#! -*- coding:utf-8 -*-
# 通过TemporalEnsembling提升模型泛化
# 官方项目：https://github.com/s-laine/tempens
# pytorch第三方实现：https://github.com/ferretj/temporal-ensembling
# 数据集：情感分类数据集
# 本示例是把监督数据当成无监督数据使用

from bert4torch.models import build_transformer_model, BaseModel
import torch
from torch.utils.data import DataLoader
import torch.nn as nn
import torch.optim as optim
from bert4torch.snippets import sequence_padding, Callback, ListDataset, seed_everything, text_segmentate, get_pool_emb
from bert4torch.tokenizers import Tokenizer
from bert4torch.losses import TemporalEnsemblingLoss

maxlen = 256
batch_size = 16
epochs = 10

# BERT base
config_path = 'F:/Projects/pretrain_ckpt/bert/[google_tf_base]--chinese_L-12_H-768_A-12/bert_config.json'
checkpoint_path = 'F:/Projects/pretrain_ckpt/bert/[google_tf_base]--chinese_L-12_H-768_A-12/pytorch_model.bin'
dict_path = 'F:/Projects/pretrain_ckpt/bert/[google_tf_base]--chinese_L-12_H-768_A-12/vocab.txt'
device = 'cuda' if torch.cuda.is_available() else 'cpu'
seed_everything(42)

# 建立分词器
tokenizer = Tokenizer(dict_path, do_lower_case=True)

# 加载数据集
class MyDataset(ListDataset):
    @staticmethod
    def load_data(filenames):
        """加载数据，并尽量划分为不超过maxlen的句子
        """
        D = []
        seps, strips = u'\n。！？!?；;，, ', u'；;，, '
        for filename in filenames:
            with open(filename, encoding='utf-8') as f:
                for l in f:
                    text, label = l.strip().split('\t')
                    for t in text_segmentate(text, maxlen - 2, seps, strips):
                        D.append((t, int(label)))
        return D

def collate_fn(batch):
    batch_token_ids, batch_labels = [], []
    for text, label in batch:
        token_ids, _ = tokenizer.encode(text, maxlen=maxlen)
        batch_token_ids.append(token_ids)
        batch_labels.append([label])
    batch_token_ids = torch.tensor(sequence_padding(batch_token_ids), dtype=torch.long, device=device)
    batch_labels = torch.tensor(batch_labels, dtype=torch.long, device=device)
    return batch_token_ids, batch_labels.flatten()

# 加载数据集，训练数据集shuffle=False
train_dataloader = DataLoader(MyDataset(['F:/Projects/data/corpus/sentence_classification/sentiment/sentiment.train.data']), batch_size=batch_size, shuffle=False, collate_fn=collate_fn) 
valid_dataloader = DataLoader(MyDataset(['F:/Projects/data/corpus/sentence_classification/sentiment/sentiment.valid.data']), batch_size=batch_size, collate_fn=collate_fn) 
test_dataloader = DataLoader(MyDataset(['F:/Projects/data/corpus/sentence_classification/sentiment/sentiment.test.data']),  batch_size=batch_size, collate_fn=collate_fn) 

# 定义bert上的模型结构
class Model(BaseModel):
    def __init__(self, pool_method='cls') -> None:
        super().__init__()
        self.pool_method = pool_method
        self.bert= build_transformer_model(config_path=config_path, checkpoint_path=checkpoint_path, segment_vocab_size=0, with_pool=True)
        self.dropout = nn.Dropout(0.1)
        self.dense = nn.Linear(self.bert.configs['hidden_size'], 2)

    def forward(self, token_ids):
        hidden_states, pooling = self.bert([token_ids])
        pooled_output = get_pool_emb(hidden_states, pooling, token_ids.gt(0).long(), self.pool_method)
        output = self.dropout(pooled_output)
        output = self.dense(output)
        return output
model = Model().to(device)

class MyLoss(TemporalEnsemblingLoss):
    def forward(self, y_pred, y_true):
        # 监督数据当成无监督数据使用，真实场景中可以用大量的无监督数据来使用
        y_pred_sup, y_pred_unsup, y_true_sup = y_pred, y_pred, y_true
        return super().forward(y_pred_sup, y_pred_unsup, y_true_sup, model.epoch, model.bti)
loss = MyLoss(epochs=epochs, max_batch_num=None)
model.compile(loss=loss, optimizer=optim.Adam(model.parameters(), lr=2e-5), metrics=['accuracy'])

class Evaluator(Callback):
    """评估与保存
    """
    def __init__(self):
        self.best_val_acc = 0.

    def on_epoch_end(self, global_step, epoch, logs=None):
        val_acc = self.evaluate(valid_dataloader)
        test_acc = self.evaluate(test_dataloader)
        if val_acc > self.best_val_acc:
            self.best_val_acc = val_acc
            # model.save_weights('best_model.pt')
        print(f'val_acc: {val_acc:.5f}, test_acc: {test_acc:.5f}, best_val_acc: {self.best_val_acc:.5f}\n')

    # 定义评价函数
    def evaluate(self, data):
        total, right = 0., 0.
        for x_true, y_true in data:
            y_pred = model.predict(x_true).argmax(axis=1)
            total += len(y_true)
            right += (y_true == y_pred).sum().item()
        return right / total


if __name__ == '__main__':
    evaluator = Evaluator()
    model.fit(train_dataloader, epochs=epochs, steps_per_epoch=None, callbacks=[evaluator])
else: 
    model.load_weights('best_model.pt')