Budget Calculator (50/30/20)

from dataclasses import dataclass, field
from typing import List

@dataclass
class BudgetItem:
    name: str
    amount: float
    category: str  # 'need' | 'want' | 'savings'

@dataclass
class Budget:
    income: float
    items: List[BudgetItem] = field(default_factory=list)

    def add_item(self, name: str, amount: float, category: str):
        self.items.append(BudgetItem(name, amount, category))

    def total_expenses(self) -> float:
        return sum(i.amount for i in self.items)

    def surplus(self) -> float:
        return self.income - self.total_expenses()

    def by_category(self) -> dict:
        totals = {'need': 0.0, 'want': 0.0, 'savings': 0.0}
        for item in self.items:
            totals[item.category] += item.amount
        return totals

    def rule_50_30_20(self) -> dict:
        """Check against the 50/30/20 guideline."""
        cats = self.by_category()
        return {
            'needs_pct':   cats['need']    / self.income * 100,
            'wants_pct':   cats['want']    / self.income * 100,
            'savings_pct': cats['savings'] / self.income * 100,
        }

# Example
budget = Budget(income=5000)
budget.add_item("Rent",          1200, "need")
budget.add_item("Groceries",      400, "need")
budget.add_item("Utilities",      150, "need")
budget.add_item("Transport",      300, "need")
budget.add_item("Dining out",     250, "want")
budget.add_item("Streaming",       50, "want")
budget.add_item("Entertainment",  200, "want")
budget.add_item("Emergency fund", 500, "savings")
budget.add_item("Investments",    500, "savings")

cats = budget.by_category()
rule = budget.rule_50_30_20()

print(f"Income:      ${budget.income:,.2f}")
print(f"Expenses:    ${budget.total_expenses():,.2f}")
print(f"Surplus:     ${budget.surplus():,.2f}")
print(f"Needs:       ${cats['need']:,.2f}  ({rule['needs_pct']:.1f}%,  target 50%)")
print(f"Wants:       ${cats['want']:,.2f}  ({rule['wants_pct']:.1f}%,  target 30%)")
print(f"Savings:     ${cats['savings']:,.2f}  ({rule['savings_pct']:.1f}%, target 20%)")