class Solution:
    def calculate(self, s: str) -> int:
        tokens = []
        for c in s:
            if c == " ":
                continue
            if c in "+-()":
                tokens.append(c)
                continue
            c = int(c)
            if not tokens or type(tokens[-1]) is str:
                tokens.append(c)
                continue
            tokens[-1] = tokens[-1] * 10 + c

        def calc(start_idx):
            """This always starts either at idx = 0 or after a opening bracket"""
            result = 0
            mult = 1
            i = start_idx
            while i < len(tokens):
                token = tokens[i]
                i += 1
                if token == "-":
                    mult = -1
                    continue
                if token == "+":
                    continue
                if token == ")":
                    break

                if token == "(":
                    to_add, new_idx = calc(i)
                    result += mult * to_add
                    i = new_idx
                else:  # token is int
                    result += mult * token
                mult = 1
            return result, i
        return calc(0)[0]