import streamlit as st
import pandas as pd
import numpy as np
from datetime import datetime
from dateutil.relativedelta import relativedelta

def main():
    st.title("Кредитный калькулятор")

    income = get_required_input("Введите совокупный доход заемщика (BYN): ")
    loan_payments = get_optional_input("Введите платежи по кредитам (если нет, то 0): ")
    has_guarantors = get_optional_input("Наличие поручителей (0 - нет, 1 - да): ") == 1
    loan_term = int(get_required_input("Введите срок кредита (мес.): "))
    interest_rate = get_percentage_input("Введите процентную ставку (%): ")
    preferential_rate = get_percentage_input("Введите льготную ставку (если имеется, 0 если нет): ")
    desired_loan_amount = get_required_input("Введите желаемую сумму кредита (BYN): ")
    payment_type = get_payment_type()

    # Расчеты
    max_loan_amount = calculate_max_loan_amount(income, loan_payments, interest_rate, loan_term)
    max_monthly_payment = calculate_max_monthly_payment(income, loan_payments)
    
    if payment_type.lower() == "annuity":
        monthly_payment = calculate_annuity_payment(desired_loan_amount, interest_rate, loan_term)
    elif payment_type.lower() == "differentiated":
        monthly_payment = calculate_differentiated_payment(desired_loan_amount, interest_rate, loan_term)
    else:
        monthly_payment_annuity = calculate_annuity_payment(desired_loan_amount, interest_rate, loan_term)
        monthly_payment_differentiated = calculate_differentiated_payment(desired_loan_amount, interest_rate, loan_term)
        st.write(f"Ежемесячный платеж (Аннуитетный): {monthly_payment_annuity:.2f} BYN")
        monthly_payment = monthly_payment_differentiated
    
    start_date = datetime.now()
    end_date = start_date + relativedelta(months=loan_term)

    # Сохранение результатов
    save_to_file(income, loan_payments, has_guarantors, loan_term, interest_rate, preferential_rate, 
                  monthly_payment, start_date, end_date, desired_loan_amount, 
                  max_monthly_payment, max_loan_amount, payment_type)

def get_required_input(prompt):
    while True:
        try:
            value = st.number_input(prompt, min_value=0.0)
            if value <= 0:
                raise ValueError("Значение должно быть больше нуля.")
            return value
        except ValueError as e:
            st.error(str(e))

def get_optional_input(prompt):
    value = st.number_input(prompt, min_value=0.0)
    return value

def get_percentage_input(prompt):
    while True:
        input_value = st.number_input(prompt, min_value=0.0)
        return input_value

def get_payment_type():
    return st.selectbox("Введите тип платежа", ["Annuity", "Differentiated", "All"])

def calculate_max_loan_amount(income, loan_payments, interest_rate, loan_term):
    max_monthly_payment = calculate_max_monthly_payment(income, loan_payments)
    return calculate_loan_amount_from_monthly_payment(max_monthly_payment, interest_rate, loan_term)

def calculate_max_monthly_payment(income, loan_payments):
    return (income / 3) - loan_payments

def calculate_loan_amount_from_monthly_payment(monthly_payment, interest_rate, loan_term):
    monthly_rate = (interest_rate / 100) / 12
    return monthly_payment * (np.power(1 + monthly_rate, loan_term) - 1) / (monthly_rate * np.power(1 + monthly_rate, loan_term))

def calculate_annuity_payment(loan_amount, interest_rate, loan_term):
    monthly_rate = (interest_rate / 100) / 12
    return loan_amount * (monthly_rate * np.power(1 + monthly_rate, loan_term)) / (np.power(1 + monthly_rate, loan_term) - 1)

def calculate_differentiated_payment(loan_amount, interest_rate, loan_term):
    monthly_rate = (interest_rate / 100) / 12
    total_payment = 0
    principal_payment = loan_amount / loan_term

    for month in range(1, loan_term + 1):
        interest_payment = (loan_amount - (principal_payment * (month - 1))) * monthly_rate
        total_payment += principal_payment + interest_payment

    return total_payment / loan_term

def save_to_file(income, loan_payments, has_guarantors, loan_term, interest_rate, 
                  preferential_rate, monthly_payment, start_date, end_date, 
                  desired_loan_amount, max_monthly_payment, max_loan_amount, payment_type):
    # Создание DataFrame с результатами расчета
    data = {
        "Сумма кредита": [desired_loan_amount],
        "Срок (мес.)": [loan_term],
        "Процентная ставка (%)": [interest_rate],
        "Ежемесячный платеж": [monthly_payment],
        "Дата начала": [start_date],
        "Дата окончания": [end_date],
        "Максимальный ежемесячный платеж": [max_monthly_payment],
        "Максимальная сумма кредита": [max_loan_amount],
        "Тип платежа": [payment_type],
        "Доход": [income],
        "Платежи по кредиту": [loan_payments],
        "Есть поручители": [has_guarantors],
        "Преференциальная ставка": [preferential_rate],
    }
    
    df = pd.DataFrame(data)
    
    # Запись в CSV
    csv = df.to_csv(index=False)
    
    # Сохранение файла в память
    st.download_button(
        label="Скачать результаты",
        data=csv,
        file_name='loan_calculation_results.csv',
        mime='text/csv'
    )


if __name__ == "__main__":
    main()