splitwise.py

from collections import defaultdict
from decimal import Decimal, ROUND_HALF_UP

# -----------------------------
# Configuration
# -----------------------------

PEOPLE = ["Buro", "Tablu", "Shreshtha", "Meghna", "Sayani"]

# All expenses: (amount, paid_by)
EXPENSES = [
    # 26th
    (2962, "Buro"),
    (3300, "Buro"),
    (913, "Tablu"),
    (4500, "Tablu"),

    # 27th
    (750, "Buro"),
    (6600, "Buro"),
    (1420, "Buro"),

    # 28th
    (730, "Buro"),
    (1180, "Buro"),
    (4050, "Tablu"),
    (10000, "Buro"),
    (1420, "Tablu"),

    # 29th
    (1250, "Tablu"),
    (3870, "Buro"),
    (2870, "Buro"),
    (550, "Buro"),
    (4050, "Tablu"),
    (4065, "Tablu"),

    # 30th
    (1065, "Buro"),
    (550, "Tablu"),
    (2000, "Buro"),
    (250, "Shreshtha"),
    (250, "Tablu"),

    # 31st
    (4000, "Buro"),
    (850, "Buro"),
    (250, "Buro"),
    (640, "Tablu"),
    (3817, "Buro"),
    (3200, "Tablu"),

    # 1st
    (5000, "Buro"),
    (2599, "Tablu"),
    (565, "Tablu"),
    (1310, "Tablu"),
    (1695, "Buro"),
]

COLLECTOR = "Tablu"
REPRESENTED_BY_COLLECTOR = ["Tablu", "Meghna", "Sayani"]

# -----------------------------
# Helpers
# -----------------------------

TWOPLACES = Decimal("0.01")

def D(value):
    return Decimal(str(value)).quantize(TWOPLACES, ROUND_HALF_UP)

# -----------------------------
# Splitwise Engine
# -----------------------------

class SplitwiseEngine:
    def __init__(self, people):
        self.people = people
        self.balance = defaultdict(Decimal)

    def add_expense(self, amount, paid_by):
        amount = D(amount)
        split = (amount / len(self.people)).quantize(TWOPLACES)

        for p in self.people:
            self.balance[p] -= split
        self.balance[paid_by] += amount

    def get_balances(self):
        return {p: self.balance[p].quantize(TWOPLACES) for p in self.people}

    def settle_with_collector(self, collector, represented):
        settlements = []

        # Step 1: represented people pay collector
        for p in represented:
            if self.balance[p] < 0:
                amt = -self.balance[p]
                settlements.append(f"{p} pays {collector}: {amt:.2f}")
                self.balance[collector] += amt
                self.balance[p] = D(0)

        # Step 2: remaining debtors and creditors
        creditors = {
            p: amt for p, amt in self.balance.items()
            if amt > 0 and p != collector
        }
        debtors = {
            p: -amt for p, amt in self.balance.items()
            if amt < 0
        }

        # Direct settlements (non-represented debtors)
        for d, d_amt in debtors.items():
            for c in list(creditors):
                if d_amt <= 0:
                    break
                pay = min(d_amt, creditors[c])
                settlements.append(f"{d} pays {c}: {pay:.2f}")
                d_amt -= pay
                creditors[c] -= pay
                self.balance[c] -= pay

        # Step 3: collector pays remaining creditors
        for c, amt in creditors.items():
            if amt > 0:
                settlements.append(f"{collector} pays {c}: {amt:.2f}")
                self.balance[collector] -= amt
                self.balance[c] = D(0)

        self.balance[collector] = D(0)
        return settlements

# -----------------------------
# Main Execution
# -----------------------------

def main():
    engine = SplitwiseEngine(PEOPLE)

    for amount, payer in EXPENSES:
        engine.add_expense(amount, payer)

    print("================================")
    print("TOTAL BALANCES")
    print("================================")
    balances = engine.get_balances()
    for p in PEOPLE:
        print(f"{p:<10}: {balances[p]:>10.2f}")

    print("\n================================")
    print("FINAL SETTLEMENT")
    print("================================")
    settlements = engine.settle_with_collector(
        collector=COLLECTOR,
        represented=REPRESENTED_BY_COLLECTOR
    )

    for s in settlements:
        print(s)

    print("\n================================")
    print("ALL SETTLED ✔")
    print("================================")

if __name__ == "__main__":
    main()