"""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")

    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