/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.tomcat.util.buf;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.BitSet;

/**
 * Efficient implementation of a UTF-8 encoder. This class is not thread safe - you need one encoder per thread. The
 * encoder will save and recycle the internal objects, avoiding garbage. You can add extra characters that you want
 * preserved, for example while encoding a URL you can add "/".
 */
public final class UEncoder {

    /**
     * Pre-defined sets of safe characters for URL encoding.
     */
    public enum SafeCharsSet {
        /**
         * Safe character set that includes the forward slash.
         */
        WITH_SLASH("/"),
        /**
         * Default safe character set.
         */
        DEFAULT("");

        private final BitSet safeChars;

        private BitSet getSafeChars() {
            return this.safeChars;
        }

        SafeCharsSet(String additionalSafeChars) {
            safeChars = initialSafeChars();
            for (char c : additionalSafeChars.toCharArray()) {
                safeChars.set(c);
            }
        }
    }

    // Not static - the set may differ ( it's better than adding
    // an extra check for "/", "+", etc
    private final BitSet safeChars;
    private C2BConverter c2b = null;
    private ByteChunk bb = null;
    private CharChunk cb = null;
    private CharChunk output = null;

    /**
     * Create a UEncoder with an unmodifiable safe character set.
     *
     * @param safeCharsSet safe characters for this encoder
     */
    public UEncoder(SafeCharsSet safeCharsSet) {
        this.safeChars = safeCharsSet.getSafeChars();
    }

    /**
     * URL Encode string, using a specified encoding.
     *
     * @param s     string to be encoded
     * @param start the beginning index, inclusive
     * @param end   the ending index, exclusive
     *
     * @return A new CharChunk contained the URL encoded string
     *
     * @throws IOException If an I/O error occurs
     */
    public CharChunk encodeURL(String s, int start, int end) throws IOException {
        if (c2b == null) {
            bb = new ByteChunk(8); // small enough.
            cb = new CharChunk(2); // small enough.
            output = new CharChunk(64); // small enough.
            c2b = new C2BConverter(StandardCharsets.UTF_8);
        } else {
            bb.recycle();
            cb.recycle();
            output.recycle();
        }

        for (int i = start; i < end; i++) {
            char c = s.charAt(i);
            if (safeChars.get(c)) {
                output.append(c);
            } else {
                cb.append(c);
                c2b.convert(cb, bb);

                // "surrogate" - UTF is _not_ 16 bit, but 21 !!!!
                // ( while UCS is 31 ). Amazing...
                if (c >= 0xD800 && c <= 0xDBFF) {
                    if ((i + 1) < end) {
                        char d = s.charAt(i + 1);
                        if (d >= 0xDC00 && d <= 0xDFFF) {
                            cb.append(d);
                            c2b.convert(cb, bb);
                            i++;
                        }
                    }
                }

                urlEncode(output, bb);
                cb.recycle();
                bb.recycle();
            }
        }

        return output;
    }

    private void urlEncode(CharChunk out, ByteChunk bb) throws IOException {
        byte[] bytes = bb.getBuffer();
        for (int j = bb.getStart(); j < bb.getEnd(); j++) {
            out.append('%');
            char ch = Character.forDigit((bytes[j] >> 4) & 0xF, 16);
            out.append(ch);
            ch = Character.forDigit(bytes[j] & 0xF, 16);
            out.append(ch);
        }
    }

    // -------------------- Internal implementation --------------------

    private static BitSet initialSafeChars() {
        BitSet initialSafeChars = new BitSet(128);
        int i;
        for (i = 'a'; i <= 'z'; i++) {
            initialSafeChars.set(i);
        }
        for (i = 'A'; i <= 'Z'; i++) {
            initialSafeChars.set(i);
        }
        for (i = '0'; i <= '9'; i++) {
            initialSafeChars.set(i);
        }
        // safe
        initialSafeChars.set('$');
        initialSafeChars.set('-');
        initialSafeChars.set('_');
        initialSafeChars.set('.');

        // Dangerous: someone may treat this as " "
        // RFC1738 does allow it, it's not reserved
        // initialSafeChars.set('+');
        // extra
        initialSafeChars.set('!');
        initialSafeChars.set('*');
        initialSafeChars.set('\'');
        initialSafeChars.set('(');
        initialSafeChars.set(')');
        initialSafeChars.set(',');
        return initialSafeChars;
    }
}
