import torch
from colossalai.tensor.op_wrapper import colo_op_impl
from colossalai.tensor.colo_tensor import ColoTensor
from colossalai.context import ParallelMode
from colossalai.nn.layer.parallel_1d._utils import split_forward_gather_backward, reduce_input
from colossalai.nn.layer.utils import divide
from colossalai.core import global_context as gpc
from packaging import version
from colossalai.tensor import ComputePattern


@colo_op_impl(torch.nn.functional.linear)
def colo_linear(types, args, kwargs, pg):
    """Handles ``__torch_function__`` dispatch for ``torch.nn.functional.linear``.
    This method computes a linear.
    """
    input_tensor = args[0]
    weight = args[1]

    if version.parse(torch.__version__) > version.parse("1.11.0"):
        if len(args) == 3:
            bias = args[2]
        else:
            bias = None
    else:
        bias = kwargs.get('bias', None)

    if isinstance(bias, ColoTensor):
        assert bias.shard_spec.num_action == 0, f"We currently only support bias is duplicated among processes in the linear operator"
        bias = bias.torch_tensor()

    # Add communication logic before and after linear call.
    if isinstance(weight, ColoTensor):
        if weight.shard_spec == None or weight.shard_spec.num_action == 0:
            if isinstance(input_tensor, ColoTensor):
                input_tensor = input_tensor.torch_tensor()
            if isinstance(weight, ColoTensor):
                weight = weight.torch_tensor()
            return ColoTensor.init_from_torch_tensor(torch.nn.functional.linear(input_tensor, weight, bias))
        elif weight.shard_spec.num_action == 1:
            if ComputePattern.TP1DRow in weight.shard_spec.compute_patterns:
                # Input:S[1] x Weight:S[0] = Output:P
                # All-Reduce(Output) + bias = res
                assert divide(input_tensor.shape[-1], gpc.tensor_parallel_size) == weight.size(-1), \
                'Invalid shapes in 1Drow forward: input={}, weight={}. Expected last dim of input {}.'.format(
                    input_tensor.shape, weight.size, weight.size(-1) * gpc.tensor_parallel_size)
                # Input:S[1]
                if isinstance(input_tensor, ColoTensor):
                    input_tensor = input_tensor.torch_tensor()
                parallel_action = weight.shard_spec.get_action_by_compute_pattern(ComputePattern.TP1DRow)
                input_per_partition = split_forward_gather_backward(input_tensor, parallel_action.parallel_mode, dim=-1)
                # Output:P
                weight_ = weight.torch_tensor()
                partial_output = torch.nn.functional.linear(input_per_partition, weight_)
                # Reduce(Output)
                output = reduce_input(partial_output, ParallelMode.PARALLEL_1D)
                # Bias
                if bias is not None:
                    output = output + bias
                return ColoTensor.init_from_torch_tensor(output)
            else:
                raise NotImplementedError
        else:
            raise NotImplementedError
    else:
        return torch.nn.functional.linear(input_tensor, weight, bias)
