app.py

import streamlit as st
from llama_cpp import Llama
from huggingface_hub import hf_hub_download
import os
import time
import threading

# ===== 配置区（CPU友好型模型）=====
MODEL_REPO = "Qwen/Qwen2.5-1.5B-Instruct-GGUF"
MODEL_FILENAME = "qwen2.5-1_5b-instruct-q4_k_m.gguf"
MODEL_DIR = "/app/models"  # Spaces持久化目录

# 全局模型变量（避免重复加载）
llm_instance = None
model_loading = False
model_error = None

def background_model_load():
    """后台线程加载模型（避免阻塞Streamlit主线程）"""
    global llm_instance, model_loading, model_error
    
    if model_loading:
        return
    
    model_loading = True
    try:
        # 创建目录
        os.makedirs(MODEL_DIR, exist_ok=True)
        model_path = os.path.join(MODEL_DIR, MODEL_FILENAME)
        
        # 检查是否已下载
        if not os.path.exists(model_path):
            st.session_state.download_status = "downloading"
            # 下载模型（自动断点续传）
            model_path = hf_hub_download(
                repo_id=MODEL_REPO,
                filename=MODEL_FILENAME,
                local_dir=MODEL_DIR,
                resume_download=True,
                token=None  # 公开模型无需token
            )
            st.session_state.download_status = "downloaded"
        
        # 加载模型到内存
        st.session_state.download_status = "loading"
        start = time.time()
        llm_instance = Llama(
            model_path=model_path,
            n_ctx=2048,
            n_threads=4,      # Spaces CPU通常4核
            n_gpu_layers=0,   # 纯CPU
            verbose=False,
            n_batch=512       # 优化批处理
        )
        st.session_state.download_status = "ready"
        st.session_state.load_time = time.time() - start
        
    except Exception as e:
        model_error = str(e)
        st.session_state.download_status = "error"
    finally:
        model_loading = False

# ===== Streamlit UI =====
st.set_page_config(page_title="🦙 CPU LLM Demo", page_icon="🦙", layout="wide")

# 初始化状态
if "download_status" not in st.session_state:
    st.session_state.download_status = "idle"
    st.session_state.load_time = 0
    # 启动后台加载线程
    threading.Thread(target=background_model_load, daemon=True).start()

# 顶部状态栏
col1, col2 = st.columns([3, 1])
with col1:
    status_map = {
        "idle": "⏳ 准备加载模型...",
        "downloading": "⬇️ 正在下载模型 (1.0GB)...",
        "downloaded": "✅ 模型下载完成，正在加载到内存...",
        "loading": "🧠 正在加载模型到内存（约60-90秒）...",
        "ready": f"✅ 模型就绪！加载耗时 {st.session_state.load_time:.1f} 秒",
        "error": f"❌ 加载失败: {model_error}"
    }
    st.info(status_map.get(st.session_state.download_status, "❓ 未知状态"))
with col2:
    st.caption("💡 首次加载需1-2分钟 | 休眠后需重新下载")

# 模型未就绪时禁止聊天
if st.session_state.download_status != "ready":
    st.stop()

# 聊天界面
st.title("🦙 本地CPU大模型 (Qwen2.5-1.5B)")
st.caption("完全离线运行 · 无外部API调用 · 适合演示用途")

if "messages" not in st.session_state:
    st.session_state.messages = []

# 显示历史消息
for msg in st.session_state.messages:
    with st.chat_message(msg["role"]):
        st.markdown(msg["content"])

# 用户输入
if prompt := st.chat_input("问点什么吧..."):
    # 保存用户消息
    st.session_state.messages.append({"role": "user", "content": prompt})
    with st.chat_message("user"):
        st.markdown(prompt)
    
    # 生成回复
    with st.chat_message("assistant"):
        message_placeholder = st.empty()
        full_response = ""
        
        # Qwen2.5对话模板
        messages = [
            {"role": "system", "content": "You are a helpful assistant."},
            *[{"role": m["role"], "content": m["content"]} for m in st.session_state.messages]
        ]
        
        # 流式生成（CPU较慢，需耐心）
        try:
            for chunk in llm_instance.create_chat_completion(
                messages=messages,
                max_tokens=256,   # 限制长度避免超时
                temperature=0.7,
                stream=True
            ):
                delta = chunk["choices"][0]["delta"]
                if "content" in delta:
                    full_response += delta["content"]
                    message_placeholder.markdown(full_response + "▌")
            message_placeholder.markdown(full_response)
            st.session_state.messages.append({"role": "assistant", "content": full_response})
        except Exception as e:
            st.error(f"生成失败: {str(e)}")
            message_placeholder.markdown("❌ 生成超时，请缩短问题长度重试")