# Copyright (c) 2021, EleutherAI
# 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.

"""Merge model parallel partitions."""

import os
import sys

sys.path.append(
    os.path.abspath(os.path.join(os.path.dirname(__file__), os.path.pardir))
)

import torch

from megatron import mpu
from megatron.checkpointing import ensure_directory_exists
from megatron.checkpointing import get_checkpoint_name
from megatron.checkpointing import get_checkpoint_tracker_filename
from megatron.global_vars import rebuild_tokenizer
from megatron.global_vars import _parse_args


def split_into_partitions(tensor, num_partitions, partition_dim, stride):

    per_partition_size = mpu.utils.divide(tensor.size(partition_dim), num_partitions)
    per_partition_per_stride_size = mpu.utils.divide(per_partition_size, stride)

    partitions_list = torch.split(
        tensor, per_partition_per_stride_size, dim=partition_dim
    )

    partitions = []
    for i in range(num_partitions):
        partition = torch.cat(partitions_list[i::num_partitions], dim=partition_dim)
        partitions.append(partition)

    return partitions


def merge_partitions(merged, partitions, partition_dim, stride):

    # Number and size of each partition.
    num_partitions = len(partitions)
    per_partition_size = None
    for partition in partitions:
        if per_partition_size is None:
            per_partition_size = partition.size(partition_dim)
        else:
            assert per_partition_size == partition.size(partition_dim)

    def concat_partitions(partitions_):
        with torch.no_grad():
            if (per_partition_size * num_partitions) == merged.size(partition_dim):
                torch.cat(partitions_, dim=partition_dim, out=merged)
            else:
                print(
                    "     ***WARNING*** sizes do not match. Will cut "
                    "the merged partitions by {} along dimension {} "
                    "to reduce the size from {} to {} ...".format(
                        (per_partition_size * num_partitions)
                        - merged.size(partition_dim),
                        partition_dim,
                        per_partition_size * num_partitions,
                        merged.size(partition_dim),
                    )
                )
                merged_ = torch.cat(partitions_, dim=partition_dim)
                merged_split = torch.split(
                    merged_, merged.size(partition_dim), dim=partition_dim
                )
                merged_ = merged_split[0]
                assert merged_.size(partition_dim) == merged.size(partition_dim)
                merged.data.copy_(merged_.data)

    # If stride is 1, then do simple concatenation.
    if stride == 1:
        concat_partitions(partitions)
        return

    # For none unity strides, first split based on stride and then group.
    per_partition_per_stride_size = mpu.utils.divide(per_partition_size, stride)
    # Chunk and build a list.
    chunks = None
    for i, partition in enumerate(partitions):
        chunk = torch.split(partition, per_partition_per_stride_size, dim=partition_dim)

        if chunks is None:
            chunks = [0] * (num_partitions * len(chunk))
        chunks[i::num_partitions] = chunk

    # Concatinate.
    concat_partitions(chunks)

    return


def get_model(model_type):

    if model_type == "GPT2":
        from pretrain_gpt2 import model_provider
    else:
        raise Exception("unrecognized model type: {}".format(model_type))

    model = model_provider()
    model = model.half()

    return model


def get_parallel_checkpoint_name(path):

    tracker_filename = get_checkpoint_tracker_filename(path)
    iteration = 0
    with open(tracker_filename, "r") as f:
        metastring = f.read().strip()
        iteration = int(metastring)
    assert iteration > 0
    checkpoint_name = get_checkpoint_name(path, iteration)

    return checkpoint_name, iteration


def test_split_merge():

    print("testing split and merge ...")

    # [QKV.ROW-COL]
    tensor = torch.FloatTensor(
        [
            [1.11, 1.12, 1.13, 1.14, 1.15],
            [1.21, 1.22, 1.23, 1.24, 1.25],
            [1.31, 1.32, 1.33, 1.34, 1.35],
            [1.41, 1.42, 1.43, 1.44, 1.45],
            [2.11, 2.12, 2.13, 2.14, 2.15],
            [2.21, 2.22, 2.23, 2.24, 2.25],
            [2.31, 2.32, 2.33, 2.34, 2.35],
            [2.41, 2.42, 2.43, 2.44, 2.45],
            [3.11, 3.12, 3.13, 3.14, 3.15],
            [3.21, 3.22, 3.23, 3.24, 3.25],
            [3.31, 3.32, 3.33, 3.34, 3.35],
            [3.41, 3.42, 3.43, 3.44, 3.45],
        ]
    )

    num_partitions = 2
    partition_dim = 0
    stride = 3
    partitions = split_into_partitions(tensor, num_partitions, partition_dim, stride)

    merged = torch.zeros_like(tensor)
    merge_partitions(merged, partitions, partition_dim, stride)

    max_error = (merged - tensor).abs().max()
    print("  > max error (should be zero): {}".format(max_error))


def get_mp_merge_args(parser):
    """Provide extra arguments required for merging."""
    group = parser.add_argument_group(title="mp merge")

    group.add_argument(
        "--model-type",
        type=str,
        required=True,
        choices=["BERT", "GPT2", "RACE", "MNLI", "QQP"],
        help="Type of the model.",
    )

    return parser


def main():

    # Args
    args = _parse_args(extra_args_provider=get_mp_merge_args)
    model_type = args.model_type
    orig_model_parallel_size = args.model_parallel_size
    args.model_parallel_size = 1
    tokenizer = rebuild_tokenizer(args)

    print("\n merging model parallel partitions ...")
    print(" > number of partitions: {}".format(orig_model_parallel_size))
    print(" > checkpoint path: {}".format(args.load))
    print(" > model parameters:")
    print("    number of tokens ................ {} ".format(tokenizer.vocab_size))
    print("    number of layers ................ {}".format(args.num_layers))
    print("    hidden size ..................... {}".format(args.hidden_size))
    print("    number of attention heads ....... {}".format(args.num_attention_heads))
    print(
        "    maximum position embeddings ..... {}".format(args.max_position_embeddings)
    )

    # Full model.
    print("> building the full model ...")
    mpu.initialize.set_model_parallel_world_size(1)
    mpu.initialize.set_model_parallel_rank(0)
    merged_model = get_model(model_type)

    # Build and load partitions.
    partitions = []
    iteration = 0
    args.model_parallel_size = orig_model_parallel_size
    tokenizer = rebuild_tokenizer(args)
    mpu.initialize.set_model_parallel_world_size(args.model_parallel_size)
    for rank in range(args.model_parallel_size):
        mpu.initialize.set_model_parallel_rank(rank)
        checkpoint_name, iteration = get_parallel_checkpoint_name(args.load)
        print("> loading {} ...".format(checkpoint_name))
        model_ = get_model(model_type)
        sd = torch.load(checkpoint_name, map_location="cpu")
        model_.load_state_dict(sd["model"])
        partitions.append(model_)

    # Parameter generators so we can loop through them semiltaneouly.
    merged_params_gen = merged_model.named_parameters()
    partitions_params_gen = [partition.named_parameters() for partition in partitions]
    while True:
        try:

            # Get the params and check names.
            name, merged_param = next(merged_params_gen)
            print(" > working on {} ...".format(name))
            print(
                "     merged         type: {}, size: {}".format(
                    merged_param.dtype, list(merged_param.size())
                )
            )
            partitions_param = []
            for rank, partition_params_gen in enumerate(partitions_params_gen):
                partition_name, partition_param = next(partition_params_gen)
                assert partition_name == name
                partitions_param.append(partition_param)
                print(
                    "     partition {}    type: {}, size: {}".format(
                        rank, partition_param.dtype, list(partition_param.size())
                    )
                )

            # For the non-parallel parameters, simply copy the rank 0 values.
            if not hasattr(merged_param, "model_parallel"):
                print("     none-parallel parameter, simple copy from rank 0")
                with torch.no_grad():
                    merged_param.data.copy_(partitions_param[0].data)
            # For parallel parameters, merge the values
            else:
                print(
                    "     parallel parameter merge with stride {} along "
                    "dimension {}".format(
                        merged_param.stride, merged_param.partition_dim
                    )
                )
                merge_partitions(
                    merged_param,
                    partitions_param,
                    merged_param.partition_dim,
                    merged_param.stride,
                )

        except StopIteration:
            break

    # Save the model.
    args.model_parallel_size = 1
    mpu.initialize.set_model_parallel_rank(0)
    sd = {}
    sd["model"] = merged_model.state_dict()
    sd["iteration"] = iteration
    merged_path = os.path.join(args.load, "merged")
    checkpoint_name = get_checkpoint_name(merged_path, iteration)
    ensure_directory_exists(checkpoint_name)
    print("> saving merged model to {}".format(checkpoint_name))
    torch.save(sd, checkpoint_name)

    print("done :-)")


if __name__ == "__main__":

    main()