/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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 com.google.errorprone.bugpatterns;

import static com.google.common.collect.ImmutableSet.toImmutableSet;

import com.google.common.collect.Iterables;
import com.google.errorprone.BugPattern;
import com.google.errorprone.BugPattern.Category;
import com.google.errorprone.BugPattern.SeverityLevel;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.google.errorprone.matchers.Matchers;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.BlockTree;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionStatementTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.ReturnTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.TreeVisitor;
import com.sun.source.util.SimpleTreeVisitor;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.TypeSymbol;
import com.sun.tools.javac.code.Types;
import java.util.Collections;
import java.util.Set;
import javax.lang.model.element.Modifier;

/** @author Louis Wasserman */
@BugPattern(
  category = Category.JDK,
  name = "FunctionalInterfaceMethodChanged",
  summary =
      "Casting a lambda to this @FunctionalInterface can cause a behavior change from casting to "
          + "a functional superinterface, which is surprising to users.  Prefer decorator methods "
          + "to this surprising behavior.",
  severity = SeverityLevel.ERROR,
  generateExamplesFromTestCases = false
)
public class FunctionalInterfaceMethodChanged extends BugChecker implements MethodTreeMatcher {

  private static final Matcher<Tree> IS_FUNCTIONAL_INTERFACE =
      Matchers.hasAnnotation(FunctionalInterface.class);

  @Override
  public Description matchMethod(MethodTree tree, VisitorState state) {
    ClassTree enclosingClazz = ASTHelpers.findEnclosingNode(state.getPath(), ClassTree.class);
    if (tree.getModifiers().getFlags().contains(Modifier.DEFAULT)
        && IS_FUNCTIONAL_INTERFACE.matches(enclosingClazz, state)) {
      Types types = Types.instance(state.context);
      Set<Symbol> functionalSuperInterfaceSams =
          enclosingClazz
              .getImplementsClause()
              .stream()
              .filter(t -> IS_FUNCTIONAL_INTERFACE.matches(t, state))
              .map(ASTHelpers::getSymbol)
              .map(TypeSymbol.class::cast)
              .map(types::findDescriptorSymbol) // TypeSymbol to single abstract method of the type
              .collect(toImmutableSet());

      // We designate an override of a superinterface SAM "behavior preserving" if it just
      // calls the SAM of this interface.
      Symbol thisInterfaceSam = types.findDescriptorSymbol(ASTHelpers.getSymbol(enclosingClazz));

      // relatively crude: doesn't verify that the same args are passed in the same order
      // so it can get false positives for behavior-preservingness (false negatives for the check)
      TreeVisitor<Boolean, VisitorState> behaviorPreserving =
          new SimpleTreeVisitor<Boolean, VisitorState>(false) {
            @Override
            public Boolean visitMethod(MethodTree node, VisitorState state) {
              return node.getBody() != null && node.getBody().accept(this, state);
            }

            @Override
            public Boolean visitBlock(BlockTree node, VisitorState state) {
              return node.getStatements().size() == 1
                  && Iterables.getOnlyElement(node.getStatements()).accept(this, state);
            }

            @Override
            public Boolean visitExpressionStatement(
                ExpressionStatementTree node, VisitorState state) {
              return node.getExpression().accept(this, state);
            }

            @Override
            public Boolean visitReturn(ReturnTree node, VisitorState state) {
              return node.getExpression().accept(this, state);
            }

            @Override
            public Boolean visitMethodInvocation(MethodInvocationTree node, VisitorState state) {
              return ASTHelpers.getSymbol(node) == thisInterfaceSam;
            }
          };

      if (!Collections.disjoint(
              ASTHelpers.findSuperMethods(ASTHelpers.getSymbol(tree), types),
              functionalSuperInterfaceSams)
          && !tree.accept(behaviorPreserving, state)) {
        return describeMatch(tree);
      }
    }
    return Description.NO_MATCH;
  }
}