# coding=utf-8
# Copyright (c) 2021, EleutherAI contributors
# This file is based on code by the authors denoted below and has been modified from its original version.
#
# Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.
#
# 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.

"""Input/output checkpointing."""

import os
import re
import shutil
import random
import sys
import numpy as np

import torch
from torch.nn.parallel import DistributedDataParallel as torchDDP
from glob import glob

from megatron import mpu, get_args
from megatron import get_args
from megatron import print_rank_0
from megatron.utils import natural_sort

def check_checkpoint_args(checkpoint_args):
    """Ensure fixed arguments for a model are the same for the input
    arguments and the one retreived frm checkpoint."""
    args = get_args()

    def _compare(arg_name):
        checkpoint_value = getattr(checkpoint_args, arg_name)
        args_value = getattr(args, arg_name)
        error_message = '{} value from checkpoint ({}) is not equal to the ' \
                        'input argument value ({}).'.format(
            arg_name, checkpoint_value, args_value)
        assert checkpoint_value == args_value, error_message

    _compare('num_layers')
    _compare('hidden_size')
    _compare('num_attention_heads')
    _compare('max_position_embeddings')
    _compare('make_vocab_size_divisible_by')
    _compare('padded_vocab_size')
    _compare('tokenizer_type')
    _compare('model_parallel_size')


def ensure_directory_exists(filename):
    """Build filename's path if it does not already exists."""
    dirname = os.path.dirname(filename)
    if not os.path.exists(dirname):
        os.makedirs(dirname)


def get_checkpoint_name(checkpoints_path, iteration,
                        release=False, mp_rank=None):
    """A unified checkpoint name."""
    if release:
        directory = 'release'
    else:
        directory = 'iter_{:07d}'.format(iteration)
    return os.path.join(checkpoints_path, directory,
                        'mp_rank_{:02d}'.format(
                            mpu.get_model_parallel_rank() if mp_rank is None
                            else mp_rank),
                        'model_optim_rng.pt')


def get_checkpoint_tracker_filename(checkpoints_path):
    """Tracker file rescords the latest chckpoint during
    training to restart from."""
    return os.path.join(checkpoints_path, 'latest_checkpointed_iteration.txt')


def delete_old_checkpoints(save_dir, n_to_keep):
    if torch.distributed.get_rank() == 0:
        ckpt_dir_regex = r'global_step[\d]*'
        if save_dir.endswith('/'):
            save_dir = save_dir.strip('/')
        all_ckpts = natural_sort([i for i in glob(f'{save_dir}/*') if os.path.isdir(i)
                                  and re.search(ckpt_dir_regex, i)])
        n_to_delete = len(all_ckpts) - n_to_keep
        if n_to_delete > 0:
            to_delete = all_ckpts[:n_to_delete]
            print(f"WARNING: Deleting old checkpoints: \n\t{', '.join(to_delete)}")
            for ckpt in to_delete:
                try:
                    shutil.rmtree(ckpt)
                except FileNotFoundError:
                    pass


def save_ds_checkpoint(iteration, model, args):
    """Save a model checkpoint."""

    sd = {}
    sd['iteration'] = iteration
    # rng states.
    if not args.no_save_rng:
        sd['random_rng_state'] = random.getstate()
        sd['np_rng_state'] = np.random.get_state()
        sd['torch_rng_state'] = torch.get_rng_state()
        sd['cuda_rng_state'] = torch.cuda.get_rng_state()
        sd['rng_tracker_states'] = mpu.get_cuda_rng_tracker().get_states()

    if args.pipe_parallel_size == 0:
        # megatron model uses state_dict_for_save_checkpointing instead of the standard state_dict
        # state_dict is used by deepspeed for module saving so it needs to point to the right function
        model.module.state_dict = model.module.state_dict_for_save_checkpoint
    else:
        # Pipeline parallelism manages its own state_dict.
        pass

    model.save_checkpoint(args.save, client_state=sd)


def save_checkpoint(iteration, model, optimizer, lr_scheduler):
    """Save a model checkpoint."""
    args = get_args()

    if args.deepspeed:
        save_ds_checkpoint(iteration, model, args)
    else:
        raise ValueError('Must be using deepspeed to use neox')

    # Wait so everyone is done (necessary)
    torch.distributed.barrier()
    # And update the latest iteration
    if torch.distributed.get_rank() == 0:
        tracker_filename = get_checkpoint_tracker_filename(args.save)
        with open(tracker_filename, 'w') as f:
            f.write(str(iteration))

    # Wait so everyone is done (necessary)
    torch.distributed.barrier()
    if args.keep_last_n_checkpoints is not None:
        delete_old_checkpoints(args.save, args.keep_last_n_checkpoints)

    # Wait so everyone is done (not necessary)
    torch.distributed.barrier()


def load_checkpoint(model, optimizer, lr_scheduler, load_arg='load'):
    """Load a model checkpoint and return the iteration."""
    args = get_args()
    load_dir = getattr(args, load_arg)

    if isinstance(model, torchDDP):
        model = model.module
    # Read the tracker file and set the iteration.
    tracker_filename = get_checkpoint_tracker_filename(load_dir)

    # If no tracker file, return iretation zero.
    if not os.path.isfile(tracker_filename):
        print_rank_0('WARNING: could not find the metadata file {} '.format(
            tracker_filename))
        print_rank_0('    will not load any checkpoints and will start from '
                     'random')
        return 0

    # Otherwise, read the tracker file and either set the iteration or
    # mark it as a release checkpoint.
    iteration = 0
    release = False
    with open(tracker_filename, 'r') as f:
        metastring = f.read().strip()
        try:
            iteration = int(metastring)
        except ValueError:
            release = metastring == 'release'
            if not release:
                print_rank_0('ERROR: Invalid metadata file {}. Exiting'.format(
                    tracker_filename))
                sys.exit()

    assert iteration > 0 or release, 'error parsing metadata file {}'.format(
        tracker_filename)

    if args.deepspeed:
        load_optim_and_scheduler = not args.no_load_optim  # TODO: These should be configured by separate args
        checkpoint_name, state_dict = model.load_checkpoint(load_dir,
                                                            load_optimizer_states=load_optim_and_scheduler,
                                                            load_lr_scheduler_states=load_optim_and_scheduler)

        if checkpoint_name is None:
            if mpu.get_data_parallel_rank() == 0:
                print("Unable to load checkpoint.")
            return iteration
    else:
        raise ValueError('Must be using deepspeed to use neox')

    # Set iteration.
    if args.finetune or release:
        iteration = 0
    else:
        try:
            iteration = state_dict['iteration']
        except KeyError:
            try:  # Backward compatible with older checkpoints
                iteration = state_dict['total_iters']
            except KeyError:
                print_rank_0('A metadata file exists but unable to load '
                             'iteration from checkpoint {}, exiting'.format(
                    checkpoint_name))
                sys.exit()

    # Check arguments.
    if 'args' in state_dict:
        checkpoint_args = state_dict['args']
        check_checkpoint_args(checkpoint_args)
    else:
        print_rank_0('could not find arguments in the checkpoint ...')

    # rng states.
    if not release and not args.finetune and not args.no_load_rng:
        try:
            random.setstate(state_dict['random_rng_state'])
            np.random.set_state(state_dict['np_rng_state'])
            torch.set_rng_state(state_dict['torch_rng_state'])
            torch.cuda.set_rng_state(state_dict['cuda_rng_state'])
            mpu.get_cuda_rng_tracker().set_states(
                state_dict['rng_tracker_states'])
        except KeyError:
            print_rank_0('Unable to load optimizer from checkpoint {}. '
                         'Specify --no-load-rng or --finetune to prevent '
                         'attempting to load the optimizer state, '
                         'exiting ...'.format(checkpoint_name))
            sys.exit()

    torch.distributed.barrier()
    if mpu.get_data_parallel_rank() == 0:
        print('  successfully loaded {}'.format(checkpoint_name))

    return iteration
