# Shared calculator tool for the "with calculator" round. Safe arithmetic only (+ - * / parentheses, decimals).
import ast, operator as o
from decimal import Decimal
OPS={ast.Add:o.add,ast.Sub:o.sub,ast.Mult:o.mul,ast.Div:o.truediv,ast.USub:o.neg,ast.UAdd:o.pos}
def _ev(n):
    if isinstance(n,ast.Expression): return _ev(n.body)
    if isinstance(n,ast.Constant) and isinstance(n.value,(int,float)): return Decimal(str(n.value))
    if isinstance(n,ast.BinOp) and type(n.op) in OPS: return OPS[type(n.op)](_ev(n.left),_ev(n.right))
    if isinstance(n,ast.UnaryOp) and type(n.op) in OPS: return OPS[type(n.op)](_ev(n.operand))
    raise ValueError("only + - * / ( ) and numbers are allowed")
CALLS=[]
def calculate(expression: str) -> str:
    """Evaluate an arithmetic expression exactly, e.g. '1840.20 + 960 - 1250'. Supports + - * / and parentheses."""
    try: r=str(_ev(ast.parse(expression.replace(",",""),mode="eval")))
    except Exception as e: r=f"error: {e}"
    CALLS.append((expression,r)); return r
NOTE="\n\nYou have a `calculate` tool. Use it for every arithmetic step; do not do sums in your head."
def report(): print(f"\nTOOL_CALLS {len(CALLS)}"); [print("  CALC",e,"=",r) for e,r in CALLS]