// Initialize on page load
document.addEventListener(‘DOMContentLoaded’, function() {
const today = new Date().toISOString().split(‘T’)[0];

// Set max date to today for date inputs
document.getElementById(‘birthDate’).max = today;
document.getElementById(‘startDate’).max = today;
document.getElementById(‘endDate’).max = today;

// Set default dates
const defaultBirthDate = new Date();
defaultBirthDate.setFullYear(defaultBirthDate.getFullYear() – 30);
document.getElementById(‘birthDate’).value = defaultBirthDate.toISOString().split(‘T’)[0];

const defaultStartDate = new Date();
defaultStartDate.setDate(defaultStartDate.getDate() – 30);
document.getElementById(‘startDate’).value = defaultStartDate.toISOString().split(‘T’)[0];
document.getElementById(‘endDate’).value = today;

// Calculate age on page load
calculateAge();
});

// 1. Age Calculator (Fixed)
function calculateAge() {
const birthDate = new Date(document.getElementById(‘birthDate’).value);
const today = new Date();

if (isNaN(birthDate.getTime())) {
alert(“Please select a valid birth date!”);
return;
}

if (birthDate > today) {
alert(“Birth date cannot be in the future!”);
return;
}

// Calculate years
let years = today.getFullYear() – birthDate.getFullYear();
let months = today.getMonth() – birthDate.getMonth();
let days = today.getDate() – birthDate.getDate();

// Adjust if current month/day is before birth month/day
if (months < 0 || (months === 0 && days < 0)) {
years–;
months += 12;
}

if (days < 0) {
const lastDayOfMonth = new Date(today.getFullYear(), today.getMonth(), 0).getDate();
days += lastDayOfMonth;
months–;
if (months < 0) {
months = 11;
years–;
}
}

// Calculate total days and hours
const diff = today – birthDate;
const totalDays = Math.floor(diff / (1000 * 60 * 60 * 24));
const totalWeeks = Math.floor(totalDays / 7);
const totalHours = totalDays * 24;
const totalMinutes = totalHours * 60;

// Update results
document.getElementById('yearsValue').textContent = years;
document.getElementById('monthsValue').textContent = months;
document.getElementById('weeksValue').textContent = totalWeeks.toLocaleString();
document.getElementById('daysValue').textContent = totalDays.toLocaleString();
document.getElementById('hoursValue').textContent = totalHours.toLocaleString();
document.getElementById('minutesValue').textContent = totalMinutes.toLocaleString();

document.getElementById('ageResults').style.display = 'block';
}

function resetAge() {
const defaultDate = new Date();
defaultDate.setFullYear(defaultDate.getFullYear() – 30);
document.getElementById('birthDate').value = defaultDate.toISOString().split('T')[0];
document.getElementById('ageResults').style.display = 'none';
}

// 2. BMI Calculator
function calculateBMI() {
const height = parseFloat(document.getElementById('height').value) / 100; // Convert cm to m
const weight = parseFloat(document.getElementById('weight').value);

if (!height || !weight || height <= 0 || weight <= 0) {
alert("Please enter valid height and weight!");
return;
}

const bmi = weight / (height * height);
let category = '';

if (bmi < 18.5) category = 'Underweight';
else if (bmi < 25) category = 'Normal weight';
else if (bmi < 30) category = 'Overweight';
else category = 'Obese';

document.getElementById('bmiValue').textContent = bmi.toFixed(1);
document.getElementById('bmiCategory').textContent = category;
document.getElementById('bmiResults').style.display = 'block';
}

function resetBMI() {
document.getElementById('height').value = '170';
document.getElementById('weight').value = '70';
document.getElementById('bmiResults').style.display = 'none';
}

// 3. Currency Converter
const exchangeRates = {
USD: { USD: 1, EUR: 0.85, GBP: 0.73, PKR: 280, INR: 83 },
EUR: { USD: 1.18, EUR: 1, GBP: 0.86, PKR: 330, INR: 98 },
GBP: { USD: 1.37, EUR: 1.16, GBP: 1, PKR: 384, INR: 114 },
PKR: { USD: 0.0036, EUR: 0.0030, GBP: 0.0026, PKR: 1, INR: 0.30 },
INR: { USD: 0.012, EUR: 0.010, GBP: 0.0088, PKR: 3.33, INR: 1 }
};

function convertCurrency() {
const amount = parseFloat(document.getElementById('amount').value);
const from = document.getElementById('fromCurrency').value;
const to = document.getElementById('toCurrency').value;

if (!amount || amount <= 0) {
alert("Please enter a valid amount!");
return;
}

const rate = exchangeRates[from][to];
const converted = amount * rate;

document.getElementById('convertedAmount').textContent = converted.toFixed(2) + ' ' + to;
document.getElementById('currencyResults').style.display = 'block';
}

function resetCurrency() {
document.getElementById('amount').value = '100';
document.getElementById('currencyResults').style.display = 'none';
}

// 4. Loan Calculator
function calculateLoan() {
const amount = parseFloat(document.getElementById('loanAmount').value);
const annualRate = parseFloat(document.getElementById('interestRate').value);
const termMonths = parseInt(document.getElementById('loanTerm').value);

if (!amount || !annualRate || !termMonths || amount <= 0 || termMonths <= 0) {
alert("Please enter valid loan details!");
return;
}

const monthlyRate = annualRate / 100 / 12;
const monthlyPayment = amount * monthlyRate * Math.pow(1 + monthlyRate, termMonths) /
(Math.pow(1 + monthlyRate, termMonths) – 1);
const totalPayment = monthlyPayment * termMonths;
const totalInterest = totalPayment – amount;

document.getElementById('monthlyPayment').textContent = '$' + monthlyPayment.toFixed(2);
document.getElementById('totalInterest').textContent = '$' + totalInterest.toFixed(2);
document.getElementById('totalPayment').textContent = '$' + totalPayment.toFixed(2);
document.getElementById('loanResults').style.display = 'block';
}

function resetLoan() {
document.getElementById('loanAmount').value = '10000';
document.getElementById('interestRate').value = '5';
document.getElementById('loanTerm').value = '60';
document.getElementById('loanResults').style.display = 'none';
}

// 5. Electricity Bill Calculator
function calculateElectricityBill() {
const units = parseFloat(document.getElementById('units').value);
const rate = parseFloat(document.getElementById('ratePerUnit').value);
const tax = parseFloat(document.getElementById('taxRate').value) / 100;

if (!units || units <= 0) {
alert("Please enter valid units!");
return;
}

const energyCharge = units * rate;
const taxAmount = energyCharge * tax;
const totalBill = energyCharge + taxAmount;

document.getElementById('energyCharge').textContent = '$' + energyCharge.toFixed(2);
document.getElementById('taxAmount').textContent = '$' + taxAmount.toFixed(2);
document.getElementById('totalBill').textContent = '$' + totalBill.toFixed(2);
document.getElementById('electricityResults').style.display = 'block';
}

function resetElectricity() {
document.getElementById('units').value = '300';
document.getElementById('ratePerUnit').value = '0.15';
document.getElementById('taxRate').value = '13';
document.getElementById('electricityResults').style.display = 'none';
}

// 6. Tip Calculator
function calculateTip() {
const bill = parseFloat(document.getElementById('billAmount').value);
const tipPercent = parseFloat(document.getElementById('tipPercentage').value) / 100;
const people = parseInt(document.getElementById('peopleCount').value);

if (!bill || bill <= 0) {
alert("Please enter a valid bill amount!");
return;
}

const tipAmount = bill * tipPercent;
const totalWithTip = bill + tipAmount;
const perPerson = totalWithTip / people;

document.getElementById('tipAmount').textContent = '$' + tipAmount.toFixed(2);
document.getElementById('totalWithTip').textContent = '$' + totalWithTip.toFixed(2);
document.getElementById('perPerson').textContent = '$' + perPerson.toFixed(2);
document.getElementById('tipResults').style.display = 'block';
}

function resetTip() {
document.getElementById('billAmount').value = '50';
document.getElementById('peopleCount').value = '2';
document.getElementById('tipResults').style.display = 'none';
}

// 7. Discount Calculator
function calculateDiscount() {
const original = parseFloat(document.getElementById('originalPrice').value);
const discount = parseFloat(document.getElementById('discountPercent').value) / 100;

if (!original || original <= 0) {
alert("Please enter a valid price!");
return;
}

const discountAmount = original * discount;
const finalPrice = original – discountAmount;

document.getElementById('discountAmount').textContent = '$' + discountAmount.toFixed(2);
document.getElementById('finalPrice').textContent = '$' + finalPrice.toFixed(2);
document.getElementById('youSave').textContent = '$' + discountAmount.toFixed(2);
document.getElementById('discountResults').style.display = 'block';
}

function resetDiscount() {
document.getElementById('originalPrice').value = '100';
document.getElementById('discountPercent').value = '20';
document.getElementById('discountResults').style.display = 'none';
}

// 8. Percentage Calculator
function calculatePercentage() {
const type = document.getElementById('percentageType').value;
const val1 = parseFloat(document.getElementById('percentageValue1').value);
const val2 = parseFloat(document.getElementById('percentageValue2').value);

if (!val1 || !val2) {
alert("Please enter both values!");
return;
}

let result = 0;

switch(type) {
case 'basic':
result = (val1 / 100) * val2;
document.getElementById('percentageResult').textContent = result.toFixed(2);
break;
case 'percentage':
result = (val1 / val2) * 100;
document.getElementById('percentageResult').textContent = result.toFixed(2) + '%';
break;
case 'increase':
result = ((val2 – val1) / val1) * 100;
document.getElementById('percentageResult').textContent = result.toFixed(2) + '% increase';
break;
case 'decrease':
result = ((val1 – val2) / val1) * 100;
document.getElementById('percentageResult').textContent = result.toFixed(2) + '% decrease';
break;
}

document.getElementById('percentageResults').style.display = 'block';
}

function resetPercentage() {
document.getElementById('percentageValue1').value = '20';
document.getElementById('percentageValue2').value = '100';
document.getElementById('percentageResults').style.display = 'none';
}

// 9. Password Generator
function updateLengthValue() {
document.getElementById('lengthValue').textContent = document.getElementById('passwordLength').value;
}

function generatePassword() {
const length = parseInt(document.getElementById('passwordLength').value);
const includeUpper = document.getElementById('includeUppercase').checked;
const includeLower = document.getElementById('includeLowercase').checked;
const includeNumbers = document.getElementById('includeNumbers').checked;
const includeSymbols = document.getElementById('includeSymbols').checked;

const upperChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
const lowerChars = 'abcdefghijklmnopqrstuvwxyz';
const numberChars = '0123456789';
const symbolChars = '!@#$%^&*()_+-=[]{}|;:,.?’;

let chars = ”;
if (includeUpper) chars += upperChars;
if (includeLower) chars += lowerChars;
if (includeNumbers) chars += numberChars;
if (includeSymbols) chars += symbolChars;

if (chars === ”) {
alert(“Please select at least one character type!”);
return;
}

let password = ”;
for (let i = 0; i = 12 && (includeUpper && includeLower && includeNumbers && includeSymbols)) {
strength = ‘Very Strong’;
} else if (length >= 10 && (includeUpper && includeLower && includeNumbers)) {
strength = ‘Strong’;
} else if (length >= 8 && ((includeUpper && includeLower) || (includeLower && includeNumbers))) {
strength = ‘Medium’;
}

document.getElementById(‘generatedPassword’).textContent = password;
document.getElementById(‘passwordStrength’).textContent = strength;
document.getElementById(‘passwordResults’).style.display = ‘block’;
}

function resetPassword() {
document.getElementById(‘passwordLength’).value = ’12’;
document.getElementById(‘includeUppercase’).checked = true;
document.getElementById(‘includeLowercase’).checked = true;
document.getElementById(‘includeNumbers’).checked = true;
document.getElementById(‘includeSymbols’).checked = false;
updateLengthValue();
document.getElementById(‘passwordResults’).style.display = ‘none’;
}

// 10. Date Calculator
function calculateDate() {
const startDate = new Date(document.getElementById(‘startDate’).value);
const endDate = new Date(document.getElementById(‘endDate’).value);
const daysToAdd = parseInt(document.getElementById(‘daysToAdd’).value);

if (!startDate || !endDate || isNaN(startDate.getTime()) || isNaN(endDate.getTime())) {
alert(“Please select valid dates!”);
return;
}

// Calculate days between dates
const diffTime = Math.abs(endDate – startDate);
const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));

// Calculate new date
const newDate = new Date(startDate);
newDate.setDate(newDate.getDate() + daysToAdd);

document.getElementById(‘daysBetween’).textContent = diffDays;
document.getElementById(‘newDate’).textContent = newDate.toDateString();
document.getElementById(‘dateResults’).style.display = ‘block’;
}

function resetDate() {
const today = new Date();
const pastDate = new Date();
pastDate.setDate(today.getDate() – 30);

document.getElementById(‘startDate’).value = pastDate.toISOString().split(‘T’)[0];
document.getElementById(‘endDate’).value = today.toISOString().split(‘T’)[0];
document.getElementById(‘daysToAdd’).value = ’30’;
document.getElementById(‘dateResults’).style.display = ‘none’;
}

// 11. Time Calculator
function calculateTime() {
const time1 = document.getElementById(‘time1’).value;
const time2 = document.getElementById(‘time2’).value;
const operation = document.getElementById(‘timeOperation’).value;

if (!time1 || !time2) {
alert(“Please enter both times!”);
return;
}

// Parse times
const parseTime = (timeStr) => {
const parts = timeStr.split(‘:’);
return {
hours: parseInt(parts[0]) || 0,
minutes: parseInt(parts[1]) || 0,
seconds: parseInt(parts[2]) || 0
};
};

const t1 = parseTime(time1);
const t2 = parseTime(time2);

let resultHours = 0, resultMinutes = 0, resultSeconds = 0;

switch(operation) {
case ‘add’:
resultSeconds = t1.seconds + t2.seconds;
resultMinutes = t1.minutes + t2.minutes;
resultHours = t1.hours + t2.hours;

if (resultSeconds >= 60) {
resultMinutes += Math.floor(resultSeconds / 60);
resultSeconds %= 60;
}

if (resultMinutes >= 60) {
resultHours += Math.floor(resultMinutes / 60);
resultMinutes %= 60;
}
break;

case ‘subtract’:
let totalSeconds1 = t1.hours * 3600 + t1.minutes * 60 + t1.seconds;
let totalSeconds2 = t2.hours * 3600 + t2.minutes * 60 + t2.seconds;
let diffSeconds = Math.abs(totalSeconds1 – totalSeconds2);

resultHours = Math.floor(diffSeconds / 3600);
diffSeconds %= 3600;
resultMinutes = Math.floor(diffSeconds / 60);
resultSeconds = diffSeconds % 60;
break;

case ‘difference’:
const sec1 = t1.hours * 3600 + t1.minutes * 60 + t1.seconds;
const sec2 = t2.hours * 3600 + t2.minutes * 60 + t2.seconds;
const diff = Math.abs(sec1 – sec2);

resultHours = Math.floor(diff / 3600);
resultMinutes = Math.floor((diff % 3600) / 60);
resultSeconds = diff % 60;
break;
}

const formatTime = (h, m, s) => {
return `${String(h).padStart(2, ‘0’)}:${String(m).padStart(2, ‘0’)}:${String(s).padStart(2, ‘0’)}`;
};

document.getElementById(‘timeResult’).textContent = formatTime(resultHours, resultMinutes, resultSeconds);
document.getElementById(‘timeResults’).style.display = ‘block’;
}

function resetTime() {
document.getElementById(‘time1′).value = ’02:30:00’;
document.getElementById(‘time2′).value = ’01:45:00’;
document.getElementById(‘timeResults’).style.display = ‘none’;
}

// 12. Unit Converter
function convertUnits() {
const type = document.getElementById(‘unitType’).value;
const value = parseFloat(document.getElementById(‘unitValue’).value);
const toUnit = document.getElementById(‘toUnit’).value;

if (!value || value < 0) {
alert("Please enter a valid value!");
return;
}

let result = 0;

// Length conversions
if (type === 'length') {
switch(toUnit) {
case 'feet':
result = value * 3.28084;
break;
case 'inches':
result = value * 39.3701;
break;
case 'cm':
result = value * 100;
break;
case 'km':
result = value / 1000;
break;
default:
result = value;
}
}
// Weight conversions
else if (type === 'weight') {
document.getElementById('fromUnit').value = 'kilogram';
switch(toUnit) {
case 'pounds':
result = value * 2.20462;
break;
case 'ounces':
result = value * 35.274;
break;
case 'grams':
result = value * 1000;
break;
case 'ton':
result = value / 1000;
break;
default:
result = value;
}
}
// Temperature conversions
else if (type === 'temperature') {
document.getElementById('fromUnit').value = 'celsius';
switch(toUnit) {
case 'fahrenheit':
result = (value * 9/5) + 32;
break;
case 'kelvin':
result = value + 273.15;
break;
default:
result = value;
}
}
// Volume conversions
else if (type === 'volume') {
document.getElementById('fromUnit').value = 'liter';
switch(toUnit) {
case 'milliliters':
result = value * 1000;
break;
case 'gallons':
result = value * 0.264172;
break;
case 'cups':
result = value * 4.22675;
break;
case 'pints':
result = value * 2.11338;
break;
default:
result = value;
}
}

document.getElementById('convertedValue').textContent = result.toFixed(4);
document.getElementById('unitResults').style.display = 'block';
}

function resetUnits() {
document.getElementById('unitValue').value = '1';
document.getElementById('unitResults').style.display = 'none';
}

// 13. Grade Calculator
function calculateGrade() {
const current = parseFloat(document.getElementById('currentGrade').value);
const target = parseFloat(document.getElementById('targetGrade').value);
const weight = parseFloat(document.getElementById('finalWeight').value) / 100;

if (!current || !target || !weight || current 100 || target 100) {
alert(“Please enter valid grade values!”);
return;
}

// Calculate required final exam score
const required = (target – (current * (1 – weight))) / weight;

document.getElementById(‘requiredScore’).textContent = required.toFixed(1) + ‘%’;
document.getElementById(‘gradeResults’).style.display = ‘block’;
}

function resetGrade() {
document.getElementById(‘currentGrade’).value = ’75’;
document.getElementById(‘targetGrade’).value = ’80’;
document.getElementById(‘finalWeight’).value = ’30’;
document.getElementById(‘gradeResults’).style.display = ‘none’;
}

// 14. Fuel Cost Calculator
function calculateFuelCost() {
const distance = parseFloat(document.getElementById(‘distance’).value);
const efficiency = parseFloat(document.getElementById(‘fuelEfficiency’).value);
const price = parseFloat(document.getElementById(‘fuelPrice’).value);

if (!distance || !efficiency || !price || distance <= 0 || efficiency <= 0 || price = max || quantity <= 0) {
alert("Please enter valid range and quantity!");
return;
}

let numbers = [];
for (let i = 0; i {
const option = document.createElement(‘option’);
option.value = unit;
option.textContent = unit.charAt(0).toUpperCase() + unit.slice(1);
toUnit.appendChild(option);
});
} else if (type === ‘weight’) {
document.getElementById(‘fromUnit’).value = ‘kilogram’;
[‘pounds’, ‘ounces’, ‘grams’, ‘ton’].forEach(unit => {
const option = document.createElement(‘option’);
option.value = unit;
option.textContent = unit.charAt(0).toUpperCase() + unit.slice(1);
toUnit.appendChild(option);
});
} else if (type === ‘temperature’) {
document.getElementById(‘fromUnit’).value = ‘celsius’;
[‘fahrenheit’, ‘kelvin’].forEach(unit => {
const option = document.createElement(‘option’);
option.value = unit;
option.textContent = unit.charAt(0).toUpperCase() + unit.slice(1);
toUnit.appendChild(option);
});
} else if (type === ‘volume’) {
document.getElementById(‘fromUnit’).value = ‘liter’;
[‘milliliters’, ‘gallons’, ‘cups’, ‘pints’].forEach(unit => {
const option = document.createElement(‘option’);
option.value = unit;
option.textContent = unit.charAt(0).toUpperCase() + unit.slice(1);
toUnit.appendChild(option);
});
}
});