feat: FastAPI server (state/step/event/demo) + static serving

backend/main.py

@@ -0,0 +1,126 @@
+"""
+Polis API — FastAPI server that drives the simulation and serves the 3D UI.
+
+Endpoints
+---------
+GET  /api/health      -> liveness + whether a real OpenAI key is wired
+GET  /api/state       -> current world snapshot
+POST /api/reset       -> new world from a seed
+POST /api/step        -> advance N ticks (live LLM or mock), returns snapshots
+POST /api/event       -> inject a world event ("a storm floods the harbor")
+GET  /api/demo        -> pre-recorded run so the Space works with zero budget
+GET  /                -> the 3D scroll site (static/index.html)
+
+The design goal: a recruiter can open the Space and immediately watch a society
+unfold via /api/demo, then flip to live mode if a key + budget are present.
+"""
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+
+from fastapi import FastAPI, Body
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import FileResponse, JSONResponse
+from fastapi.staticfiles import StaticFiles
+from pydantic import BaseModel
+
+from .llm import llm, BudgetExceeded
+from .world import World, LOCATIONS
+
+ROOT = Path(__file__).resolve().parent.parent
+STATIC = ROOT / "static"
+DEMO_FILE = ROOT / "data" / "demo_run.json"
+
+app = FastAPI(title="Polis", version="1.0.0",
+              description="A living society of generative AI agents.")
+app.add_middleware(CORSMiddleware, allow_origins=["*"], allow_methods=["*"],
+                   allow_headers=["*"])
+
+WORLD = World.bootstrap()
+
+
+class StepReq(BaseModel):
+    ticks: int = 1
+
+
+class EventReq(BaseModel):
+    text: str
+
+
+class ResetReq(BaseModel):
+    seed: int = 42
+
+
+@app.get("/api/health")
+def health():
+    return {"status": "ok", "live_llm": llm.live, "budget": llm.ledger.as_dict(),
+            "locations": LOCATIONS}
+
+
+@app.get("/api/state")
+def state():
+    return {
+        "tick": WORLD.tick,
+        "agents": [a.snapshot() for a in WORLD.agents],
+        "locations": LOCATIONS,
+        "budget": llm.ledger.as_dict(),
+        "live": llm.live,
+    }
+
+
+@app.post("/api/reset")
+def reset(req: ResetReq = Body(default=ResetReq())):
+    global WORLD
+    WORLD = World.bootstrap(seed=req.seed)
+    return state()
+
+
+@app.post("/api/step")
+def step(req: StepReq = Body(default=StepReq())):
+    snapshots = []
+    n = max(1, min(20, req.ticks))
+    for _ in range(n):
+        try:
+            snapshots.append(WORLD.step())
+        except BudgetExceeded as exc:
+            return JSONResponse(
+                status_code=402,
+                content={"error": str(exc), "budget": llm.ledger.as_dict(),
+                         "snapshots": snapshots},
+            )
+    return {"snapshots": snapshots, "budget": llm.ledger.as_dict()}
+
+
+@app.post("/api/event")
+def event(req: EventReq):
+    WORLD.inject_event(req.text)
+    return {"ok": True, "queued": req.text}
+
+
+@app.get("/api/demo")
+def demo():
+    if DEMO_FILE.exists():
+        return json.loads(DEMO_FILE.read_text())
+    return JSONResponse(status_code=404,
+                        content={"error": "demo_run.json not generated yet"})
+
+
+# ---- static site -------------------------------------------------------------
+if STATIC.exists():
+    app.mount("/static", StaticFiles(directory=str(STATIC)), name="static")
+
+
+@app.get("/")
+def index():
+    idx = STATIC / "index.html"
+    if idx.exists():
+        return FileResponse(str(idx))
+    return {"message": "Polis API running. Build static/index.html for the UI."}
+
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run("backend.main:app", host="0.0.0.0",
+                port=int(os.getenv("PORT", "7860")), reload=False)