# Copyright (C) 2013  Internet Systems Consortium.
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SYSTEMS CONSORTIUM
# DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
# INTERNET SYSTEMS CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
# FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
# WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

import errno
import os
import select
import signal

import isc.log
import isc.config
from isc.server_common.logger import logger
from isc.log_messages.server_common_messages import *

class BIND10ServerFatal(Exception):
    """Exception raised when the server program encounters a fatal error."""
    pass

class BIND10Server:
    """A mixin class for common BIND 10 server implementations.

    It takes care of common initialization such as setting up a module CC
    session, and running main event loop.  It also handles the "shutdown"
    command for its normal behavior.  If a specific server class wants to
    handle this command differently or if it does not support the command,
    it should override the _command_handler method.

    Specific modules can define module-specific class inheriting this class,
    instantiate it, and call run() with the module name.

    Methods to be implemented in the actual class:
      _config_handler: config handler method as specified in ModuleCCSession.
                       must be exception free; errors should be signaled by
                       the return value.
      _mod_command_handler: can be optionally defined to handle
                            module-specific commands.  should conform to
                            command handlers as specified in ModuleCCSession.
                            must be exception free; errors should be signaled
                            by the return value.
      _setup_module: can be optionally defined for module-specific
                     initialization.  This is called after the module CC
                     session has started, and can be used for registering
                     interest on remote modules, etc.  If it raises an
                     exception, the server will be immediately stopped.
                     Parameter: None, Return: None
      _shutdown_module: can be optionally defined for module-specific
                        finalization. This is called right before the
                        module CC session is stopped. If it raises an
                        exception, the server will be immediately
                        stopped.
                        Parameter: None, Return: None

    """
    # Will be set to True when the server should stop and shut down.
    # Can be read via accessor method 'shutdown', mainly for testing.
    __shutdown = False

    # ModuleCCSession used in the server.  Defined as 'protectd' so tests
    # can refer to it directly; others should access it via the
    # 'mod_ccsession' accessor.
    _mod_cc = None

    # Will be set in run().  Define a tentative value so other methods can
    # be tested directly.
    __module_name = ''

    # Basically constant, but allow tests to override it.
    _select_fn = select.select

    def __init__(self):
        self._read_callbacks = {}
        self._write_callbacks = {}
        self._error_callbacks = {}

    @property
    def shutdown(self):
        return self.__shutdown

    @property
    def mod_ccsession(self):
        return self._mod_cc

    def _setup_ccsession(self):
        """Create and start module CC session.

        This is essentially private, but allows tests to override it.

        """
        self._mod_cc = isc.config.ModuleCCSession(
            self._get_specfile_location(), self._config_handler,
            self._command_handler)
        self._mod_cc.start()

    def _get_specfile_location(self):
        """Return the path to the module spec file following common convetion.

        This method generates the path commonly used by most BIND 10 modules,
        determined by a well known prefix and the module name.

        A specific module can override this method if it uses a different
        path for the spec file.

        """
        # First check if it's running under an 'in-source' environment,
        # then try commonly used paths and file names.  If found, use it.
        for ev in ['B10_FROM_SOURCE', 'B10_FROM_BUILD']:
            if ev in os.environ:
                specfile = os.environ[ev] + '/src/bin/' + self.__module_name +\
                    '/' + self.__module_name + '.spec'
                if os.path.exists(specfile):
                    return specfile
        # Otherwise, just use the installed path, whether or not it really
        # exists; leave error handling to the caller.
        specfile_path = '${datarootdir}/bind10'\
            .replace('${datarootdir}', '${prefix}/share')\
            .replace('${prefix}', '/Users/jinmei/opt')
        return specfile_path + '/' + self.__module_name + '.spec'

    def _trigger_shutdown(self):
        """Initiate a shutdown sequence.

        This method is expected to be called in various ways including
        in the middle of a signal handler, and is designed to be as simple
        as possible to minimize side effects.  Actual shutdown will take
        place in a normal control flow.

        This method is defined as 'protected'.  User classes can use it
        to shut down the server.

        """
        self.__shutdown = True

    def _run_internal(self):
        """Main event loop.

        This method is essentially private, but allows tests to override it.

        """

        logger.info(PYSERVER_COMMON_SERVER_STARTED, self.__module_name)
        cc_fileno = self._mod_cc.get_socket().fileno()
        while not self.__shutdown:
            try:
                read_fds = list(self._read_callbacks.keys())
                read_fds.append(cc_fileno)
                write_fds = list(self._write_callbacks.keys())
                error_fds = list(self._error_callbacks.keys())

                (reads, writes, errors) = \
                    self._select_fn(read_fds, write_fds, error_fds)
            except select.error as ex:
                # ignore intterruption by signal; regard other select errors
                # fatal.
                if ex.args[0] == errno.EINTR:
                    continue
                else:
                    raise

            for fileno in reads:
                if fileno in self._read_callbacks:
                    for callback in self._read_callbacks[fileno]:
                        callback()

            for fileno in writes:
                if fileno in self._write_callbacks:
                    for callback in self._write_callbacks[fileno]:
                        callback()

            for fileno in errors:
                if fileno in self._error_callbacks:
                    for callback in self._error_callbacks[fileno]:
                        callback()

            if cc_fileno in reads:
                # this shouldn't raise an exception (if it does, we'll
                # propagate it)
                self._mod_cc.check_command(True)

        self._shutdown_module()
        self._mod_cc.send_stopping()

    def _command_handler(self, cmd, args):
        logger.debug(logger.DBGLVL_TRACE_BASIC, PYSERVER_COMMON_COMMAND,
                     self.__module_name, cmd)
        if cmd == 'shutdown':
            self._trigger_shutdown()
            answer = isc.config.create_answer(0)
        else:
            answer = self._mod_command_handler(cmd, args)

        return answer

    def _mod_command_handler(self, cmd, args):
        """The default implementation of the module specific command handler"""
        return isc.config.create_answer(1, "Unknown command: " + str(cmd))

    def _setup_module(self):
        """The default implementation of the module specific initialization"""
        pass

    def _shutdown_module(self):
        """The default implementation of the module specific finalization"""
        pass

    def watch_fileno(self, fileno, rcallback=None, wcallback=None, \
                         xcallback=None):
        """Register the fileno for the internal select() call.

        *callback's are callable objects which would be called when
        read, write, error events occur on the specified fileno.
        """
        if rcallback is not None:
            if fileno in self._read_callbacks:
                self._read_callbacks[fileno].append(rcallback)
            else:
                self._read_callbacks[fileno] = [rcallback]

        if wcallback is not None:
            if fileno in self._write_callbacks:
                self._write_callbacks[fileno].append(wcallback)
            else:
                self._write_callbacks[fileno] = [wcallback]

        if xcallback is not None:
            if fileno in self._error_callbacks:
                self._error_callbacks[fileno].append(xcallback)
            else:
                self._error_callbacks[fileno] = [xcallback]

    def run(self, module_name):
        """Start the server and let it run until it's told to stop.

        Usually this must be the first method of this class that is called
        from its user.

        Parameter:
          module_name (str): the Python module name for the actual server
            implementation.  Often identical to the directory name in which
            the implementation files are placed.

        Returns: values expected to be used as program's exit code.
          0: server has run and finished successfully.
          1: some error happens

          """
        try:
            self.__module_name = module_name
            shutdown_sighandler = \
                lambda signal, frame: self._trigger_shutdown()
            signal.signal(signal.SIGTERM, shutdown_sighandler)
            signal.signal(signal.SIGINT, shutdown_sighandler)
            self._setup_ccsession()
            self._setup_module()
            self._run_internal()
            logger.info(PYSERVER_COMMON_SERVER_STOPPED, self.__module_name)
            return 0
        except BIND10ServerFatal as ex:
            logger.error(PYSERVER_COMMON_SERVER_FATAL, self.__module_name,
                         ex)
        except Exception as ex:
            logger.error(PYSERVER_COMMON_UNCAUGHT_EXCEPTION, type(ex).__name__,
                         ex)

        return 1