app.py

from fastapi import FastAPI, Request, Form
from fastapi.responses import HTMLResponse
from fastapi.staticfiles import StaticFiles
from fastapi.templating import Jinja2Templates
import sys
import io
import json

app = FastAPI()

# Mount static files (for CSS, JS)
app.mount("/static", StaticFiles(directory="static"), name="static")
templates = Jinja2Templates(directory="templates")


def run_code_with_trace(code: str):
    trace_data = []
    stdout_capture = io.StringIO()

    # ✅ Safely serialize objects (avoid JSON TypeError)
    def safe_serialize(obj):
        try:
            json.dumps(obj)
            return obj
        except (TypeError, OverflowError):
            return str(obj)

    # ✅ Tracer function
    def tracer(frame, event, arg):
        if event == "line":
            locals_serialized = {k: safe_serialize(v) for k, v in frame.f_locals.items()}
            trace_data.append({
                "line": frame.f_lineno,
                "locals": locals_serialized
            })
        return tracer

    # Redirect stdout temporarily (if user uses print)
    sys.settrace(tracer)
    sys.stdout = stdout_capture
    try:
        safe_globals = {"__builtins__": {"print": print, "range": range, "len": len}}
        exec(code, safe_globals)
    except Exception as e:
        trace_data.append({"error": str(e)})
    finally:
        sys.settrace(None)
        sys.stdout = sys.__stdout__  # reset stdout

    output = stdout_capture.getvalue()
    stdout_capture.close()
    return trace_data, output


@app.get("/", response_class=HTMLResponse)
async def index(request: Request):
    return templates.TemplateResponse("index.html", {"request": request})


@app.post("/run", response_class=HTMLResponse)
async def run_code(request: Request, code: str = Form(...)):
    trace, output = run_code_with_trace(code)
    return templates.TemplateResponse(
        "index.html",
        {
            "request": request,
            "trace_json": json.dumps(trace),
            "output": output,
            "code": code
        }
    )