Initial commit — Moon Household Budget

mortgage.py

@@ -0,0 +1,124 @@
+import json
+import os
+from datetime import date
+from dateutil.relativedelta import relativedelta
+import math
+
+DATA_DIR = os.path.join(os.path.dirname(__file__), "data")
+MORTGAGE_FILE = os.path.join(DATA_DIR, "mortgage.json")
+
+
+def load_mortgage():
+    if os.path.exists(MORTGAGE_FILE):
+        with open(MORTGAGE_FILE) as f:
+            return json.load(f)
+    return {}
+
+
+def save_mortgage(data):
+    with open(MORTGAGE_FILE, "w") as f:
+        json.dump(data, f, indent=2)
+
+
+def monthly_payment(principal, annual_rate, term_years):
+    if annual_rate == 0:
+        return round(principal / (term_years * 12), 2)
+    r = (annual_rate / 100) / 12
+    n = term_years * 12
+    payment = principal * (r * (1 + r) ** n) / ((1 + r) ** n - 1)
+    return round(payment, 2)
+
+
+def amortization_schedule(principal, annual_rate, term_years, start_date_str, extra_monthly=0):
+    r = (annual_rate / 100) / 12 if annual_rate > 0 else 0
+    n = term_years * 12
+    base_payment = monthly_payment(principal, annual_rate, term_years)
+    total_payment = base_payment + extra_monthly
+
+    try:
+        current = date.fromisoformat(start_date_str)
+    except Exception:
+        current = date.today().replace(day=1)
+
+    schedule = []
+    balance = principal
+    total_interest = 0
+    total_principal = 0
+
+    for i in range(1, n + 1):
+        if balance <= 0:
+            break
+        interest = round(balance * r, 2)
+        principal_paid = min(round(total_payment - interest, 2), balance)
+        if principal_paid < 0:
+            principal_paid = 0
+        balance = round(balance - principal_paid, 2)
+        total_interest += interest
+        total_principal += principal_paid
+
+        schedule.append({
+            "month": i,
+            "date": current.strftime("%b %Y"),
+            "payment": round(interest + principal_paid, 2),
+            "principal": principal_paid,
+            "interest": interest,
+            "balance": max(balance, 0),
+        })
+
+        if balance <= 0:
+            break
+        current = current + relativedelta(months=1)
+
+    return schedule, round(total_interest, 2), len(schedule)
+
+
+def biweekly_schedule(principal, annual_rate, term_years, start_date_str):
+    base = monthly_payment(principal, annual_rate, term_years)
+    biweekly_payment = round(base / 2, 2)
+    r_biweekly = (annual_rate / 100) / 26 if annual_rate > 0 else 0
+
+    try:
+        current = date.fromisoformat(start_date_str)
+    except Exception:
+        current = date.today().replace(day=1)
+
+    balance = principal
+    total_interest = 0
+    payments = 0
+    max_payments = term_years * 26 + 52
+
+    while balance > 0 and payments < max_payments:
+        interest = round(balance * r_biweekly, 2)
+        principal_paid = min(round(biweekly_payment - interest, 2), balance)
+        if principal_paid < 0:
+            principal_paid = 0
+        balance = round(balance - principal_paid, 2)
+        total_interest += interest
+        payments += 1
+        if balance <= 0:
+            break
+
+    years = payments / 26
+    months_total = round(payments / 26 * 12)
+    return round(total_interest, 2), payments, round(years, 1), months_total
+
+
+def current_balance_estimate(principal, annual_rate, term_years, start_date_str, extra_monthly=0):
+    schedule, _, _ = amortization_schedule(
+        principal, annual_rate, term_years, start_date_str, extra_monthly)
+    today = date.today()
+    for row in schedule:
+        try:
+            row_date = date.strptime(row["date"], "%b %Y") if False else None
+        except Exception:
+            pass
+    # Count months elapsed
+    try:
+        start = date.fromisoformat(start_date_str)
+        months_elapsed = (today.year - start.year) * 12 + (today.month - start.month)
+        months_elapsed = max(0, months_elapsed)
+        if months_elapsed < len(schedule):
+            return schedule[months_elapsed]["balance"]
+        return 0
+    except Exception:
+        return principal