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Core processing architecture for json-schema-validator
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/*
 * Copyright (c) 2013, Francis Galiegue 
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Lesser GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program 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
 * Lesser GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package com.github.fge.jsonschema.util;

import org.mozilla.javascript.Context;
import org.mozilla.javascript.Function;
import org.mozilla.javascript.Scriptable;

import javax.annotation.concurrent.ThreadSafe;
import java.util.regex.Pattern;

/**
 * ECMA 262 validation helper. Rhino is used instead of {@link
 * java.util.regex} because the latter doesn't comply with ECMA 262:
 *
 * 
 *     ECMA 262 doesn't have {@link Pattern#DOTALL};
 *     ECMA 262 doesn't have "possessive" quantifiers ({@code ++},
 *     {@code ?+}, etc);
 *     there is only one word delimiter in ECMA 262, which is {@code \b};
 *     {@code \<} (for beginning of word) and {@code \>} (for end of word) are
 *     not understood.
 * 
 *
 * And many, many other things. See
 * here for
 * the full story. And if you don't yet have Jeffrey Friedl's "Mastering regular
 * expressions", just buy it :p
 */
@ThreadSafe
public final class RhinoHelper
{
    /**
     * JavaScript scriptlet defining functions {@link #REGEX_IS_VALID}
     * and {@link #REG_MATCH}
     */
    private static final String jsAsString
        = "function regexIsValid(re)"
        + '{'
        + "    try {"
        + "         new RegExp(re);"
        + "         return true;"
        + "    } catch (e) {"
        + "        return false;"
        + "    }"
        + '}'
        + ""
        + "function regMatch(re, input)"
        + '{'
        + "    return new RegExp(re).test(input);"
        + '}';

    /**
     * Script scope
     */
    private static final Scriptable SCOPE;

    /**
     * Reference to Javascript function for regex validation
     */
    private static final Function REGEX_IS_VALID;

    /**
     * Reference to Javascript function for regex matching
     */
    private static final Function REG_MATCH;

    private RhinoHelper()
    {
    }

    static {
        final Context ctx = Context.enter();
        try {
            SCOPE = ctx.initStandardObjects(null, true);
            ctx.evaluateString(SCOPE, jsAsString, "re", 1, null);
            REGEX_IS_VALID = (Function) SCOPE.get("regexIsValid", SCOPE);
            REG_MATCH = (Function) SCOPE.get("regMatch", SCOPE);
        } finally {
            Context.exit();
        }
    }

    /**
     * Validate that a regex is correct
     *
     * @param regex the regex to validate
     * @return true if the regex is valid
     */
    public static boolean regexIsValid(final String regex)
    {
        final Context context = Context.enter();
        try {
            return (Boolean) REGEX_IS_VALID.call(context, SCOPE, SCOPE,
                new Object[]{ regex });
        } finally {
            Context.exit();
        }
    }

    /**
     * Matches an input against a given regex, in the real sense
     * of matching, that is, the regex can match anywhere in the input. Java's
     * {@link java.util.regex} makes the unfortunate mistake to make people
     * believe that matching is done on the whole input... Which is not true.
     * 
     *
     * Also note that the regex MUST have been validated at this point
     * (using {@link #regexIsValid(String)}).
     *
     * @param regex the regex to use
     * @param input the input to match against (and again, see description)
     * @return true if the regex matches the input
     */
    public static boolean regMatch(final String regex, final String input)
    {
        final Context context = Context.enter();
        try {
            return (Boolean) REG_MATCH.call(context, SCOPE, SCOPE,
                new Object[]{ regex, input });
        } finally {
            Context.exit();
        }

    }
}