Custom Date Range Validation

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
  // Exit if form is loading
  if (isLoading) {
    return;
  }

  // Configuration
  var minimumLeadTimeDays = 3;  // Minimum days in advance
  var minimumDurationHours = 1;  // Minimum change window
  var maximumDurationHours = 8;  // Maximum change window

  // Blackout periods (no changes allowed)
  var blackoutPeriods = [
    {start: '2024-12-24', end: '2024-12-26', reason: 'Holiday Freeze'},
    {start: '2024-12-31', end: '2025-01-02', reason: 'New Year Freeze'}
  ];

  // Restricted days (require additional approval)
  var restrictedDays = [0, 6];  // Sunday = 0, Saturday = 6

  // Get both date fields
  var startDate = g_form.getValue('start_date');
  var endDate = g_form.getValue('end_date');

  // Clear previous messages
  g_form.hideFieldMsg('start_date');
  g_form.hideFieldMsg('end_date');

  if (!startDate) {
    return;
  }

  var start = new Date(startDate);
  var now = new Date();

  // Validation 1: Check minimum lead time
  var leadTimeMs = start - now;
  var leadTimeDays = leadTimeMs / (1000 * 60 * 60 * 24);

  if (leadTimeDays < minimumLeadTimeDays) {
    var message = 'Start date must be at least ' + minimumLeadTimeDays + 
                  ' days in advance. Current lead time: ' + 
                  leadTimeDays.toFixed(1) + ' days.';
    g_form.showFieldMsg('start_date', message, 'error');
    g_form.addErrorMessage(message);
  }

  // Validation 2: Check if date is in the past
  if (start < now) {
    g_form.showFieldMsg('start_date', 'Start date cannot be in the past', 'error');
  }

  // Validation 3: Check blackout periods
  for (var i = 0; i < blackoutPeriods.length; i++) {
    var blackout = blackoutPeriods[i];
    var blackoutStart = new Date(blackout.start);
    var blackoutEnd = new Date(blackout.end);

    if (start >= blackoutStart && start <= blackoutEnd) {
      var message = 'Change cannot be scheduled during ' + blackout.reason + 
                   ' (' + blackout.start + ' to ' + blackout.end + ')';
      g_form.showFieldMsg('start_date', message, 'error');
      g_form.addErrorMessage(message);
    }
  }

  // Validation 4: Check restricted days (weekends)
  var dayOfWeek = start.getDay();
  if (restrictedDays.indexOf(dayOfWeek) !== -1) {
    var dayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 
                    'Thursday', 'Friday', 'Saturday'];
    var message = 'Changes scheduled on ' + dayNames[dayOfWeek] + 
                 ' require additional approval';
    g_form.showFieldMsg('start_date', message, 'warning');
    g_form.addInfoMessage(message);
    
    // Set flag for additional approval requirement
    g_form.setValue('u_requires_additional_approval', 'true');
  }

  // Validation 5: Check business hours (e.g., 9 AM - 5 PM)
  var hour = start.getHours();
  var isBusinessHours = (hour >= 9 && hour < 17);
  
  if (!isBusinessHours) {
    g_form.showFieldMsg('start_date', 
                       'After-hours change: Additional approval may be required', 
                       'warning');
  }

  // Validation 6: Validate against end date if present
  if (endDate) {
    var end = new Date(endDate);

    // End must be after start
    if (end <= start) {
      g_form.showFieldMsg('end_date', 'End date must be after start date', 'error');
    } else {
      // Check duration
      var durationMs = end - start;
      var durationHours = durationMs / (1000 * 60 * 60);

      if (durationHours < minimumDurationHours) {
        var message = 'Change window must be at least ' + 
                     minimumDurationHours + ' hour(s)';
        g_form.showFieldMsg('end_date', message, 'error');
      }

      if (durationHours > maximumDurationHours) {
        var message = 'Change window exceeds maximum of ' + 
                     maximumDurationHours + ' hours. ' +
                     'Consider breaking into multiple changes.';
        g_form.showFieldMsg('end_date', message, 'warning');
      }

      // Show duration info
      var durationInfo = 'Change window: ' + durationHours.toFixed(1) + ' hours';
      g_form.showFieldMsg('end_date', durationInfo, 'info');
    }
  }

  // Validation 7: Check for conflicts with other changes
  // This would require GlideAjax call to check server-side
  // Simplified example:
  /*
  var ga = new GlideAjax('ChangeConflictChecker');
  ga.addParam('sysparm_name', 'checkConflicts');
  ga.addParam('sysparm_start_date', startDate);
  ga.addParam('sysparm_end_date', endDate);
  ga.addParam('sysparm_ci', g_form.getValue('cmdb_ci'));
  
  ga.getXMLAnswer(function(response) {
    if (response === 'true') {
      g_form.showFieldMsg('start_date', 
                         'Warning: Another change is scheduled during this time', 
                         'warning');
    }
  });
  */
}