import logging
import json
import types
from traceback import format_tb
from simplegeneric import generic


@generic
def encode_log_record(obj):
    return repr(obj)


@encode_log_record.when_type(types.TracebackType)
def encode_log_record_traceback(obj):
    return format_tb(obj)


class LogRecordEncoder(json.JSONEncoder):

    def default(self, obj):
        return encode_log_record(obj)


class TTYOrJSONStreamHandler(logging.StreamHandler):
    """ StreamHandler that use standard when logging to a TTY.

        JSON logging good for machines but ugly for humans.
        We check if logging to a TTY stream and use normal
        log formatting. Otherwise we encode the `LogRecord`
        in JSON .

        We also fall back to the JSON encoded LogRecord if the
        formatting raises an exception (e.g. wrong arguments).

        You can set the `force_formatted` variable to
        log formatted messages even if logging to non-TTY
        (e.g. redirecting stderr).
    """

    force_formatted = False

    def format(self, record):
        try:
            formatted = super(TTYOrJSONStreamHandler, self).format(record)
        except Exception as exc:
            formatted = None
            fmt_exc = exc
        else:
            fmt_exc = None

        if (self.stream.isatty() or self.force_formatted) and fmt_exc is None:
            return formatted
        else:
            copy = dict(record.__dict__)
            if fmt_exc is None:
                copy['formatted'] = formatted
            else:
                copy['fmt_exc'] = fmt_exc
            return json.dumps(copy, cls=LogRecordEncoder)