Lib/fontTools/merge/base.py

# Copyright 2013 Google, Inc. All Rights Reserved.
#
# Google Author(s): Behdad Esfahbod, Roozbeh Pournader

from fontTools.ttLib.tables.DefaultTable import DefaultTable
import logging


log = logging.getLogger("fontTools.merge")


def add_method(*clazzes, **kwargs):
	"""Returns a decorator function that adds a new method to one or
	more classes."""
	allowDefault = kwargs.get('allowDefaultTable', False)
	def wrapper(method):
		done = []
		for clazz in clazzes:
			if clazz in done: continue # Support multiple names of a clazz
			done.append(clazz)
			assert allowDefault or clazz != DefaultTable, 'Oops, table class not found.'
			assert method.__name__ not in clazz.__dict__, \
				"Oops, class '%s' has method '%s'." % (clazz.__name__, method.__name__)
			setattr(clazz, method.__name__, method)
		return None
	return wrapper

def mergeObjects(lst):
	lst = [item for item in lst if item is not NotImplemented]
	if not lst:
		return NotImplemented
	lst = [item for item in lst if item is not None]
	if not lst:
		return None

	clazz = lst[0].__class__
	assert all(type(item) == clazz for item in lst), lst

	logic = clazz.mergeMap
	returnTable = clazz()
	returnDict = {}

	allKeys = set.union(set(), *(vars(table).keys() for table in lst))
	for key in allKeys:
		try:
			mergeLogic = logic[key]
		except KeyError:
			try:
				mergeLogic = logic['*']
			except KeyError:
				raise Exception("Don't know how to merge key %s of class %s" %
						(key, clazz.__name__))
		if mergeLogic is NotImplemented:
			continue
		value = mergeLogic(getattr(table, key, NotImplemented) for table in lst)
		if value is not NotImplemented:
			returnDict[key] = value

	returnTable.__dict__ = returnDict

	return returnTable

@add_method(DefaultTable, allowDefaultTable=True)
def merge(self, m, tables):
	if not hasattr(self, 'mergeMap'):
		log.info("Don't know how to merge '%s'.", self.tableTag)
		return NotImplemented

	logic = self.mergeMap

	if isinstance(logic, dict):
		return m.mergeObjects(self, self.mergeMap, tables)
	else:
		return logic(tables)