from transformers import AutoModelForCausalLM, AutoTokenizer

class ChatEngine:
    def __init__(self, model_name: str, system_prompt: str):
        self.model_name = model_name
        self.system_prompt = system_prompt
        self.tokenizer = AutoTokenizer.from_pretrained(model_name)
        self.model = AutoModelForCausalLM.from_pretrained(model_name)

    def _generate(self, prompt: str) -> str:
        inputs = self.tokenizer(prompt, return_tensors="pt")
        outputs = self.model.generate(**inputs, max_new_tokens=512)
        return self.tokenizer.decode(outputs[0], skip_special_tokens=True)

    def chat(self, user_input: str) -> str:
        prompt = f"{self.system_prompt}\nUser: {user_input}\nAI:"
        return self._generate(prompt)