CUIBase.java

package immibis.bon.cui;

import java.io.File;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.util.List;

public abstract class CUIBase {
	@Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME)
	public static @interface Option {
		String value();
	}
	@Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME)
	public static @interface Required {
		
	}
	
	protected abstract void showUsage() throws Exception;
	protected abstract void run() throws Exception;
	
	private Field getOptionField(String name) {
		for(Field f : getClass().getFields()) {
			Option o = f.getAnnotation(Option.class);
			if(o != null && o.value().equals(name))
				return f;
		}
		return null;
	}
	
	@SuppressWarnings("unchecked")
	private boolean parseOptions(String[] args) throws Exception {
		if((args.length % 2) == 1) {
			System.err.println("Expected an even number of arguments.");
			return false;
		}
		
		boolean ok = true;
		
		for(int k = 0; k < args.length; k += 2) {
			String opt = args[k];
			String val = args[k + 1];
			
			Field f = getOptionField(opt);
			if(f == null) {
				System.err.println("Unknown option: " + opt);
				ok = false;
				continue;
			}
			
			if(Enum.class.isAssignableFrom(f.getType())) {
				try {
					f.set(this, Enum.valueOf(f.getType().asSubclass(Enum.class), val));
				} catch(EnumConstantNotPresentException e) {
					System.err.println("Invalid option for "+opt+": "+val);
					System.err.println("Valid values: " + f.getType().getEnumConstants());
					ok = false;
					continue;
				}
				
			} else if(f.getType() == String.class) {
				if(f.get(this) != null) {
					System.err.println("Option specified more than once: " + opt);
					ok = false;
				} else
					f.set(this, val);
				
			} else if(f.getType() == File.class) {
				if(f.get(this) != null) {
					System.err.println("Option specified more than once: " + opt);
					ok = false;
				} else
					f.set(this, new File(val));
				
			} else if(f.getType() == List.class) {
				((List<String>)f.get(this)).add(val);
				
			} else {
				System.err.println("BUG: Invalid option type "+f.getType().getName()+" for option field "+f.getName()+" for option "+opt);
				ok = false;
			}
		}
		
		return ok;
	}
	
	protected boolean checkOptions() throws Exception {
		boolean ok = true;
		for(Field f : getClass().getFields()) {
			if(f.isAnnotationPresent(Required.class) && f.get(this) == null) {
				System.err.println("Required option "+f.getAnnotation(Option.class).value()+" not present.");
				ok = false;
			}
		}
		return ok;
	}
	
	protected void run(String[] args) throws Exception {
		if(args.length == 0)
			showUsage();
		else if(parseOptions(args) && checkOptions())
			run();
	}
}