/*
 * 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.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.matchers.Description.NO_MATCH;

import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.BinaryTreeMatcher;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.sun.source.tree.BinaryTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.Tree.Kind;
import com.sun.tools.javac.tree.JCTree.JCBinary;
import com.sun.tools.javac.tree.TreeInfo;
import java.util.EnumSet;

/** @author cushon@google.com (Liam Miller-Cushon) */
@BugPattern(
  name = "OperatorPrecedence",
  category = JDK,
  summary = "Use grouping parenthesis to make the operator precedence explicit",
  severity = WARNING
)
public class OperatorPrecedence extends BugChecker implements BinaryTreeMatcher {

  private static final EnumSet<Kind> CONDITIONAL =
      EnumSet.of(Kind.AND, Kind.OR, Kind.XOR, Kind.CONDITIONAL_AND, Kind.CONDITIONAL_OR);

  private static final EnumSet<Kind> SHIFT =
      EnumSet.of(Kind.LEFT_SHIFT, Kind.RIGHT_SHIFT, Kind.UNSIGNED_RIGHT_SHIFT);

  private static final EnumSet<Kind> ARITHMETIC =
      EnumSet.of(Kind.PLUS, Kind.MULTIPLY, Kind.DIVIDE, Kind.MINUS);

  @Override
  public Description matchBinary(BinaryTree tree, VisitorState state) {
    Tree parent = state.getPath().getParentPath().getLeaf();
    if (!(parent instanceof BinaryTree)) {
      return NO_MATCH;
    }
    if (TreeInfo.opPrec(((JCBinary) tree).getTag())
        == TreeInfo.opPrec(((JCBinary) parent).getTag())) {
      return NO_MATCH;
    }
    if (!isConfusing(tree.getKind(), parent.getKind())) {
      return NO_MATCH;
    }
    return describeMatch(
        tree, SuggestedFix.builder().prefixWith(tree, "(").postfixWith(tree, ")").build());
  }

  private boolean isConfusing(Kind thisKind, Kind parentKind) {
    if (CONDITIONAL.contains(thisKind) && CONDITIONAL.contains(parentKind)) {
      return true;
    }
    if ((SHIFT.contains(thisKind) && ARITHMETIC.contains(parentKind))
        || (SHIFT.contains(parentKind) && ARITHMETIC.contains(thisKind))) {
      return true;
    }
    return false;
  }
}