# ---------------------------------------------------------------
# Copyright (c) 2021, NVIDIA Corporation. All rights reserved.
#
# This work is licensed under the NVIDIA Source Code License
# ---------------------------------------------------------------
import math
import warnings
import numpy as np
from functools import partial

import torch
import torch.nn as nn


def _no_grad_trunc_normal_(tensor, mean, std, a, b):
    # Cut & paste from PyTorch official master until it's in a few official releases - RW
    # Method based on https://people.sc.fsu.edu/~jburkardt/presentations/truncated_normal.pdf
    def norm_cdf(x):
        # Computes standard normal cumulative distribution function
        return (1. + math.erf(x / math.sqrt(2.))) / 2.

    if (mean < a - 2 * std) or (mean > b + 2 * std):
        warnings.warn("mean is more than 2 std from [a, b] in nn.init.trunc_normal_. "
                      "The distribution of values may be incorrect.",
                      stacklevel=2)

    with torch.no_grad():
        # Values are generated by using a truncated uniform distribution and
        # then using the inverse CDF for the normal distribution.
        # Get upper and lower cdf values
        l = norm_cdf((a - mean) / std)
        u = norm_cdf((b - mean) / std)

        # Uniformly fill tensor with values from [l, u], then translate to
        # [2l-1, 2u-1].
        tensor.uniform_(2 * l - 1, 2 * u - 1)

        # Use inverse cdf transform for normal distribution to get truncated
        # standard normal
        tensor.erfinv_()

        # Transform to proper mean, std
        tensor.mul_(std * math.sqrt(2.))
        tensor.add_(mean)

        # Clamp to ensure it's in the proper range
        tensor.clamp_(min=a, max=b)
        return tensor


def trunc_normal_(tensor, mean=0., std=1., a=-2., b=2.):
    r"""
    Fills the input Tensor with values drawn from a truncated
    normal distribution. The values are effectively drawn from the
    normal distribution :math:`\mathcal{N}(\text{mean}, \text{std}^2)`
    with values outside :math:`[a, b]` redrawn until they are within
    the bounds. The method used for generating the random values works
    best when :math:`a \leq \text{mean} \leq b`.
    Args:
        tensor: an n-dimensional `torch.Tensor`
        mean: the mean of the normal distribution
        std: the standard deviation of the normal distribution
        a: the minimum cutoff value
        b: the maximum cutoff value
    Examples:
        >>> w = torch.empty(3, 5)
        >>> nn.init.trunc_normal_(w)
    """
    return _no_grad_trunc_normal_(tensor, mean, std, a, b)

#--------------------------------------#
#   Gelu激活函数的实现
#   利用近似的数学公式
#--------------------------------------#
class GELU(nn.Module):
    def __init__(self):
        super(GELU, self).__init__()

    def forward(self, x):
        return 0.5 * x * (1 + torch.tanh(np.sqrt(2 / np.pi) * (x + 0.044715 * torch.pow(x,3))))

class OverlapPatchEmbed(nn.Module):
    def __init__(self, patch_size=7, stride=4, in_chans=3, embed_dim=768):
        super().__init__()
        patch_size  = (patch_size, patch_size)
        self.proj   = nn.Conv2d(in_chans, embed_dim, kernel_size=patch_size, stride=stride,
                              padding=(patch_size[0] // 2, patch_size[1] // 2))
        self.norm   = nn.LayerNorm(embed_dim)

        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)
        elif isinstance(m, nn.Conv2d):
            fan_out = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
            fan_out //= m.groups
            m.weight.data.normal_(0, math.sqrt(2.0 / fan_out))
            if m.bias is not None:
                m.bias.data.zero_()

    def forward(self, x):
        x = self.proj(x)
        _, _, H, W = x.shape
        x = x.flatten(2).transpose(1, 2)
        x = self.norm(x)

        return x, H, W

#--------------------------------------------------------------------------------------------------------------------#
#   Attention机制
#   将输入的特征qkv特征进行划分，首先生成query, key, value。query是查询向量、key是键向量、v是值向量。
#   然后利用 查询向量query 叉乘 转置后的键向量key，这一步可以通俗的理解为，利用查询向量去查询序列的特征，获得序列每个部分的重要程度score。
#   然后利用 score 叉乘 value，这一步可以通俗的理解为，将序列每个部分的重要程度重新施加到序列的值上去。
#   
#   在segformer中，为了减少计算量，首先对特征图进行了浓缩，所有特征层都压缩到原图的1/32。
#   当输入图片为512, 512时，Block1的特征图为128, 128，此时就先将特征层压缩为16, 16。
#   在Block1的Attention模块中，相当于将8x8个特征点进行特征浓缩，浓缩为一个特征点。
#   然后利用128x128个查询向量对16x16个键向量与值向量进行查询。尽管键向量与值向量的数量较少，但因为查询向量的不同，依然可以获得不同的输出。
#--------------------------------------------------------------------------------------------------------------------#
class Attention(nn.Module):
    def __init__(self, dim, num_heads=8, qkv_bias=False, qk_scale=None, attn_drop=0., proj_drop=0., sr_ratio=1):
        super().__init__()
        assert dim % num_heads == 0, f"dim {dim} should be divided by num_heads {num_heads}."

        self.dim        = dim
        self.num_heads  = num_heads
        head_dim        = dim // num_heads
        self.scale      = qk_scale or head_dim ** -0.5

        self.q          = nn.Linear(dim, dim, bias=qkv_bias)
        
        self.sr_ratio = sr_ratio
        if sr_ratio > 1:
            self.sr     = nn.Conv2d(dim, dim, kernel_size=sr_ratio, stride=sr_ratio)
            self.norm   = nn.LayerNorm(dim)
        self.kv         = nn.Linear(dim, dim * 2, bias=qkv_bias)
        
        self.attn_drop  = nn.Dropout(attn_drop)
        
        self.proj       = nn.Linear(dim, dim)
        self.proj_drop  = nn.Dropout(proj_drop)

        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)
        elif isinstance(m, nn.Conv2d):
            fan_out = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
            fan_out //= m.groups
            m.weight.data.normal_(0, math.sqrt(2.0 / fan_out))
            if m.bias is not None:
                m.bias.data.zero_()

    def forward(self, x, H, W):
        B, N, C = x.shape
        # bs, 16384, 32 => bs, 16384, 32 => bs, 16384, 8, 4 => bs, 8, 16384, 4
        q = self.q(x).reshape(B, N, self.num_heads, C // self.num_heads).permute(0, 2, 1, 3)

        if self.sr_ratio > 1:
            # bs, 16384, 32 => bs, 32, 128, 128
            x_ = x.permute(0, 2, 1).reshape(B, C, H, W)
            # bs, 32, 128, 128 => bs, 32, 16, 16 => bs, 256, 32
            x_ = self.sr(x_).reshape(B, C, -1).permute(0, 2, 1)
            x_ = self.norm(x_)
            # bs, 256, 32 => bs, 256, 64 => bs, 256, 2, 8, 4 => 2, bs, 8, 256, 4
            kv = self.kv(x_).reshape(B, -1, 2, self.num_heads, C // self.num_heads).permute(2, 0, 3, 1, 4)
        else:
            kv = self.kv(x).reshape(B, -1, 2, self.num_heads, C // self.num_heads).permute(2, 0, 3, 1, 4)
        k, v = kv[0], kv[1]

        # bs, 8, 16384, 4 @ bs, 8, 4, 256 => bs, 8, 16384, 256 
        attn = (q @ k.transpose(-2, -1)) * self.scale
        attn = attn.softmax(dim=-1)
        attn = self.attn_drop(attn)

        # bs, 8, 16384, 256  @ bs, 8, 256, 4 => bs, 8, 16384, 4 => bs, 16384, 32
        x = (attn @ v).transpose(1, 2).reshape(B, N, C)
        # bs, 16384, 32 => bs, 16384, 32
        x = self.proj(x)
        x = self.proj_drop(x)

        return x

def drop_path(x, drop_prob: float = 0., training: bool = False, scale_by_keep: bool = True):
    """
    Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks).
    This is the same as the DropConnect impl I created for EfficientNet, etc networks, however,
    the original name is misleading as 'Drop Connect' is a different form of dropout in a separate paper...
    See discussion: https://github.com/tensorflow/tpu/issues/494#issuecomment-532968956 ... I've opted for
    changing the layer and argument names to 'drop path' rather than mix DropConnect as a layer name and use
    'survival rate' as the argument.
    """
    if drop_prob == 0. or not training:
        return x
    keep_prob       = 1 - drop_prob
    shape           = (x.shape[0],) + (1,) * (x.ndim - 1)  # work with diff dim tensors, not just 2D ConvNets
    random_tensor   = x.new_empty(shape).bernoulli_(keep_prob)
    if keep_prob > 0.0 and scale_by_keep:
        random_tensor.div_(keep_prob)
    return x * random_tensor

class DropPath(nn.Module):
    def __init__(self, drop_prob=None, scale_by_keep=True):
        super(DropPath, self).__init__()
        self.drop_prob = drop_prob
        self.scale_by_keep = scale_by_keep

    def forward(self, x):
        return drop_path(x, self.drop_prob, self.training, self.scale_by_keep)
    
class DWConv(nn.Module):
    def __init__(self, dim=768):
        super(DWConv, self).__init__()
        self.dwconv = nn.Conv2d(dim, dim, 3, 1, 1, bias=True, groups=dim)

    def forward(self, x, H, W):
        B, N, C = x.shape
        x = x.transpose(1, 2).view(B, C, H, W)
        x = self.dwconv(x)
        x = x.flatten(2).transpose(1, 2)

        return x
    
class Mlp(nn.Module):
    def __init__(self, in_features, hidden_features=None, out_features=None, act_layer=GELU, drop=0.):
        super().__init__()
        out_features    = out_features or in_features
        hidden_features = hidden_features or in_features
        
        self.fc1    = nn.Linear(in_features, hidden_features)
        self.dwconv = DWConv(hidden_features)
        self.act    = act_layer()
        
        self.fc2    = nn.Linear(hidden_features, out_features)
        
        self.drop   = nn.Dropout(drop)

        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)
        elif isinstance(m, nn.Conv2d):
            fan_out = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
            fan_out //= m.groups
            m.weight.data.normal_(0, math.sqrt(2.0 / fan_out))
            if m.bias is not None:
                m.bias.data.zero_()

    def forward(self, x, H, W):
        x = self.fc1(x)
        x = self.dwconv(x, H, W)
        x = self.act(x)
        x = self.drop(x)
        x = self.fc2(x)
        x = self.drop(x)
        return x

class Block(nn.Module):
    def __init__(self, dim, num_heads, mlp_ratio=4., qkv_bias=False, qk_scale=None, drop=0., attn_drop=0.,
                 drop_path=0., act_layer=GELU, norm_layer=nn.LayerNorm, sr_ratio=1):
        super().__init__()
        self.norm1      = norm_layer(dim)
        
        self.attn       = Attention(
            dim, num_heads=num_heads, qkv_bias=qkv_bias, qk_scale=qk_scale,
            attn_drop=attn_drop, proj_drop=drop, sr_ratio=sr_ratio
        )
        self.norm2      = norm_layer(dim)
        self.mlp        = Mlp(in_features=dim, hidden_features=int(dim * mlp_ratio), act_layer=act_layer, drop=drop)

        self.drop_path  = DropPath(drop_path) if drop_path > 0. else nn.Identity()
        
        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)
        elif isinstance(m, nn.Conv2d):
            fan_out = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
            fan_out //= m.groups
            m.weight.data.normal_(0, math.sqrt(2.0 / fan_out))
            if m.bias is not None:
                m.bias.data.zero_()

    def forward(self, x, H, W):
        x = x + self.drop_path(self.attn(self.norm1(x), H, W))
        x = x + self.drop_path(self.mlp(self.norm2(x), H, W))
        return x

class MixVisionTransformer(nn.Module):
    def __init__(self, in_chans=3, num_classes=1000, embed_dims=[32, 64, 160, 256],
                 num_heads=[1, 2, 4, 8], mlp_ratios=[4, 4, 4, 4], qkv_bias=False, qk_scale=None, drop_rate=0.,
                 attn_drop_rate=0., drop_path_rate=0., norm_layer=nn.LayerNorm,
                 depths=[3, 4, 6, 3], sr_ratios=[8, 4, 2, 1]):
        super().__init__()
        self.num_classes    = num_classes
        self.depths         = depths

        #----------------------------------#
        #   Transformer模块，共有四个部分
        #----------------------------------#
        dpr = [x.item() for x in torch.linspace(0, drop_path_rate, sum(depths))]
        
        #----------------------------------#
        #   block1
        #----------------------------------#
        #-----------------------------------------------#
        #   对输入图像进行分区，并下采样
        #   512, 512, 3 => 128, 128, 32 => 16384, 32
        #-----------------------------------------------#
        self.patch_embed1 = OverlapPatchEmbed(patch_size=7, stride=4, in_chans=in_chans, embed_dim=embed_dims[0])
        #-----------------------------------------------#
        #   利用transformer模块进行特征提取
        #   16384, 32 => 16384, 32
        #-----------------------------------------------#
        cur = 0
        self.block1 = nn.ModuleList(
            [
                Block(
                    dim=embed_dims[0], num_heads=num_heads[0], mlp_ratio=mlp_ratios[0], qkv_bias=qkv_bias, qk_scale=qk_scale,
                    drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[cur + i], norm_layer=norm_layer, sr_ratio=sr_ratios[0]
                )
                for i in range(depths[0])
            ]
        )
        self.norm1 = norm_layer(embed_dims[0])
        
        #----------------------------------#
        #   block2
        #----------------------------------#
        #-----------------------------------------------#
        #   对输入图像进行分区，并下采样
        #   128, 128, 32 => 64, 64, 64 => 4096, 64
        #-----------------------------------------------#
        self.patch_embed2 = OverlapPatchEmbed(patch_size=3, stride=2, in_chans=embed_dims[0], embed_dim=embed_dims[1])
        #-----------------------------------------------#
        #   利用transformer模块进行特征提取
        #   4096, 64 => 4096, 64
        #-----------------------------------------------#
        cur += depths[0]
        self.block2 = nn.ModuleList(
            [
                Block(
                    dim=embed_dims[1], num_heads=num_heads[1], mlp_ratio=mlp_ratios[1], qkv_bias=qkv_bias, qk_scale=qk_scale,
                    drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[cur + i], norm_layer=norm_layer, sr_ratio=sr_ratios[1]
                )
                for i in range(depths[1])
            ]
        )
        self.norm2 = norm_layer(embed_dims[1])

        #----------------------------------#
        #   block3
        #----------------------------------#
        #-----------------------------------------------#
        #   对输入图像进行分区，并下采样
        #   64, 64, 64 => 32, 32, 160 => 1024, 160
        #-----------------------------------------------#
        self.patch_embed3 = OverlapPatchEmbed(patch_size=3, stride=2, in_chans=embed_dims[1], embed_dim=embed_dims[2])
        #-----------------------------------------------#
        #   利用transformer模块进行特征提取
        #   1024, 160 => 1024, 160
        #-----------------------------------------------#
        cur += depths[1]
        self.block3 = nn.ModuleList(
            [
                Block(
                    dim=embed_dims[2], num_heads=num_heads[2], mlp_ratio=mlp_ratios[2], qkv_bias=qkv_bias, qk_scale=qk_scale,
                    drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[cur + i], norm_layer=norm_layer, sr_ratio=sr_ratios[2]
                )
                for i in range(depths[2])
            ]
        )
        self.norm3 = norm_layer(embed_dims[2])

        #----------------------------------#
        #   block4
        #----------------------------------#
        #-----------------------------------------------#
        #   对输入图像进行分区，并下采样
        #   32, 32, 160 => 16, 16, 256 => 256, 256
        #-----------------------------------------------#
        self.patch_embed4 = OverlapPatchEmbed(patch_size=3, stride=2, in_chans=embed_dims[2], embed_dim=embed_dims[3])
        #-----------------------------------------------#
        #   利用transformer模块进行特征提取
        #   256, 256 => 256, 256
        #-----------------------------------------------#
        cur += depths[2]
        self.block4 = nn.ModuleList(
            [
                Block(
                    dim=embed_dims[3], num_heads=num_heads[3], mlp_ratio=mlp_ratios[3], qkv_bias=qkv_bias, qk_scale=qk_scale,
                    drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[cur + i], norm_layer=norm_layer, sr_ratio=sr_ratios[3]
                )
                for i in range(depths[3])
            ]
        )
        self.norm4 = norm_layer(embed_dims[3])

        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)
        elif isinstance(m, nn.Conv2d):
            fan_out = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
            fan_out //= m.groups
            m.weight.data.normal_(0, math.sqrt(2.0 / fan_out))
            if m.bias is not None:
                m.bias.data.zero_()
                
    def forward(self, x):
        B = x.shape[0]
        outs = []

        #----------------------------------#
        #   block1
        #----------------------------------#
        x, H, W = self.patch_embed1.forward(x)
        for i, blk in enumerate(self.block1):
            x = blk.forward(x, H, W)
        x = self.norm1(x)
        x = x.reshape(B, H, W, -1).permute(0, 3, 1, 2).contiguous()
        outs.append(x)

        #----------------------------------#
        #   block2
        #----------------------------------#
        x, H, W = self.patch_embed2.forward(x)
        for i, blk in enumerate(self.block2):
            x = blk.forward(x, H, W)
        x = self.norm2(x)
        x = x.reshape(B, H, W, -1).permute(0, 3, 1, 2).contiguous()
        outs.append(x)

        #----------------------------------#
        #   block3
        #----------------------------------#
        x, H, W = self.patch_embed3.forward(x)
        for i, blk in enumerate(self.block3):
            x = blk.forward(x, H, W)
        x = self.norm3(x)
        x = x.reshape(B, H, W, -1).permute(0, 3, 1, 2).contiguous()
        outs.append(x)

        #----------------------------------#
        #   block4
        #----------------------------------#
        x, H, W = self.patch_embed4.forward(x)
        for i, blk in enumerate(self.block4):
            x = blk.forward(x, H, W)
        x = self.norm4(x)
        x = x.reshape(B, H, W, -1).permute(0, 3, 1, 2).contiguous()
        outs.append(x)

        return outs

class mit_b0(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b0, self).__init__(
            embed_dims=[32, 64, 160, 256], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[2, 2, 2, 2], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b0_backbone_weights.pth"), strict=False)

class mit_b1(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b1, self).__init__(
            embed_dims=[64, 128, 320, 512], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[2, 2, 2, 2], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b1_backbone_weights.pth"), strict=False)

class mit_b2(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b2, self).__init__(
            embed_dims=[64, 128, 320, 512], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[3, 4, 6, 3], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b2_backbone_weights.pth"), strict=False)

class mit_b3(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b3, self).__init__(
            embed_dims=[64, 128, 320, 512], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[3, 4, 18, 3], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b3_backbone_weights.pth"), strict=False)

class mit_b4(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b4, self).__init__(
            embed_dims=[64, 128, 320, 512], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[3, 8, 27, 3], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b4_backbone_weights.pth"), strict=False)

class mit_b5(MixVisionTransformer):
    def __init__(self, pretrained = False):
        super(mit_b5, self).__init__(
            embed_dims=[64, 128, 320, 512], num_heads=[1, 2, 5, 8], mlp_ratios=[4, 4, 4, 4],
            qkv_bias=True, norm_layer=partial(nn.LayerNorm, eps=1e-6), depths=[3, 6, 40, 3], sr_ratios=[8, 4, 2, 1],
            drop_rate=0.0, drop_path_rate=0.1)
        if pretrained:
            print("Load backbone weights")
            self.load_state_dict(torch.load("model_data/segformer_b5_backbone_weights.pth"), strict=False)