""" Pyramid Vision Transformer v2

@misc{wang2021pvtv2,
      title={PVTv2: Improved Baselines with Pyramid Vision Transformer},
      author={Wenhai Wang and Enze Xie and Xiang Li and Deng-Ping Fan and Kaitao Song and Ding Liang and
        Tong Lu and Ping Luo and Ling Shao},
      year={2021},
      eprint={2106.13797},
      archivePrefix={arXiv},
      primaryClass={cs.CV}
}

Based on Apache 2.0 licensed code at https://github.com/whai362/PVT

Modifications and timm support by / Copyright 2022, Ross Wightman
"""

import math
from functools import partial
from typing import Tuple, List, Callable, Union

import torch
import torch.nn as nn
import torch.utils.checkpoint as checkpoint

from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD
from timm.layers import DropPath, to_2tuple, to_ntuple, trunc_normal_
from ._builder import build_model_with_cfg
from ._registry import register_model

__all__ = ['PyramidVisionTransformerV2']


def _cfg(url='', **kwargs):
    return {
        'url': url, 'num_classes': 1000, 'input_size': (3, 224, 224), 'pool_size': (7, 7),
        'crop_pct': 0.9, 'interpolation': 'bicubic',
        'mean': IMAGENET_DEFAULT_MEAN, 'std': IMAGENET_DEFAULT_STD,
        'first_conv': 'patch_embed.proj', 'classifier': 'head', 'fixed_input_size': False,
        **kwargs
    }


default_cfgs = {
    'pvt_v2_b0': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b0.pth'),
    'pvt_v2_b1': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b1.pth'),
    'pvt_v2_b2': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b2.pth'),
    'pvt_v2_b3': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b3.pth'),
    'pvt_v2_b4': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b4.pth'),
    'pvt_v2_b5': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b5.pth'),
    'pvt_v2_b2_li': _cfg(url='https://github.com/whai362/PVT/releases/download/v2/pvt_v2_b2_li.pth')
}


class MlpWithDepthwiseConv(nn.Module):
    def __init__(
            self, in_features, hidden_features=None, out_features=None, act_layer=nn.GELU,
            drop=0., extra_relu=False):
        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.relu = nn.ReLU() if extra_relu else nn.Identity()
        self.dwconv = nn.Conv2d(hidden_features, hidden_features, 3, 1, 1, bias=True, groups=hidden_features)
        self.act = act_layer()
        self.fc2 = nn.Linear(hidden_features, out_features)
        self.drop = nn.Dropout(drop)

    def forward(self, x, feat_size: List[int]):
        x = self.fc1(x)
        B, N, C = x.shape
        x = x.transpose(1, 2).view(B, C, feat_size[0], feat_size[1])
        x = self.relu(x)
        x = self.dwconv(x)
        x = x.flatten(2).transpose(1, 2)
        x = self.act(x)
        x = self.drop(x)
        x = self.fc2(x)
        x = self.drop(x)
        return x


class Attention(nn.Module):
    def __init__(
            self,
            dim,
            num_heads=8,
            sr_ratio=1,
            linear_attn=False,
            qkv_bias=True,
            attn_drop=0.,
            proj_drop=0.
    ):
        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
        self.head_dim = dim // num_heads
        self.scale = self.head_dim ** -0.5

        self.q = nn.Linear(dim, dim, bias=qkv_bias)
        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)

        if not linear_attn:
            self.pool = None
            if sr_ratio > 1:
                self.sr = nn.Conv2d(dim, dim, kernel_size=sr_ratio, stride=sr_ratio)
                self.norm = nn.LayerNorm(dim)
            else:
                self.sr = None
                self.norm = None
            self.act = None
        else:
            self.pool = nn.AdaptiveAvgPool2d(7)
            self.sr = nn.Conv2d(dim, dim, kernel_size=1, stride=1)
            self.norm = nn.LayerNorm(dim)
            self.act = nn.GELU()

    def forward(self, x, feat_size: List[int]):
        B, N, C = x.shape
        H, W = feat_size
        q = self.q(x).reshape(B, N, self.num_heads, -1).permute(0, 2, 1, 3)

        if self.pool is not None:
            x_ = x.permute(0, 2, 1).reshape(B, C, H, W)
            x_ = self.sr(self.pool(x_)).reshape(B, C, -1).permute(0, 2, 1)
            x_ = self.norm(x_)
            x_ = self.act(x_)
            kv = self.kv(x_).reshape(B, -1, 2, self.num_heads, self.head_dim).permute(2, 0, 3, 1, 4)
        else:
            if self.sr is not None:
                x_ = x.permute(0, 2, 1).reshape(B, C, H, W)
                x_ = self.sr(x_).reshape(B, C, -1).permute(0, 2, 1)
                x_ = self.norm(x_)
                kv = self.kv(x_).reshape(B, -1, 2, self.num_heads, self.head_dim).permute(2, 0, 3, 1, 4)
            else:
                kv = self.kv(x).reshape(B, -1, 2, self.num_heads, self.head_dim).permute(2, 0, 3, 1, 4)
        k, v = kv.unbind(0)

        attn = (q @ k.transpose(-2, -1)) * self.scale
        attn = attn.softmax(dim=-1)
        attn = self.attn_drop(attn)

        x = (attn @ v).transpose(1, 2).reshape(B, N, C)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class Block(nn.Module):

    def __init__(
            self, dim, num_heads, mlp_ratio=4., sr_ratio=1, linear_attn=False, qkv_bias=False,
            drop=0., attn_drop=0., drop_path=0., act_layer=nn.GELU, norm_layer=nn.LayerNorm):
        super().__init__()
        self.norm1 = norm_layer(dim)
        self.attn = Attention(
            dim,
            num_heads=num_heads,
            sr_ratio=sr_ratio,
            linear_attn=linear_attn,
            qkv_bias=qkv_bias,
            attn_drop=attn_drop,
            proj_drop=drop,
        )
        self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
        self.norm2 = norm_layer(dim)
        self.mlp = MlpWithDepthwiseConv(
            in_features=dim,
            hidden_features=int(dim * mlp_ratio),
            act_layer=act_layer,
            drop=drop,
            extra_relu=linear_attn
        )

    def forward(self, x, feat_size: List[int]):
        x = x + self.drop_path(self.attn(self.norm1(x), feat_size))
        x = x + self.drop_path(self.mlp(self.norm2(x), feat_size))

        return x


class OverlapPatchEmbed(nn.Module):
    """ Image to Patch Embedding
    """
    def __init__(self, patch_size=7, stride=4, in_chans=3, embed_dim=768):
        super().__init__()
        patch_size = to_2tuple(patch_size)
        assert max(patch_size) > stride, "Set larger patch_size than stride"
        self.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)

    def forward(self, x):
        x = self.proj(x)
        feat_size = x.shape[-2:]
        x = x.flatten(2).transpose(1, 2)
        x = self.norm(x)
        return x, feat_size


class PyramidVisionTransformerStage(nn.Module):
    def __init__(
            self,
            dim: int,
            dim_out: int,
            depth: int,
            downsample: bool = True,
            num_heads: int = 8,
            sr_ratio: int = 1,
            linear_attn: bool = False,
            mlp_ratio: float = 4.0,
            qkv_bias: bool = True,
            drop: float = 0.,
            attn_drop: float = 0.,
            drop_path: Union[List[float], float] = 0.0,
            norm_layer: Callable = nn.LayerNorm,
    ):
        super().__init__()
        self.grad_checkpointing = False

        if downsample:
            self.downsample = OverlapPatchEmbed(
                patch_size=3,
                stride=2,
                in_chans=dim,
                embed_dim=dim_out)
        else:
            assert dim == dim_out
            self.downsample = None

        self.blocks = nn.ModuleList([Block(
            dim=dim_out,
            num_heads=num_heads,
            sr_ratio=sr_ratio,
            linear_attn=linear_attn,
            mlp_ratio=mlp_ratio,
            qkv_bias=qkv_bias,
            drop=drop,
            attn_drop=attn_drop,
            drop_path=drop_path[i] if isinstance(drop_path, list) else drop_path,
            norm_layer=norm_layer,
        ) for i in range(depth)])

        self.norm = norm_layer(dim_out)

    def forward(self, x, feat_size: List[int]) -> Tuple[torch.Tensor, List[int]]:
        if self.downsample is not None:
            x, feat_size = self.downsample(x)
        for blk in self.blocks:
            if self.grad_checkpointing and not torch.jit.is_scripting():
                x = checkpoint.checkpoint(blk, x, feat_size)
            else:
                x = blk(x, feat_size)
        x = self.norm(x)
        x = x.reshape(x.shape[0], feat_size[0], feat_size[1], -1).permute(0, 3, 1, 2).contiguous()
        return x, feat_size


class PyramidVisionTransformerV2(nn.Module):
    def __init__(
            self,
            img_size=None,
            in_chans=3,
            num_classes=1000,
            global_pool='avg',
            depths=(3, 4, 6, 3),
            embed_dims=(64, 128, 256, 512),
            num_heads=(1, 2, 4, 8),
            sr_ratios=(8, 4, 2, 1),
            mlp_ratios=(8., 8., 4., 4.),
            qkv_bias=True,
            linear=False,
            drop_rate=0.,
            attn_drop_rate=0.,
            drop_path_rate=0.,
            norm_layer=nn.LayerNorm,
    ):
        super().__init__()
        self.num_classes = num_classes
        assert global_pool in ('avg', '')
        self.global_pool = global_pool
        self.depths = depths
        num_stages = len(depths)
        mlp_ratios = to_ntuple(num_stages)(mlp_ratios)
        num_heads = to_ntuple(num_stages)(num_heads)
        sr_ratios = to_ntuple(num_stages)(sr_ratios)
        assert(len(embed_dims)) == num_stages

        self.patch_embed = OverlapPatchEmbed(
            patch_size=7,
            stride=4,
            in_chans=in_chans,
            embed_dim=embed_dims[0])

        dpr = [x.tolist() for x in torch.linspace(0, drop_path_rate, sum(depths)).split(depths)]
        cur = 0
        prev_dim = embed_dims[0]
        self.stages = nn.ModuleList()
        for i in range(num_stages):
            self.stages.append(PyramidVisionTransformerStage(
                dim=prev_dim,
                dim_out=embed_dims[i],
                depth=depths[i],
                downsample=i > 0,
                num_heads=num_heads[i],
                sr_ratio=sr_ratios[i],
                mlp_ratio=mlp_ratios[i],
                linear_attn=linear,
                qkv_bias=qkv_bias,
                drop=drop_rate,
                attn_drop=attn_drop_rate,
                drop_path=dpr[i],
                norm_layer=norm_layer
            ))
            prev_dim = embed_dims[i]
            cur += depths[i]

        # classification head
        self.num_features = embed_dims[-1]
        self.head = nn.Linear(embed_dims[-1], num_classes) if num_classes > 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.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 freeze_patch_emb(self):
        self.patch_embed.requires_grad = False

    @torch.jit.ignore
    def no_weight_decay(self):
        return {}

    @torch.jit.ignore
    def group_matcher(self, coarse=False):
        matcher = dict(
            stem=r'^patch_embed',  # stem and embed
            blocks=r'^stages\.(\d+)'
        )
        return matcher

    @torch.jit.ignore
    def set_grad_checkpointing(self, enable=True):
        for s in self.stages:
            s.grad_checkpointing = enable

    def get_classifier(self):
        return self.head

    def reset_classifier(self, num_classes, global_pool=None):
        self.num_classes = num_classes
        if global_pool is not None:
            assert global_pool in ('avg', '')
            self.global_pool = global_pool
        self.head = nn.Linear(self.embed_dim, num_classes) if num_classes > 0 else nn.Identity()

    def forward_features(self, x):
        x, feat_size = self.patch_embed(x)
        for stage in self.stages:
            x, feat_size = stage(x, feat_size=feat_size)
        return x

    def forward_head(self, x, pre_logits: bool = False):
        if self.global_pool:
            x = x.mean(dim=(-1, -2))
        return x if pre_logits else self.head(x)

    def forward(self, x):
        x = self.forward_features(x)
        x = self.forward_head(x)
        return x


def _checkpoint_filter_fn(state_dict, model):
    """ Remap original checkpoints -> timm """
    if 'patch_embed.proj.weight' in state_dict:
        return state_dict  # non-original checkpoint, no remapping needed

    out_dict = {}
    import re
    for k, v in state_dict.items():
        if k.startswith('patch_embed'):
            k = k.replace('patch_embed1', 'patch_embed')
            k = k.replace('patch_embed2', 'stages.1.downsample')
            k = k.replace('patch_embed3', 'stages.2.downsample')
            k = k.replace('patch_embed4', 'stages.3.downsample')
        k = k.replace('dwconv.dwconv', 'dwconv')
        k = re.sub(r'block(\d+).(\d+)', lambda x: f'stages.{int(x.group(1)) - 1}.blocks.{x.group(2)}', k)
        k = re.sub(r'^norm(\d+)', lambda x: f'stages.{int(x.group(1)) - 1}.norm', k)
        out_dict[k] = v
    return out_dict


def _create_pvt2(variant, pretrained=False, **kwargs):
    if kwargs.get('features_only', None):
        raise RuntimeError('features_only not implemented for Vision Transformer models.')
    model = build_model_with_cfg(
        PyramidVisionTransformerV2, variant, pretrained,
        pretrained_filter_fn=_checkpoint_filter_fn,
        **kwargs
    )
    return model


@register_model
def pvt_v2_b0(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(2, 2, 2, 2), embed_dims=(32, 64, 160, 256), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    return _create_pvt2('pvt_v2_b0', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b1(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(2, 2, 2, 2), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    return _create_pvt2('pvt_v2_b1', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b2(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(3, 4, 6, 3), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6),  **kwargs)
    return _create_pvt2('pvt_v2_b2', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b3(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(3, 4, 18, 3), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    return _create_pvt2('pvt_v2_b3', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b4(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(3, 8, 27, 3), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    return _create_pvt2('pvt_v2_b4', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b5(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(3, 6, 40, 3), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        mlp_ratios=(4, 4, 4, 4), norm_layer=partial(nn.LayerNorm, eps=1e-6),
        **kwargs)
    return _create_pvt2('pvt_v2_b5', pretrained=pretrained, **model_kwargs)


@register_model
def pvt_v2_b2_li(pretrained=False, **kwargs):
    model_kwargs = dict(
        depths=(3, 4, 6, 3), embed_dims=(64, 128, 320, 512), num_heads=(1, 2, 5, 8),
        norm_layer=partial(nn.LayerNorm, eps=1e-6), linear=True, **kwargs)
    return _create_pvt2('pvt_v2_b2_li', pretrained=pretrained, **model_kwargs)

