@Named("dtColumnsView")
@ViewScoped
public class ColumnsView implements Serializable {
    
    private final static List<String> VALID_COLUMN_KEYS = Arrays.asList("id", "brand", "year", "color", "price");
	
    private String columnTemplate = "id brand year";
    
    private List<ColumnModel> columns;
    
    private List<Car> cars;
    
    private List<Car> filteredCars;
    
    @Inject
    private CarService service;

    @PostConstruct
    public void init() {
        cars = service.createCars(10);
        
        createDynamicColumns();
    }
    
    public List<Car> getCars() {
        return cars;
    }

    public List<Car> getFilteredCars() {
        return filteredCars;
    }

    public void setFilteredCars(List<Car> filteredCars) {
        this.filteredCars = filteredCars;
    }

    public void setService(CarService service) {
        this.service = service;
    }

    public String getColumnTemplate() {
        return columnTemplate;
    }

    public void setColumnTemplate(String columnTemplate) {
        this.columnTemplate = columnTemplate;
    }

    public List<ColumnModel> getColumns() {
        return columns;
    }

    private void createDynamicColumns() {
        String[] columnKeys = columnTemplate.split(" ");
        columns = new ArrayList<ColumnModel>();   
        
        for(String columnKey : columnKeys) {
            String key = columnKey.trim();
            
            if(VALID_COLUMN_KEYS.contains(key)) {
                columns.add(new ColumnModel(columnKey.toUpperCase(), columnKey));
            }
        }
    }
    
    public void updateColumns() {
        //reset table state
        UIComponent table = FacesContext.getCurrentInstance().getViewRoot().findComponent(":form:cars");
        table.setValueExpression("sortBy", null);
        
        //update columns
        createDynamicColumns();
    }
    
    static public class ColumnModel implements Serializable {

        private String header;
        private String property;

        public ColumnModel(String header, String property) {
            this.header = header;
            this.property = property;
        }

        public String getHeader() {
            return header;
        }

        public String getProperty() {
            return property;
        }
    }
}

@Named
@ApplicationScoped
public class CarService {
    
    private final static String[] colors;
	
	private final static String[] brands;
    
    static {
		colors = new String[10];
		colors[0] = "Black";
		colors[1] = "White";
		colors[2] = "Green";
		colors[3] = "Red";
		colors[4] = "Blue";
		colors[5] = "Orange";
		colors[6] = "Silver";
		colors[7] = "Yellow";
		colors[8] = "Brown";
		colors[9] = "Maroon";
		
		brands = new String[10];
		brands[0] = "BMW";
		brands[1] = "Mercedes";
		brands[2] = "Volvo";
		brands[3] = "Audi";
		brands[4] = "Renault";
		brands[5] = "Fiat";
		brands[6] = "Volkswagen";
		brands[7] = "Honda";
		brands[8] = "Jaguar";
		brands[9] = "Ford";
	}
    
    public List<Car> createCars(int size) {
        List<Car> list = new ArrayList<Car>();
		for(int i = 0 ; i < size ; i++) {
			list.add(new Car(getRandomId(), getRandomBrand(), getRandomYear(), getRandomColor(), getRandomPrice(), getRandomSoldState()));
        }
        
        return list;
    }
    
    private String getRandomId() {
		return UUID.randomUUID().toString().substring(0, 8);
	}
    
    private int getRandomYear() {
		return (int) (Math.random() * 50 + 1960);
	}
	
	private String getRandomColor() {
		return colors[(int) (Math.random() * 10)];
	}
	
	private String getRandomBrand() {
		return brands[(int) (Math.random() * 10)];
	}
    
    private int getRandomPrice() {
		return (int) (Math.random() * 100000);
	}
    
    private boolean getRandomSoldState() {
		return (Math.random() > 0.5) ? true: false;
	}
    
    public List<String> getColors() {
        return Arrays.asList(colors);
    }
    
    public List<String> getBrands() {
        return Arrays.asList(brands);
    }
}