# Copyright 2020 Huawei Technologies Co., Ltd
#
# 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.
# ============================================================================
"""sgd"""
from mindspore.ops import functional as F, composite as C, operations as P
from mindspore.common.parameter import Parameter
from mindspore.common.tensor import Tensor
import mindspore.common.dtype as mstype
from mindspore._checkparam import Validator as validator
from .optimizer import Optimizer

sgd_opt = C.MultitypeFuncGraph("sgd_opt")


@sgd_opt.register("Function", "Tensor", "Tensor", "Tensor", "Tensor", "Tensor", "Tensor")
def _tensor_run_opt_ext(opt, momentum, learning_rate, gradient, weight, accum, stat):
    """Apply sgd optimizer to the weight parameter using Tensor."""
    success = True
    success = F.depend(success, opt(weight, gradient, learning_rate, accum, momentum, stat))
    return success


class SGD(Optimizer):
    """
    Implements stochastic gradient descent (optionally with momentum).

    Introduction to SGD can be found at https://en.wikipedia.org/wiki/Stochastic_gradient_descent.
    Nesterov momentum is based on the formula from paper `On the importance of initialization and
    momentum in deep learning <http://proceedings.mlr.press/v28/sutskever13.html>`_.

    Note:
        The SGD optimizer supports separating parameter groups. Different parameter groups can set different
        `learning_rate` and `weight_decay`.

        When separating parameter groups, the weight decay in each group will be applied on the parameters if the
        value of weight_decay > 0. When not separating parameter groups, the `weight_decay` in the API will be
        applied on the parameters if `weight_decay` > 0 and the 'beta' and 'gamma' are not in the name of parameters.

    Args:
        params (Union[list[Parameter], list[dict]]): When the `params` is a list of `Parameter` which will be updated,
            the element in `params` should be class `Parameter`. When the `params` is a list of `dict`, the "params",
            "lr" and "weight_decay" are the keys can be parsed.

            - params: Required. The value should be a list of `Parameter`.

            - lr: Optional. If "lr" in the keys, the value of corresponding learning rate will be used.
              If not, the `learning_rate` in the API will be used.

            - weight_decay: Optional. If "weight_decay" in the keys, the value of corresponding weight decay
              will be used. If not, the `weight_decay` in the API will be used.

        learning_rate (Union[float, Tensor, Iterable]): A value for the learning rate. When the learning_rate is
                                                        Iterable or a Tensor and the dims of the Tensor is 1,
                                                        use dynamic learning rate, then the i-th step will
                                                        take the i-th value as the learning rate.
                                                        When the learning_rate is float or learning_rate is a Tensor
                                                        but the dims of the Tensor is 0, use fixed learning rate.
                                                        Other cases are not supported. Default: 0.1.
        momentum (float): A floating point value the momentum. Default: 0.0.
        dampening (float): A floating point value of dampening for momentum. Default: 0.0.
        weight_decay (float): Weight decay (L2 penalty). Default: 0.0.
        nesterov (bool): Enables the Nesterov momentum. Default: False.
        loss_scale (float): A floating point value for the loss scale, which should be larger
                            than 0.0. Default: 1.0.

    Inputs:
        - **gradients** (tuple[Tensor]) - The gradients of `params`, the shape is the same as `params`.

    Outputs:
        Tensor[bool], the value is True.

    Raises:
        ValueError: If the momentum, dampening or weight_decay value is less than 0.0.

    Examples:
        >>> net = Net()
        >>> #1) All parameters use the same learning rate and weight decay
        >>> optim = nn.SGD(params=net.trainable_params())
        >>>
        >>> #2) Use parameter groups and set different values
        >>> conv_params = list(filter(lambda x: 'conv' in x.name, net.trainable_params()))
        >>> no_conv_params = list(filter(lambda x: 'conv' not in x.name, net.trainable_params()))
        >>> group_params = [{'params': conv_params, 'weight_decay': 0.01, 'lr': 0.01},
        >>>                 {'params': no_conv_params}]
        >>> opt = nn.SGD(group_params, learning_rate=0.1, weight_decay=0.0)
        >>> # the conv_params's parameters will use a learning rate of 0.01 and a weight decay of 0.01
        >>> # the no_cov_params's parameters don't set learning and weight decay. So they will use a
        >>> # learning rate of 0.1 and a weight decay of 0.0.
        >>>
        >>> loss = nn.SoftmaxCrossEntropyWithLogits()
        >>> model = Model(net, loss_fn=loss, optimizer=optim)
    """
    def __init__(self, params, learning_rate=0.1, momentum=0.0, dampening=0.0, weight_decay=0.0, nesterov=False,
                 loss_scale=1.0):

        super(SGD, self).__init__(learning_rate, params, weight_decay, loss_scale)

        if not isinstance(momentum, float):
            raise TypeError("momentum should be float number!")

        if isinstance(momentum, float) and momentum < 0.0:
            raise ValueError("momentum should be at least 0.0, but got momentum {}".format(momentum))

        if not isinstance(dampening, float):
            raise TypeError("dampening should be float number")

        if isinstance(dampening, int):
            dampening = float(dampening)

        if dampening < 0.0:
            raise ValueError("dampening should be at least 0.0, but got dampening {}".format(dampening))
        self.dampening = dampening

        validator.check_value_type("nesterov", nesterov, [bool], self.cls_name)
        self.nesterov = nesterov

        self.opt = P.SGD(dampening, weight_decay, nesterov)

        self.momentum = Parameter(Tensor(momentum, mstype.float32), name="momentum")
        self.accum = self.parameters.clone(prefix="accum", init='zeros')
        self.stat = self.parameters.clone(prefix="stat", init='ones')
        self.hyper_map = C.HyperMap()

    def construct(self, gradients):
        params = self.parameters
        accum = self.accum
        stat = self.stat
        gradients = self.decay_weight(gradients)
        gradients = self.scale_grad(gradients)
        lr = self.get_lr()
        if self.is_group:
            success = self.hyper_map(F.partial(sgd_opt, self.opt, self.momentum), lr, gradients, params, accum, stat)
        else:
            success = self.hyper_map(F.partial(sgd_opt, self.opt, self.momentum, lr), gradients, params, accum, stat)
        return success
