"""独立加载本目录中的商品标题分类模型，无需原项目和基座权重。"""

import json
from pathlib import Path

import torch
from torch import nn
from transformers import AutoConfig, AutoModel


class BertTitleClassifier(nn.Module):
    def __init__(self, bert_config, num_classes):
        super().__init__()
        self.bert = AutoModel.from_config(bert_config)
        self.classifier = nn.Linear(bert_config.hidden_size, num_classes)

    def forward(self, input_ids, attention_mask=None):
        outputs = self.bert(input_ids=input_ids, attention_mask=attention_mask)
        return self.classifier(outputs.last_hidden_state[:, 0, :])

    @classmethod
    def from_pretrained(cls, model_dir, device="cpu"):
        model_dir = Path(model_dir)
        labels = json.loads((model_dir / "labels.json").read_text(encoding="utf-8"))
        bert_config = AutoConfig.from_pretrained(model_dir, local_files_only=True)
        model = cls(bert_config, len(labels["id2label"]))
        state = torch.load(model_dir / "model.pt", map_location="cpu", weights_only=True)
        model.load_state_dict(state)
        return model.to(device).eval()