""" Class-Attention in Image Transformers (CaiT)

Paper: 'Going deeper with Image Transformers' - https://arxiv.org/abs/2103.17239

Original code and weights from https://github.com/facebookresearch/deit, copyright below

Modifications and additions for timm hacked together by / Copyright 2021, Ross Wightman
"""
# Copyright (c) 2015-present, Facebook, Inc.
# All rights reserved.
from functools import partial
from typing import List, Optional, Tuple, Union

import torch
import torch.nn as nn

from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD
from timm.layers import PatchEmbed, Mlp, DropPath, trunc_normal_, use_fused_attn
from ._builder import build_model_with_cfg
from ._features import feature_take_indices
from ._manipulate import checkpoint, checkpoint_seq
from ._registry import register_model, generate_default_cfgs

__all__ = ['Cait', 'ClassAttn', 'LayerScaleBlockClassAttn', 'LayerScaleBlock', 'TalkingHeadAttn']


class ClassAttn(nn.Module):
    # taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py
    # with slight modifications to do CA
    fused_attn: torch.jit.Final[bool]

    def __init__(self, dim, num_heads=8, qkv_bias=False, attn_drop=0., proj_drop=0.):
        super().__init__()
        self.num_heads = num_heads
        head_dim = dim // num_heads
        self.scale = head_dim ** -0.5
        self.fused_attn = use_fused_attn()

        self.q = nn.Linear(dim, dim, bias=qkv_bias)
        self.k = nn.Linear(dim, dim, bias=qkv_bias)
        self.v = nn.Linear(dim, dim, bias=qkv_bias)
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim, dim)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x):
        B, N, C = x.shape
        q = self.q(x[:, 0]).unsqueeze(1).reshape(B, 1, self.num_heads, C // self.num_heads).permute(0, 2, 1, 3)
        k = self.k(x).reshape(B, N, self.num_heads, C // self.num_heads).permute(0, 2, 1, 3)
        v = self.v(x).reshape(B, N, self.num_heads, C // self.num_heads).permute(0, 2, 1, 3)

        if self.fused_attn:
            x_cls = torch.nn.functional.scaled_dot_product_attention(
                q, k, v,
                dropout_p=self.attn_drop.p if self.training else 0.,
            )
        else:
            q = q * self.scale
            attn = q @ k.transpose(-2, -1)
            attn = attn.softmax(dim=-1)
            attn = self.attn_drop(attn)
            x_cls = attn @ v

        x_cls = x_cls.transpose(1, 2).reshape(B, 1, C)
        x_cls = self.proj(x_cls)
        x_cls = self.proj_drop(x_cls)

        return x_cls


class LayerScaleBlockClassAttn(nn.Module):
    # taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py
    # with slight modifications to add CA and LayerScale
    def __init__(
            self,
            dim,
            num_heads,
            mlp_ratio=4.,
            qkv_bias=False,
            proj_drop=0.,
            attn_drop=0.,
            drop_path=0.,
            act_layer=nn.GELU,
            norm_layer=nn.LayerNorm,
            attn_block=ClassAttn,
            mlp_block=Mlp,
            init_values=1e-4,
    ):
        super().__init__()
        self.norm1 = norm_layer(dim)
        self.attn = attn_block(
            dim,
            num_heads=num_heads,
            qkv_bias=qkv_bias,
            attn_drop=attn_drop,
            proj_drop=proj_drop,
        )
        self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
        self.norm2 = norm_layer(dim)
        mlp_hidden_dim = int(dim * mlp_ratio)
        self.mlp = mlp_block(
            in_features=dim,
            hidden_features=mlp_hidden_dim,
            act_layer=act_layer,
            drop=proj_drop,
        )
        self.gamma_1 = nn.Parameter(init_values * torch.ones(dim))
        self.gamma_2 = nn.Parameter(init_values * torch.ones(dim))

    def forward(self, x, x_cls):
        u = torch.cat((x_cls, x), dim=1)
        x_cls = x_cls + self.drop_path(self.gamma_1 * self.attn(self.norm1(u)))
        x_cls = x_cls + self.drop_path(self.gamma_2 * self.mlp(self.norm2(x_cls)))
        return x_cls


class TalkingHeadAttn(nn.Module):
    # taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py
    # with slight modifications to add Talking Heads Attention (https://arxiv.org/pdf/2003.02436v1.pdf)
    def __init__(self, dim, num_heads=8, qkv_bias=False, attn_drop=0., proj_drop=0.):
        super().__init__()

        self.num_heads = num_heads

        head_dim = dim // num_heads

        self.scale = head_dim ** -0.5

        self.qkv = nn.Linear(dim, dim * 3, bias=qkv_bias)
        self.attn_drop = nn.Dropout(attn_drop)

        self.proj = nn.Linear(dim, dim)

        self.proj_l = nn.Linear(num_heads, num_heads)
        self.proj_w = nn.Linear(num_heads, num_heads)

        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x):
        B, N, C = x.shape
        qkv = self.qkv(x).reshape(B, N, 3, self.num_heads, C // self.num_heads).permute(2, 0, 3, 1, 4)
        q, k, v = qkv[0] * self.scale, qkv[1], qkv[2]

        attn = q @ k.transpose(-2, -1)

        attn = self.proj_l(attn.permute(0, 2, 3, 1)).permute(0, 3, 1, 2)

        attn = attn.softmax(dim=-1)

        attn = self.proj_w(attn.permute(0, 2, 3, 1)).permute(0, 3, 1, 2)
        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 LayerScaleBlock(nn.Module):
    # taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py
    # with slight modifications to add layerScale
    def __init__(
            self,
            dim,
            num_heads,
            mlp_ratio=4.,
            qkv_bias=False,
            proj_drop=0.,
            attn_drop=0.,
            drop_path=0.,
            act_layer=nn.GELU,
            norm_layer=nn.LayerNorm,
            attn_block=TalkingHeadAttn,
            mlp_block=Mlp,
            init_values=1e-4,
    ):
        super().__init__()
        self.norm1 = norm_layer(dim)
        self.attn = attn_block(
            dim,
            num_heads=num_heads,
            qkv_bias=qkv_bias,
            attn_drop=attn_drop,
            proj_drop=proj_drop,
        )
        self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
        self.norm2 = norm_layer(dim)
        mlp_hidden_dim = int(dim * mlp_ratio)
        self.mlp = mlp_block(
            in_features=dim,
            hidden_features=mlp_hidden_dim,
            act_layer=act_layer,
            drop=proj_drop,
        )
        self.gamma_1 = nn.Parameter(init_values * torch.ones(dim))
        self.gamma_2 = nn.Parameter(init_values * torch.ones(dim))

    def forward(self, x):
        x = x + self.drop_path(self.gamma_1 * self.attn(self.norm1(x)))
        x = x + self.drop_path(self.gamma_2 * self.mlp(self.norm2(x)))
        return x


class Cait(nn.Module):
    # taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py
    # with slight modifications to adapt to our cait models
    def __init__(
            self,
            img_size=224,
            patch_size=16,
            in_chans=3,
            num_classes=1000,
            global_pool='token',
            embed_dim=768,
            depth=12,
            num_heads=12,
            mlp_ratio=4.,
            qkv_bias=True,
            drop_rate=0.,
            pos_drop_rate=0.,
            proj_drop_rate=0.,
            attn_drop_rate=0.,
            drop_path_rate=0.,
            block_layers=LayerScaleBlock,
            block_layers_token=LayerScaleBlockClassAttn,
            patch_layer=PatchEmbed,
            norm_layer=partial(nn.LayerNorm, eps=1e-6),
            act_layer=nn.GELU,
            attn_block=TalkingHeadAttn,
            mlp_block=Mlp,
            init_values=1e-4,
            attn_block_token_only=ClassAttn,
            mlp_block_token_only=Mlp,
            depth_token_only=2,
            mlp_ratio_token_only=4.0
    ):
        super().__init__()
        assert global_pool in ('', 'token', 'avg')

        self.num_classes = num_classes
        self.global_pool = global_pool
        self.num_features = self.head_hidden_size = self.embed_dim = embed_dim
        self.grad_checkpointing = False

        self.patch_embed = patch_layer(
            img_size=img_size,
            patch_size=patch_size,
            in_chans=in_chans,
            embed_dim=embed_dim,
        )
        num_patches = self.patch_embed.num_patches
        r = self.patch_embed.feat_ratio() if hasattr(self.patch_embed, 'feat_ratio') else patch_size

        self.cls_token = nn.Parameter(torch.zeros(1, 1, embed_dim))
        self.pos_embed = nn.Parameter(torch.zeros(1, num_patches, embed_dim))
        self.pos_drop = nn.Dropout(p=pos_drop_rate)

        dpr = [drop_path_rate for i in range(depth)]
        self.blocks = nn.Sequential(*[block_layers(
            dim=embed_dim,
            num_heads=num_heads,
            mlp_ratio=mlp_ratio,
            qkv_bias=qkv_bias,
            proj_drop=proj_drop_rate,
            attn_drop=attn_drop_rate,
            drop_path=dpr[i],
            norm_layer=norm_layer,
            act_layer=act_layer,
            attn_block=attn_block,
            mlp_block=mlp_block,
            init_values=init_values,
        ) for i in range(depth)])
        self.feature_info = [dict(num_chs=embed_dim, reduction=r, module=f'blocks.{i}') for i in range(depth)]

        self.blocks_token_only = nn.ModuleList([block_layers_token(
            dim=embed_dim,
            num_heads=num_heads,
            mlp_ratio=mlp_ratio_token_only,
            qkv_bias=qkv_bias,
            norm_layer=norm_layer,
            act_layer=act_layer,
            attn_block=attn_block_token_only,
            mlp_block=mlp_block_token_only,
            init_values=init_values,
        ) for _ in range(depth_token_only)])

        self.norm = norm_layer(embed_dim)

        self.head_drop = nn.Dropout(drop_rate)
        self.head = nn.Linear(embed_dim, num_classes) if num_classes > 0 else nn.Identity()

        trunc_normal_(self.pos_embed, std=.02)
        trunc_normal_(self.cls_token, std=.02)
        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)

    @torch.jit.ignore
    def no_weight_decay(self):
        return {'pos_embed', 'cls_token'}

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

    @torch.jit.ignore
    def group_matcher(self, coarse=False):
        def _matcher(name):
            if any([name.startswith(n) for n in ('cls_token', 'pos_embed', 'patch_embed')]):
                return 0
            elif name.startswith('blocks.'):
                return int(name.split('.')[1]) + 1
            elif name.startswith('blocks_token_only.'):
                # overlap token only blocks with last blocks
                to_offset = len(self.blocks) - len(self.blocks_token_only) + 1
                return int(name.split('.')[1]) + to_offset
            elif name.startswith('norm.'):
                return len(self.blocks)
            else:
                return float('inf')
        return _matcher

    @torch.jit.ignore
    def get_classifier(self) -> nn.Module:
        return self.head

    def reset_classifier(self, num_classes: int, global_pool: Optional[str] = None):
        self.num_classes = num_classes
        if global_pool is not None:
            assert global_pool in ('', 'token', 'avg')
            self.global_pool = global_pool
        self.head = nn.Linear(self.num_features, num_classes) if num_classes > 0 else nn.Identity()

    def forward_intermediates(
            self,
            x: torch.Tensor,
            indices: Optional[Union[int, List[int]]] = None,
            norm: bool = False,
            stop_early: bool = False,
            output_fmt: str = 'NCHW',
            intermediates_only: bool = False,
    ) -> Union[List[torch.Tensor], Tuple[torch.Tensor, List[torch.Tensor]]]:
        """ Forward features that returns intermediates.

        Args:
            x: Input image tensor
            indices: Take last n blocks if int, all if None, select matching indices if sequence
            norm: Apply norm layer to all intermediates
            stop_early: Stop iterating over blocks when last desired intermediate hit
            output_fmt: Shape of intermediate feature outputs
            intermediates_only: Only return intermediate features
        """
        assert output_fmt in ('NCHW', 'NLC'), 'Output format must be one of NCHW or NLC.'
        reshape = output_fmt == 'NCHW'
        intermediates = []
        take_indices, max_index = feature_take_indices(len(self.blocks), indices)

        # forward pass
        B, _, height, width = x.shape
        x = self.patch_embed(x)
        x = x + self.pos_embed
        x = self.pos_drop(x)

        if torch.jit.is_scripting() or not stop_early:  # can't slice blocks in torchscript
            blocks = self.blocks
        else:
            blocks = self.blocks[:max_index + 1]
        for i, blk in enumerate(blocks):
            if self.grad_checkpointing and not torch.jit.is_scripting():
                x = checkpoint(blk, x)
            else:
                x = blk(x)
            if i in take_indices:
                # normalize intermediates with final norm layer if enabled
                intermediates.append(self.norm(x) if norm else x)

        # process intermediates
        if reshape:
            # reshape to BCHW output format
            H, W = self.patch_embed.dynamic_feat_size((height, width))
            intermediates = [y.reshape(B, H, W, -1).permute(0, 3, 1, 2).contiguous() for y in intermediates]

        if intermediates_only:
            return intermediates

        # NOTE not supporting return of class tokens
        cls_tokens = self.cls_token.expand(x.shape[0], -1, -1)
        for i, blk in enumerate(self.blocks_token_only):
            cls_tokens = blk(x, cls_tokens)
        x = torch.cat((cls_tokens, x), dim=1)
        x = self.norm(x)

        return x, intermediates

    def prune_intermediate_layers(
            self,
            indices: Union[int, List[int]] = 1,
            prune_norm: bool = False,
            prune_head: bool = True,
    ):
        """ Prune layers not required for specified intermediates.
        """
        take_indices, max_index = feature_take_indices(len(self.blocks), indices)
        self.blocks = self.blocks[:max_index + 1]  # truncate blocks
        if prune_norm:
            self.norm = nn.Identity()
        if prune_head:
            self.blocks_token_only = nn.ModuleList()  # prune token blocks with head
            self.reset_classifier(0, '')
        return take_indices

    def forward_features(self, x):
        x = self.patch_embed(x)
        x = x + self.pos_embed
        x = self.pos_drop(x)
        if self.grad_checkpointing and not torch.jit.is_scripting():
            x = checkpoint_seq(self.blocks, x)
        else:
            x = self.blocks(x)
        cls_tokens = self.cls_token.expand(x.shape[0], -1, -1)
        for i, blk in enumerate(self.blocks_token_only):
            cls_tokens = blk(x, cls_tokens)
        x = torch.cat((cls_tokens, x), dim=1)
        x = self.norm(x)
        return x

    def forward_head(self, x, pre_logits: bool = False):
        if self.global_pool:
            x = x[:, 1:].mean(dim=1) if self.global_pool == 'avg' else x[:, 0]
        x = self.head_drop(x)
        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=None):
    if 'model' in state_dict:
        state_dict = state_dict['model']
    checkpoint_no_module = {}
    for k, v in state_dict.items():
        checkpoint_no_module[k.replace('module.', '')] = v
    return checkpoint_no_module


def _create_cait(variant, pretrained=False, **kwargs):
    out_indices = kwargs.pop('out_indices', 3)
    model = build_model_with_cfg(
        Cait,
        variant,
        pretrained,
        pretrained_filter_fn=checkpoint_filter_fn,
        feature_cfg=dict(out_indices=out_indices, feature_cls='getter'),
        **kwargs,
    )
    return model


def _cfg(url='', **kwargs):
    return {
        'url': url,
        'num_classes': 1000, 'input_size': (3, 384, 384), 'pool_size': None,
        'crop_pct': 1.0, 'interpolation': 'bicubic', 'fixed_input_size': True,
        'mean': IMAGENET_DEFAULT_MEAN, 'std': IMAGENET_DEFAULT_STD,
        'first_conv': 'patch_embed.proj', 'classifier': 'head',
        **kwargs
    }


default_cfgs = generate_default_cfgs({
    'cait_xxs24_224.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/XXS24_224.pth',
        input_size=(3, 224, 224),
    ),
    'cait_xxs24_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/XXS24_384.pth',
    ),
    'cait_xxs36_224.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/XXS36_224.pth',
        input_size=(3, 224, 224),
    ),
    'cait_xxs36_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/XXS36_384.pth',
    ),
    'cait_xs24_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/XS24_384.pth',
    ),
    'cait_s24_224.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/S24_224.pth',
        input_size=(3, 224, 224),
    ),
    'cait_s24_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/S24_384.pth',
    ),
    'cait_s36_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/S36_384.pth',
    ),
    'cait_m36_384.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/M36_384.pth',
    ),
    'cait_m48_448.fb_dist_in1k': _cfg(
        hf_hub_id='timm/',
        url='https://dl.fbaipublicfiles.com/deit/M48_448.pth',
        input_size=(3, 448, 448),
    ),
})


@register_model
def cait_xxs24_224(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=192, depth=24, num_heads=4, init_values=1e-5)
    model = _create_cait('cait_xxs24_224', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_xxs24_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=192, depth=24, num_heads=4, init_values=1e-5)
    model = _create_cait('cait_xxs24_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_xxs36_224(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=192, depth=36, num_heads=4, init_values=1e-5)
    model = _create_cait('cait_xxs36_224', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_xxs36_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=192, depth=36, num_heads=4, init_values=1e-5)
    model = _create_cait('cait_xxs36_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_xs24_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=288, depth=24, num_heads=6, init_values=1e-5)
    model = _create_cait('cait_xs24_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_s24_224(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=384, depth=24, num_heads=8, init_values=1e-5)
    model = _create_cait('cait_s24_224', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_s24_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=384, depth=24, num_heads=8, init_values=1e-5)
    model = _create_cait('cait_s24_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_s36_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=384, depth=36, num_heads=8, init_values=1e-6)
    model = _create_cait('cait_s36_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_m36_384(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=768, depth=36, num_heads=16, init_values=1e-6)
    model = _create_cait('cait_m36_384', pretrained=pretrained, **dict(model_args, **kwargs))
    return model


@register_model
def cait_m48_448(pretrained=False, **kwargs) -> Cait:
    model_args = dict(patch_size=16, embed_dim=768, depth=48, num_heads=16, init_values=1e-6)
    model = _create_cait('cait_m48_448', pretrained=pretrained, **dict(model_args, **kwargs))
    return model
