import json
import os
from datetime import date
from dateutil.relativedelta import relativedelta
import math

DATA_DIR = os.environ.get("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