import javax.annotation.processing.*;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.*;
import javax.tools.Diagnostic.Kind;
import java.lang.reflect.*;
import java.lang.reflect.Modifier;
import java.util.*;
import java.lang.annotation.*;

/** Check that a class marked {@code @Utility} is indeed a utility class. */
@SupportedAnnotationTypes("Utility")
@SupportedSourceVersion(SourceVersion.RELEASE_11)
public class UtilityProcessor extends AbstractProcessor {

	@Override
	public boolean process(
			Set<? extends TypeElement> annotations,
			RoundEnvironment roundingEnvironment)
	{
		Messager messager = processingEnv.getMessager();
		messager.printMessage(Kind.NOTE,
				"UtilityProcessor executed.");
		messager.printMessage(Kind.WARNING,
				"The provided UtilityProcessor class is wrong.  Correct it!");
		for (TypeElement te : annotations) {
			for (Element elt : roundingEnvironment.getElementsAnnotatedWith(te)) {

				// check if elt is a class
				if (elt.getKind() == ElementKind.CLASS) {

					// Check that the class is declared final
					if (Modifier.isFinal(elt.getModifiers())) {

						Class<?> cl = Class.forName(elt.getTagName());
											
						// Check that enclosed elements are static
						Method[] methods = cl.getMethods();
						for (Method method : methods) {
							if (!Modifier.isStatic(method.getModifiers())) {
								messager.printMessage(Kind.ERROR, "@Utility applies to class with STATIC mehthods only:", elt);
								break;
							}
						}
						// Check for constructors issues
						Constructor[] constructors = cl.getConstructors();
						System.out.println("nb construct : " + constructors.length);
						if (constructors.length != 1) {
							messager.printMessage(Kind.ERROR, "@Utility applies to class with only ONE constructor only:", elt);
							break;
						} 
						for (Constructor constructor : constructors) {
							if (Modifier.isPrivate(constructor.getModifiers())) {
								messager.printMessage(Kind.ERROR, "@Utility applies to class with only a PRIVATE constructor only:", elt);
								break;
							}
						}
					} else {
						messager.printMessage(Kind.ERROR, "@Utility applies to FINAL class only:", elt);
					}
				} else {
					messager.printMessage(Kind.ERROR, "@Utility applies to CLASS only:", elt);
				}
			}
		}
		return true;
	}

}