calculator.py

from fastapi import FastAPI, HTTPException
from fastapi.responses import JSONResponse, RedirectResponse
from fastapi.staticfiles import StaticFiles
from pydantic import BaseModel
import uvicorn
import ast
import operator as op

app = FastAPI(title="Modern Calculator API", description="A simple calculator API with a modern UI", version="1.0")

# Serve the modern calculator UI from the static/ folder
app.mount("/static", StaticFiles(directory="static"), name="static")


@app.get("/")
async def root():
	return RedirectResponse(url="/static/index.html")


# Minimal, safe expression evaluator using ast
operators = {
	ast.Add: op.add,
	ast.Sub: op.sub,
	ast.Mult: op.mul,
	ast.Div: op.truediv,
	ast.Pow: op.pow,
	ast.Mod: op.mod,
	ast.FloorDiv: op.floordiv,
}


def eval_node(node):
	if isinstance(node, ast.Expression):
		return eval_node(node.body)
	if isinstance(node, ast.BinOp):
		left = eval_node(node.left)
		right = eval_node(node.right)
		op_type = type(node.op)
		if op_type in operators:
			return operators[op_type](left, right)
		raise ValueError("Unsupported operator")
	if isinstance(node, ast.UnaryOp):
		if isinstance(node.op, ast.UAdd):
			return +eval_node(node.operand)
		if isinstance(node.op, ast.USub):
			return -eval_node(node.operand)
		raise ValueError("Unsupported unary operator")
	if isinstance(node, ast.Num):
		return node.n
	if isinstance(node, ast.Constant):
		if isinstance(node.value, (int, float)):
			return node.value
		raise ValueError("Unsupported constant")
	raise ValueError("Unsupported expression")


def safe_eval(expr: str):
	parsed = ast.parse(expr, mode="eval")
	return eval_node(parsed)


class CalcRequest(BaseModel):
	expression: str


@app.post("/api/calc")
async def calculate(req: CalcRequest):
	expr = req.expression.strip()
	try:
		result = safe_eval(expr)
	except Exception as e:
		return JSONResponse({"error": str(e)}, status_code=400)
	return {"result": result, "expression": expr}


if __name__ == "__main__":
	# Run with: uvicorn calculator:app --reload
	print("calculator FastAPI app. Run with: uvicorn calculator:app --reload")