# background_remover/services.py
import torch
from PIL import Image
from torchvision import transforms
from transformers import AutoModelForImageSegmentation

class BiRefNetService:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super(BiRefNetService, cls).__new__(cls)
            cls._instance._init_model()
        return cls._instance

    def _init_model(self):
        self.device = "cuda" if torch.cuda.is_available() else "cpu"
        self.model = AutoModelForImageSegmentation.from_pretrained(
            "ZhengPeng7/BiRefNet", trust_remote_code=True
        )
        self.model.to(self.device)
        self.model.eval()
        self.transform = transforms.Compose([
            transforms.Resize((1024, 1024)),
            transforms.ToTensor(),
            transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225]),
        ])

    def remove_background(self, input_image: Image.Image) -> Image.Image:
        image_size = input_image.size
        input_tensor = self.transform(input_image.convert("RGB")).unsqueeze(0).to(self.device)

        with torch.no_grad():
            preds = self.model(input_tensor)[-1].sigmoid().cpu()

        mask = transforms.ToPILImage()(preds[0].squeeze()).resize(image_size)
        
        # Create white background
        white_bg = Image.new("RGB", image_size, (255, 255, 255))
        white_bg.paste(input_image, (0, 0), mask)
        return white_bg