# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import os
import pickle
import socket
import struct
import subprocess
import warnings

import torch
import torch.distributed as dist

from fairseq import utils1 as utils


def is_master(args):
    return args.distributed_rank == 0


def infer_init_method(args):
    if args.distributed_init_method is not None:
        return

    # support torch.distributed.launch
    if all(key in os.environ for key in [
        'MASTER_ADDR', 'MASTER_PORT', 'WORLD_SIZE', 'RANK'
    ]):
        args.distributed_init_method = 'env://'
        args.distributed_world_size = int(os.environ['WORLD_SIZE'])
        args.distributed_rank = int(os.environ['RANK'])

    # we can determine the init method automatically for Slurm
    elif args.distributed_port > 0:
        node_list = os.environ.get('SLURM_STEP_NODELIST')
        if node_list is None:
            node_list = os.environ.get('SLURM_JOB_NODELIST')
        if node_list is not None:
            try:
                hostnames = subprocess.check_output(['scontrol', 'show', 'hostnames', node_list])
                args.distributed_init_method = 'tcp://{host}:{port}'.format(
                    host=hostnames.split()[0].decode('utf-8'),
                    port=args.distributed_port,
                )
                nnodes = int(os.environ.get('SLURM_NNODES'))
                ntasks_per_node = os.environ.get('SLURM_NTASKS_PER_NODE')
                if ntasks_per_node is not None:
                    ntasks_per_node = int(ntasks_per_node)
                else:
                    ntasks = int(os.environ.get('SLURM_NTASKS'))
                    nnodes = int(os.environ.get('SLURM_NNODES'))
                    assert ntasks % nnodes == 0
                    ntasks_per_node = int(ntasks / nnodes)
                if ntasks_per_node == 1:
                    assert args.distributed_world_size % nnodes == 0
                    gpus_per_node = args.distributed_world_size // nnodes
                    node_id = int(os.environ.get('SLURM_NODEID'))
                    args.distributed_rank = node_id * gpus_per_node
                else:
                    assert ntasks_per_node == args.distributed_world_size // nnodes
                    args.distributed_no_spawn = True
                    args.distributed_rank = int(os.environ.get('SLURM_PROCID'))
                    args.device_id = int(os.environ.get('SLURM_LOCALID'))
            except subprocess.CalledProcessError as e:  # scontrol failed
                raise e
            except FileNotFoundError:  # Slurm is not installed
                pass


def distributed_init(args):
    if args.distributed_world_size == 1:
        raise ValueError('Cannot initialize distributed with distributed_world_size=1')

    if torch.distributed.is_initialized():
        warnings.warn('Distributed is already initialized, cannot initialize twice!')
    else:
        print('| distributed init (rank {}): {}'.format(
            args.distributed_rank, args.distributed_init_method), flush=True)
        dist.init_process_group(
            backend=args.distributed_backend,
            init_method=args.distributed_init_method,
            world_size=args.distributed_world_size,
            rank=args.distributed_rank,
        )
        print('| initialized host {} as rank {}'.format(
            socket.gethostname(), args.distributed_rank), flush=True)

        # perform a dummy all-reduce to initialize the NCCL communicator
        if torch.cuda.is_available():
            dist.all_reduce(torch.zeros(1).cuda())
        else:
            dist.all_reduce(torch.zeros(1))

        suppress_output(is_master(args))

    args.distributed_rank = torch.distributed.get_rank()
    return args.distributed_rank


def suppress_output(is_master):
    """Suppress printing on the current device. Force printing with `force=True`."""
    import builtins as __builtin__
    builtin_print = __builtin__.print

    def print(*args, **kwargs):
        force = kwargs.pop('force', False)
        if is_master or force:
            builtin_print(*args, **kwargs)

    __builtin__.print = print


def get_rank():
    return dist.get_rank()


def get_world_size():
    return dist.get_world_size()


def get_default_group():
    return dist.group.WORLD


def all_reduce(tensor, group=None):
    if group is None:
        group = get_default_group()
    return dist.all_reduce(tensor, group=group)


def all_gather_list(data, group=None, max_size=16384):
    """Gathers arbitrary data from all nodes into a list.

    Similar to :func:`~torch.distributed.all_gather` but for arbitrary Python
    data. Note that *data* must be picklable.

    Args:
        data (Any): data from the local worker to be gathered on other workers
        group (optional): group of the collective
        max_size (int, optional): maximum size of the data to be gathered
            across workers
    """
    rank = get_rank()
    world_size = get_world_size()

    buffer_size = max_size * world_size
    if not hasattr(all_gather_list, '_buffer') or \
            all_gather_list._buffer.numel() < buffer_size:
        all_gather_list._buffer = torch.cuda.ByteTensor(buffer_size)
        all_gather_list._cpu_buffer = torch.ByteTensor(max_size).pin_memory()
    buffer = all_gather_list._buffer
    buffer.zero_()
    cpu_buffer = all_gather_list._cpu_buffer

    enc = pickle.dumps(data)
    enc_size = len(enc)
    header_size = 4  # size of header that contains the length of the encoded data
    size = header_size + enc_size
    if size > max_size:
        raise ValueError('encoded data size ({}) exceeds max_size ({})'.format(size, max_size))

    header = struct.pack(">I", enc_size)
    cpu_buffer[:size] = torch.ByteTensor(list(header + enc))
    start = rank * max_size
    buffer[start:start + size].copy_(cpu_buffer[:size])

    all_reduce(buffer, group=group)

    buffer = buffer.cpu()
    try:
        result = []
        for i in range(world_size):
            out_buffer = buffer[i * max_size:(i + 1) * max_size]
            enc_size, = struct.unpack(">I", bytes(out_buffer[:header_size].tolist()))
            if enc_size > 0:
                result.append(pickle.loads(bytes(out_buffer[header_size:header_size + enc_size].tolist())))
        return result
    except pickle.UnpicklingError:
        raise Exception(
            'Unable to unpickle data from other workers. all_gather_list requires all '
            'workers to enter the function together, so this error usually indicates '
            'that the workers have fallen out of sync somehow. Workers can fall out of '
            'sync if one of them runs out of memory, or if there are other conditions '
            'in your training script that can cause one worker to finish an epoch '
            'while other workers are still iterating over their portions of the data. '
            'Try rerunning with --ddp-backend=no_c10d and see if that helps.'
        )
