/*
 * Copyright (C) 2014 Google, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package dagger.internal.codegen;

import com.google.auto.common.MoreElements;
import com.google.auto.common.Visibility;
import com.google.common.base.Function;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Sets;
import dagger.Module;
import dagger.producers.ProducerModule;
import java.lang.annotation.Annotation;
import java.util.Collection;
import java.util.List;
import java.util.Map.Entry;
import java.util.Set;
import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.DeclaredType;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.ElementFilter;
import javax.lang.model.util.Elements;
import javax.lang.model.util.SimpleTypeVisitor6;
import javax.lang.model.util.Types;

import static com.google.auto.common.MoreElements.getAnnotationMirror;
import static com.google.auto.common.MoreElements.isAnnotationPresent;
import static com.google.auto.common.Visibility.PRIVATE;
import static com.google.auto.common.Visibility.PUBLIC;
import static com.google.auto.common.Visibility.effectiveVisibilityOfElement;
import static com.google.common.collect.Iterables.any;
import static dagger.internal.codegen.ConfigurationAnnotations.getModuleIncludes;
import static dagger.internal.codegen.ErrorMessages.BINDING_METHOD_WITH_SAME_NAME;
import static dagger.internal.codegen.ErrorMessages.METHOD_OVERRIDES_PROVIDES_METHOD;
import static dagger.internal.codegen.ErrorMessages.MODULES_WITH_TYPE_PARAMS_MUST_BE_ABSTRACT;
import static dagger.internal.codegen.ErrorMessages.PROVIDES_METHOD_OVERRIDES_ANOTHER;
import static dagger.internal.codegen.ErrorMessages.REFERENCED_MODULES_MUST_NOT_BE_ABSTRACT;
import static dagger.internal.codegen.ErrorMessages.REFERENCED_MODULE_MUST_NOT_HAVE_TYPE_PARAMS;
import static dagger.internal.codegen.ErrorMessages.REFERENCED_MODULE_NOT_ANNOTATED;
import static javax.lang.model.element.Modifier.ABSTRACT;

/**
 * A {@linkplain ValidationReport validator} for {@link Module}s or {@link ProducerModule}s.
 *
 * @author Gregory Kick
 * @since 2.0
 */
final class ModuleValidator {
  private final Types types;
  private final Elements elements;
  private final Class<? extends Annotation> moduleClass;
  private final ImmutableList<Class<? extends Annotation>> includedModuleClasses;
  private final Class<? extends Annotation> methodClass;
  private final MethodSignatureFormatter methodSignatureFormatter;

  ModuleValidator(
      Types types,
      Elements elements,
      MethodSignatureFormatter methodSignatureFormatter,
      Class<? extends Annotation> moduleClass,
      ImmutableList<Class<? extends Annotation>> includedModuleClasses,
      Class<? extends Annotation> methodClass) {
    this.types = types;
    this.elements = elements;
    this.moduleClass = moduleClass;
    this.includedModuleClasses = includedModuleClasses;
    this.methodClass = methodClass;
    this.methodSignatureFormatter = methodSignatureFormatter;
  }

  ValidationReport<TypeElement> validate(final TypeElement subject) {
    final ValidationReport.Builder<TypeElement> builder = ValidationReport.about(subject);

    List<ExecutableElement> moduleMethods = ElementFilter.methodsIn(subject.getEnclosedElements());
    ListMultimap<String, ExecutableElement> allMethodsByName = ArrayListMultimap.create();
    ListMultimap<String, ExecutableElement> bindingMethodsByName = ArrayListMultimap.create();
    for (ExecutableElement moduleMethod : moduleMethods) {
      if (isAnnotationPresent(moduleMethod, methodClass)) {
        bindingMethodsByName.put(moduleMethod.getSimpleName().toString(), moduleMethod);
      }
      allMethodsByName.put(moduleMethod.getSimpleName().toString(), moduleMethod);
    }

    validateModuleVisibility(subject, builder);
    validateMethodsWithSameName(builder, bindingMethodsByName);
    if (subject.getKind() != ElementKind.INTERFACE) {
      validateProvidesOverrides(subject, builder, allMethodsByName, bindingMethodsByName);
    }
    validateModifiers(subject, builder);
    validateReferencedModules(subject, builder);

    // TODO(gak): port the dagger 1 module validation?
    return builder.build();
  }

  private void validateModifiers(
      TypeElement subject, ValidationReport.Builder<TypeElement> builder) {
    // This coupled with the check for abstract modules in ComponentValidator guarantees that
    // only modules without type parameters are referenced from @Component(modules={...}).
    if (!subject.getTypeParameters().isEmpty() && !subject.getModifiers().contains(ABSTRACT)) {
      builder.addError(MODULES_WITH_TYPE_PARAMS_MUST_BE_ABSTRACT, subject);
    }
  }

  private void validateMethodsWithSameName(
      ValidationReport.Builder<TypeElement> builder,
      ListMultimap<String, ExecutableElement> bindingMethodsByName) {
    for (Entry<String, Collection<ExecutableElement>> entry :
        bindingMethodsByName.asMap().entrySet()) {
      if (entry.getValue().size() > 1) {
        for (ExecutableElement offendingMethod : entry.getValue()) {
          builder.addError(
              String.format(BINDING_METHOD_WITH_SAME_NAME, methodClass.getSimpleName()),
              offendingMethod);
        }
      }
    }
  }

  private void validateReferencedModules(
      TypeElement subject, ValidationReport.Builder<TypeElement> builder) {
    // Validate that all the modules we include are valid for inclusion.
    AnnotationMirror mirror = getAnnotationMirror(subject, moduleClass).get();
    ImmutableList<TypeMirror> includedTypes = getModuleIncludes(mirror);
    validateReferencedModules(subject,  builder, includedTypes);
  }

  /**
   * Used by {@link ModuleValidator} & {@link ComponentValidator} to validate referenced modules.
   */
  void validateReferencedModules(
      final TypeElement subject,
      final ValidationReport.Builder<TypeElement> builder,
      ImmutableList<TypeMirror> includedTypes) {
    for (TypeMirror includedType : includedTypes) {
      includedType.accept(
          new SimpleTypeVisitor6<Void, Void>() {
            @Override
            protected Void defaultAction(TypeMirror mirror, Void p) {
              builder.addError(mirror + " is not a valid module type.", subject);
              return null;
            }

            @Override
            public Void visitDeclared(DeclaredType t, Void p) {
              final TypeElement element = MoreElements.asType(t.asElement());
              if (!t.getTypeArguments().isEmpty()) {
                builder.addError(
                    String.format(
                        REFERENCED_MODULE_MUST_NOT_HAVE_TYPE_PARAMS, element.getQualifiedName()),
                    subject);
              }
              boolean isIncludedModule =
                  any(
                      includedModuleClasses,
                      new Predicate<Class<? extends Annotation>>() {
                        @Override
                        public boolean apply(Class<? extends Annotation> otherClass) {
                          return MoreElements.isAnnotationPresent(element, otherClass);
                        }
                      });
              if (!isIncludedModule) {
                builder.addError(
                    String.format(
                        REFERENCED_MODULE_NOT_ANNOTATED,
                        element.getQualifiedName(),
                        (includedModuleClasses.size() > 1 ? "one of " : "")
                            + Joiner.on(", ")
                                .join(
                                    FluentIterable.from(includedModuleClasses)
                                        .transform(
                                            new Function<Class<? extends Annotation>, String>() {
                                              @Override
                                              public String apply(
                                                  Class<? extends Annotation> otherClass) {
                                                return "@" + otherClass.getSimpleName();
                                              }
                                            }))),
                    subject);
              }
              if (element.getModifiers().contains(ABSTRACT)) {
                builder.addError(
                    String.format(
                        REFERENCED_MODULES_MUST_NOT_BE_ABSTRACT, element.getQualifiedName()),
                    subject);
              }
              return null;
            }
          },
          null);
    }
  }

  private void validateProvidesOverrides(
      TypeElement subject,
      ValidationReport.Builder<TypeElement> builder,
      ListMultimap<String, ExecutableElement> allMethodsByName,
      ListMultimap<String, ExecutableElement> bindingMethodsByName) {
    // For every @Provides method, confirm it overrides nothing *and* nothing overrides it.
    // Consider the following hierarchy:
    // class Parent {
    //    @Provides Foo a() {}
    //    @Provides Foo b() {}
    //    Foo c() {}
    // }
    // class Child extends Parent {
    //    @Provides Foo a() {}
    //    Foo b() {}
    //    @Provides Foo c() {}
    // }
    // In each of those cases, we want to fail.  "a" is clear, "b" because Child is overriding
    // a method marked @Provides in Parent, and "c" because Child is defining an @Provides
    // method that overrides Parent.
    TypeElement currentClass = subject;
    TypeMirror objectType = elements.getTypeElement(Object.class.getCanonicalName()).asType();
    // We keep track of methods that failed so we don't spam with multiple failures.
    Set<ExecutableElement> failedMethods = Sets.newHashSet();
    while (!types.isSameType(currentClass.getSuperclass(), objectType)) {
      currentClass = MoreElements.asType(types.asElement(currentClass.getSuperclass()));
      List<ExecutableElement> superclassMethods =
          ElementFilter.methodsIn(currentClass.getEnclosedElements());
      for (ExecutableElement superclassMethod : superclassMethods) {
        String name = superclassMethod.getSimpleName().toString();
        // For each method in the superclass, confirm our @Provides methods don't override it
        for (ExecutableElement providesMethod : bindingMethodsByName.get(name)) {
          if (!failedMethods.contains(providesMethod)
              && elements.overrides(providesMethod, superclassMethod, subject)) {
            failedMethods.add(providesMethod);
            builder.addError(
                String.format(
                    PROVIDES_METHOD_OVERRIDES_ANOTHER,
                    methodClass.getSimpleName(),
                    methodSignatureFormatter.format(superclassMethod)),
                providesMethod);
          }
        }
        // For each @Provides method in superclass, confirm our methods don't override it.
        if (isAnnotationPresent(superclassMethod, methodClass)) {
          for (ExecutableElement method : allMethodsByName.get(name)) {
            if (!failedMethods.contains(method)
                && elements.overrides(method, superclassMethod, subject)) {
              failedMethods.add(method);
              builder.addError(
                  String.format(
                      METHOD_OVERRIDES_PROVIDES_METHOD,
                      methodClass.getSimpleName(),
                      methodSignatureFormatter.format(superclassMethod)),
                  method);
            }
          }
        }
        allMethodsByName.put(superclassMethod.getSimpleName().toString(), superclassMethod);
      }
    }
  }

  private void validateModuleVisibility(final TypeElement moduleElement,
      final ValidationReport.Builder<?> reportBuilder) {
    Visibility moduleVisibility = Visibility.ofElement(moduleElement);
    if (moduleVisibility.equals(PRIVATE)) {
      reportBuilder.addError("Modules cannot be private.", moduleElement);
    } else if (effectiveVisibilityOfElement(moduleElement).equals(PRIVATE)) {
      reportBuilder.addError("Modules cannot be enclosed in private types.", moduleElement);
    }

    switch (moduleElement.getNestingKind()) {
      case ANONYMOUS:
        throw new IllegalStateException("Can't apply @Module to an anonymous class");
      case LOCAL:
        throw new IllegalStateException("Local classes shouldn't show up in the processor");
      case MEMBER:
      case TOP_LEVEL:
        if (moduleVisibility.equals(PUBLIC)) {
          ImmutableSet<Element> nonPublicModules = FluentIterable.from(getModuleIncludes(
              getAnnotationMirror(moduleElement, moduleClass).get()))
                  .transform(new Function<TypeMirror, Element>() {
                    @Override public Element apply(TypeMirror input) {
                      return types.asElement(input);
                    }
                  })
                  .filter(new Predicate<Element>() {
                    @Override public boolean apply(Element input) {
                      return effectiveVisibilityOfElement(input).compareTo(PUBLIC) < 0;
                    }
                  })
                  .toSet();
          if (!nonPublicModules.isEmpty()) {
            reportBuilder.addError(
                String.format(
                    "This module is public, but it includes non-public "
                        + "(or effectively non-public) modules. "
                        + "Either reduce the visibility of this module or make %s public.",
                    formatListForErrorMessage(nonPublicModules.asList())),
                moduleElement);
          }
        }
        break;
      default:
        throw new AssertionError();
    }
  }

  private static String formatListForErrorMessage(List<?> things) {
    switch (things.size()) {
      case 0:
        return "";
      case 1:
        return things.get(0).toString();
      default:
        StringBuilder output = new StringBuilder();
        Joiner.on(", ").appendTo(output, things.subList(0, things.size() - 1));
        output.append(" and ").append(things.get(things.size() - 1));
        return output.toString();
    }
  }
}