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A packaging of the IntelliJ Community Edition python-community library. This is release number 1 of trunk branch 142.
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/*
 * Copyright 2000-2014 JetBrains s.r.o.
 *
 * 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.jetbrains.python.inspections;

import com.intellij.codeInspection.LocalInspectionToolSession;
import com.intellij.codeInspection.ProblemsHolder;
import com.intellij.psi.PsiElementVisitor;
import com.intellij.psi.tree.TokenSet;
import com.jetbrains.python.PyBundle;
import com.jetbrains.python.PyTokenTypes;
import com.jetbrains.python.inspections.quickfix.AugmentedAssignmentQuickFix;
import com.jetbrains.python.psi.*;
import com.jetbrains.python.psi.impl.PyBuiltinCache;
import com.jetbrains.python.psi.types.PyType;
import com.jetbrains.python.psi.types.PyTypeChecker;
import org.jetbrains.annotations.Nls;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * User: catherine
 *
 * Inspection to detect assignments that can be replaced with augmented assignments.
 */
public class PyAugmentAssignmentInspection extends PyInspection {
  @Nls
  @NotNull
  @Override
  public String getDisplayName() {
    return PyBundle.message("INSP.NAME.augment.assignment");
  }

  @NotNull
  @Override
  public PsiElementVisitor buildVisitor(@NotNull ProblemsHolder holder,
                                        boolean isOnTheFly,
                                        @NotNull LocalInspectionToolSession session) {
    return new Visitor(holder, session);
  }

  private static class Visitor extends PyInspectionVisitor {
    public Visitor(@Nullable ProblemsHolder holder, @NotNull LocalInspectionToolSession session) {
      super(holder, session);
    }

    @Override
    public void visitPyAssignmentStatement(final PyAssignmentStatement node) {
      final PyExpression value = node.getAssignedValue();
      if (value instanceof PyBinaryExpression) {
        final PyExpression target = node.getLeftHandSideExpression();
        final PyBinaryExpression expression = (PyBinaryExpression)value;
        PyExpression leftExpression = expression.getLeftExpression();
        PyExpression rightExpression = expression.getRightExpression();

        if (rightExpression instanceof PyParenthesizedExpression) {
          rightExpression = ((PyParenthesizedExpression)rightExpression).getContainedExpression();
        }
        if (rightExpression == null || target == null) {
          return;
        }
        boolean changedParts = false;
        final String targetText = target.getText();
        final String rightText = rightExpression.getText();
        if (rightText.equals(targetText)) {
          final PyExpression tmp = rightExpression;
          rightExpression = leftExpression;
          leftExpression = tmp;
          changedParts = true;
        }

        final PyElementType op = expression.getOperator();
        final TokenSet operations = TokenSet.create(PyTokenTypes.PLUS, PyTokenTypes.MINUS, PyTokenTypes.MULT,
                                                    PyTokenTypes.FLOORDIV, PyTokenTypes.DIV, PyTokenTypes.PERC, PyTokenTypes.AND,
                                                    PyTokenTypes.OR, PyTokenTypes.XOR, PyTokenTypes.LTLT, PyTokenTypes.GTGT,
                                                    PyTokenTypes.EXP);
        final TokenSet commutativeOperations = TokenSet.create(PyTokenTypes.PLUS, PyTokenTypes.MULT, PyTokenTypes.OR, PyTokenTypes.AND);
        if ((operations.contains(op) && !changedParts) || (changedParts && commutativeOperations.contains(op))) {
          if (leftExpression.getText().equals(targetText) && (leftExpression instanceof PyReferenceExpression || leftExpression instanceof PySubscriptionExpression)) {
            final PyType type = myTypeEvalContext.getType(rightExpression);
            if (type != null && !PyTypeChecker.isUnknown(type)) {
              final PyBuiltinCache cache = PyBuiltinCache.getInstance(rightExpression);
              final LanguageLevel languageLevel = LanguageLevel.forElement(rightExpression);
              if (isNumeric(type, cache) || (isString(type, cache, languageLevel) && !changedParts)) {
                registerProblem(node, "Assignment can be replaced with augmented assignment", new AugmentedAssignmentQuickFix());
              }
            }
          }
        }
      }
    }

    private boolean isString(PyType type, PyBuiltinCache cache, LanguageLevel level) {
      return PyTypeChecker.match(cache.getStringType(level), type, myTypeEvalContext);
    }

    private boolean isNumeric(PyType type, PyBuiltinCache cache) {
      return PyTypeChecker.match(cache.getComplexType(), type, myTypeEvalContext);
    }
  }
}