import Dinero from 'dinero.js';
import { Currency } from './types';
import { CURRENCY_CONFIGS } from './constants';

/**
 * Round amount to the minimum unit for the given currency
 * RWF: rounds to nearest 100
 * XOF: returns the integer value
 */
export const roundToMinimumUnit = (
    amount: number,
    currency: Currency
): number => {
    const { minimumUnit } = CURRENCY_CONFIGS[currency];
    return Math.round(amount / minimumUnit) * minimumUnit;
};

/**
 * Create a Dinero money object with the appropriate currency
 */
export const createMoney = (
    amount: number,
    currency: Currency
): Dinero.Dinero => {
    return Dinero({ amount: Math.round(amount), currency, precision: 0 });
};

/**
 * Calculate installments with precise distribution and proper rounding
 * For RWF: each installment (except the last) is rounded to multiples of 100
 * For XOF: no rounding constraint
 * The last installment absorbs any difference to ensure total = totalPrice
 *
 * @param totalPrice Total price to split
 * @param count Number of installments
 * @param currency Currency to use for calculations
 * @returns Array of installment amounts that sum exactly to totalPrice
 */
export const calculateInstallments = (
    totalPrice: number,
    count: number,
    currency: Currency
): number[] => {
    if (count <= 0) return [];
    if (count === 1) return [totalPrice];

    const money = createMoney(totalPrice, currency);
    const ratios = Array(count).fill(1); // Equal distribution
    const allocated = money.allocate(ratios);

    const installments: number[] = [];
    let runningTotal = 0;

    for (let i = 0; i < count - 1; i++) {
        let amount = allocated[i].getAmount();

        if (currency === 'RWF') {
            amount = roundToMinimumUnit(amount, currency);
        }

        installments.push(amount);
        runningTotal += amount;
    }

    const lastInstallment = totalPrice - runningTotal;
    installments.push(lastInstallment);

    return installments;
};

/**
 * Calculate monthly repayment details for investors
 *
 * @param amountFunded Amount funded by investor
 * @param expectedProfit Expected profit for investor
 * @param paymentLength Number of months
 * @param currency Currency to use
 * @returns Object with monthly return, principal, and profit
 */
export const calculateMonthlyRepayment = (
    amountFunded: number,
    expectedProfit: number,
    paymentLength: number,
    currency: Currency
) => {
    const totalExpectedReturn = amountFunded + expectedProfit;
    const returnInstallments = calculateInstallments(
        totalExpectedReturn,
        paymentLength,
        currency
    );
    const principalInstallments = calculateInstallments(
        amountFunded,
        paymentLength,
        currency
    );

    const monthlyReturn = returnInstallments[0];
    const monthlyPrincipal = principalInstallments[0];
    const monthlyProfit = monthlyReturn - monthlyPrincipal;

    return {
        monthlyReturn,
        monthlyPrincipal,
        monthlyProfit,
    };
};