FinalLocalVariableCheck

////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2015 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.coding;

import com.puppycrawl.tools.checkstyle.api.Check;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.FastStack;
import com.puppycrawl.tools.checkstyle.api.ScopeUtils;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import java.util.HashMap;
import java.util.Map;

/**
 * <p>
 * Ensures that local variables that never get their values changed,
 * must be declared final.
 * </p>
 * <p>
 * An example of how to configure the check is:
 * </p>
 * <pre>
 * &lt;module name="FinalLocalVariable"&gt;
 *     &lt;property name="token" value="VARIABLE_DEF"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * By default, this Check skip final validation on
 *  <a href = "http://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.14.2">
 * Enhanced For-Loop</a>
 * </p>
 * <p>
 * Option 'validateEnhancedForLoopVariable' could be used to make Check to validate even variable
 *  from Enhanced For Loop.
 * </p>
 * <p>
 * An example of how to configure the check so that it also validates enhanced For Loop Variable is:
 * </p>
 * <pre>
 * &lt;module name="FinalLocalVariable"&gt;
 *     &lt;property name="token" value="VARIABLE_DEF"/&gt;
 *     &lt;property name="validateEnhancedForLoopVariable" value="true"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>Example:</p>
 * <p>
 * <code>
 * for (int number : myNumbers) { // violation
 *    System.out.println(number);
 * }
 * </code>
 * </p>
 * @author k_gibbs, r_auckenthaler
 */
public class FinalLocalVariableCheck extends Check
{

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_KEY = "final.variable";

    /** Scope Stack */
    private final FastStack<Map<String, DetailAST>> scopeStack =
        FastStack.newInstance();

    /** Controls whether to check enhanced for-loop variable. */
    private boolean validateEnhancedForLoopVariable;

    /**
     * Whether to check enhanced for-loop variable or not.
     * @param validateEnhancedForLoopVariable whether to check for-loop variable
     */
    public final void setValidateEnhancedForLoopVariable(boolean validateEnhancedForLoopVariable)
    {
        this.validateEnhancedForLoopVariable = validateEnhancedForLoopVariable;
    }

    @Override
    public int[] getDefaultTokens()
    {
        return new int[] {
            TokenTypes.IDENT,
            TokenTypes.CTOR_DEF,
            TokenTypes.METHOD_DEF,
            TokenTypes.VARIABLE_DEF,
            TokenTypes.INSTANCE_INIT,
            TokenTypes.STATIC_INIT,
            TokenTypes.LITERAL_FOR,
            TokenTypes.SLIST,
            TokenTypes.OBJBLOCK,
        };
    }

    @Override
    public int[] getAcceptableTokens()
    {
        return new int[] {
            TokenTypes.IDENT,
            TokenTypes.CTOR_DEF,
            TokenTypes.METHOD_DEF,
            TokenTypes.VARIABLE_DEF,
            TokenTypes.INSTANCE_INIT,
            TokenTypes.STATIC_INIT,
            TokenTypes.LITERAL_FOR,
            TokenTypes.SLIST,
            TokenTypes.OBJBLOCK,
            TokenTypes.PARAMETER_DEF,
        };
    }

    @Override
    public int[] getRequiredTokens()
    {
        return new int[] {
            TokenTypes.IDENT,
            TokenTypes.CTOR_DEF,
            TokenTypes.METHOD_DEF,
            TokenTypes.INSTANCE_INIT,
            TokenTypes.STATIC_INIT,
            TokenTypes.LITERAL_FOR,
            TokenTypes.SLIST,
            TokenTypes.OBJBLOCK,
        };
    }

    @Override
    public void visitToken(DetailAST ast)
    {
        switch (ast.getType()) {
            case TokenTypes.OBJBLOCK:
            case TokenTypes.SLIST:
            case TokenTypes.LITERAL_FOR:
            case TokenTypes.METHOD_DEF:
            case TokenTypes.CTOR_DEF:
            case TokenTypes.STATIC_INIT:
            case TokenTypes.INSTANCE_INIT:
                scopeStack.push(new HashMap<String, DetailAST>());
                break;

            case TokenTypes.PARAMETER_DEF:
                if (ScopeUtils.inInterfaceBlock(ast)
                    || inAbstractOrNativeMethod(ast))
                {
                    break;
                }
            case TokenTypes.VARIABLE_DEF:
                if (ast.getParent().getType() != TokenTypes.OBJBLOCK
                    && shouldCheckEnhancedForLoopVariable(ast)
                    && isVariableInForInit(ast))
                {
                    insertVariable(ast);
                }
                break;

            case TokenTypes.IDENT:
                final int parentType = ast.getParent().getType();
                if (TokenTypes.POST_DEC        == parentType
                    || TokenTypes.DEC          == parentType
                    || TokenTypes.POST_INC     == parentType
                    || TokenTypes.INC          == parentType
                    || TokenTypes.ASSIGN       == parentType
                    || TokenTypes.PLUS_ASSIGN  == parentType
                    || TokenTypes.MINUS_ASSIGN == parentType
                    || TokenTypes.DIV_ASSIGN   == parentType
                    || TokenTypes.STAR_ASSIGN  == parentType
                    || TokenTypes.MOD_ASSIGN   == parentType
                    || TokenTypes.SR_ASSIGN    == parentType
                    || TokenTypes.BSR_ASSIGN   == parentType
                    || TokenTypes.SL_ASSIGN    == parentType
                    || TokenTypes.BXOR_ASSIGN  == parentType
                    || TokenTypes.BOR_ASSIGN   == parentType
                    || TokenTypes.BAND_ASSIGN  == parentType)
                {
                    // TODO: is there better way to check is ast
                    // in left part of assignment?
                    if (ast.getParent().getFirstChild() == ast) {
                        removeVariable(ast);
                    }
                }
                break;

            default:
        }
    }

    /**
     * Determines whether enhanced for-loop variable should be checked or not.
     * @param ast The ast to compare.
     * @return true if enhanced for-loop variable should be checked.
     */
    private boolean shouldCheckEnhancedForLoopVariable(DetailAST ast)
    {
        return validateEnhancedForLoopVariable
                || ast.getParent().getType() != TokenTypes.FOR_EACH_CLAUSE;
    }

    /**
     * Checks if current variable is defined in
     *  {@link TokenTypes#FOR_INIT for-loop init}, e.g.:
     * <p>
     * <code>
     * for (int i = 0, j = 0; i < j; i++) { . . . }
     * </code>
     * </p>
     * <code>i, j</code> are defined in {@link TokenTypes#FOR_INIT for-loop init}
     * @param variableDef variable definition node.
     * @return true if variable is defined in {@link TokenTypes#FOR_INIT for-loop init}
     */
    private static boolean isVariableInForInit(DetailAST variableDef)
    {
        return variableDef.getParent().getType() != TokenTypes.FOR_INIT;
    }

    /**
     * Determines whether an AST is a descendant of an abstract or native method.
     * @param ast the AST to check.
     * @return true if ast is a descendant of an abstract or native method.
     */
    private static boolean inAbstractOrNativeMethod(DetailAST ast)
    {
        DetailAST parent = ast.getParent();
        while (parent != null) {
            if (parent.getType() == TokenTypes.METHOD_DEF) {
                final DetailAST modifiers =
                    parent.findFirstToken(TokenTypes.MODIFIERS);
                return modifiers.branchContains(TokenTypes.ABSTRACT)
                        || modifiers.branchContains(TokenTypes.LITERAL_NATIVE);
            }
            parent = parent.getParent();
        }
        return false;
    }

    /**
     * Inserts a variable at the topmost scope stack
     * @param ast the variable to insert
     */
    private void insertVariable(DetailAST ast)
    {
        if (!ast.branchContains(TokenTypes.FINAL)) {
            final Map<String, DetailAST> state = scopeStack.peek();
            final DetailAST astNode = ast.findFirstToken(TokenTypes.IDENT);
            state.put(astNode.getText(), astNode);
        }
    }

    /**
     * Removes the variable from the Stacks
     * @param ast Variable to remove
     */
    private void removeVariable(DetailAST ast)
    {
        for (int i = scopeStack.size() - 1; i >= 0; i--) {
            final Map<String, DetailAST> state = scopeStack.peek(i);
            final Object obj = state.remove(ast.getText());
            if (obj != null) {
                break;
            }
        }
    }

    @Override
    public void leaveToken(DetailAST ast)
    {
        super.leaveToken(ast);

        switch (ast.getType()) {
            case TokenTypes.OBJBLOCK:
            case TokenTypes.SLIST:
            case TokenTypes.LITERAL_FOR:
            case TokenTypes.CTOR_DEF:
            case TokenTypes.STATIC_INIT:
            case TokenTypes.INSTANCE_INIT:
            case TokenTypes.METHOD_DEF:
                final Map<String, DetailAST> state = scopeStack.pop();
                for (DetailAST var : state.values()) {
                    log(var.getLineNo(), var.getColumnNo(), MSG_KEY, var
                        .getText());
                }
                break;

            default:
        }
    }
}