# -*- coding: utf-8 -*-
# Copyright 2017 New Vector Ltd
#
# 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.


import StringIO
import logging
import traceback


class LogFormatter(logging.Formatter):
    """Log formatter which gives more detail for exceptions

    This is the same as the standard log formatter, except that when logging
    exceptions [typically via log.foo("msg", exc_info=1)], it prints the
    sequence that led up to the point at which the exception was caught.
    (Normally only stack frames between the point the exception was raised and
    where it was caught are logged).
    """
    def __init__(self, *args, **kwargs):
        super(LogFormatter, self).__init__(*args, **kwargs)

    def formatException(self, ei):
        sio = StringIO.StringIO()
        (typ, val, tb) = ei

        # log the stack above the exception capture point if possible, but
        # check that we actually have an f_back attribute to work around
        # https://twistedmatrix.com/trac/ticket/9305

        if tb and hasattr(tb.tb_frame, 'f_back'):
            sio.write("Capture point (most recent call last):\n")
            traceback.print_stack(tb.tb_frame.f_back, None, sio)

        traceback.print_exception(typ, val, tb, None, sio)
        s = sio.getvalue()
        sio.close()
        if s[-1:] == "\n":
            s = s[:-1]
        return s
