#   Copyright (c) 2021 PaddlePaddle Authors. 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.

# The file has been adapted from fairscale file:
# https://github.com/facebookresearch/fairscale/blob/main/fairscale/nn/data_parallel/sharded_ddp.py
# Git commit hash: 8acbec718f3c70a6b9785470bb9e05cd84fc3f8e
# We retain the following license from the original files:

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

import os
import contextlib
import logging
import time
import functools
import numpy as np
from itertools import chain
from functools import reduce
from collections import deque
from types import MethodType

import paddle
from paddle import nn
from paddle.distributed import collective as dist
from paddle.distributed.collective import _get_global_group

from ...utils.internal_storage import GradStorage
from ...meta_optimizers.dygraph_optimizer.sharding_optimizer_stage2 import ShardingOptimizerStage2
from .sharding_utils import Taskflow, Type


def _trainable(param):
    return param.trainable


class ShardingStage2(nn.Layer):
    """ 
    A wrapper for Sharding Stage2 Layer in Dygraph. 
    .. warning: ShardingStage2 encapsulates the layer strategy and integrates it into the nn.Layer.
    .. ZeRO: https://arxiv.org/pdf/1910.02054.pdf.
    """

    # TODO (Baibaifan)
    # Feature Notes::
    # 1. Unified memory for param and param.grad to InternalStorage.
    # 2. Divide param.grad according to rank to centrally apply for and release GPU memory.
    # 3. Dynamically adjust training parameters and models.
    # 4. Support offload function.
    # 5. Support the establishment of independent communication groups.

    def __init__(
            self,
            layer,
            sharding_optimizer,
            group=None,
            sync_buffers=False,
            buffer_max_size=2**23,  #8MB
            auto_refresh_trainable=True,
            device="gpu"):
        super().__init__()

        # training options
        self._layer = layer
        self._sharding_optimizers = [
            sharding_optimizer
        ] if not isinstance(sharding_optimizer, list) else sharding_optimizer
        assert all(
            list(
                map(lambda opt: isinstance(opt, ShardingOptimizerStage2),
                    self._sharding_optimizers))
        ), "Please use ShardingOptimizerStage2 optimizer"
        self._sync_buffers = sync_buffers
        self._auto_refresh_trainable = auto_refresh_trainable

        # Communication related attributes
        self._group = dist.new_group(
            _get_global_group().ranks) if group is None else group
        self._world_size_scaling = 1.0 / self._group.nranks
        assert self._group.nranks > 1, "Training must be distributed, ranks must be greater than 1"
        self._rank = self._group.rank
        self._global_root_rank = self._group.ranks[
            0]  # picking rank 0 as the reference
        self._default_device = device

        # Global statistical parameters
        self._all_params = list(
            chain(*[optim.local_params for optim in self._sharding_optimizers]))
        self._trainable_params = []
        self._grad_reduced = []
        self._trainable_param2rank = {}
        self._trainable_param2align = {}
        self._trainable_mask = list(map(_trainable, self._all_params))
        self._param_grads = []

        # Set grad storage size & Display param sizes and model sizes
        model_size = sum([np.prod(p.shape)
                          for p in self._layer.parameters()]).item()
        assert buffer_max_size >= 0, "buffer_max_size must be GE than 0."
        self._buffer_max_size = self._rank_buffer_size(buffer_max_size,
                                                       model_size)
        self._use_grad_storage = buffer_max_size > 0
        self._grad_storages = {}  # {dtype: {rank: GradStorage}}
        self._has_grad_storage = []
        self._grad_storage_list = []

        # Offload
        # TODO(haohongxiang): Now it's not be supported for multi-optimizers using Offload strategy
        self._offload_optims = list(
            filter(lambda optim: optim.offload, self._sharding_optimizers))
        if len(self._offload_optims) > 0:
            assert len(
                self._sharding_optimizers
            ) == 1, "Only support offload strategy for single optimizer"

        self._offload = self._sharding_optimizers[0].offload
        self._offload_device = "cpu"

        # Set backward pass hooks
        self._bw_hooks = []

        # Set tasks flow
        self._tasks_flow = deque()

        # Define optimizer step and clear_grad
        self._redefine_opt_step()
        self._redefine_opt_clear()

    def forward(self, *inputs, **kwargs):
        """
        A wrapper for Sharding Stage2 layer.
        - Fresh trainable params or rebuild grad storage
        - Sync layer's buffer params
        - Clear all flags states
        - Forward for origin layers
        """

        # Whether to need to reset trainable parameters
        needs_fresh = len(self._bw_hooks) == 0 and self.training

        if self._auto_refresh_trainable:
            needs_fresh |= self._detect_train_change()

        # Front hook
        self._init_internal_storage(needs_fresh)

        # Sync layer's buffers state
        if self._sync_buffers:
            self.__sync_buffers()

        # Normal FW on the base model
        fw = self._layer(*inputs, **kwargs)

        return fw

    def set_state_dict(self, state_dict, use_structured_name=True):
        self._layer.set_state_dict(state_dict,
                                   use_structured_name=use_structured_name)

    def state_dict(self,
                   destination=None,
                   include_sublayers=True,
                   structured_name_prefix=""):
        return self._layer.state_dict(destination=None,
                                      include_sublayers=True,
                                      structured_name_prefix="")

    def _clear_gradients(self):
        """
        Set zero to the gradient of the optimizer's current rank trainable parameters.
        """
        # Release grad storages
        for dtype in self._grad_storages.keys():
            if not self._offload and self._rank in self._grad_storages[
                    dtype].keys():
                self._grad_storages[dtype][self._rank].buffer.zero_()

        # Release grads of params
        for param in self._trainable_params:
            if param.name in self._param_grads and param.grad is not None:
                param.clear_gradient()

        # Release grads of master params with offload strategy
        if self._offload:
            self._sharding_optimizers[0]._offload_clear_grad()

    def _grad_scale(self):
        """
        Before the gradient accumulation, scale the gradient.
        """
        # Scale grad storages
        for dtype in self._grad_storages.keys():
            if not self._offload and self._rank in self._grad_storages[
                    dtype].keys():
                self._grad_storages[dtype][self._rank].buffer.scale_(
                    scale=self._world_size_scaling)

        # Scale grads of params
        for param in self._trainable_params:
            if param.name in self._param_grads and param.grad is not None:
                param.grad.scale_(scale=self._world_size_scaling)
                param._reset_grad_inplace_version(True)

        # Scale grads of master params with offload strategy
        if self._offload:
            self._sharding_optimizers[0]._offload_scale_grad(
                self._world_size_scaling)

    def _init_internal_storage(self, needs_fresh):
        """
        Judge Fresh trainable params or rebuild grad storage.
        """
        if needs_fresh:
            self._fresh_trainable()
        else:
            self._build_grad_storages()

        # Clear all flags state
        self._clear_counters()

    def to(self, device=None, dtype=None, blocking=True):
        """
        Synchronously or asynchronously convert the data type of the layer, the device is not supported now.
        """
        assert isinstance(device, str), "Device must be type str"
        assert device == self._default_device, "New devices are not supported, because of the optimizer state is not sync"

        self._layer.to(device=device, dtype=dtype, blocking=blocking)

        # Re-build the buckets, hooks, etc..
        self._fresh_trainable()

    def _fresh_trainable(self):
        """ Whether to update training parameters. """

        # Make sure that this is not done while gradients are waiting to be reduced (if no_sync context for instance)
        if reduce(lambda x, y: x or y, self._grad_reduced, False):
            logging.warning("Grads waiting to be reduced.")

        self._trainable_params = list(
            filter(lambda x: x.trainable, self._all_params))
        self._trainable_params.sort(key=lambda x: np.prod(x.shape))

        self._trainable_param2rank = {}
        for optim in self._sharding_optimizers:
            # Need to be wrappered for Sharding Stage2 Optimizer
            if len(optim.param_storages.keys()) == 0:
                optim.update_opt_status()

            # Get the parameters split by the optimizer according to rank
            for per_rank_params in optim.dtype_rank_params.values(
            ):  # all the params from all ranks
                for params in per_rank_params:
                    for param in filter(lambda x: x.trainable, params):
                        self._trainable_param2rank[
                            param.name] = optim.param2rank[param.name]
                        self._trainable_param2align[
                            param.name] = optim._param2align[param.name]

        self._setup_use_grad_storage()

        # wait next func hook support
        self._setup_backward_hooks()

    @paddle.autograd.no_grad()
    def __sync_buffers(self):
        """
        Sync all the param buffers from all ranks (exp: batch norm statistics).
        """

        for buffer in self._layer.buffers(include_sublayers=True):
            dist.broadcast(buffer,
                           self._global_root_rank,
                           self._group,
                           use_calc_stream=True)
        # Multi stream operation will be supported later
        dist.wait(tensor=buffer, group=self._group, use_calc_stream=True)

    def __getattr__(self, name):
        """Forward missing attributes to wrapped layer."""
        try:
            return super().__getattr__(name)
        except AttributeError:
            return getattr(self._layer, name)

    @paddle.autograd.no_grad()
    def _clear_counters(self):
        """Reset all the grad reduce and call counters."""
        if self.training:
            self._grad_reduced = [True for _ in self._trainable_params]

        if self._use_grad_storage:
            for grad_storage in self._grad_storage_list:
                grad_storage.reset_checked_in()

    def _get_reduce_fn(self, index, param, dst_rank):
        """
        There are two ways to reduce gradient.
        - 1. Do not use self._use_grad_storage or exceeded buffer_max_size will be reduced separately.
        - 2. Use grad_storage Reduce the storage to get the full gradient from different ranks.
        """

        if not self._use_grad_storage or not self._has_grad_storage[index]:
            # Direct reduction
            @paddle.autograd.no_grad()
            def reduce(*_):
                # Skip gradient reduction, do not change status information
                if self._grad_reduced[index]:
                    assert param.grad is not None, "Parameter gradient cannot be None"

                    # Change reduce information
                    self._grad_reduced[index] = False

                    # Clear the gradient that does not belong to the current rank through the callback function
                    def cleanup():
                        if dst_rank != self._rank:
                            param.clear_gradient(False)
                        elif self._offload:
                            self._sharding_optimizers[0]._offload_acc_grad(
                                param.name,
                                param.grad.cast(dtype=Type.fp32.value).cpu())
                            param.clear_gradient(False)

                    # Synchronize the reduce parameter gradient
                    self._tasks_flow.append(
                        Taskflow(task=dist.reduce(
                            tensor=param.grad,
                            dst=self._group.ranks[dst_rank],
                            group=self._group,
                            use_calc_stream=True),
                                 callback=cleanup))

                    # Multi stream operation will be supported later
                    dist.wait(tensor=param.grad,
                              group=self._group,
                              use_calc_stream=True)

                    # Clear the task flow and trigger callback to clear the redundant gradient
                    self._clear_task_flow()

        else:
            # Buffer reduction
            @paddle.autograd.no_grad()
            def reduce(*_):
                # Skip gradient reduction, do not change status information
                if self._grad_reduced[index]:
                    assert param.grad is not None, "Parameter gradient cannot be None"

                    # Change reduce information
                    self._grad_reduced[index] = False
                    grad_storage = self._grad_storages[param.dtype][dst_rank]
                    grad_storage.params_checked_in += 1

                    if grad_storage.all_checked_in:
                        assert grad_storage.buffer is not None

                        # Clearing up the grad_storage buffer
                        def cleanup():
                            if dst_rank != self._rank:
                                for p in grad_storage._params:
                                    p.clear_gradient(False)
                                    p._gradient_set_empty(False)

                                grad_storage.buffer.value().get_tensor()._clear(
                                )
                            elif self._offload:
                                grad_storage.to(device=self._offload_device)
                                for p in grad_storage._params:
                                    self._sharding_optimizers[
                                        0]._offload_acc_grad(
                                            p.name,
                                            p.grad.cast(dtype=Type.fp32.value))
                                    p.clear_gradient(False)
                                    p._gradient_set_empty(False)
                                grad_storage._device = self._default_device
                                grad_storage.buffer.value().get_tensor()._clear(
                                )

                        # Reduce the bucket
                        grad_storage.sent = True
                        self._tasks_flow.append(
                            Taskflow(task=dist.reduce(
                                tensor=grad_storage.buffer,
                                dst=self._group.ranks[grad_storage.destination],
                                group=self._group,
                                use_calc_stream=True),
                                     callback=cleanup))

                        # Multi stream operation will be supported later
                        dist.wait(tensor=grad_storage.buffer,
                                  group=self._group,
                                  use_calc_stream=True)

                    # Clear the task flow and trigger callback to clear the redundant gradient
                    self._clear_task_flow()

        return reduce

    def _setup_backward_hooks(self):
        """
        Set the backward hook to synchronize the gradients of all rank by reduce group ranks.
        """

        # Remove previous backward hooks
        while len(self._bw_hooks) > 0:
            self._bw_hooks.pop().remove()

        # Go through the parameters, attach the hook
        if not self.training:
            return

        for index, param in enumerate(self._trainable_params):
            dst_rank = self._trainable_param2rank[param.name]

            reduce_function = self._get_reduce_fn(index, param, dst_rank)

            self._bw_hooks.append(
                param._register_backward_hook(reduce_function))

    def _setup_use_grad_storage(self):
        """
        Integrate the parameters gradient into a continuous memory according to rank, and support the update of training parameters.
        """

        # According to parameters's numel sort, allocate memory of parameter gradient to continuous memory according to rank
        self._grad_storages = {}
        self._has_grad_storage = [False for _ in self._trainable_params]

        for index, param in enumerate(self._trainable_params):
            dst_rank = self._trainable_param2rank[param.name]

            if param.dtype not in self._grad_storages.keys():
                self._grad_storages[param.dtype] = {}

            if dst_rank not in self._grad_storages[param.dtype].keys():
                self._grad_storages[param.dtype][dst_rank] = GradStorage(
                    self._buffer_max_size[param.dtype],
                    dtype=param.dtype,
                    device=self._default_device,
                    destination=dst_rank,
                    parm2align=self._trainable_param2align)

            # Criteria to decide whether this parameter is to be put in GradStorage
            if self._grad_storages[param.dtype][dst_rank].can_add_grad_view(
                    param, self._trainable_param2align[param.name]):
                self._grad_storages[param.dtype][dst_rank].add_grad(
                    param, self._trainable_param2align[param.name])
                self._has_grad_storage[index] = True
            else:
                self._param_grads.append(param.name)
                print(
                    "Can not add param: {}, param's shape: {}, param align: {}, grad_storages fill: {}, "
                    .format(param.name, param.shape,
                            self._trainable_param2align[param.name],
                            self._grad_storages[param.dtype][dst_rank]._fill))

        self._grad_storage_list = list(
            chain(*[
                self._grad_storages[dtype].values()
                for dtype in self._grad_storages.keys()
            ]))

    def _clear_task_flow(self):
        """Try to consume the previous tasks."""
        while len(self._tasks_flow) > 0:
            task = self._tasks_flow.popleft()
            if task.callback is not None:
                task.callback()

    def _detect_train_change(self):
        # Current trainable parameters
        trainable_mask = list(map(_trainable, self._all_params))

        # Whether parameters trainability changed
        trainability_changed = trainable_mask != self._trainable_mask

        if trainability_changed:
            logging.warning(
                "Trainable params changed, because of eval/train mode or parameter freezing/unfreeze."
            )
            self._trainable_mask = trainable_mask

        return trainability_changed

    def _build_grad_storages(self):
        """
        Rebuild grad storages.
        """
        # Rebuild fp16/fp32 grad storages
        for dtype in self._grad_storages.keys():
            for dst_rank, grad_storage in self._grad_storages[dtype].items():
                if self._offload or dst_rank != self._rank:
                    grad_storage.manumal_relase()
                    grad_storage.rebuild()

    def _rank_buffer_size(self, buffer_max_size, model_size):
        """
        Generate the minimum buffer size for each rank & Display param sizes and model sizes.
        """

        # Initialize buffer size
        rank_buffer_size = {}
        for shard_opt in self._sharding_optimizers:
            if shard_opt.rank_buffer_size:
                for dtype in shard_opt.rank_buffer_size.keys():
                    sizes = max(shard_opt.rank_buffer_size[dtype].values())
                    rank_buffer_size[dtype] = min(sizes, buffer_max_size)

        if Type.fp16.value in rank_buffer_size.keys():
            # FP16 GradStorage and model size
            print(
                "====== FP16 GradStorage size: {:.2f}M parameters, Model size {:.2f}M parameters ======"
                .format(rank_buffer_size[Type.fp16.value] / 2**19,
                        model_size / 2**19))
        if Type.fp32.value in rank_buffer_size.keys():
            # FP32 GradStorage and model size
            print(
                "====== FP32 GradStorage size: {:.2f}M parameters, Model size {:.2f}M parameters ======"
                .format(rank_buffer_size[Type.fp32.value] / 2**18,
                        model_size / 2**18))
        return rank_buffer_size

    def _redefine_opt_step(self):
        grad_func = self._grad_scale
        for opt in self._sharding_optimizers:
            opt_step = opt.step

            def _opt_step(self):
                grad_func()
                opt_step()

            opt.step = MethodType(_opt_step, opt)

    def _redefine_opt_clear(self):
        clear_func = self._clear_gradients

        def _opt_clear(self):
            clear_func()

        for opt in self._sharding_optimizers:
            opt.clear_grad = MethodType(_opt_clear, opt)
