# --------------------------------------------------------
# BEIT: BERT Pre-Training of Image Transformers (https://arxiv.org/abs/2106.08254)
# Github source: https://github.com/microsoft/unilm/tree/master/beit
# Copyright (c) 2021 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# By Hangbo Bao
# Based on timm and DeiT code bases
# https://github.com/rwightman/pytorch-image-models/tree/master/timm
# https://github.com/facebookresearch/deit/
# --------------------------------------------------------'
import math
import torch
import torch.nn as nn
from functools import partial

from modeling_finetune import Block, _cfg, PatchEmbed, RelativePositionBias
from timm.models.registry import register_model
from timm.models.layers import trunc_normal_ as __call_trunc_normal_


def trunc_normal_(tensor, mean=0., std=1.):
    __call_trunc_normal_(tensor, mean=mean, std=std, a=-std, b=std)


__all__ = [
    'beit_base_patch16_224_8k_vocab', 
    'beit_large_patch16_224_8k_vocab', 
]


class VisionTransformerForMaskedImageModeling(nn.Module):
    def __init__(self, img_size=224, patch_size=16, in_chans=3, vocab_size=8192, embed_dim=768, depth=12,
                 num_heads=12, mlp_ratio=4., qkv_bias=True, qk_scale=None, drop_rate=0., attn_drop_rate=0.,
                 drop_path_rate=0., norm_layer=None, init_values=None, attn_head_dim=None,
                 use_abs_pos_emb=True, use_rel_pos_bias=False, use_shared_rel_pos_bias=False, init_std=0.02, **kwargs):
        super().__init__()
        self.num_features = self.embed_dim = embed_dim  # num_features for consistency with other models

        self.patch_embed = PatchEmbed(
            img_size=img_size, patch_size=patch_size, in_chans=in_chans, embed_dim=embed_dim)
        num_patches = self.patch_embed.num_patches

        self.cls_token = nn.Parameter(torch.zeros(1, 1, embed_dim))
        self.mask_token = nn.Parameter(torch.zeros(1, 1, embed_dim))
        if use_abs_pos_emb:
            self.pos_embed = nn.Parameter(torch.zeros(1, num_patches + 1, embed_dim))
        else:
            self.pos_embed = None
        self.pos_drop = nn.Dropout(p=drop_rate)

        if use_shared_rel_pos_bias:
            self.rel_pos_bias = RelativePositionBias(window_size=self.patch_embed.patch_shape, num_heads=num_heads)
        else:
            self.rel_pos_bias = None

        dpr = [x.item() for x in torch.linspace(0, drop_path_rate, depth)]  # stochastic depth decay rule
        self.blocks = nn.ModuleList([
            Block(
                dim=embed_dim, num_heads=num_heads, mlp_ratio=mlp_ratio, qkv_bias=qkv_bias, qk_scale=qk_scale,
                drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[i], norm_layer=norm_layer,
                init_values=init_values, window_size=self.patch_embed.patch_shape if use_rel_pos_bias else None,
                attn_head_dim=attn_head_dim,
            )
            for i in range(depth)])
        self.norm = norm_layer(embed_dim)

        self.init_std = init_std
        self.lm_head = nn.Linear(embed_dim, vocab_size)

        if self.pos_embed is not None:
            trunc_normal_(self.pos_embed, std=self.init_std)
        trunc_normal_(self.cls_token, std=self.init_std)
        trunc_normal_(self.mask_token, std=self.init_std)
        trunc_normal_(self.lm_head.weight, std=self.init_std)
        self.apply(self._init_weights)
        self.fix_init_weight()

    def fix_init_weight(self):
        def rescale(param, layer_id):
            param.div_(math.sqrt(2.0 * layer_id))

        for layer_id, layer in enumerate(self.blocks):
            rescale(layer.attn.proj.weight.data, layer_id + 1)
            rescale(layer.mlp.fc2.weight.data, layer_id + 1)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=self.init_std)
            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):
            trunc_normal_(m.weight, std=self.init_std)
            if m.bias is not None:
                nn.init.constant_(m.bias, 0)

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

    def get_num_layers(self):
        return len(self.blocks)

    def forward_features(self, x, bool_masked_pos):
        x = self.patch_embed(x, bool_masked_pos=bool_masked_pos)
        batch_size, seq_len, _ = x.size()

        cls_tokens = self.cls_token.expand(batch_size, -1, -1)  # stole cls_tokens impl from Phil Wang, thanks
        mask_token = self.mask_token.expand(batch_size, seq_len, -1)

        # replace the masked visual tokens by mask_token
        w = bool_masked_pos.unsqueeze(-1).type_as(mask_token)
        x = x * (1 - w) + mask_token * w

        x = torch.cat((cls_tokens, x), dim=1)
        if self.pos_embed is not None:
            x = x + self.pos_embed
        x = self.pos_drop(x)

        rel_pos_bias = self.rel_pos_bias() if self.rel_pos_bias is not None else None
        for blk in self.blocks:
            x = blk(x, rel_pos_bias=rel_pos_bias)

        return self.norm(x)

    def forward(self, x, bool_masked_pos, return_all_tokens=False):
        x = self.forward_features(x, bool_masked_pos=bool_masked_pos)
        x = x[:, 1:]
        if return_all_tokens:
            return self.lm_head(x)
        else:
            # return the masked tokens
            return self.lm_head(x[bool_masked_pos])


@register_model
def beit_base_patch16_224_8k_vocab(pretrained=False, **kwargs):
    model = VisionTransformerForMaskedImageModeling(
        patch_size=16, embed_dim=768, depth=12, num_heads=12, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), vocab_size=8192, **kwargs)
    model.default_cfg = _cfg()
    if pretrained:
        checkpoint = torch.load(
            kwargs["init_ckpt"], map_location="cpu"
        )
        model.load_state_dict(checkpoint["model"])
    return model


@register_model
def beit_large_patch16_224_8k_vocab(pretrained=False, **kwargs):
    model = VisionTransformerForMaskedImageModeling(
        patch_size=16, embed_dim=1024, depth=24, num_heads=16, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), vocab_size=8192, **kwargs)
    model.default_cfg = _cfg()
    if pretrained:
        checkpoint = torch.load(
            kwargs["init_ckpt"], map_location="cpu"
        )
        model.load_state_dict(checkpoint["model"])
    return model
