generator/src/main/java/com/google/autofactory/ProvidedChecker.java

package com.google.autofactory;

import static com.google.common.base.Preconditions.checkArgument;
import static javax.tools.Diagnostic.Kind.ERROR;

import javax.annotation.processing.Messager;
import javax.inject.Inject;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.util.ElementKindVisitor6;

final class ProvidedChecker {
  private final Messager messager;

  @Inject ProvidedChecker(Messager messager) {
    this.messager = messager;
  }

  void checkProvidedParameter(Element element) {
    checkArgument(element.getAnnotation(Provided.class) != null);
    element.accept(new ElementKindVisitor6<Void, Void>() {
      @Override
      protected Void defaultAction(Element e, Void p) {
        throw new AssertionError("Provided can only be applied to parameters");
      }

      @Override
      public Void visitVariableAsParameter(final VariableElement providedParameter, Void p) {
        providedParameter.getEnclosingElement().accept(new ElementKindVisitor6<Void, Void>() {
          @Override
          protected Void defaultAction(Element e, Void p) {
            raiseError(providedParameter, "@%s may only be applied to constructor parameters");
            return null;
          }

          @Override
          public Void visitExecutableAsConstructor(ExecutableElement constructor, Void p) {
            if (!(annotatedWithAutoFactory(constructor)
                || annotatedWithAutoFactory(constructor.getEnclosingElement()))) {
              raiseError(providedParameter,
                  "@%s may only be applied to classes requesting an auto-factory");
            }
            return null;
          }
        }, p);
        return null;
      }
    }, null);
  }

  private void raiseError(VariableElement providedParameter, String messageFormat) {
    messager.printMessage(ERROR, String.format(messageFormat, Provided.class.getSimpleName()),
        providedParameter);
  }

  private static boolean annotatedWithAutoFactory(Element e) {
    return e.getAnnotation(AutoFactory.class) != null;
  }
}