'''
 * Copyright (c) 2022, salesforce.com, inc.
 * All rights reserved.
 * SPDX-License-Identifier: BSD-3-Clause
 * For full license text, see LICENSE.txt file in the repo root or https://opensource.org/licenses/BSD-3-Clause
 * By Junnan Li
'''
from models.med import BertConfig, BertModel, BertLMHeadModel
from transformers import BertTokenizer
import transformers
transformers.logging.set_verbosity_error()

import torch
from torch import nn
import torch.nn.functional as F

from models.blip import create_vit, init_tokenizer, load_checkpoint

class BLIP_Pretrain(nn.Module):
    def __init__(self,                 
                 med_config = 'configs/bert_config.json',  
                 image_size = 224,
                 vit = 'base',
                 vit_grad_ckpt = False,
                 vit_ckpt_layer = 0,                    
                 embed_dim = 256,     
                 queue_size = 57600,
                 momentum = 0.995,
                 ):
        """
        Args:
            med_config (str): path for the mixture of encoder-decoder model's configuration file
            image_size (int): input image size
            vit (str): model size of vision transformer
        """               
        super().__init__()
        
        self.visual_encoder, vision_width = create_vit(vit,image_size, vit_grad_ckpt, vit_ckpt_layer, 0)
        
        if vit=='base':
            checkpoint = torch.hub.load_state_dict_from_url(
                url="https://dl.fbaipublicfiles.com/deit/deit_base_patch16_224-b5f2ef4d.pth",
                map_location="cpu", check_hash=True)
            state_dict = checkpoint["model"]     
            msg = self.visual_encoder.load_state_dict(state_dict,strict=False)
        elif vit=='large':
            from timm.models.helpers import load_custom_pretrained
            from timm.models.vision_transformer import default_cfgs
            load_custom_pretrained(self.visual_encoder,default_cfgs['vit_large_patch16_224_in21k'])        
               
        self.tokenizer = init_tokenizer()   
        encoder_config = BertConfig.from_json_file(med_config)
        encoder_config.encoder_width = vision_width
        self.text_encoder = BertModel.from_pretrained('bert-base-uncased',config=encoder_config, add_pooling_layer=False)
        self.text_encoder.resize_token_embeddings(len(self.tokenizer)) 

        text_width = self.text_encoder.config.hidden_size
        
        self.vision_proj = nn.Linear(vision_width, embed_dim)
        self.text_proj = nn.Linear(text_width, embed_dim)

        self.itm_head = nn.Linear(text_width, 2) 
        
        # create momentum encoders  
        self.visual_encoder_m, vision_width = create_vit(vit,image_size)              
        self.vision_proj_m = nn.Linear(vision_width, embed_dim)
        self.text_encoder_m = BertModel(config=encoder_config, add_pooling_layer=False)      
        self.text_proj_m = nn.Linear(text_width, embed_dim)
        
        self.model_pairs = [[self.visual_encoder,self.visual_encoder_m],
                            [self.vision_proj,self.vision_proj_m],
                            [self.text_encoder,self.text_encoder_m],
                            [self.text_proj,self.text_proj_m],
                           ]       
        self.copy_params()

        # create the queue
        self.register_buffer("image_queue", torch.randn(embed_dim, queue_size))
        self.register_buffer("text_queue", torch.randn(embed_dim, queue_size))
        self.register_buffer("queue_ptr", torch.zeros(1, dtype=torch.long))  

        self.image_queue = nn.functional.normalize(self.image_queue, dim=0)
        self.text_queue = nn.functional.normalize(self.text_queue, dim=0)
        
        self.queue_size = queue_size
        self.momentum = momentum
        self.temp = nn.Parameter(0.07*torch.ones([]))   
        
        # create the decoder
        decoder_config = BertConfig.from_json_file(med_config)
        decoder_config.encoder_width = vision_width        
        self.text_decoder = BertLMHeadModel.from_pretrained('bert-base-uncased',config=decoder_config)    
        self.text_decoder.resize_token_embeddings(len(self.tokenizer)) 
        tie_encoder_decoder_weights(self.text_encoder,self.text_decoder.bert,'','/attention')
        
        
    def forward(self, image, caption, alpha):
        with torch.no_grad():
            self.temp.clamp_(0.001,0.5)
        
        image_embeds = self.visual_encoder(image) 
        image_atts = torch.ones(image_embeds.size()[:-1],dtype=torch.long).to(image.device)        
        image_feat = F.normalize(self.vision_proj(image_embeds[:,0,:]),dim=-1)          
        
        text = self.tokenizer(caption, padding='max_length', truncation=True, max_length=30, 
                              return_tensors="pt").to(image.device)  
        text_output = self.text_encoder(text.input_ids, attention_mask = text.attention_mask,                      
                                        return_dict = True, mode = 'text')            
        text_feat = F.normalize(self.text_proj(text_output.last_hidden_state[:,0,:]),dim=-1)                 
             
        # get momentum features
        with torch.no_grad():
            self._momentum_update()
            image_embeds_m = self.visual_encoder_m(image) 
            image_feat_m = F.normalize(self.vision_proj_m(image_embeds_m[:,0,:]),dim=-1)  
            image_feat_all = torch.cat([image_feat_m.t(),self.image_queue.clone().detach()],dim=1)                   
            
            text_output_m = self.text_encoder_m(text.input_ids, attention_mask = text.attention_mask,                      
                                                return_dict = True, mode = 'text')    
            text_feat_m = F.normalize(self.text_proj_m(text_output_m.last_hidden_state[:,0,:]),dim=-1) 
            text_feat_all = torch.cat([text_feat_m.t(),self.text_queue.clone().detach()],dim=1)

            sim_i2t_m = image_feat_m @ text_feat_all / self.temp  
            sim_t2i_m = text_feat_m @ image_feat_all / self.temp 

            sim_targets = torch.zeros(sim_i2t_m.size()).to(image.device)
            sim_targets.fill_diagonal_(1)          

            sim_i2t_targets = alpha * F.softmax(sim_i2t_m, dim=1) + (1 - alpha) * sim_targets
            sim_t2i_targets = alpha * F.softmax(sim_t2i_m, dim=1) + (1 - alpha) * sim_targets        

        sim_i2t = image_feat @ text_feat_all / self.temp
        sim_t2i = text_feat @ image_feat_all / self.temp
                             
        loss_i2t = -torch.sum(F.log_softmax(sim_i2t, dim=1)*sim_i2t_targets,dim=1).mean()
        loss_t2i = -torch.sum(F.log_softmax(sim_t2i, dim=1)*sim_t2i_targets,dim=1).mean() 

        loss_ita = (loss_i2t+loss_t2i)/2

        self._dequeue_and_enqueue(image_feat_m, text_feat_m)        

        ###============== Image-text Matching ===================###
        encoder_input_ids = text.input_ids.clone()
        encoder_input_ids[:,0] = self.tokenizer.enc_token_id
        
        # forward the positve image-text pair
        bs = image.size(0)
        output_pos = self.text_encoder(encoder_input_ids,
                                       attention_mask = text.attention_mask,
                                       encoder_hidden_states = image_embeds,
                                       encoder_attention_mask = image_atts,      
                                       return_dict = True,
                                      )            
        with torch.no_grad():       
            weights_t2i = F.softmax(sim_t2i[:,:bs],dim=1)+1e-4 
            weights_t2i.fill_diagonal_(0)            
            weights_i2t = F.softmax(sim_i2t[:,:bs],dim=1)+1e-4  
            weights_i2t.fill_diagonal_(0)   
            
        # select a negative image for each text
        image_embeds_neg = []    
        for b in range(bs):
            neg_idx = torch.multinomial(weights_t2i[b], 1).item()
            image_embeds_neg.append(image_embeds[neg_idx])
        image_embeds_neg = torch.stack(image_embeds_neg,dim=0)   

        # select a negative text for each image
        text_ids_neg = []
        text_atts_neg = []
        for b in range(bs):
            neg_idx = torch.multinomial(weights_i2t[b], 1).item()
            text_ids_neg.append(encoder_input_ids[neg_idx])
            text_atts_neg.append(text.attention_mask[neg_idx])

        text_ids_neg = torch.stack(text_ids_neg,dim=0)   
        text_atts_neg = torch.stack(text_atts_neg,dim=0)      

        text_ids_all = torch.cat([encoder_input_ids, text_ids_neg],dim=0)     
        text_atts_all = torch.cat([text.attention_mask, text_atts_neg],dim=0)     

        image_embeds_all = torch.cat([image_embeds_neg,image_embeds],dim=0)
        image_atts_all = torch.cat([image_atts,image_atts],dim=0)

        output_neg = self.text_encoder(text_ids_all,
                                       attention_mask = text_atts_all,
                                       encoder_hidden_states = image_embeds_all,
                                       encoder_attention_mask = image_atts_all,      
                                       return_dict = True,
                                      )                            

        vl_embeddings = torch.cat([output_pos.last_hidden_state[:,0,:], output_neg.last_hidden_state[:,0,:]],dim=0)
        vl_output = self.itm_head(vl_embeddings)            

        itm_labels = torch.cat([torch.ones(bs,dtype=torch.long),torch.zeros(2*bs,dtype=torch.long)],
                               dim=0).to(image.device)
        loss_itm = F.cross_entropy(vl_output, itm_labels)  
        
        ##================= LM ========================##     
        decoder_input_ids = text.input_ids.clone()      
        decoder_input_ids[:,0] = self.tokenizer.bos_token_id
        decoder_targets = decoder_input_ids.masked_fill(decoder_input_ids == self.tokenizer.pad_token_id, -100) 

        decoder_output = self.text_decoder(decoder_input_ids, 
                                           attention_mask = text.attention_mask, 
                                           encoder_hidden_states = image_embeds,
                                           encoder_attention_mask = image_atts,                  
                                           labels = decoder_targets,
                                           return_dict = True,   
                                          )   
          
        loss_lm = decoder_output.loss                
        return loss_ita, loss_itm, loss_lm
 


    @torch.no_grad()    
    def copy_params(self):
        for model_pair in self.model_pairs:           
            for param, param_m in zip(model_pair[0].parameters(), model_pair[1].parameters()):
                param_m.data.copy_(param.data)  # initialize
                param_m.requires_grad = False  # not update by gradient    

            
    @torch.no_grad()        
    def _momentum_update(self):
        for model_pair in self.model_pairs:           
            for param, param_m in zip(model_pair[0].parameters(), model_pair[1].parameters()):
                param_m.data = param_m.data * self.momentum + param.data * (1. - self.momentum)

                        
    @torch.no_grad()
    def _dequeue_and_enqueue(self, image_feat, text_feat):
        # gather keys before updating queue
        image_feats = concat_all_gather(image_feat)
        text_feats = concat_all_gather(text_feat)

        batch_size = image_feats.shape[0]

        ptr = int(self.queue_ptr)
        assert self.queue_size % batch_size == 0  # for simplicity

        # replace the keys at ptr (dequeue and enqueue)
        self.image_queue[:, ptr:ptr + batch_size] = image_feats.T
        self.text_queue[:, ptr:ptr + batch_size] = text_feats.T
        ptr = (ptr + batch_size) % self.queue_size  # move pointer

        self.queue_ptr[0] = ptr 


def blip_pretrain(**kwargs):
    model = BLIP_Pretrain(**kwargs)
    return model 


@torch.no_grad()
def concat_all_gather(tensor):
    """
    Performs all_gather operation on the provided tensors.
    *** Warning ***: torch.distributed.all_gather has no gradient.
    """
    tensors_gather = [torch.ones_like(tensor)
        for _ in range(torch.distributed.get_world_size())]
    torch.distributed.all_gather(tensors_gather, tensor, async_op=False)

    output = torch.cat(tensors_gather, dim=0)
    return output     


from typing import List
def tie_encoder_decoder_weights(encoder: nn.Module, decoder: nn.Module, base_model_prefix: str, skip_key:str):
    uninitialized_encoder_weights: List[str] = []
    if decoder.__class__ != encoder.__class__:
        logger.info(
            f"{decoder.__class__} and {encoder.__class__} are not equal. In this case make sure that all encoder weights are correctly initialized."
        )

    def tie_encoder_to_decoder_recursively(
        decoder_pointer: nn.Module,
        encoder_pointer: nn.Module,
        module_name: str,
        uninitialized_encoder_weights: List[str],
        skip_key: str,
        depth=0,
    ):
        assert isinstance(decoder_pointer, nn.Module) and isinstance(
            encoder_pointer, nn.Module
        ), f"{decoder_pointer} and {encoder_pointer} have to be of type torch.nn.Module"
        if hasattr(decoder_pointer, "weight") and skip_key not in module_name:
            assert hasattr(encoder_pointer, "weight")
            encoder_pointer.weight = decoder_pointer.weight
            if hasattr(decoder_pointer, "bias"):
                assert hasattr(encoder_pointer, "bias")
                encoder_pointer.bias = decoder_pointer.bias                
            print(module_name+' is tied')    
            return

        encoder_modules = encoder_pointer._modules
        decoder_modules = decoder_pointer._modules
        if len(decoder_modules) > 0:
            assert (
                len(encoder_modules) > 0
            ), f"Encoder module {encoder_pointer} does not match decoder module {decoder_pointer}"

            all_encoder_weights = set([module_name + "/" + sub_name for sub_name in encoder_modules.keys()])
            encoder_layer_pos = 0
            for name, module in decoder_modules.items():
                if name.isdigit():
                    encoder_name = str(int(name) + encoder_layer_pos)
                    decoder_name = name
                    if not isinstance(decoder_modules[decoder_name], type(encoder_modules[encoder_name])) and len(
                        encoder_modules
                    ) != len(decoder_modules):
                        # this can happen if the name corresponds to the position in a list module list of layers
                        # in this case the decoder has added a cross-attention that the encoder does not have
                        # thus skip this step and subtract one layer pos from encoder
                        encoder_layer_pos -= 1
                        continue
                elif name not in encoder_modules:
                    continue
                elif depth > 500:
                    raise ValueError(
                        "Max depth of recursive function `tie_encoder_to_decoder` reached. It seems that there is a circular dependency between two or more `nn.Modules` of your model."
                    )
                else:
                    decoder_name = encoder_name = name
                tie_encoder_to_decoder_recursively(
                    decoder_modules[decoder_name],
                    encoder_modules[encoder_name],
                    module_name + "/" + name,
                    uninitialized_encoder_weights,
                    skip_key,
                    depth=depth + 1,
                )
                all_encoder_weights.remove(module_name + "/" + encoder_name)

            uninitialized_encoder_weights += list(all_encoder_weights)

    # tie weights recursively
    tie_encoder_to_decoder_recursively(decoder, encoder, base_model_prefix, uninitialized_encoder_weights, skip_key)  
