from __future__ import absolute_import, division, print_function, unicode_literals

import sys
import tempfile
import time
import unittest
import logging
import six
import traceback

from collections import namedtuple
from functools import wraps

import torch
import torch.distributed as c10d

from common_utils import TestCase

TestSkip = namedtuple('TestSkip', 'exit_code, message')


TEST_SKIPS = {
    "multi-gpu": TestSkip(75, "Need at least 2 CUDA devices"),
    "nccl": TestSkip(76, "c10d not compiled with NCCL support"),
    "known_issues": TestSkip(77, "Test skipped due to known issues")
}


def skip_if_not_multigpu(func):
    """Multi-GPU tests requires at least 2 GPUS. Skip if this is not met."""
    @wraps(func)
    def wrapper(*args, **kwargs):
        if torch.cuda.is_available() and torch.cuda.device_count() >= 2:
            return func(*args, **kwargs)
        sys.exit(TEST_SKIPS['multi-gpu'].exit_code)

    return wrapper


def skip_if_lt_x_gpu(x):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            if torch.cuda.is_available() and torch.cuda.device_count() >= x:
                return func(*args, **kwargs)
            sys.exit(TEST_SKIPS['multi-gpu'].exit_code)
        return wrapper

    return decorator


def skip_for_known_issues(func):
    """Skips a test due to known issues (for c10d)."""
    @wraps(func)
    def wrapper(*args, **kwargs):
        sys.exit(TEST_SKIPS['known_issues'].exit_code)

    return wrapper


def requires_gloo():
    return unittest.skipUnless(
        c10d.is_gloo_available(),
        "c10d was not compiled with the Gloo backend",
    )

def requires_nccl_version(version, msg):
    if not c10d.is_nccl_available():
        return unittest.skip(
            "c10d was not compiled with the NCCL backend",
        )
    else:
        return unittest.skipIf(
            torch.cuda.nccl.version() < version,
            "Requires NCCL version greater than or equal to: {}, found: {}, reason: {}".format(
                version,
                torch.cuda.nccl.version(), msg),
        )

def requires_nccl():
    return unittest.skipUnless(
        c10d.is_nccl_available(),
        "c10d was not compiled with the NCCL backend",
    )


def requires_mpi():
    return unittest.skipUnless(
        c10d.is_mpi_available(),
        "c10d was not compiled with the MPI backend",
    )


TIMEOUT_DEFAULT = 100
TIMEOUT_OVERRIDE = {}


def get_timeout(test_id):
    return TIMEOUT_OVERRIDE.get(test_id.split('.')[-1], TIMEOUT_DEFAULT)


class MultiProcessTestCase(TestCase):
    MAIN_PROCESS_RANK = -1
    # This exit code is used to indicate that the test code had an error and
    # exited abnormally. There are certain tests that might use sys.exit() to
    # simulate failures and in those cases, we can't have an exit code of 0,
    # but we still want to ensure we didn't run into any other errors.
    TEST_ERROR_EXIT_CODE = 10

    @property
    def world_size(self):
        return 4

    @staticmethod
    def join_or_run(fn):
        @wraps(fn)
        def wrapper(self):
            if self.rank == self.MAIN_PROCESS_RANK:
                self._join_processes(fn)
            else:
                try:
                    fn(self)
                except Exception as e:
                    logging.error('Caught exception: \n{}exiting process with exit code: {}'
                                  .format(traceback.format_exc(), MultiProcessTestCase.TEST_ERROR_EXIT_CODE))
                    sys.exit(MultiProcessTestCase.TEST_ERROR_EXIT_CODE)
        return wrapper

    # The main process spawns N subprocesses that run the test.
    # This function patches overwrites every test function to either
    # assume the role of the main process and join its subprocesses,
    # or run the underlying test function.
    @classmethod
    def setUpClass(cls):
        for attr in dir(cls):
            if attr.startswith('test'):
                fn = getattr(cls, attr)
                setattr(cls, attr, cls.join_or_run(fn))

    def setUp(self):
        super(MultiProcessTestCase, self).setUp()
        self.skip_return_code_checks = []
        self.rank = self.MAIN_PROCESS_RANK
        self.file_name = tempfile.NamedTemporaryFile(delete=False).name

    def tearDown(self):
        super(MultiProcessTestCase, self).tearDown()
        for p in self.processes:
            p.terminate()

    def _current_test_name(self):
        # self.id() == e.g. '__main__.TestDistributed.TestAdditive.test_get_rank'
        return self.id().split(".")[-1]

    def _start_processes(self, proc):
        self.processes = []
        for rank in range(int(self.world_size)):
            process = proc(
                target=self.__class__._run,
                name='process ' + str(rank),
                args=(rank, self._current_test_name(), self.file_name))
            process.start()
            self.processes.append(process)

    def _fork_processes(self):
        if six.PY3:
            proc = torch.multiprocessing.get_context("fork").Process
        else:
            proc = torch.multiprocessing.Process
        self._start_processes(proc)

    def _spawn_processes(self):
        if six.PY3:
            proc = torch.multiprocessing.get_context("spawn").Process
        else:
            raise RuntimeError("Cannot use spawn start method with Python 2")
        self._start_processes(proc)

    @classmethod
    def _run(cls, rank, test_name, file_name):
        self = cls(test_name)
        self.rank = rank
        self.file_name = file_name

        # self.id() == e.g. '__main__.TestDistributed.test_get_rank'
        # We're retreiving a corresponding test and executing it.
        getattr(self, test_name)()
        # exit to avoid run teardown() for fork processes
        sys.exit(0)

    def _join_processes(self, fn):
        timeout = get_timeout(self.id())
        start_time = time.time()
        for p in self.processes:
            p.join(timeout)
        elapsed_time = time.time() - start_time
        if fn in self.skip_return_code_checks:
            self._check_no_test_errors(elapsed_time)
        else:
            self._check_return_codes(elapsed_time)

    def _check_no_test_errors(self, elapsed_time):
        """
        Checks that we didn't have any errors thrown in the child processes.
        """
        for i, p in enumerate(self.processes):
            if p.exitcode is None:
                raise RuntimeError('Process {} timed out after {} seconds'.format(i, elapsed_time))
            self.assertNotEqual(self.TEST_ERROR_EXIT_CODE, p.exitcode)

    def _check_return_codes(self, elapsed_time):
        """
        Checks that the return codes of all spawned processes match, and skips
        tests if they returned a return code indicating a skipping condition.
        """
        first_process = self.processes[0]
        for i, p in enumerate(self.processes):
            if p.exitcode is None:
                raise RuntimeError('Process {} terminated or timed out after {} seconds'.format(i, elapsed_time))
            self.assertEqual(p.exitcode, first_process.exitcode)
        for skip in TEST_SKIPS.values():
            if first_process.exitcode == skip.exit_code:
                raise unittest.SkipTest(skip.message)
        self.assertEqual(first_process.exitcode, 0)

    @property
    def is_master(self):
        return self.rank == 0