import torch.nn as nn
import numpy as np
import itertools

from mmseg.models.builder import BACKBONES
from mmseg.utils import get_root_logger
from mmcv.runner import _load_checkpoint

from torch.nn.modules.batchnorm import _BatchNorm

def _make_divisible(v, divisor, min_value=None):
    """
    This function is taken from the original tf repo.
    It ensures that all layers have a channel number that is divisible by 8
    It can be seen here:
    https://github.com/tensorflow/models/blob/master/research/slim/nets/mobilenet/mobilenet.py
    :param v:
    :param divisor:
    :param min_value:
    :return:
    """
    if min_value is None:
        min_value = divisor
    new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
    # Make sure that round down does not go down by more than 10%.
    if new_v < 0.9 * v:
        new_v += divisor
    return new_v

from timm.models.layers import SqueezeExcite

import torch

class Conv2d_BN(torch.nn.Sequential):
    def __init__(self, a, b, ks=1, stride=1, pad=0, dilation=1,
                 groups=1, bn_weight_init=1, resolution=-10000):
        super().__init__()
        self.add_module('c', torch.nn.Conv2d(
            a, b, ks, stride, pad, dilation, groups, bias=False))
        self.add_module('bn', torch.nn.BatchNorm2d(b))
        torch.nn.init.constant_(self.bn.weight, bn_weight_init)
        torch.nn.init.constant_(self.bn.bias, 0)

    @torch.no_grad()
    def fuse(self):
        c, bn = self._modules.values()
        w = bn.weight / (bn.running_var + bn.eps)**0.5
        w = c.weight * w[:, None, None, None]
        b = bn.bias - bn.running_mean * bn.weight / \
            (bn.running_var + bn.eps)**0.5
        m = torch.nn.Conv2d(w.size(1) * self.c.groups, w.size(
            0), w.shape[2:], stride=self.c.stride, padding=self.c.padding, dilation=self.c.dilation, groups=self.c.groups,
            device=c.weight.device)
        m.weight.data.copy_(w)
        m.bias.data.copy_(b)
        return m

class Residual(torch.nn.Module):
    def __init__(self, m, drop=0.):
        super().__init__()
        self.m = m
        self.drop = drop

    def forward(self, x):
        if self.training and self.drop > 0:
            return x + self.m(x) * torch.rand(x.size(0), 1, 1, 1,
                                              device=x.device).ge_(self.drop).div(1 - self.drop).detach()
        else:
            return x + self.m(x)
    
    @torch.no_grad()
    def fuse(self):
        if isinstance(self.m, Conv2d_BN):
            m = self.m.fuse()
            assert(m.groups == m.in_channels)
            identity = torch.ones(m.weight.shape[0], m.weight.shape[1], 1, 1)
            identity = torch.nn.functional.pad(identity, [1,1,1,1])
            m.weight += identity.to(m.weight.device)
            return m
        elif isinstance(self.m, torch.nn.Conv2d):
            m = self.m
            assert(m.groups != m.in_channels)
            identity = torch.ones(m.weight.shape[0], m.weight.shape[1], 1, 1)
            identity = torch.nn.functional.pad(identity, [1,1,1,1])
            m.weight += identity.to(m.weight.device)
            return m
        else:
            return self


class RepVGGDW(torch.nn.Module):
    def __init__(self, ed) -> None:
        super().__init__()
        self.conv = Conv2d_BN(ed, ed, 3, 1, 1, groups=ed)
        self.conv1 = torch.nn.Conv2d(ed, ed, 1, 1, 0, groups=ed)
        self.dim = ed
        self.bn = torch.nn.BatchNorm2d(ed)
    
    def forward(self, x):
        return self.bn((self.conv(x) + self.conv1(x)) + x)
    
    @torch.no_grad()
    def fuse(self):
        conv = self.conv.fuse()
        conv1 = self.conv1
        
        conv_w = conv.weight
        conv_b = conv.bias
        conv1_w = conv1.weight
        conv1_b = conv1.bias
        
        conv1_w = torch.nn.functional.pad(conv1_w, [1,1,1,1])

        identity = torch.nn.functional.pad(torch.ones(conv1_w.shape[0], conv1_w.shape[1], 1, 1, device=conv1_w.device), [1,1,1,1])

        final_conv_w = conv_w + conv1_w + identity
        final_conv_b = conv_b + conv1_b

        conv.weight.data.copy_(final_conv_w)
        conv.bias.data.copy_(final_conv_b)

        bn = self.bn
        w = bn.weight / (bn.running_var + bn.eps)**0.5
        w = conv.weight * w[:, None, None, None]
        b = bn.bias + (conv.bias - bn.running_mean) * bn.weight / \
            (bn.running_var + bn.eps)**0.5
        conv.weight.data.copy_(w)
        conv.bias.data.copy_(b)
        return conv


class RepViTBlock(nn.Module):
    def __init__(self, inp, hidden_dim, oup, kernel_size, stride, use_se, use_hs):
        super(RepViTBlock, self).__init__()
        assert stride in [1, 2]

        self.identity = stride == 1 and inp == oup
        assert(hidden_dim == 2 * inp)

        if stride == 2:
            self.token_mixer = nn.Sequential(
                Conv2d_BN(inp, inp, kernel_size, stride, (kernel_size - 1) // 2, groups=inp),
                SqueezeExcite(inp, 0.25) if use_se else nn.Identity(),
                Conv2d_BN(inp, oup, ks=1, stride=1, pad=0)
            )
            self.channel_mixer = Residual(nn.Sequential(
                    # pw
                    Conv2d_BN(oup, 2 * oup, 1, 1, 0),
                    nn.GELU() if use_hs else nn.GELU(),
                    # pw-linear
                    Conv2d_BN(2 * oup, oup, 1, 1, 0, bn_weight_init=0),
                ))
        else:
            assert(self.identity)
            self.token_mixer = nn.Sequential(
                RepVGGDW(inp),
                SqueezeExcite(inp, 0.25) if use_se else nn.Identity(),
            )
            self.channel_mixer = Residual(nn.Sequential(
                    # pw
                    Conv2d_BN(inp, hidden_dim, 1, 1, 0),
                    nn.GELU() if use_hs else nn.GELU(),
                    # pw-linear
                    Conv2d_BN(hidden_dim, oup, 1, 1, 0, bn_weight_init=0),
                ))

    def forward(self, x):
        return self.channel_mixer(self.token_mixer(x))

from timm.models.vision_transformer import trunc_normal_
class BN_Linear(torch.nn.Sequential):
    def __init__(self, a, b, bias=True, std=0.02):
        super().__init__()
        self.add_module('bn', torch.nn.BatchNorm1d(a))
        self.add_module('l', torch.nn.Linear(a, b, bias=bias))
        trunc_normal_(self.l.weight, std=std)
        if bias:
            torch.nn.init.constant_(self.l.bias, 0)

    @torch.no_grad()
    def fuse(self):
        bn, l = self._modules.values()
        w = bn.weight / (bn.running_var + bn.eps)**0.5
        b = bn.bias - self.bn.running_mean * \
            self.bn.weight / (bn.running_var + bn.eps)**0.5
        w = l.weight * w[None, :]
        if l.bias is None:
            b = b @ self.l.weight.T
        else:
            b = (l.weight @ b[:, None]).view(-1) + self.l.bias
        m = torch.nn.Linear(w.size(1), w.size(0), device=l.weight.device)
        m.weight.data.copy_(w)
        m.bias.data.copy_(b)
        return m

class RepViT(nn.Module):
    def __init__(self, cfgs, distillation=False, pretrained=None, init_cfg=None, out_indices=[]):
        super(RepViT, self).__init__()
        # setting of inverted residual blocks
        self.cfgs = cfgs

        # building first layer
        input_channel = self.cfgs[0][2]
        patch_embed = torch.nn.Sequential(Conv2d_BN(3, input_channel // 2, 3, 2, 1), torch.nn.GELU(),
                           Conv2d_BN(input_channel // 2, input_channel, 3, 2, 1))
        layers = [patch_embed]
        # building inverted residual blocks
        block = RepViTBlock
        for k, t, c, use_se, use_hs, s in self.cfgs:
            output_channel = _make_divisible(c, 8)
            exp_size = _make_divisible(input_channel * t, 8)
            layers.append(block(input_channel, exp_size, output_channel, k, s, use_se, use_hs))
            input_channel = output_channel
        self.features = nn.ModuleList(layers)
        
        self.init_cfg = init_cfg
        assert(self.init_cfg is not None)
        self.out_indices = out_indices
        self.init_weights()
        self = torch.nn.SyncBatchNorm.convert_sync_batchnorm(self)
        self.train()

    def init_weights(self, pretrained=None):
        logger = get_root_logger()
        if self.init_cfg is None and pretrained is None:
            logger.warn(f'No pre-trained weights for '
                        f'{self.__class__.__name__}, '
                        f'training start from scratch')
            pass
        else:
            assert 'checkpoint' in self.init_cfg, f'Only support ' \
                                                  f'specify `Pretrained` in ' \
                                                  f'`init_cfg` in ' \
                                                  f'{self.__class__.__name__} '
            if self.init_cfg is not None:
                ckpt_path = self.init_cfg['checkpoint']
            elif pretrained is not None:
                ckpt_path = pretrained

            ckpt = _load_checkpoint(
                ckpt_path, logger=logger, map_location='cpu')
            if 'state_dict' in ckpt:
                _state_dict = ckpt['state_dict']
            elif 'model' in ckpt:
                _state_dict = ckpt['model']
            else:
                _state_dict = ckpt

            state_dict = _state_dict
            missing_keys, unexpected_keys = \
                self.load_state_dict(state_dict, False)
            logger.info(f"Miss {missing_keys}")
            logger.info(f"Unexpected {unexpected_keys}")

    def train(self, mode=True):
        """Convert the model into training mode while keep layers freezed."""
        super(RepViT, self).train(mode)
        if mode:
            for m in self.modules():
                if isinstance(m, _BatchNorm):
                    m.eval()


    def forward(self, x):
        outs = []
        for i, f in enumerate(self.features):
            x = f(x)
            if i in self.out_indices:
                outs.append(x)
        assert(len(outs) == 4)
        return outs

from timm.models import register_model


@BACKBONES.register_module()
def repvit_m1_1(pretrained=False, num_classes = 1000, distillation=False, init_cfg=None, out_indices=[], **kwargs):
    """
    Constructs a MobileNetV3-Large model
    """
    cfgs = [
        # k, t, c, SE, HS, s 
        [3,   2,  64, 1, 0, 1],
        [3,   2,  64, 0, 0, 1],
        [3,   2,  64, 0, 0, 1],
        [3,   2,  128, 0, 0, 2],
        [3,   2,  128, 1, 0, 1],
        [3,   2,  128, 0, 0, 1],
        [3,   2,  128, 0, 0, 1],
        [3,   2,  256, 0, 1, 2],
        [3,   2,  256, 1, 1, 1],
        [3,   2,  256, 0, 1, 1],
        [3,   2,  256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 512, 0, 1, 2],
        [3,   2, 512, 1, 1, 1],
        [3,   2, 512, 0, 1, 1]
    ]
    return RepViT(cfgs, init_cfg=init_cfg, pretrained=pretrained, distillation=distillation, out_indices=out_indices)

@BACKBONES.register_module()
def repvit_m1_5(pretrained=False, num_classes = 1000, distillation=False, init_cfg=None, out_indices=[], **kwargs):
    """
    Constructs a MobileNetV3-Large model
    """
    cfgs = [
        # k, t, c, SE, HS, s 
        [3,   2,  64, 1, 0, 1],
        [3,   2,  64, 0, 0, 1],
        [3,   2,  64, 1, 0, 1],
        [3,   2,  64, 0, 0, 1],
        [3,   2,  64, 0, 0, 1],
        [3,   2,  128, 0, 0, 2],
        [3,   2,  128, 1, 0, 1],
        [3,   2,  128, 0, 0, 1],
        [3,   2,  128, 1, 0, 1],
        [3,   2,  128, 0, 0, 1],
        [3,   2,  128, 0, 0, 1],
        [3,   2,  256, 0, 1, 2],
        [3,   2,  256, 1, 1, 1],
        [3,   2,  256, 0, 1, 1],
        [3,   2,  256, 1, 1, 1],
        [3,   2,  256, 0, 1, 1],
        [3,   2,  256, 1, 1, 1],
        [3,   2,  256, 0, 1, 1],
        [3,   2,  256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 1, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 256, 0, 1, 1],
        [3,   2, 512, 0, 1, 2],
        [3,   2, 512, 1, 1, 1],
        [3,   2, 512, 0, 1, 1],
        [3,   2, 512, 1, 1, 1],
        [3,   2, 512, 0, 1, 1]
    ]
    return RepViT(cfgs, init_cfg=init_cfg, pretrained=pretrained, distillation=distillation, out_indices=out_indices)


@BACKBONES.register_module()
def repvit_m2_3(pretrained=False, num_classes = 1000, distillation=False, init_cfg=None, out_indices=[], **kwargs):
    """
    Constructs a MobileNetV3-Large model
    """
    cfgs = [
        # k, t, c, SE, HS, s 
        [3,   2,  80, 1, 0, 1],
        [3,   2,  80, 0, 0, 1],
        [3,   2,  80, 1, 0, 1],
        [3,   2,  80, 0, 0, 1],
        [3,   2,  80, 1, 0, 1],
        [3,   2,  80, 0, 0, 1],
        [3,   2,  80, 0, 0, 1],
        [3,   2,  160, 0, 0, 2],
        [3,   2,  160, 1, 0, 1],
        [3,   2,  160, 0, 0, 1],
        [3,   2,  160, 1, 0, 1],
        [3,   2,  160, 0, 0, 1],
        [3,   2,  160, 1, 0, 1],
        [3,   2,  160, 0, 0, 1],
        [3,   2,  160, 0, 0, 1],
        [3,   2,  320, 0, 1, 2],
        [3,   2,  320, 1, 1, 1],
        [3,   2,  320, 0, 1, 1],
        [3,   2,  320, 1, 1, 1],
        [3,   2,  320, 0, 1, 1],
        [3,   2,  320, 1, 1, 1],
        [3,   2,  320, 0, 1, 1],
        [3,   2,  320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 1, 1, 1],
        [3,   2, 320, 0, 1, 1],
        # [3,   2, 320, 1, 1, 1],
        # [3,   2, 320, 0, 1, 1],
        [3,   2, 320, 0, 1, 1],
        [3,   2, 640, 0, 1, 2],
        [3,   2, 640, 1, 1, 1],
        [3,   2, 640, 0, 1, 1],
        # [3,   2, 640, 1, 1, 1],
        # [3,   2, 640, 0, 1, 1]
    ]    
    return RepViT(cfgs, init_cfg=init_cfg, pretrained=pretrained, distillation=distillation, out_indices=out_indices)