"""Parser for future statements

"""

from compiler import ast, walk

def is_future(stmt):
"""Return true if statement is a well-formed future statement"""
if not isinstance(stmt, ast.From):
return 0
if stmt.modname == "__future__":
return 1
else:
return 0

class FutureParser:

features = ("nested_scopes", "generators", "division",
"absolute_import", "with_statement", "print_function",
"unicode_literals")

def __init__(self):
self.found = {} # set

def visitModule(self, node):
stmt = node.node
for s in stmt.nodes:
if not self.check_stmt(s):
break

def check_stmt(self, stmt):
if is_future(stmt):
for name, asname in stmt.names:
if name in self.features:
self.found[name] = 1
else:
raise SyntaxError, \
"future feature %s is not defined" % name
stmt.valid_future = 1
return 1
return 0

def get_features(self):
"""Return list of features enabled by future statements"""
return self.found.keys()

class BadFutureParser:
"""Check for invalid future statements"""

def visitFrom(self, node):
if hasattr(node, 'valid_future'):
return
if node.modname != "__future__":
return
raise SyntaxError, "invalid future statement " + repr(node)

def find_futures(node):
p1 = FutureParser()
p2 = BadFutureParser()
walk(node, p1)
walk(node, p2)
return p1.get_features()

if __name__ == "__main__":
import sys
from compiler import parseFile, walk

for file in sys.argv[1:]:
print file
tree = parseFile(file)
v = FutureParser()
walk(tree, v)
print v.found
print