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templates/python-backend/fastapi-chat.py

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+"""
+TheSys Generative UI - FastAPI Backend Example
+
+This example demonstrates how to set up a FastAPI backend that integrates
+with TheSys C1 API for streaming generative UI responses.
+
+Dependencies:
+    - fastapi
+    - uvicorn
+    - thesys-genui-sdk
+    - openai
+    - python-dotenv
+"""
+
+from fastapi import FastAPI
+from fastapi.responses import StreamingResponse
+from fastapi.middleware.cors import CORSMiddleware
+from pydantic import BaseModel
+from thesys_genui_sdk import with_c1_response, write_content
+import openai
+import os
+from dotenv import load_dotenv
+
+# Load environment variables
+load_dotenv()
+
+# Initialize FastAPI app
+app = FastAPI(
+    title="TheSys C1 API Backend",
+    description="FastAPI backend for TheSys Generative UI",
+    version="1.0.0"
+)
+
+# Configure CORS
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],  # Configure for your frontend URL in production
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Initialize OpenAI client for TheSys C1 API
+client = openai.OpenAI(
+    base_url="https://api.thesys.dev/v1/embed",
+    api_key=os.getenv("THESYS_API_KEY")
+)
+
+# Request model
+class ChatRequest(BaseModel):
+    prompt: str
+    thread_id: str | None = None
+    response_id: str | None = None
+
+
+@app.get("/")
+async def root():
+    """Health check endpoint"""
+    return {
+        "status": "ok",
+        "message": "TheSys C1 API Backend is running"
+    }
+
+
+@app.post("/api/chat")
+@with_c1_response  # Automatically handles streaming headers
+async def chat_endpoint(request: ChatRequest):
+    """
+    Streaming chat endpoint that generates UI components.
+
+    Args:
+        request: ChatRequest with prompt and optional thread/response IDs
+
+    Returns:
+        StreamingResponse with C1-formatted UI chunks
+    """
+    try:
+        # Create streaming completion request
+        stream = client.chat.completions.create(
+            model="c1/anthropic/claude-sonnet-4/v-20250930",
+            messages=[
+                {
+                    "role": "system",
+                    "content": "You are a helpful AI assistant that creates interactive user interfaces."
+                },
+                {
+                    "role": "user",
+                    "content": request.prompt
+                }
+            ],
+            stream=True,
+            temperature=0.7,
+            max_tokens=4096
+        )
+
+        # Stream chunks to frontend
+        async def generate():
+            for chunk in stream:
+                content = chunk.choices[0].delta.content
+                if content:
+                    yield write_content(content)
+
+        return StreamingResponse(
+            generate(),
+            media_type="text/event-stream"
+        )
+
+    except Exception as e:
+        return {
+            "error": str(e),
+            "message": "Failed to generate response"
+        }
+
+
+if __name__ == "__main__":
+    import uvicorn
+
+    # Run the server
+    uvicorn.run(
+        "fastapi-chat:app",
+        host="0.0.0.0",
+        port=8000,
+        reload=True,
+        log_level="info"
+    )