import torch
import torch.nn.quantized as nnq
from torch.nn.quantized.modules.utils import _quantize_weight

class Linear(nnq.Linear):
    r"""
    A dynamic quantized linear module with floating point tensor as inputs and outputs.
    We adopt the same interface as `torch.nn.Linear`, please see
    https://pytorch.org/docs/stable/nn.html#torch.nn.Linear for documentation.

    Similar to :class:`torch.nn.Linear`, attributes will be randomly
    initialized at module creation time and will be overwritten later

    Attributes:
        weight (Tensor): the non-learnable quantized weights of the module which are of
                         shape :math:`(\text{out\_features}, \text{in\_features})`.
        bias (Tensor): the non-learnable floating point bias of the module of shape
                       :math:`(\text{out\_features})`. If :attr:`bias` is ``True``,
                       the values are initialized to zero.

    Examples::

        >>> m = nn.quantized.dynamic.Linear(20, 30)
        >>> input = torch.randn(128, 20)
        >>> output = m(input)
        >>> print(output.size())
        torch.Size([128, 30])
    """
    # version used in this class is different from the parent class nnq.Linear
    _version = 4

    def __init__(self, in_features, out_features, bias_=True, dtype=torch.qint8):
        super(Linear, self).__init__(in_features, out_features, bias_, dtype=dtype)
        # We don't muck around with buffers or attributes or anything here
        # to keep the module simple. *everything* is simply a Python attribute.
        # Serialization logic is explicitly handled in the below serialization and
        # deserialization modules
        self.version = 4

    def forward(self, x):
        # Note that we can handle self.bias == None case.
        if self._packed_params.dtype == torch.qint8:
            if self.version is None or self.version < 4:
                Y = torch.ops.quantized.linear_dynamic(
                    x, self._packed_params._packed_params)
            else:
                Y = torch.ops.quantized.linear_dynamic(
                    x, self._packed_params._packed_params, reduce_range=True)
        elif self._packed_params.dtype == torch.float16:
            Y = torch.ops.quantized.linear_dynamic_fp16(
                x, self._packed_params._packed_params)
        else:
            raise RuntimeError('Unsupported dtype on dynamic quantized linear!')
        return Y.to(x.dtype)

    def _get_name(self):
        return 'DynamicQuantizedLinear'

    def extra_repr(self):
        extra_repr_str = 'in_features={}, out_features={}, dtype={}'.format(
            self.in_features, self.out_features, self._packed_params.dtype
        )
        if self._packed_params.dtype == torch.qint8:
            extra_repr_str += ', qscheme={}'.format(self.weight().qscheme())
        return extra_repr_str

    def _load_from_state_dict(self, state_dict, prefix, local_metadata, strict,
                              missing_keys, unexpected_keys, error_msgs):
        version = local_metadata.get('version', None)
        self.version = version
        super(Linear, self)._load_from_state_dict(state_dict, prefix, local_metadata, False,
                                                  missing_keys, unexpected_keys, error_msgs)

    @classmethod
    def from_float(cls, mod):
        r"""Create a dynamic quantized module from a float module or qparams_dict

        Args:
            mod (Module): a float module, either produced by torch.quantization
                          utilities or provided by the user
        """
        float_modules = [torch.nn.Linear, torch.nn.modules.linear._LinearWithBias]
        assert type(mod) in float_modules, \
            'nn.quantized.dynamic.Linear.from_float only works for one of' + \
            str([float_mod.__name__ for float_mod in float_modules])
        assert hasattr(mod, 'qconfig'), 'Input float module must have qconfig defined'
        if mod.qconfig is not None and mod.qconfig.weight is not None:
            weight_observer = mod.qconfig.weight()
        else:
            # We have the circular import issues if we import the qconfig in the beginning of this file:
            # https://github.com/pytorch/pytorch/pull/24231. The current workaround is to postpone the
            # import until we need it.
            from torch.quantization.qconfig import default_dynamic_qconfig
            weight_observer = default_dynamic_qconfig.weight()
        dtype = weight_observer.dtype
        assert dtype in [torch.qint8, torch.float16], "The only supported dtypes for " \
            "dynamic quantized linear are qint8 and float16 got: {}".format(dtype)
        weight_observer(mod.weight)
        if dtype == torch.qint8:
            qweight = _quantize_weight(mod.weight.float(), weight_observer)
        elif dtype == torch.float16:
            qweight = mod.weight.float()
        else:
            raise RuntimeError('Unsupported dtype specified for dynamic quantized Linear!')
        qlinear = Linear(mod.in_features, mod.out_features, dtype=dtype)
        qlinear.set_weight_bias(qweight, mod.bias)
        return qlinear
