# Copyright (c) 2021, 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.

"""GPT style dataset."""

import os
import time

import numpy as np
import torch

from nemo.collections.nlp.data.language_modeling.megatron.blendable_dataset import BlendableDataset
from nemo.collections.nlp.data.language_modeling.megatron.dataset_utils import (
    get_datasets_weights_and_num_samples,
    get_train_valid_test_split_,
)
from nemo.collections.nlp.data.language_modeling.megatron.indexed_dataset import make_dataset as make_indexed_dataset
from nemo.collections.nlp.data.language_modeling.megatron.megatron_dataset import MegatronDataset
from nemo.utils import logging

try:
    from apex.transformer import parallel_state

    HAVE_APEX = True

except (ImportError, ModuleNotFoundError):

    HAVE_APEX = False


def build_train_valid_test_datasets(
    cfg, trainer, data_prefix, data_impl, splits_string, train_valid_test_num_samples, seq_length, seed, skip_warmup
):
    """Build train, valid, and test datasets."""

    # Single dataset.
    if len(data_prefix) == 1:
        return _build_train_valid_test_datasets(
            cfg,
            trainer,
            data_prefix[0],
            data_impl,
            splits_string,
            train_valid_test_num_samples,
            seq_length,
            seed,
            skip_warmup,
        )

    # Blending dataset.
    # Parse the values.
    output = get_datasets_weights_and_num_samples(data_prefix, train_valid_test_num_samples)
    prefixes, weights, datasets_train_valid_test_num_samples = output

    # Build individual datasets.
    train_datasets = []
    valid_datasets = []
    test_datasets = []
    for i in range(len(prefixes)):
        train_ds, valid_ds, test_ds = _build_train_valid_test_datasets(
            cfg,
            trainer,
            prefixes[i],
            data_impl,
            splits_string,
            datasets_train_valid_test_num_samples[i],
            seq_length,
            seed,
            skip_warmup,
        )
        if train_ds:
            train_datasets.append(train_ds)
        if valid_ds:
            valid_datasets.append(valid_ds)
        if test_ds:
            test_datasets.append(test_ds)

    # Blend.
    blending_train_dataset = None
    if train_datasets:
        blending_train_dataset = BlendableDataset(train_datasets, weights)
    blending_valid_dataset = None
    if valid_datasets:
        blending_valid_dataset = BlendableDataset(valid_datasets, weights)
    blending_test_dataset = None
    if test_datasets:
        blending_test_dataset = BlendableDataset(test_datasets, weights)

    return (blending_train_dataset, blending_valid_dataset, blending_test_dataset)


def _build_train_valid_test_datasets(
    cfg, trainer, data_prefix, data_impl, splits_string, train_valid_test_num_samples, seq_length, seed, skip_warmup
):
    """Build train, valid, and test datasets."""

    # Indexed dataset.
    indexed_dataset = get_indexed_dataset_(data_prefix, data_impl, skip_warmup)

    total_num_of_documents = indexed_dataset.sizes.shape[0]
    splits = get_train_valid_test_split_(splits_string, total_num_of_documents)

    # Print stats about the splits.
    logging.info(' > dataset split:')

    def print_split_stats(name, index):
        logging.info('    {}:'.format(name))
        logging.info(
            '     document indices in [{}, {}) total of {} '
            'documents'.format(splits[index], splits[index + 1], splits[index + 1] - splits[index])
        )

    print_split_stats('train', 0)
    print_split_stats('validation', 1)
    print_split_stats('test', 2)

    def build_dataset(index, name):
        dataset = None
        if splits[index + 1] > splits[index]:
            documents = np.arange(start=splits[index], stop=splits[index + 1], step=1, dtype=np.int32)
            dataset = GPTDataset(
                cfg,
                trainer,
                name,
                data_prefix,
                documents,
                indexed_dataset,
                train_valid_test_num_samples[index],
                seq_length,
                seed,
            )
        return dataset

    train_dataset = build_dataset(0, 'train')
    valid_dataset = build_dataset(1, 'valid')
    test_dataset = build_dataset(2, 'test')

    return (train_dataset, valid_dataset, test_dataset)


def get_indexed_dataset_(data_prefix, data_impl, skip_warmup):
    """Build indexed dataset."""
    logging.info(' > building dataset index ...')

    start_time = time.time()
    indexed_dataset = make_indexed_dataset(data_prefix, data_impl, skip_warmup)
    logging.info(' > finished creating indexed dataset in {:4f} ' 'seconds'.format(time.time() - start_time))
    logging.info('    number of documents: {}'.format(indexed_dataset.sizes.shape[0]))

    return indexed_dataset


class GPTDataset(MegatronDataset):
    def __init__(self, cfg, trainer, name, data_prefix, documents, indexed_dataset, num_samples, seq_length, seed):
        if not HAVE_APEX:
            raise ImportError(
                "Apex was not found. Please see the NeMo README for installation instructions: https://github.com/NVIDIA/NeMo#megatron-gpt."
            )

        super().__init__(cfg, trainer=trainer)
        self.name = name
        self.indexed_dataset = indexed_dataset

        # Checks
        assert np.min(documents) >= 0
        assert np.max(documents) < indexed_dataset.sizes.shape[0]

        # Build index mappings.
        self.doc_idx, self.sample_idx, self.shuffle_idx = _build_index_mappings(
            self.name, data_prefix, documents, self.indexed_dataset.sizes, num_samples, seq_length, seed
        )

    def __len__(self):
        # -1 is due to data structure used to retieve the index:
        #    sample i --> [sample_idx[i], sample_idx[i+1])
        return self.sample_idx.shape[0] - 1

    def __getitem__(self, idx):
        # Get the shuffled index.
        idx = self.shuffle_idx[idx]
        # Start and end documents and offsets.
        doc_index_f = self.sample_idx[idx][0]
        doc_index_l = self.sample_idx[idx + 1][0]
        offset_f = self.sample_idx[idx][1]
        offset_l = self.sample_idx[idx + 1][1]
        # If we are within the same document, just extract the chunk.
        if doc_index_f == doc_index_l:
            sample = self.indexed_dataset.get(
                self.doc_idx[doc_index_f], offset=offset_f, length=offset_l - offset_f + 1
            )
        else:
            # Otherwise, get the rest of the initial document.
            sample_list = [self.indexed_dataset.get(self.doc_idx[doc_index_f], offset=offset_f)]
            # Loop over all in between documents and add the entire document.
            for i in range(doc_index_f + 1, doc_index_l):
                sample_list.append(self.indexed_dataset.get(self.doc_idx[i]))
            # And finally add the relevant portion of last document.
            sample_list.append(self.indexed_dataset.get(self.doc_idx[doc_index_l], length=offset_l + 1))
            sample = np.concatenate(sample_list)

        return {'text': np.array(sample, dtype=np.int64)}


def _build_index_mappings(name, data_prefix, documents, sizes, num_samples, seq_length, seed):
    """Build doc-idx, sample-idx, and shuffle-idx.
    doc-idx: is an array (ordered) of documents to be used in training.
    sample-idx: is the start document index and document offset for each
       training sample.
    shuffle-idx: maps the sample index into a random index into sample-idx.
    """
    # Number of tokens in each epoch and number of required epochs.
    tokens_per_epoch = _num_tokens(documents, sizes)
    num_epochs = _num_epochs(tokens_per_epoch, seq_length, num_samples)
    # rng state
    np_rng = np.random.RandomState(seed=seed)

    # Filename of the index mappings.
    _filename = data_prefix
    _filename += '_{}_indexmap'.format(name)
    _filename += '_{}ns'.format(num_samples)
    _filename += '_{}sl'.format(seq_length)
    _filename += '_{}s'.format(seed)
    doc_idx_filename = _filename + '_doc_idx.npy'
    sample_idx_filename = _filename + '_sample_idx.npy'
    shuffle_idx_filename = _filename + '_shuffle_idx.npy'

    # Build the indexed mapping if not exist.
    if torch.distributed.get_rank() == 0:
        if (
            (not os.path.isfile(doc_idx_filename))
            or (not os.path.isfile(sample_idx_filename))
            or (not os.path.isfile(shuffle_idx_filename))
        ):

            logging.info(' > WARNING: could not find index map files, building ' 'the indices on rank 0 ...')

            # For the last epoch, decide whether include the entire epoch
            # in the global shuffle or not.

            # If we need only one epoch, then separating last epoch  does
            # not mean anything.
            if num_epochs == 1:
                separate_last_epoch = False
                print(' > only one epoch required, setting ' 'separate_last_epoch to False', flush=True)

            else:
                # Get the number of samples for the last epoch
                num_samples_from_epochs_minus_one = ((num_epochs - 1) * tokens_per_epoch - 1) // seq_length
                last_epoch_num_samples = num_samples - num_samples_from_epochs_minus_one
                assert last_epoch_num_samples >= 0, 'last epoch number of samples should be non-negative.'
                num_samples_per_epoch = (tokens_per_epoch - 1) // seq_length
                assert last_epoch_num_samples < (
                    num_samples_per_epoch + 1
                ), 'last epoch number of samples exceeded max value.'
                # If we have less than 80% of the samples for the last epoch,
                # seperate out the epoch and treat it differently.
                # Note: the 80% number is just based on common sense and can
                # be adjusted if needed.
                separate_last_epoch = last_epoch_num_samples < int(0.80 * num_samples_per_epoch)
                if separate_last_epoch:
                    string = (
                        ' > last epoch number of samples ({}) is smaller '
                        'than 80% of number of samples per epoch ({}), '
                        'setting separate_last_epoch to True'
                    )
                else:
                    string = (
                        ' > last epoch number of samples ({}) is larger '
                        'than 80% of number of samples per epoch ({}), '
                        'setting separate_last_epoch to False'
                    )
                print(string.format(last_epoch_num_samples, num_samples_per_epoch), flush=True)

            # doc-idx.
            start_time = time.time()
            doc_idx = _build_doc_idx(documents, num_epochs, np_rng, separate_last_epoch)
            np.save(doc_idx_filename, doc_idx, allow_pickle=True)
            logging.info(
                ' > elasped time to build and save doc-idx mapping '
                '(seconds): {:4f}'.format(time.time() - start_time)
            )
            # sample-idx.
            start_time = time.time()
            # Use C++ implementation for speed.
            # First compile and then import.
            assert doc_idx.dtype == np.int32
            assert sizes.dtype == np.int32
            try:
                from nemo.collections.nlp.data.language_modeling.megatron.dataset_utils import compile_helper

                compile_helper()
                from nemo.collections.nlp.data.language_modeling.megatron import helpers
            except ImportError:
                raise ImportError(
                    f'Could not compile megatron dataset C++ helper functions and therefore cannot import helpers python file.'
                )

            sample_idx = helpers.build_sample_idx(sizes, doc_idx, seq_length, num_epochs, tokens_per_epoch)
            # sample_idx = _build_sample_idx(sizes, doc_idx, seq_length,
            #                               num_epochs, tokens_per_epoch)
            np.save(sample_idx_filename, sample_idx, allow_pickle=True)
            logging.info(
                ' > elasped time to build and save sample-idx mapping '
                '(seconds): {:4f}'.format(time.time() - start_time)
            )
            # shuffle-idx.
            start_time = time.time()
            # -1 is due to data structure used to retieve the index:
            #    sample i --> [sample_idx[i], sample_idx[i+1])
            if separate_last_epoch:
                num_samples_ = num_samples_from_epochs_minus_one
            else:
                num_samples_ = sample_idx.shape[0] - 1
            shuffle_idx = _build_shuffle_idx(num_samples_, sample_idx.shape[0] - 1, np_rng)
            np.save(shuffle_idx_filename, shuffle_idx, allow_pickle=True)
            logging.info(
                ' > elasped time to build and save shuffle-idx mapping'
                ' (seconds): {:4f}'.format(time.time() - start_time)
            )

    torch.distributed.barrier()
    counts = torch.cuda.LongTensor([1])
    torch.distributed.all_reduce(counts, group=parallel_state.get_data_parallel_group())
    torch.distributed.all_reduce(counts, group=parallel_state.get_pipeline_model_parallel_group())
    assert counts[0].item() == (
        torch.distributed.get_world_size()
        // torch.distributed.get_world_size(group=parallel_state.get_tensor_model_parallel_group())
    )

    # Load mappings.
    start_time = time.time()
    logging.info(' > loading doc-idx mapping from {}'.format(doc_idx_filename))
    doc_idx = np.load(doc_idx_filename, allow_pickle=True, mmap_mode='r')
    logging.info(' > loading sample-idx mapping from {}'.format(sample_idx_filename))
    sample_idx = np.load(sample_idx_filename, allow_pickle=True, mmap_mode='r')
    logging.info(' > loading shuffle-idx mapping from {}'.format(shuffle_idx_filename))
    shuffle_idx = np.load(shuffle_idx_filename, allow_pickle=True, mmap_mode='r')
    logging.info('    loaded indexed file in {:3.3f} seconds'.format(time.time() - start_time))
    logging.info('    total number of samples: {}'.format(sample_idx.shape[0]))
    logging.info('    total number of epochs: {}'.format(num_epochs))

    return doc_idx, sample_idx, shuffle_idx


def _num_tokens(documents, sizes):
    """Total number of tokens in the dataset."""
    return np.sum(sizes[documents])


def _num_epochs(tokens_per_epoch, seq_length, num_samples):
    """Based on number of samples and sequence lenght, calculate how many
    epochs will be needed."""
    num_epochs = 0
    total_tokens = 0
    while True:
        num_epochs += 1
        total_tokens += tokens_per_epoch
        # -1 is because we need to retrieve seq_length + 1 token each time
        # but the last token will overlap with the first token of the next
        # sample except for the last sample.
        if ((total_tokens - 1) // seq_length) >= num_samples:
            return num_epochs


def _build_doc_idx(documents, num_epochs, np_rng, separate_last_epoch):
    """Build an array with length = number-of-epochs * number-of-dcuments.
    Each index is mapped to a corresponding document."""
    if not separate_last_epoch or num_epochs == 1:
        doc_idx = np.mgrid[0:num_epochs, 0 : len(documents)][1]
        doc_idx[:] = documents
        doc_idx = doc_idx.reshape(-1)
        doc_idx = doc_idx.astype(np.int32)
        np_rng.shuffle(doc_idx)
        return doc_idx

    doc_idx_first = _build_doc_idx(documents, num_epochs - 1, np_rng, False)
    doc_idx_last = _build_doc_idx(documents, 1, np_rng, False)
    return np.concatenate((doc_idx_first, doc_idx_last))


def _build_sample_idx(sizes, doc_idx, seq_length, num_epochs, tokens_per_epoch):
    """Sample index mapping is a 2D array with sizes
    [number-of-samples + 1, 2] where [..., 0] contains
    the index into `doc_idx` and [..., 1] is the
    starting offset in that document."""

    # Total number of samples. For -1 see comments in `_num_epochs`.
    num_samples = (num_epochs * tokens_per_epoch - 1) // seq_length
    sample_idx = np.zeros([num_samples + 1, 2], dtype=np.int32)

    # Index into sample_idx.
    sample_index = 0
    # Index into doc_idx.
    doc_idx_index = 0
    # Begining offset for each document.
    doc_offset = 0
    # Start with first document and no offset.
    sample_idx[sample_index][0] = doc_idx_index
    sample_idx[sample_index][1] = doc_offset
    sample_index += 1
    while sample_index <= num_samples:
        # Start with a fresh sequence.
        remaining_seq_length = seq_length + 1
        while remaining_seq_length != 0:
            # Get the document length.
            doc_id = doc_idx[doc_idx_index]
            doc_length = sizes[doc_id] - doc_offset
            # And add it to the current sequence.
            remaining_seq_length -= doc_length
            # If we have more than a full sequence, adjust offset and set
            # remaining length to zero so we return from the while loop.
            # Note that -1 here is for the same reason we have -1 in
            # `_num_epochs` calculations.
            if remaining_seq_length <= 0:
                doc_offset += remaining_seq_length + doc_length - 1
                remaining_seq_length = 0
            else:
                # Otherwise, start from the begining of the next document.
                doc_idx_index += 1
                doc_offset = 0
        # Record the sequence.
        sample_idx[sample_index][0] = doc_idx_index
        sample_idx[sample_index][1] = doc_offset
        sample_index += 1

    return sample_idx


def _build_shuffle_idx(num_samples, total_size, np_rng):
    """Build the range [0, size) and shuffle."""
    print(
        ' > building shuffle index with split [0, {}) and [{}, {}) '
        '...'.format(num_samples, num_samples, total_size),
        flush=True,
    )

    dtype_ = np.uint32
    if total_size >= (np.iinfo(np.uint32).max - 1):
        dtype_ = np.int64

    shuffle_idx_first = np.arange(start=0, stop=num_samples, step=1, dtype=dtype_)
    np_rng.shuffle(shuffle_idx_first)
    if num_samples == total_size:
        return shuffle_idx_first

    shuffle_idx_last = np.arange(start=num_samples, stop=total_size, step=1, dtype=dtype_)
    np_rng.shuffle(shuffle_idx_last)

    return np.concatenate((shuffle_idx_first, shuffle_idx_last))
