document.addEventListener("DOMContentLoaded", function () {

    function getVal(id) {
        var el = document.getElementsByName(id)[0];
        return el ? parseFloat(el.value) || 0 : 0;
    }

    function setVal(id, value) {
        var el = document.getElementsByName(id)[0];
        if (el) el.value = Number(value).toFixed(2);
    }

    // MAIN CALC FUNCTION
    window.calculate = function () {

        // BASIC VALUES
        var gross_total_income = getVal("gross_total_income");
        var disallowance_14a = getVal("disallowance_14a");
        var disallowance_37 = getVal("disallowance_37");

        var d80_business = getVal("deduction_80ia_business");
        var deduction_sec37 = getVal("deduction_sec37_disallowance");
        var deduction_80g = getVal("deduction_80g");

        // NET TAXABLE INCOME
        var net_taxable_income =
            (gross_total_income + disallowance_14a + disallowance_37)
            - (d80_business + deduction_sec37)
            - deduction_80g;

        setVal("net_taxable_income", net_taxable_income);

        // TAX @ 30%
        var tax_30_percent = net_taxable_income * 0.30;
        setVal("tax_30_percent", tax_30_percent);

        // TAX PAYABLE = 18.5% BOOK PROFIT (user enters)
        var tax_payable = getVal("tax_book_profit_18_5");
        setVal("tax_payable", tax_payable);

        // SURCHARGE
        var surcharge_12 = tax_payable * 0.12;
        setVal("surcharge_12", surcharge_12);

        // CESS
        var edu_cess_3 = (tax_payable + surcharge_12) * 0.03;
        setVal("edu_cess_3", edu_cess_3);

        // TOTAL TAX PAYABLE
        var total_tax_payable = tax_payable + surcharge_12 + edu_cess_3;
        setVal("total_tax_payable", total_tax_payable);

        // OTHER VALUES
        var mat_credit = getVal("mat_credit");
        var interest_234c = getVal("interest_234c");

        // FINAL TAX
        var total_tax = total_tax_payable + mat_credit + interest_234c;
        setVal("total_tax", total_tax);

        // PAYMENTS
        var advance_tax = getVal("advance_tax");
        var tds = getVal("tds");
        var tcs = getVal("tcs");

        var tax_on_assessment = advance_tax + tds + tcs;
        setVal("tax_on_assessment", tax_on_assessment);

        // REFUND
        var refund = total_tax - tax_on_assessment;
        setVal("refund", refund);
    };

});