# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
# Copyright 2020 Huawei Technologies Co., Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
import torch
import torch.distributed as dist
import torch.multiprocessing as mp
import os

from detectron2.utils import comm

__all__ = ["launch"]


def _find_free_port():
    import socket

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # Binding to port 0 will cause the OS to find an available port for us
    sock.bind(("", 0))
    port = sock.getsockname()[1]
    sock.close()
    # NOTE: there is still a chance the port could be taken by other processes.
    return port


def launch(main_func, num_gpus_per_machine, num_machines=1, machine_rank=0, dist_url=None, args=()):
    """
    Launch multi-gpu or distributed training.
    This function must be called on all machines involved in the training.
    It will spawn child processes (defined by ``num_gpus_per_machine`) on each machine.

    Args:
        main_func: a function that will be called by `main_func(*args)`
        num_gpus_per_machine (int): number of GPUs per machine
        num_machines (int): the total number of machines
        machine_rank (int): the rank of this machine
        dist_url (str): url to connect to for distributed jobs, including protocol
                       e.g. "tcp://127.0.0.1:8686".
                       Can be set to "auto" to automatically select a free port on localhost
        args (tuple): arguments passed to main_func
    """
    world_size = num_machines * num_gpus_per_machine
    if world_size > 1:
        # https://github.com/pytorch/pytorch/pull/14391
        # TODO prctl in spawned processes

        if dist_url == "auto":
            assert num_machines == 1, "dist_url=auto not supported in multi-machine jobs."
            port = _find_free_port()
            dist_url = f"tcp://127.0.0.1:{port}"
        if num_machines > 1 and dist_url.startswith("file://"):
            logger = logging.getLogger(__name__)
            logger.warning(
                "file:// is not a reliable init_method in multi-machine jobs. Prefer tcp://"
            )
        os.environ['MASTER_ADDR'] = '127.0.0.1'
        os.environ['MASTER_PORT'] = str(_find_free_port())
        os.environ["WORLD_SIZE"] = str(world_size)

        mp.spawn(
            _distributed_worker,
            nprocs=num_gpus_per_machine,
            args=(main_func, world_size, num_gpus_per_machine, machine_rank, dist_url, args),
            daemon=False,
        )
    else:
        argsd = dict(zip(args[0].opts[0::2], args[0].opts[1::2]))
        os.environ['KERNEL_NAME_ID'] = \
            argsd['MODEL.DEVICE'].split(':')[-1]
        torch.npu.set_device(argsd['MODEL.DEVICE'])

        main_func(*args)


def _distributed_worker(
    local_rank,
    main_func,
    world_size,
    num_gpus_per_machine,
    machine_rank,
    dist_url,
    args
):
    assert torch.npu.is_available(), \
        "npu is not available. Please check your installation."
    global_rank = machine_rank * num_gpus_per_machine + local_rank
    os.environ["RANK"] = str(local_rank)
    os.environ['KERNEL_NAME_ID'] = str(local_rank)

    try:
        dist.init_process_group(
            backend="hccl", # init_method=dist_url,
            world_size=world_size, rank=global_rank
        )
    except Exception as e:
        logger = logging.getLogger(__name__)
        logger.error("Process group URL: {}".format(dist_url))
        raise e

    assert num_gpus_per_machine <= torch.npu.device_count()
    if args[0].device_ids:
        device = 'npu:{}'.format(args[0].device_ids[local_rank])
    else:
        device = 'npu:{}'.format(local_rank)

    torch.npu.set_device(device)

    # synchronize is needed here to prevent a possible timeout after calling init_process_group
    # See: https://github.com/facebookresearch/maskrcnn-benchmark/issues/172

    # Setup the local process group (which contains ranks within the same machine)
    assert comm._LOCAL_PROCESS_GROUP is None
    num_machines = world_size // num_gpus_per_machine
    for i in range(num_machines):
        ranks_on_i = list(range(i * num_gpus_per_machine, (i + 1) * num_gpus_per_machine))
        pg = dist.new_group(ranks_on_i)
        if i == machine_rank:
            comm._LOCAL_PROCESS_GROUP = pg

    main_func(*args)