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package net.zerobuilder.compiler.common;

import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ElementVisitor;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.PackageElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.TypeKind;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.SimpleElementVisitor6;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.function.Predicate;

import static javax.lang.model.element.ElementKind.PACKAGE;
import static javax.lang.model.util.ElementFilter.methodsIn;
import static net.zerobuilder.compiler.common.LessTypes.asTypeElement;

/**
 * Guava-free versions of some helpers from auto-common.
 */
public final class LessElements {

  private static final ElementVisitor TYPE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override
        protected TypeElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override
        public TypeElement visitType(TypeElement e, Void p) {
          return e;
        }
      };

  private static final ElementVisitor EXECUTABLE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override
        protected ExecutableElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override
        public ExecutableElement visitExecutable(ExecutableElement e, Void p) {
          return e;
        }
      };

  /**
   * Find all non-static, visible methods that match the predicate, and group by name.
   * In case of name conflict, the first found wins.
   * The iteration order is:
   * 
   * {@code type} first, {@code Object} last
   * concrete types before interfaces
   * 
   * Ideally the {@code predicate} should prevent name conflicts.
   *
   * @param type      type to search
   * @param predicate filter
   * @return methods by name
   */
  public static Map getLocalAndInheritedMethods(
      TypeElement type, Predicate predicate) {
    Map methods = new LinkedHashMap<>();
    PackageElement packageElement = getPackage(type);
    addFromSuperclass(packageElement, type, methods, predicate);
    addFromInterfaces(packageElement, type, methods, predicate);
    return methods;
  }

  private static void addFromSuperclass(
      PackageElement pkg, TypeElement type, Map methods,
      Predicate predicate) {
    addEnclosed(pkg, type, methods, predicate);
    if (type.getSuperclass().getKind() == TypeKind.NONE) {
      return;
    }
    addFromSuperclass(pkg, asTypeElement(type.getSuperclass()), methods,
        predicate);
  }

  private static void addFromInterfaces(
      PackageElement pkg, TypeElement type, Map methods,
      Predicate predicate) {
    addEnclosed(pkg, type, methods, predicate);
    for (TypeMirror superInterface : type.getInterfaces()) {
      addFromInterfaces(pkg, asTypeElement(superInterface), methods,
          predicate);
    }
  }

  private static void addEnclosed(PackageElement pkg, TypeElement type, Map methods,
                                  Predicate predicate) {
    methodsIn(type.getEnclosedElements())
        .stream()
        .filter(predicate)
        .forEach(method -> {
          if (method.getKind() == ElementKind.METHOD
              && !method.getModifiers().contains(Modifier.STATIC)
              && methodVisibleFromPackage(method, pkg)) {
            methods.computeIfAbsent(method.getSimpleName().toString(), name -> method);
          }
        });
  }

  private static boolean methodVisibleFromPackage(ExecutableElement method, PackageElement pkg) {
    Visibility visibility = Visibility.ofElement(method);
    switch (visibility) {
      case PRIVATE:
        return false;
      case DEFAULT:
        return getPackage(method).equals(pkg);
      default:
        return true;
    }
  }

  private static PackageElement getPackage(Element element) {
    while (element.getKind() != PACKAGE) {
      element = element.getEnclosingElement();
    }
    return (PackageElement) element;
  }

  public static ExecutableElement asExecutable(Element element) {
    return element.accept(EXECUTABLE_ELEMENT_VISITOR, null);
  }

  static TypeElement asType(Element element) {
    return element.accept(TYPE_ELEMENT_VISITOR, null);
  }

  private LessElements() {
    throw new UnsupportedOperationException("no instances");
  }
}