from datetime import datetime, timedelta
from dateutil.relativedelta import relativedelta


def calculate_monthly_rate(interest_rate: float, rate_type: str) -> float:
    if rate_type == "annual":
        return interest_rate / 100 / 12
    return interest_rate / 100


def generate_equal_installment_plan(
    amount: int, interest_rate: float, rate_type: str,
    period_count: int, start_date: datetime
) -> list[dict]:
    mr = calculate_monthly_rate(interest_rate, rate_type)
    if mr == 0:
        principal_each = amount // period_count
        plans = []
        for i in range(period_count):
            due = start_date + relativedelta(months=i + 1)
            p = principal_each if i < period_count - 1 else amount - principal_each * (period_count - 1)
            plans.append({"due_date": due, "principal_due": p, "interest_due": 0, "total_due": p})
        return plans

    mp = amount * mr * (1 + mr) ** period_count / ((1 + mr) ** period_count - 1)
    plans = []
    remaining = amount
    for i in range(period_count):
        due = start_date + relativedelta(months=i + 1)
        interest = int(remaining * mr)
        principal = int(mp) - interest
        if i == period_count - 1:
            principal = remaining
            interest = int(remaining * mr)
        remaining -= principal
        total = principal + interest
        plans.append({"due_date": due, "principal_due": principal, "interest_due": interest, "total_due": total})
    return plans


def generate_interest_first_plan(
    amount: int, interest_rate: float, rate_type: str,
    period_count: int, start_date: datetime
) -> list[dict]:
    mr = calculate_monthly_rate(interest_rate, rate_type)
    plans = []
    for i in range(period_count):
        due = start_date + relativedelta(months=i + 1)
        interest = int(amount * mr)
        principal = amount if i == period_count - 1 else 0
        total = principal + interest
        plans.append({"due_date": due, "principal_due": principal, "interest_due": interest, "total_due": total})
    return plans


def generate_lump_sum_plan(
    amount: int, interest_rate: float, rate_type: str,
    period_count: int, period_unit: str, start_date: datetime
) -> list[dict]:
    if period_unit == "year":
        total_interest = int(amount * interest_rate / 100 * period_count)
    else:
        total_interest = int(amount * interest_rate / 100 / 12 * period_count)
    due = start_date + relativedelta(months=period_count) if period_unit == "month" else start_date + relativedelta(years=period_count)
    return [{"due_date": due, "principal_due": amount, "interest_due": total_interest, "total_due": amount + total_interest}]


def generate_repayment_plan(
    amount: int, interest_rate: float, rate_type: str,
    repayment_method: str, period_count: int, period_unit: str,
    start_date: datetime
) -> list[dict]:
    if repayment_method == "equal_installment":
        return generate_equal_installment_plan(amount, interest_rate, rate_type, period_count, start_date)
    elif repayment_method == "interest_first":
        return generate_interest_first_plan(amount, interest_rate, rate_type, period_count, start_date)
    elif repayment_method == "lump_sum":
        return generate_lump_sum_plan(amount, interest_rate, rate_type, period_count, period_unit, start_date)
    return []