#############################################################################
# Copyright (c) 2022 Balazs Scheidler <bazsi77@gmail.com>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
#
# As an additional exemption you are allowed to compile & link against the
# OpenSSL libraries as published by the OpenSSL project. See the file
# COPYING for details.
#
#############################################################################
try:
    from _syslogng import LogSource, LogFetcher, LogFetcherResult
    from _syslogng import InstantAckTracker, ConsecutiveAckTracker, BatchedAckTracker

except ImportError:
    import warnings
    from enum import Enum, auto

    warnings.warn("You have imported the syslogng package outside of syslog-ng, thus some of the functionality is not available. Defining fake classes for those exported by the underlying syslog-ng code")

    LogSource = object
    LogFetcher = object
    InstantAckTracker = object
    ConsecutiveAckTracker = object
    BatchedAckTracker = object

    class LogFetcherResult(Enum):
        ERROR = auto()
        NOT_CONNECTED = auto()
        SUCCESS = auto()
        TRY_AGAIN = auto()
        NO_DATA = auto()


class LogSource(LogSource):
    """Base class for building an asynchronous source driver

    A LogSource is a base class that allows the implementation of a
    syslog-ng source driver.  Derive your source implementation from this
    class and override the run() method to add your specific behaviour.

    Internally, this class starts a dedicated thread and allows you to
    use an asynchronous framework such as asyncio to produce messages.

    It easily maps to any source mechanism that pushes messages to syslog-ng
    (e.g.  queueing protocols such as mqtt or HTTP server implementations)
    """

    def init(self, options):
        """Initialize this LogSource instance

        Returns:
            bool: True to indicate success
        """
        return True

    def run(self):
        """Run the main loop for the source

        This method is invoked by syslog-ng to start producing messages in
        an asynchronous manner.  This function is executed in a dedicated
        thread and should run until request_exit() is invoked.

        Usually this would either start polling some API or implement the
        server side of a push based protocol, using a framework such as asyncio.

        Whenever a new message is available, just call post_message() with
        the new message.

        Returns:
            None
        """
        pass

    def post_message(self, msg):
        """Post a message as an output for this source

        post_message() can be called from within run() to post messages to
        syslog-ng, as the output of the source driver being implemented.

        Flow control is implemented in two ways:
          - blocking mode: post_message() would block if flow control kicks
            in (e.g.  there's no room in our output window).  This is simple
            but your main event loop will be suspended until syslog-ng is
            able to accept messages again.

          - non-blocking mode: if suspend() and wakeup() methods are
            implemented in your class, post_message() would not block,
            rather invoke suspend() to indicate that no further messages
            is to be produced and wakeup() when it is possible to produce
            messages again.  This mode allows the continued execution of the
            async main loop even while syslog-ng is unable to accept
            messages.

        Arguments:
            msg: LogMessage
                the log message to be posted
        """
        super().post_message(msg)

    def request_exit(self):
        """Request the main loop to exit

        This function is invoked by syslog-ng from its main thread when this
        source should stop executing.  The expected result of this function
        is that its run() method returns to its caller.
        """
        pass


class LogFetcher(LogFetcher):
    """Base class for building synchronous (blocking) source driver

    A LogFetcher is a base class that allows the implementation of a
    syslog-ng source driver.  This class starts a dedicated thread and
    regularly executes the fetch() method in that thread to fetch the next
    message to be emitted as the output of the log source.

    It easily maps to any source mechanism that you need to poll regularly
    for new messages (e.g.  HTTP based log access APIs).
    """
    ERROR = FETCH_ERROR = LogFetcherResult.ERROR
    NOT_CONNECTED = FETCH_NOT_CONNECTED = LogFetcherResult.NOT_CONNECTED
    SUCCESS = FETCH_SUCCESS = LogFetcherResult.SUCCESS
    TRY_AGAIN = FETCH_TRY_AGAIN = LogFetcherResult.TRY_AGAIN
    NO_DATA = FETCH_NO_DATA = LogFetcherResult.NO_DATA

    def init(self, options):
        """Initialize this LogFetcher instance

        Returns:
            bool: True to indicate success
        """
        return True

    def open(self):
        """Open the connection to the target service

        This function is called by syslog-ng to open a connection to the
        target service.  It should return True to indicate success or False
        otherwise.  If the connection to the target service fails, syslog-ng
        will try to reconnect until it succeeds, retrying every
        time_reopen() seconds.
        """
        return True

    def close(self):
        """Close the connection to the target service"""
        pass

    def fetch(self):
        """Function to fetch the next message

        This function is executed from the thread associated with LogFetcher
        every time syslog-ng is able to consume a new message.

        Returns:
            (result, message): (LogFetcherResult, LogMessage)
                the function needs to return a 2-tuple, which comprises of a
                status code and a message instance.  Possible status codes
                are defined as members in the LogFetcher class or as values
                in the LogFetchrResult enum.
        """
        return self.TRY_AGAIN, None
