"""Fixer that changes 'a ,b' into 'a, b'.

This also changes '{a :b}' into '{a: b}', but does not touch other
uses of colons. It does not touch other uses of whitespace.

"""

from .. import pytree
from ..pgen2 import token
from .. import fixer_base

class FixWsComma(fixer_base.BaseFix):

explicit = True # The user must ask for this fixers

PATTERN = """
any<(not(',') any)+ ',' ((not(',') any)+ ',')* [not(',') any]>
"""

COMMA = pytree.Leaf(token.COMMA, ",")
COLON = pytree.Leaf(token.COLON, ":")
SEPS = (COMMA, COLON)

def transform(self, node, results):
new = node.clone()
comma = False
for child in new.children:
if child in self.SEPS:
prefix = child.prefix
if prefix.isspace() and "\n" not in prefix:
child.prefix = ""
comma = True
else:
if comma:
prefix = child.prefix
if not prefix:
child.prefix = " "
comma = False
return new