import json
import logging
import platform
import sys
import time
import traceback

class JSONFormatter:
    """A formatter for the standard logging module that converts a LogRecord into JSON

    Output matches JSONLayout from https://github.com/kdgregory/log4j-aws-appenders. Any
    keyword arguments supplied to the constructor are output in a "tags" sub-object.
    """

    def __init__(self, **tags):
        self.tags = tags

    def format(self, record):
        result = {
            'timestamp':    time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime(record.created)) +
                            (".%03dZ" % (1000 * (record.created % 1))),
            'level':        record.levelname,
            'logger':       record.name,
            'message':      record.msg % record.args,
            'hostname':     platform.node(),
            'processId':    record.process,
            'thread':       record.threadName,
            'locationInfo': {
                            'fileName':     record.filename,
                            'lineNumber':   record.lineno
                            }
            }

        if self.tags:
            result['tags'] = self.tags
            
        if (record.exc_info):
            result['exception'] = traceback.format_exception(record.exc_info[0], record.exc_info[1], record.exc_info[2])

        return json.dumps(result)

def configure_logging():
    handler = logging.StreamHandler(sys.stderr)
    handler.setFormatter(JSONFormatter(application="example"))
    logging.basicConfig(level=logging.DEBUG, handlers=[handler])


if __name__ == '__main__':
    configure_logging()
    logger = logging.getLogger(__name__)
    logger.info('Started')
    logger.debug('this is a test of %s %s', "value", "substitutions")
    try:
        raise Exception("example")
    except Exception as ex:
        logger.exception("caught exception")
    logger.info('Finished')