.isValid(): boolean

import { fdu } from '@pyyupsk/fdu';

fdu('2024-01-15').isValid();              // true
fdu(new Date()).isValid();                // true
fdu(1705276800000).isValid();             // true
fdu('2024-02-29').isValid();              // true (2024 is a leap year)
fdu().isValid();                          // true (current date)

fdu('invalid-date').isValid();            // false
fdu('2023-02-29').isValid();              // false (2023 is not a leap year)
fdu('2024-13-01').isValid();              // false (month 13 doesn't exist)
fdu('2024-01-32').isValid();              // false (day 32 doesn't exist)
fdu(NaN).isValid();                       // false
fdu('not a date at all').isValid();       // false

function processDate(input: string): string | null {
  const date = fdu(input);

  if (!date.isValid()) {
    console.error('Invalid date provided');
    return null;
  }

  return date.format('YYYY-MM-DD');
}

// Usage
processDate('2024-01-15');  // '2024-01-15'
processDate('invalid');     // null

function validateDateInput(value: string): string | undefined {
  const date = fdu(value);

  if (!date.isValid()) {
    return 'Please enter a valid date';
  }

  if (date.isBefore(fdu())) {
    return 'Date cannot be in the past';
  }

  return undefined;  // No error
}

const userInput = getUserInput();
const date = fdu(userInput);

if (date.isValid()) {
  console.log(`Valid date: ${date.format('YYYY-MM-DD')}`);
  processDate(date);
} else {
  console.log('Please enter a valid date');
  showError('Invalid date format');
}

function parseUserDate(input: string): FduInstance | null {
  const date = fdu(input);
  return date.isValid() ? date : null;
}

const result = parseUserDate('2024-01-15');
if (result) {
  console.log('Valid date:', result.format('YYYY-MM-DD'));
} else {
  console.log('Invalid date');
}

const inputs = [
  '2024-01-15',
  'invalid',
  '2024-02-29',  // Valid (leap year)
  '2023-02-29',  // Invalid (not leap year)
  '2024-12-25'
];

const validDates = inputs
  .map(input => fdu(input))
  .filter(date => date.isValid());

console.log(`Found ${validDates.length} valid dates`);

interface ApiResponse {
  date: string;
  value: number;
}

function processApiResponse(response: ApiResponse): void {
  const date = fdu(response.date);

  if (!date.isValid()) {
    throw new Error(`Invalid date in API response: ${response.date}`);
  }

  // Safe to use date
  console.log(`Data for ${date.format('YYYY-MM-DD')}: ${response.value}`);
}

function calculateDaysUntil(targetDate: FduInstance): number | null {
  if (!targetDate.isValid()) {
    console.warn('Invalid target date provided');
    return null;
  }

  const now = fdu();
  return targetDate.diff(now, 'day');
}

// ❌ Avoid
function parseDate(input: string): FduInstance | null {
  try {
    const date = fdu(input);
    return date;
  } catch (e) {
    return null;
  }
}

// ✅ Better
function parseDate(input: string): FduInstance | null {
  const date = fdu(input);
  return date.isValid() ? date : null;
}

function isValidFduDate(date: FduInstance): boolean {
  return date.isValid();
}

const dates = [
  fdu('2024-01-15'),
  fdu('invalid'),
  fdu('2024-12-25')
];

const validDates = dates.filter(isValidFduDate);