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/*
 * Copyright 2008-present MongoDB, Inc.
 *
 * 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 org.bson;

import java.util.regex.Pattern;

/**
 * Contains byte representations of all the BSON types (see the BSON Specification). Also
 * supports the registration of encoding and decoding hooks to transform BSON types during encoding or decoding.
 *
 * @see org.bson.Transformer
 */
class BSON {


    static final byte B_GENERAL = 0;
    static final byte B_BINARY = 2;

    // --- regex flags

    private static final int FLAG_GLOBAL = 256;

    private static final int[] FLAG_LOOKUP = new int[Character.MAX_VALUE];

    static {
        FLAG_LOOKUP['g'] = FLAG_GLOBAL;
        FLAG_LOOKUP['i'] = Pattern.CASE_INSENSITIVE;
        FLAG_LOOKUP['m'] = Pattern.MULTILINE;
        FLAG_LOOKUP['s'] = Pattern.DOTALL;
        FLAG_LOOKUP['c'] = Pattern.CANON_EQ;
        FLAG_LOOKUP['x'] = Pattern.COMMENTS;
        FLAG_LOOKUP['d'] = Pattern.UNIX_LINES;
        FLAG_LOOKUP['t'] = Pattern.LITERAL;
        FLAG_LOOKUP['u'] = Pattern.UNICODE_CASE;
    }

    /**
     * Converts a sequence of regular expression modifiers from the database into Java regular expression flags.
     *
     * @param s regular expression modifiers
     * @return the Java flags
     * @throws IllegalArgumentException If sequence contains invalid flags.
     */
    static int regexFlags(final String s) {
        int flags = 0;

        if (s == null) {
            return flags;
        }

        for (final char f : s.toLowerCase().toCharArray()) {
            flags |= regexFlag(f);
        }

        return flags;
    }

    /**
     * Converts a regular expression modifier from the database into Java regular expression flags.
     *
     * @param c regular expression modifier
     * @return the Java flags
     * @throws IllegalArgumentException If sequence contains invalid flags.
     */
    private static int regexFlag(final char c) {

        int flag = FLAG_LOOKUP[c];

        if (flag == 0) {
            throw new IllegalArgumentException(String.format("Unrecognized flag [%c]", c));
        }

        return flag;
    }

    /**
     * Converts Java regular expression flags into regular expression modifiers from the database.
     *
     * @param flags the Java flags
     * @return the Java flags
     * @throws IllegalArgumentException if some flags couldn't be recognized.
     */
    static String regexFlags(final int flags) {
        int processedFlags = flags;
        StringBuilder buf = new StringBuilder();

        for (int i = 0; i < FLAG_LOOKUP.length; i++) {
            if ((processedFlags & FLAG_LOOKUP[i]) > 0) {
                buf.append((char) i);
                processedFlags -= FLAG_LOOKUP[i];
            }
        }

        if (processedFlags > 0) {
            throw new IllegalArgumentException("Some flags could not be recognized.");
        }

        return buf.toString();
    }
}