"""
Utility functions used for parsing.
"""
import struct


def can_be_mark(argument):
	"""
	The ``argument`` can be interpreted as a Mark.
	"""
	a = ord("a")
	a_z = [chr(a + i) for i in range(26)]
	A = ord("A")
	A_Z = [chr(A + i) for i in range(26)]
	null = ord("0")
	null_9 = [chr(null + i) for i in range(10)]

	if(not argument[0] in a_z):
		return False

	for char in argument[1:]:
		if(not (char in a_z
			or char in A_Z
			or char in null_9
			or char == "_")):
			return False
	return True

	

def can_convert_to_int(value):
	"""
	``value`` can be converted to an integer.

	**Note** that this returns ``True`` if the value is a 
	character definition like ``'a'``.
	"""
	if(value.startswith("0x")):
		try:
			int(value[2:], 16)
			return True
		except:
			return False

	if(value.startswith("0b")):
		try:
			int(value[2:], 2)
			return True
		except:
			return False

	if(value.startswith("'") and value.endswith("'")):
		if(len(value) == 3):
			return True
		if(len(value) == 4):
			if(value[1:-1] in {"\\n", "\\r", "\\t"}):
				return True
		return False

	try:
		int(value)
		return True
	except:
		return False

def autoint(value):
	"""
	Convert ``value`` to an integer automatically.
	"""
	escape_sequences = {"\\n": "\n", "\\r": "\r", "\\t":"\t"}
	if(value.startswith("0x")):
		return int(value[2:], 16)

	if(value.startswith("0b")):
		return int(value[2:], 2)

	if(value.startswith("'") and value.endswith("'")):
		if(len(value) == 3):
			return ord(value[1:-1])
		if(len(value) == 4):
			if(value[1:-1] in escape_sequences):
				return ord(escape_sequences[value[1:-1]])

	return int(value)
	

def int16_2_bytes(value):
	"""
	Return the bytes representation of a 16bit unsigned
	integer in 8bit words.
	"""
	if(value < 0):
		return struct.pack("<h", value)
	return struct.pack("<H", value)