import collections.abc
from itertools import repeat
from typing import List, Optional, Tuple, Union

import torch
from torch import nn as nn
from torch import _assert
from torchvision.ops.misc import FrozenBatchNorm2d


def freeze_batch_norm_2d(module, module_match={}, name=''):
    """
    Converts all `BatchNorm2d` and `SyncBatchNorm` layers of provided module into `FrozenBatchNorm2d`. If `module` is
    itself an instance of either `BatchNorm2d` or `SyncBatchNorm`, it is converted into `FrozenBatchNorm2d` and
    returned. Otherwise, the module is walked recursively and submodules are converted in place.

    Args:
        module (torch.nn.Module): Any PyTorch module.
        module_match (dict): Dictionary of full module names to freeze (all if empty)
        name (str): Full module name (prefix)

    Returns:
        torch.nn.Module: Resulting module

    Inspired by https://github.com/pytorch/pytorch/blob/a5895f85be0f10212791145bfedc0261d364f103/torch/nn/modules/batchnorm.py#L762
    """
    res = module
    is_match = True
    if module_match:
        is_match = name in module_match
    if is_match and isinstance(module, (nn.modules.batchnorm.BatchNorm2d, nn.modules.batchnorm.SyncBatchNorm)):
        res = FrozenBatchNorm2d(module.num_features)
        res.num_features = module.num_features
        res.affine = module.affine
        if module.affine:
            res.weight.data = module.weight.data.clone().detach()
            res.bias.data = module.bias.data.clone().detach()
        res.running_mean.data = module.running_mean.data
        res.running_var.data = module.running_var.data
        res.eps = module.eps
    else:
        for child_name, child in module.named_children():
            full_child_name = '.'.join([name, child_name]) if name else child_name
            new_child = freeze_batch_norm_2d(child, module_match, full_child_name)
            if new_child is not child:
                res.add_module(child_name, new_child)
    return res


# From PyTorch internals
def _ntuple(n):
    def parse(x):
        if isinstance(x, collections.abc.Iterable):
            return x
        return tuple(repeat(x, n))
    return parse


to_1tuple = _ntuple(1)
to_2tuple = _ntuple(2)
to_3tuple = _ntuple(3)
to_4tuple = _ntuple(4)
to_ntuple = lambda n, x: _ntuple(n)(x)

# Replaces all linear layers with linear_replacement
# TODO: add int8 support for other linear layers including attn and convnets
def replace_linear(model, linear_replacement, include_modules=['c_fc', 'c_proj'], copy_weights=True):
    for name, module in model.named_children():
        if len(list(module.children())) > 0:
            replace_linear(module, linear_replacement, include_modules, copy_weights)

        if isinstance(module, torch.nn.Linear) and name in include_modules:
            old_module = model._modules[name]
            model._modules[name] = linear_replacement(
                module.in_features,
                module.out_features,
                module.bias is not None,
            )
            if copy_weights:
                model._modules[name].weight.data.copy_(old_module.weight.data)
                if model._modules[name].bias is not None:
                    model._modules[name].bias.data.copy_(old_module.bias)

    return model

def convert_int8_model_to_inference_mode(model):
    for m in model.modules():
        if hasattr(m, 'prepare_for_eval'):
            int8_original_dtype = m.weight.dtype
            m.prepare_for_eval()
            m.int8_original_dtype = int8_original_dtype


def feature_take_indices(
        num_features: int,
        indices: Optional[Union[int, List[int]]] = None,
        as_set: bool = False,
) -> Tuple[List[int], int]:
    """ Determine the absolute feature indices to 'take' from.

    Note: This function can be called in forward() so must be torchscript compatible,
    which requires some incomplete typing and workaround hacks.

    Args:
        num_features: total number of features to select from
        indices: indices to select,
          None -> select all
          int -> select last n
          list/tuple of int -> return specified (-ve indices specify from end)
        as_set: return as a set

    Returns:
        List (or set) of absolute (from beginning) indices, Maximum index
    """
    if indices is None:
        indices = num_features  # all features if None

    if isinstance(indices, int):
        # convert int -> last n indices
        _assert(0 < indices <= num_features, f'last-n ({indices}) is out of range (1 to {num_features})')
        take_indices = [num_features - indices + i for i in range(indices)]
    else:
        take_indices: List[int] = []
        for i in indices:
            idx = num_features + i if i < 0 else i
            _assert(0 <= idx < num_features, f'feature index {idx} is out of range (0 to {num_features - 1})')
            take_indices.append(idx)

    if not torch.jit.is_scripting() and as_set:
        return set(take_indices), max(take_indices)

    return take_indices, max(take_indices)


def _out_indices_as_tuple(x: Union[int, Tuple[int, ...]]) -> Tuple[int, ...]:
    if isinstance(x, int):
        # if indices is an int, take last N features
        return tuple(range(-x, 0))
    return tuple(x)