# coding=utf-8
# 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 random
import sys
import numpy as np

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

from megatron import mpu
from megatron import get_args
from megatron import print_rank_0


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

    # Only rank zero of the data parallel writes to the disk.
    if isinstance(model, torchDDP):
        model = model.module
    if mpu.get_data_parallel_rank() == 0:

        # Arguments, iteration, and model.
        state_dict = {}
        state_dict['args'] = args
        state_dict['iteration'] = iteration
        state_dict['model'] = model.state_dict_for_save_checkpoint()

        # Optimizer stuff.
        if not args.no_save_optim:
            if optimizer is not None:
                state_dict['optimizer'] = optimizer.state_dict()
            if lr_scheduler is not None:
                state_dict['lr_scheduler'] = lr_scheduler.state_dict()

        # RNG states.
        if not args.no_save_rng:
            state_dict['random_rng_state'] = random.getstate()
            state_dict['np_rng_state'] = np.random.get_state()
            state_dict['torch_rng_state'] = torch.get_rng_state()
            state_dict['cuda_rng_state'] = torch.cuda.get_rng_state()
            state_dict['rng_tracker_states'] \
                = mpu.get_cuda_rng_tracker().get_states()

        # Save.
        checkpoint_name = get_checkpoint_name(args.save, iteration)
        print('global rank {} is saving checkpoint at iteration {:7d} to {}'.
              format(torch.distributed.get_rank(), iteration, checkpoint_name))
        ensure_directory_exists(checkpoint_name)
        torch.save(state_dict, checkpoint_name)
        print('  successfully saved {}'.format(checkpoint_name))

    # 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 (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)

    # Checkpoint.
    checkpoint_name = get_checkpoint_name(load_dir, iteration, release)
    if mpu.get_data_parallel_rank() == 0:
        print('global rank {} is loading checkpoint {}'.format(
            torch.distributed.get_rank(), checkpoint_name))

    # Load the checkpoint.
    try:
        state_dict = torch.load(checkpoint_name, map_location='cpu')
    except ModuleNotFoundError:
        # For backward compatibility.
        print_rank_0(' > deserializing using the old code structure ...')
        sys.modules['fp16.loss_scaler'] = sys.modules[
            'megatron.fp16.loss_scaler']
        state_dict = torch.load(checkpoint_name, map_location='cpu')
        sys.modules.pop('fp16.loss_scaler', None)
    except BaseException:
        print_rank_0('could not load the checkpoint')
        sys.exit()

    # 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 ...')

    # Model.
    model.load_state_dict(state_dict['model'])

    # Optimizer.
    if not release and not args.finetune and not args.no_load_optim:
        try:
            if optimizer is not None:
                optimizer.load_state_dict(state_dict['optimizer'])
            if lr_scheduler is not None:
                lr_scheduler.load_state_dict(state_dict['lr_scheduler'])
        except KeyError:
            print_rank_0('Unable to load optimizer from checkpoint {}. '
                         'Specify --no-load-optim or --finetune to prevent '
                         'attempting to load the optimizer state, '
                         'exiting ...'.format(checkpoint_name))
            sys.exit()

    # 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