import functools
from inspect import getfullargspec

import torch

from .utils import cast_tensor_type


def auto_fp16(apply_to=None, out_fp32=False):
    """Decorator to enable fp16 training automatically.

    This decorator is useful when you write custom modules and want to support
    mixed precision training. If inputs arguments are fp32 tensors, they will
    be converted to fp16 automatically. Arguments other than fp32 tensors are
    ignored.

    Args:
        apply_to (Iterable, optional): The argument names to be converted.
            `None` indicates all arguments.
        out_fp32 (bool): Whether to convert the output back to fp32.

    :Example:

        class MyModule1(nn.Module)

            # Convert x and y to fp16
            @auto_fp16()
            def forward(self, x, y):
                pass

        class MyModule2(nn.Module):

            # convert pred to fp16
            @auto_fp16(apply_to=('pred', ))
            def do_something(self, pred, others):
                pass
    """

    def auto_fp16_wrapper(old_func):

        @functools.wraps(old_func)
        def new_func(*args, **kwargs):
            # check if the module has set the attribute `fp16_enabled`, if not,
            # just fallback to the original method.
            if not isinstance(args[0], torch.nn.Module):
                raise TypeError('@auto_fp16 can only be used to decorate the '
                                'method of nn.Module')
            if not (hasattr(args[0], 'fp16_enabled') and args[0].fp16_enabled):
                return old_func(*args, **kwargs)
            # get the arg spec of the decorated method
            args_info = getfullargspec(old_func)
            # get the argument names to be casted
            args_to_cast = args_info.args if apply_to is None else apply_to
            # convert the args that need to be processed
            new_args = []
            # NOTE: default args are not taken into consideration
            if args:
                arg_names = args_info.args[:len(args)]
                for i, arg_name in enumerate(arg_names):
                    if arg_name in args_to_cast:
                        new_args.append(
                            cast_tensor_type(args[i], torch.float, torch.half))
                    else:
                        new_args.append(args[i])
            # convert the kwargs that need to be processed
            new_kwargs = {}
            if kwargs:
                for arg_name, arg_value in kwargs.items():
                    if arg_name in args_to_cast:
                        new_kwargs[arg_name] = cast_tensor_type(
                            arg_value, torch.float, torch.half)
                    else:
                        new_kwargs[arg_name] = arg_value
            # apply converted arguments to the decorated method
            output = old_func(*new_args, **new_kwargs)
            # cast the results back to fp32 if necessary
            if out_fp32:
                output = cast_tensor_type(output, torch.half, torch.float)
            return output

        return new_func

    return auto_fp16_wrapper


def force_fp32(apply_to=None, out_fp16=False):
    """Decorator to convert input arguments to fp32 in force.

    This decorator is useful when you write custom modules and want to support
    mixed precision training. If there are some inputs that must be processed
    in fp32 mode, then this decorator can handle it. If inputs arguments are
    fp16 tensors, they will be converted to fp32 automatically. Arguments other
    than fp16 tensors are ignored.

    Args:
        apply_to (Iterable, optional): The argument names to be converted.
            `None` indicates all arguments.
        out_fp16 (bool): Whether to convert the output back to fp16.

    :Example:

        class MyModule1(nn.Module)

            # Convert x and y to fp32
            @force_fp32()
            def loss(self, x, y):
                pass

        class MyModule2(nn.Module):

            # convert pred to fp32
            @force_fp32(apply_to=('pred', ))
            def post_process(self, pred, others):
                pass
    """

    def force_fp32_wrapper(old_func):

        @functools.wraps(old_func)
        def new_func(*args, **kwargs):
            # check if the module has set the attribute `fp16_enabled`, if not,
            # just fallback to the original method.
            if not isinstance(args[0], torch.nn.Module):
                raise TypeError('@force_fp32 can only be used to decorate the '
                                'method of nn.Module')
            if not (hasattr(args[0], 'fp16_enabled') and args[0].fp16_enabled):
                return old_func(*args, **kwargs)
            # get the arg spec of the decorated method
            args_info = getfullargspec(old_func)
            # get the argument names to be casted
            args_to_cast = args_info.args if apply_to is None else apply_to
            # convert the args that need to be processed
            new_args = []
            if args:
                arg_names = args_info.args[:len(args)]
                for i, arg_name in enumerate(arg_names):
                    if arg_name in args_to_cast:
                        new_args.append(
                            cast_tensor_type(args[i], torch.half, torch.float))
                    else:
                        new_args.append(args[i])
            # convert the kwargs that need to be processed
            new_kwargs = dict()
            if kwargs:
                for arg_name, arg_value in kwargs.items():
                    if arg_name in args_to_cast:
                        new_kwargs[arg_name] = cast_tensor_type(
                            arg_value, torch.half, torch.float)
                    else:
                        new_kwargs[arg_name] = arg_value
            # apply converted arguments to the decorated method
            output = old_func(*new_args, **new_kwargs)
            # cast the results back to fp32 if necessary
            if out_fp16:
                output = cast_tensor_type(output, torch.float, torch.half)
            return output

        return new_func

    return force_fp32_wrapper
