
			if isinstance(value, BaseTable):
				yield self.SubTableEntry(name, value)
			elif isinstance(value, list):
				yield from (
					self.SubTableEntry(name, v, index=i)
					for i, v in enumerate(value)
					if isinstance(v, BaseTable)
				)

	# instance (not @class)method for consistency with FormatSwitchingBaseTable
	def getVariableAttrs(self):
		return getVariableAttrs(self.__class__)


class FormatSwitchingBaseTable(BaseTable):

	"""Minor specialization of BaseTable, for tables that have multiple
	formats, eg. CoverageFormat1 vs. CoverageFormat2."""

	@classmethod
	def getRecordSize(cls, reader):
		return NotImplemented

	def getConverters(self):
		try:
			fmt = self.Format
		except AttributeError:
			# some FormatSwitchingBaseTables (e.g. Coverage) no longer have 'Format'
			# attribute after fully decompiled, only gain one in preWrite before being
			# recompiled. In the decompiled state, these hand-coded classes defined in
			# otTables.py lose their format-specific nature and gain more high-level
			# attributes that are not tied to converters.
			return []
		return self.converters.get(self.Format, [])

	def getConverterByName(self, name):
		return self.convertersByName[self.Format][name]

	def readFormat(self, reader):
		self.Format = reader.readUShort()

	def writeFormat(self, writer):
		writer.writeUShort(self.Format)

	def toXML(self, xmlWriter, font, attrs=None, name=None):
		BaseTable.toXML(self, xmlWriter, font, attrs, name)

	def getVariableAttrs(self):
		return getVariableAttrs(self.__class__, self.Format)


class UInt8FormatSwitchingBaseTable(FormatSwitchingBaseTable):
	def readFormat(self, reader):
		self.Format = reader.readUInt8()

	def writeFormat(self, writer):
		writer.writeUInt8(self.Format)


formatSwitchingBaseTables = {
	"uint16": FormatSwitchingBaseTable,
	"uint8": UInt8FormatSwitchingBaseTable,
}

def getFormatSwitchingBaseTableClass(formatType):
	try:
		return formatSwitchingBaseTables[formatType]
	except KeyError:
		raise TypeError(f"Unsupported format type: {formatType!r}")


# memoize since these are parsed from otData.py, thus stay constant
@lru_cache()
def getVariableAttrs(cls: BaseTable, fmt: Optional[int] = None) -> Tuple[str]:
	"""Return sequence of variable table field names (can be empty).

	Attributes are deemed "variable" when their otData.py's description contain
	'VarIndexBase + {offset}', e.g. COLRv1 PaintVar* tables.
	"""
	if not issubclass(cls, BaseTable):
		raise TypeError(cls)
	if issubclass(cls, FormatSwitchingBaseTable):
		if fmt is None:
			raise TypeError(f"'fmt' is required for format-switching {cls.__name__}")
		converters = cls.convertersByName[fmt]
	else:
		converters = cls.convertersByName
	# assume if no 'VarIndexBase' field is present, table has no variable fields
	if "VarIndexBase" not in converters:
		return ()
	varAttrs = {}
	for name, conv in converters.items():
		offset = conv.getVarIndexOffset()
		if offset is not None:
			varAttrs[name] = offset
	return tuple(sorted(varAttrs, key=varAttrs.__getitem__))


#
# Support for ValueRecords
#
# This data type is so different from all other OpenType data types that
# it requires quite a bit of code for itself. It even has special support
# in OTTableReader and OTTableWriter...
#

valueRecordFormat = [
#	Mask	 Name		isDevice signed
	(0x0001, "XPlacement",	0,	1),
	(0x0002, "YPlacement",	0,	1),
	(0x0004, "XAdvance",	0,	1),
	(0x0008, "YAdvance",	0,	1),
	(0x0010, "XPlaDevice",	1,	0),
	(0x0020, "YPlaDevice",	1,	0),
	(0x0040, "XAdvDevice",	1,	0),
	(0x0080, "YAdvDevice",	1,	0),
#	reserved:
	(0x0100, "Reserved1",	0,	0),
	(0x0200, "Reserved2",	0,	0),
	(0x0400, "Reserved3",	0,	0),
	(0x0800, "Reserved4",	0,	0),
	(0x1000, "Reserved5",	0,	0),
	(0x2000, "Reserved6",	0,	0),
	(0x4000, "Reserved7",	0,	0),
	(0x8000, "Reserved8",	0,	0),
]

def _buildDict():
	d = {}
	for mask, name, isDevice, signed in valueRecordFormat:
		d[name] = mask, isDevice, signed
	return d

valueRecordFormatDict = _buildDict()


class ValueRecordFactory(object):

	"""Given a format code, this object convert ValueRecords."""

	def __init__(self, valueFormat):
		format = []
		for mask, name, isDevice, signed in valueRecordFormat:
			if valueFormat & mask:
				format.append((name, isDevice, signed))
		self.format = format

	def __len__(self):
		return len(self.format)

	def readValueRecord(self, reader, font):
		format = self.format
		if not format:
			return None
		valueRecord = ValueRecord()
		for name, isDevice, signed in format:
			if signed:
				value = reader.readShort()
			else:
				value = reader.readUShort()
			if isDevice:
				if value:
					from . import otTables
					subReader = reader.getSubReader(value)
					value = getattr(otTables, name)()
					value.decompile(subReader, font)
				else:
					value = None
			setattr(valueRecord, name, value)
		return valueRecord

	def writeValueRecord(self, writer, font, valueRecord):
		for name, isDevice, signed in self.format:
			value = getattr(valueRecord, name, 0)
			if isDevice:
				if value:
					subWriter = writer.getSubWriter()
					writer.writeSubTable(subWriter)
					value.compile(subWriter, font)
				else:
					writer.writeUShort(0)
			elif signed:
				writer.writeShort(value)
			else:
				writer.writeUShort(value)


class ValueRecord(object):

	# see ValueRecordFactory

	def __init__(self, valueFormat=None, src=None):
		if valueFormat is not None:
			for mask, name, isDevice, signed in valueRecordFormat:
				if valueFormat & mask:
					setattr(self, name, None if isDevice else 0)
			if src is not None:
				for key,val in src.__dict__.items():
					if not hasattr(self, key):
						continue
					setattr(self, key, val)
		elif src is not None:
			self.__dict__ = src.__dict__.copy()

	def getFormat(self):
		format = 0
		for name in self.__dict__.keys():
			format = format | valueRecordFormatDict[name][0]
		return format

	def getEffectiveFormat(self):
		format = 0
		for name,value in self.__dict__.items():
			if value:
				format = format | valueRecordFormatDict[name][0]
		return format

	def toXML(self, xmlWriter, font, valueName, attrs=None):
		if attrs is None:
			simpleItems = []
		else:
			simpleItems = list(attrs)
		for mask, name, isDevice, format in valueRecordFormat[:4]:  # "simple" values
			if hasattr(self, name):
				simpleItems.append((name, getattr(self, name)))
		deviceItems = []
		for mask, name, isDevice, format in valueRecordFormat[4:8]:  # device records
			if hasattr(self, name):
				device = getattr(self, name)
				if device is not None:
					deviceItems.append((name, device))
		if deviceItems:
			xmlWriter.begintag(valueName, simpleItems)
			xmlWriter.newline()
			for name, deviceRecord in deviceItems:
				if deviceRecord is not None:
					deviceRecord.toXML(xmlWriter, font, name=name)
			xmlWriter.endtag(valueName)
			xmlWriter.newline()
		else:
			xmlWriter.simpletag(valueName, simpleItems)
			xmlWriter.newline()

	def fromXML(self, name, attrs, content, font):
		from . import otTables
		for k, v in attrs.items():
			setattr(self, k, int(v))
		for element in content:
			if not isinstance(element, tuple):
				continue
			name, attrs, content = element
			value = getattr(otTables, name)()
			for elem2 in content:
				if not isinstance(elem2, tuple):
					continue
				name2, attrs2, content2 = elem2
				value.fromXML(name2, attrs2, content2, font)
			setattr(self, name, value)

	def __ne__(self, other):
		result = self.__eq__(other)
		return result if result is NotImplemented else not result

	def __eq__(self, other):
		if type(self) != type(other):
			return NotImplemented
		return self.__dict__ == other.__dict__