#   Copyright (c) 2022 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.

import contextlib

import numpy as np

import paddle
from paddle import _legacy_C_ops
from paddle.common_ops_import import Variable
from paddle.fluid import core
from paddle.fluid.data_feeder import check_variable_and_dtype
from paddle.framework import LayerHelper, in_dynamic_mode

__all__ = []

MODEL_PARALLEL_RNG = 'model_parallel_rng'

# This file is inspired by Megatron to control random states for MP:
# https://github.com/NVIDIA/Megatron-LM/blob/main/megatron/mpu/random.py


class RNGStatesTracker:
    """
    Tracker the RNG states.
    """

    def __init__(self):
        # Map from name to the rng state.
        self.states_ = {}
        self.seeds_ = set()

    def reset(self):
        self.states_ = {}
        self.seeds_ = set()

    def add(self, name, seed):
        if seed in self.seeds_:
            raise ValueError(f'seed {seed} already exists')
        self.seeds_.add(seed)
        if name in self.states_:
            raise ValueError(f'state {name} already exists')
        orig_rng_state = paddle.get_rng_state()
        paddle.seed(seed)
        self.states_[name] = paddle.get_rng_state()
        paddle.set_rng_state(orig_rng_state)

    def get_states_tracker(self):
        states = {}
        for name in self.states_:
            states[name] = self.states_[name]
        return states

    def set_states_tracker(self, states):
        self.states_ = states

    @contextlib.contextmanager
    def rng_state(self, name=MODEL_PARALLEL_RNG):
        if name not in self.states_:
            raise ValueError(f'state {name} does not exist')
        orig_rng_state = paddle.get_rng_state()
        paddle.set_rng_state(self.states_[name])
        try:
            yield
        finally:
            self.states_[name] = paddle.get_rng_state()
            paddle.set_rng_state(orig_rng_state)


RNG_STATE_TRACKER = RNGStatesTracker()


def get_rng_state_tracker():
    return RNG_STATE_TRACKER


def model_parallel_random_seed(seed=None):
    from paddle.distributed import fleet

    hcg = fleet.get_hybrid_communicate_group()

    mp_rank = hcg.get_model_parallel_rank()
    mp_size = hcg.get_model_parallel_world_size()

    pp_rank = hcg.get_stage_id()
    pp_size = hcg.get_pipe_parallel_world_size()

    if seed:
        global_seed = seed
        # dp/sharding seed is same
        local_seed = seed + 1 + mp_rank * pp_size + pp_rank
    else:
        global_seed = np.random.randint(0, 10000)
        local_seed = global_seed + 1 + mp_rank * pp_size + pp_rank

    RNG_STATE_TRACKER.reset()
    RNG_STATE_TRACKER.add(MODEL_PARALLEL_RNG, local_seed)
    paddle.seed(global_seed)


def determinate_seed(rng_name):
    assert rng_name is not None and rng_name != ""
    helper = LayerHelper('seed', **locals())
    out = helper.create_variable_for_type_inference(dtype=paddle.int32)
    # set force_cpu to reduce sync copy from CPU->GPU->CPU, and reduce pipeline hang
    helper.append_op(
        type='seed',
        outputs={'Out': out},
        attrs={'deterministic': True, 'rng_name': rng_name, 'force_cpu': True},
    )
    return out


def dropout(
    x,
    p=0.5,
    axis=None,
    rng_name=None,
    training=True,
    mode="upscale_in_train",
    name=None,
):
    """
    Dropout is a regularization technique for reducing overfitting by preventing
    neuron co-adaption during training. The dropout operator randomly sets the
    outputs of some units to zero, while upscale others according to the given
    dropout probability.

    Args:
        x (Tensor): The input tensor. The data type is float32 or float64.
        p (float|int): Probability of setting units to zero. Default 0.5.
        axis (int|list|tuple): The axis along which the dropout is performed. Default None.
        rng_name (str): The random seed generator name, which used to obtain deterministic results.
        training (bool): A flag indicating whether it is in train phrase or not. Default True.
        mode(str): ['upscale_in_train'(default) | 'downscale_in_infer'].

                           1. upscale_in_train(default), upscale the output at training time

                              - train: out = input * mask / ( 1.0 - dropout_prob )
                              - inference: out = input

                           2. downscale_in_infer, downscale the output at inference

                              - train: out = input * mask
                              - inference: out = input * (1.0 - dropout_prob)
        name (str, optional): Name for the operation (optional, default is None). For more information, please refer to :ref:`api_guide_Name`.

    Returns:
        A Tensor representing the dropout, has same shape and data type as `x` .


    Examples:
        We use ``p=0.5`` in the following description for simplicity.

        1. When ``axis=None`` , this is commonly used dropout, which dropout each element of x randomly.

        ..  code-block:: text

            Let's see a simple case when x is a 2d tensor with shape 2*3:
            [[1 2 3]
             [4 5 6]]
            we generate mask with the same shape as x, which is 2*3. The value of mask is
            sampled from a Bernoulli distribution randomly. For example, we may get such mask:
            [[0 1 0]
             [1 0 1]]
            So the output is obtained from elementwise multiply of x and mask:
            [[0 2 0]
             [4 0 6]]
            Using default setting, i.e. ``mode='upscale_in_train'`` ,
            if in training phase, the final upscale output is:
            [[0 4 0 ]
             [8 0 12]]
            if in test phase, the output is the same as input:
            [[1 2 3]
             [4 5 6]]
            we can also set ``mode='downscale_in_infer'`` , then
            if in training phase, the final output is:
            [[0 2 0]
             [4 0 6]]
            if in test phase, the scale output is:
            [[0.5 1.  1.5]
             [2.  2.5 3. ]]

    """
    if rng_name is None:
        return paddle.nn.functional.dropout(x, p, axis, training, mode, name)

    if not isinstance(p, (float, int, Variable)):
        raise TypeError("p argument should be a number(int|float) or Variable")

    # fast return for p == 0
    if isinstance(p, (int, float)) and p == 0:
        return x

    assert 0 <= p <= 1, ValueError("p argument should between 0 and 1")
    assert mode in ('downscale_in_infer', 'upscale_in_train'), ValueError(
        "mode argument should be 'downscale_in_infer' or 'upscale_in_train'"
    )

    assert axis is None, TypeError(
        "unsupport axis when using random seed generator"
    )

    mode = (
        'downgrade_in_infer' if mode == 'downscale_in_infer' else mode
    )  # semantic transfer

    # dygraph using tracker, doesn't need determinate seed
    if in_dynamic_mode():
        out, mask = _legacy_C_ops.dropout(
            x,
            'dropout_prob',
            p,
            'is_test',
            not training,
            'fix_seed',
            False,
            'seed',
            0,
            'dropout_implementation',
            mode,
        )
        return out
    else:
        seed = determinate_seed(rng_name)

        if isinstance(p, Variable) and not p.shape != [1]:
            raise TypeError(
                "Required p.shape == [1] if type(p) is Variable, but received p.shape = {}".format(
                    p.shape
                )
            )

        helper = LayerHelper('dropout', **locals())
        check_variable_and_dtype(
            x, 'x', ['float16', 'float32', 'float64'], 'dropout'
        )

        out = helper.create_variable_for_type_inference(dtype=x.dtype)
        mask = helper.create_variable_for_type_inference(
            dtype=core.VarDesc.VarType.UINT8, stop_gradient=True
        )

        helper.append_op(
            type='dropout',
            inputs={'X': [x], 'Seed': seed},
            outputs={'Out': [out], 'Mask': [mask]},
            attrs={
                'dropout_prob': p,
                'is_test': not training,
                'dropout_implementation': mode,
            },
        )
        return out
