PermissionSet pstCoveo  = [SELECT Id,Name FROM PermissionSet WHERE Name = 'Coveo_Dealer_Portal'];
// Coveo_Dealer_Portal permission set Id
String permissionSetId = pstCoveo.Id;
 // Retrieve all active users 
List<User> users = [SELECT Id FROM User WHERE IsActive = true AND (Profile.Name = 'API User' OR Profile.Name = 'Bobcat Sales Support Representative' OR Profile.Name = 'E-Commerce Sales Specialist' OR Profile.Name = 'General_Sales Read Only' OR Profile.Name = 'IRW API' OR Profile.Name = 'Marketing User' OR Profile.Name = 'Marketing_Coop' OR Profile.Name = 'Marketing_Internal User' OR Profile.Name = 'Marketing_Training Administrator' OR Profile.Name = 'Media Internal User' OR Profile.Name = 'Sales_Dealer Development' OR Profile.Name = 'Sales_District Manager' OR Profile.Name = 'Sales_National Accounts' OR Profile.Name = 'Sales_Regional Director' OR Profile.Name = 'System_IBB' OR Profile.Name = 'Vendor_Inside Sales Agent' OR Profile.Name = 'Dealer User' OR Profile.Name = 'System_Data Administrator' OR Profile.Name = 'Marketing_User' OR Profile.Name = 'System Administrator') LIMIT 10000];
 Set<Id> userIds = new Set<Id>();
for (User user : users) {
    userIds.add(user.Id);
}
// Get existing permission set assignment for these users
Map<Id, PermissionSetAssignment> existingAssignments = new Map<Id, PermissionSetAssignment>();
for (PermissionSetAssignment psa : [
    SELECT AssigneeId FROM PermissionSetAssignment
    WHERE AssigneeId IN :userIds AND PermissionSetId = :permissionSetId
]) {
    existingAssignments.put(psa.AssigneeId, psa);
}
 // Prepare list for new permission set assignments
List<PermissionSetAssignment> permissionSetAssignmentsToInsert = new List<PermissionSetAssignment>();
 for (User user : users) {
    if (!existingAssignments.containsKey(user.Id)) {
        permissionSetAssignmentsToInsert.add(
            new PermissionSetAssignment(AssigneeId = user.Id, PermissionSetId = permissionSetId)
        );
    }
}
// Insert the new assignments
if (!permissionSetAssignmentsToInsert.isEmpty()) {
    try {
        insert permissionSetAssignmentsToInsert;
    } catch (Exception e) {
        System.debug('Error during permission set assignment: ' + e.getMessage());
    }
}