添加GraphRAG后端

backend/app.py

@@ -0,0 +1,80 @@
+"""
+大唐双龙传 GraphRAG — FastAPI 后端
+
+端点:
+  GET  /api/health    — 健康检查（含 Neo4j 连通性）
+  GET  /api/stats     — 图谱节点/关系统计
+  POST /api/import    — 触发数据导入（一次性操作）
+  POST /api/chat      — 知识问答（Text-to-Cypher + LLM 回答）
+"""
+
+from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from pydantic import BaseModel
+
+from graph_query import get_driver, get_graph_stats
+from graph_builder import build_graph
+from llm_router import answer_question
+
+app = FastAPI(title="大唐双龙传 GraphRAG API", version="1.0.0")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=[
+        "http://localhost:5173",   # Vite dev server
+        "http://localhost:4173",   # Vite preview
+        "http://127.0.0.1:5173",
+    ],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+# ── Models ────────────────────────────────────────────────
+
+class ChatRequest(BaseModel):
+    question: str
+
+
+class ImportRequest(BaseModel):
+    clear: bool = False   # True = 先清空图谱再重新导入
+
+
+# ── Endpoints ─────────────────────────────────────────────
+
+@app.get("/api/health")
+def health():
+    driver = get_driver()
+    try:
+        driver.verify_connectivity()
+        return {"status": "ok", "neo4j": "connected"}
+    except Exception as e:
+        raise HTTPException(status_code=503, detail=f"Neo4j 连接失败: {e}")
+
+
+@app.get("/api/stats")
+def stats():
+    try:
+        return get_graph_stats()
+    except Exception as e:
+        raise HTTPException(status_code=503, detail=str(e))
+
+
+@app.post("/api/import")
+def import_data(req: ImportRequest = ImportRequest()):
+    """导入所有卷数据到 Neo4j（耗时约 1-3 分钟，请勿重复调用）"""
+    driver = get_driver()
+    try:
+        build_graph(driver, clear=req.clear)
+        stats = get_graph_stats()
+        return {"status": "ok", "stats": stats}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+
+@app.post("/api/chat")
+def chat(req: ChatRequest):
+    if not req.question.strip():
+        raise HTTPException(status_code=400, detail="问题不能为空")
+    return answer_question(req.question)