"""
Tools aimed at the interaction between Tahoe-LAFS implementation and Eliot.
"""

from __future__ import (
    unicode_literals,
    print_function,
    absolute_import,
    division,
)

__all__ = [
    "use_generator_context",
    "eliot_friendly_generator_function",
    "inline_callbacks",
    "eliot_logging_service",
    "opt_eliot_destination",
]

from sys import (
    exc_info,
    stdout,
)
from functools import wraps
from contextlib import contextmanager
from weakref import WeakKeyDictionary
from logging import (
    INFO,
    Handler,
    getLogger,
)
from json import loads

from zope.interface import (
    implementer,
)

import attr
from attr.validators import (
    optional,
    provides,
)

from eliot import (
    ILogger,
    Message,
    FileDestination,
    add_destinations,
    remove_destination,
    write_traceback,
)

from twisted.python.filepath import (
    FilePath,
)
from twisted.python.logfile import (
    LogFile,
)
from twisted.logger import (
    ILogObserver,
    eventAsJSON,
    globalLogPublisher,
)
from twisted.internet.defer import (
    inlineCallbacks,
)
from twisted.application.service import Service


class _GeneratorContext(object):
    def __init__(self, execution_context):
        self._execution_context = execution_context
        self._contexts = WeakKeyDictionary()
        self._current_generator = None

    def init_stack(self, generator):
        stack = list(self._execution_context._get_stack())
        self._contexts[generator] = stack

    def get_stack(self):
        if self._current_generator is None:
            # If there is no currently active generator then we have no
            # special stack to supply.  Let the execution context figure out a
            # different answer on its own.
            return None
        # Otherwise, give back the action context stack we've been tracking
        # for the currently active generator.  It must have been previously
        # initialized (it's too late to do it now)!
        return self._contexts[self._current_generator]

    @contextmanager
    def context(self, generator):
        previous_generator = self._current_generator
        try:
            self._current_generator = generator
            yield
        finally:
            self._current_generator = previous_generator


from eliot._action import _context
_the_generator_context = _GeneratorContext(_context)


def use_generator_context():
    _context.get_sub_context = _the_generator_context.get_stack
use_generator_context()


def eliot_friendly_generator_function(original):
    """
    Decorate a generator function so that the Eliot action context is
    preserved across ``yield`` expressions.
    """
    @wraps(original)
    def wrapper(*a, **kw):
        # Keep track of whether the next value to deliver to the generator is
        # a non-exception or an exception.
        ok = True

        # Keep track of the next value to deliver to the generator.
        value_in = None

        # Create the generator with a call to the generator function.  This
        # happens with whatever Eliot action context happens to be active,
        # which is fine and correct and also irrelevant because no code in the
        # generator function can run until we call send or throw on it.
        gen = original(*a, **kw)

        # Initialize the per-generator Eliot action context stack to the
        # current action stack.  This might be the main stack or, if another
        # decorated generator is running, it might be the stack for that
        # generator.  Not our business.
        _the_generator_context.init_stack(gen)
        while True:
            try:
                # Whichever way we invoke the generator, we will do it
                # with the Eliot action context stack we've saved for it.
                # Then the context manager will re-save it and restore the
                # "outside" stack for us.
                with _the_generator_context.context(gen):
                    if ok:
                        value_out = gen.send(value_in)
                    else:
                        value_out = gen.throw(*value_in)
                    # We have obtained a value from the generator.  In
                    # giving it to us, it has given up control.  Note this
                    # fact here.  Importantly, this is within the
                    # generator's action context so that we get a good
                    # indication of where the yield occurred.
                    #
                    # This might be too noisy, consider dropping it or
                    # making it optional.
                    Message.log(message_type=u"yielded")
            except StopIteration:
                # When the generator raises this, it is signaling
                # completion.  Leave the loop.
                break
            else:
                try:
                    # Pass the generator's result along to whoever is
                    # driving.  Capture the result as the next value to
                    # send inward.
                    value_in = yield value_out
                except:
                    # Or capture the exception if that's the flavor of the
                    # next value.
                    ok = False
                    value_in = exc_info()
                else:
                    ok = True

    return wrapper


def inline_callbacks(original):
    """
    Decorate a function like ``inlineCallbacks`` would but in a more
    Eliot-friendly way.  Use it just like ``inlineCallbacks`` but where you
    want Eliot action contexts to Do The Right Thing inside the decorated
    function.
    """
    return inlineCallbacks(
        eliot_friendly_generator_function(original)
    )


def eliot_logging_service(reactor, destinations):
    """
    Parse the given Eliot destination descriptions and return an ``IService``
    which will add them when started and remove them when stopped.

    The following destinations are supported:

    * ``file:<path>[:rotated_length=<bytes>][:max_rotated_files=<count>]``
      Sensible defaults are supplied for rotated_length and max_rotated_files
      if they are not given.
    """
    return _EliotLogging(destinations=list(
        get_destination(reactor)
        for get_destination
        in destinations
    ))


# An Options-based argument parser for configuring Eliot logging.  Set this as
# a same-named attribute on your Options subclass.
def opt_eliot_destination(self, description):
    """
    Add an Eliot logging destination.  May be given more than once.
    """
    self.setdefault("destinations", []).append(
        _parse_destination_description(description)
    )



class _EliotLogging(Service):
    """
    A service which adds stdout as an Eliot destination while it is running.
    """
    def __init__(self, destinations):
        """
        :param list destinations: The Eliot destinations which will is added by this
            service.
        """
        self.destinations = destinations


    def startService(self):
        self.stdlib_cleanup = _stdlib_logging_to_eliot_configuration(getLogger())
        self.twisted_observer = _TwistedLoggerToEliotObserver()
        globalLogPublisher.addObserver(self.twisted_observer)
        add_destinations(*self.destinations)


    def stopService(self):
        for dest in self.destinations:
            remove_destination(dest)
        globalLogPublisher.removeObserver(self.twisted_observer)
        self.stdlib_cleanup()



@implementer(ILogObserver)
@attr.s(frozen=True)
class _TwistedLoggerToEliotObserver(object):
    """
    An ``ILogObserver`` which re-publishes events as Eliot messages.
    """
    logger = attr.ib(default=None, validator=optional(provides(ILogger)))

    def _observe(self, event):
        flattened = loads(eventAsJSON(event))
        # We get a timestamp from Eliot.
        flattened.pop(u"log_time")
        # This is never serializable anyway.  "Legacy" log events (from
        # twisted.python.log) don't have this so make it optional.
        flattened.pop(u"log_logger", None)

        Message.new(
            message_type=u"eliot:twisted",
            **flattened
        ).write(self.logger)


    # The actual ILogObserver interface uses this.
    __call__ = _observe


class _StdlibLoggingToEliotHandler(Handler):
    def __init__(self, logger=None):
        Handler.__init__(self)
        self.logger = logger

    def emit(self, record):
        Message.new(
            message_type=u"eliot:stdlib",
            log_level=record.levelname,
            logger=record.name,
            message=record.getMessage()
        ).write(self.logger)

        if record.exc_info:
            write_traceback(
                logger=self.logger,
                exc_info=record.exc_info,
            )


def _stdlib_logging_to_eliot_configuration(stdlib_logger, eliot_logger=None):
    """
    Add a handler to ``stdlib_logger`` which will relay events to
    ``eliot_logger`` (or the default Eliot logger if ``eliot_logger`` is
    ``None``).
    """
    handler = _StdlibLoggingToEliotHandler(eliot_logger)
    handler.set_name(u"eliot")
    handler.setLevel(INFO)
    stdlib_logger.addHandler(handler)
    return lambda: stdlib_logger.removeHandler(handler)


class _DestinationParser(object):
    def parse(self, description):
        description = description.decode(u"ascii")

        kind, args = description.split(u":", 1)
        try:
            parser = getattr(self, u"_parse_{}".format(kind))
        except AttributeError:
            raise ValueError(
                u"Unknown destination description: {}".format(description)
            )
        else:
            return parser(kind, args)

    def _get_arg(self, arg_name, default, arg_list):
        return dict(
            arg.split(u"=", 1)
            for arg
            in arg_list
        ).get(
            arg_name,
            default,
        )

    def _parse_file(self, kind, arg_text):
        # Reserve the possibility of an escape character in the future.
        if u"\\" in arg_text:
            raise ValueError(
                u"Unsupported escape character (\\) in destination text ({!r}).".format(arg_text),
            )
        arg_list = arg_text.split(u":")
        path_name = arg_list.pop(0)
        if path_name == "-":
            get_file = lambda: stdout
        else:
            path = FilePath(path_name)
            rotate_length = int(self._get_arg(
                u"rotate_length",
                1024 * 1024 * 1024,
                arg_list,
            ))
            max_rotated_files = int(self._get_arg(
                u"max_rotated_files",
                10,
                arg_list,
            ))
            get_file = lambda: LogFile(
                path.basename(),
                path.dirname(),
                rotateLength=rotate_length,
                maxRotatedFiles=max_rotated_files,
            )
        return lambda reactor: FileDestination(get_file())


_parse_destination_description = _DestinationParser().parse