# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Checkers for detecting unsupported Python features."""

import gast

from ..pyct import errors


class UnsupportedFeaturesChecker(gast.NodeVisitor):
    """Quick check for Python features we know we don't support.

    Any features detected will cause AutoGraph to not compile a function.
    """

    def visit_Attribute(self, node):
        if (
            node.attr is not None
            and node.attr.startswith("__")
            and not node.attr.endswith("__")
        ):
            raise errors.UnsupportedLanguageElementError(
                "mangled names are not yet supported"
            )
        self.generic_visit(node)

    def visit_For(self, node):
        if node.orelse:
            raise errors.UnsupportedLanguageElementError(
                "for/else statement not yet supported"
            )
        self.generic_visit(node)

    def visit_While(self, node):
        if node.orelse:
            raise errors.UnsupportedLanguageElementError(
                "while/else statement not yet supported"
            )
        self.generic_visit(node)

    # These checks could potentially be replaced with inspect.isgeneratorfunction
    # to avoid a getsource/parse/ast-walk round trip.
    def visit_Yield(self, node):
        raise errors.UnsupportedLanguageElementError("generators are not supported")

    def visit_YieldFrom(self, node):
        raise errors.UnsupportedLanguageElementError("generators are not supported")


def verify(node):
    UnsupportedFeaturesChecker().visit(node)
