/*
 *  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.ByteArrayOutputStream;
import java.io.CharConversionException;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Serial;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

import org.apache.tomcat.util.res.StringManager;

/**
 * All URL decoding happens here. This way we can reuse, review, optimize without adding complexity to the buffers. The
 * conversion will modify the original buffer.
 *
 * @author Costin Manolache
 */
public final class UDecoder {

    private static final StringManager sm = StringManager.getManager(UDecoder.class);

    private static class DecodeException extends CharConversionException {
        @Serial
        private static final long serialVersionUID = 1L;

        DecodeException(String s) {
            super(s);
        }

        @Override
        public synchronized Throwable fillInStackTrace() {
            // This class does not provide a stack trace
            return this;
        }
    }

    /** Unexpected end of data. */
    private static final IOException EXCEPTION_EOF = new DecodeException(sm.getString("uDecoder.eof"));

    /** %xx with not-hex digit */
    private static final IOException EXCEPTION_NOT_HEX_DIGIT = new DecodeException(sm.getString("uDecoder.isHexDigit"));

    /** %-encoded slash is forbidden in resource path */
    private static final IOException EXCEPTION_SLASH = new DecodeException(sm.getString("uDecoder.noSlash"));

    /** %-encoded backslash is forbidden in resource path */
    private static final IOException EXCEPTION_BACKSLASH = new DecodeException(sm.getString("uDecoder.noBackslash"));

    /**
     * URLDecode, will modify the source. Assumes source bytes are encoded using a superset of US-ASCII as per RFC 7230.
     * "%5c" will be decoded. "%2f" will be rejected unless the input is a query string.
     *
     * @param mb    The URL encoded bytes
     * @param query {@code true} if this is a query string. For a query string '+' will be decoded to ' '
     *
     * @throws IOException Invalid %xx URL encoding
     */
    public void convert(ByteChunk mb, boolean query) throws IOException {
        if (query) {
            convert(mb, true, EncodedSolidusHandling.DECODE, EncodedSolidusHandling.DECODE);
        } else {
            convert(mb, false, EncodedSolidusHandling.REJECT, EncodedSolidusHandling.DECODE);
        }
    }


    /**
     * URLDecode, will modify the source. Assumes source bytes are encoded using a superset of US-ASCII as per RFC 7230.
     *
     * @param mb                     The URL encoded bytes
     * @param encodedSolidusHandling How should the %2f sequence handled by the decoder? For query strings this
     *                                   parameter will be ignored and the %2f sequence will be decoded
     *
     * @throws IOException Invalid %xx URL encoding
     *
     * @deprecated Unused. Will be removed in Tomcat 12. Use
     *                 {@link #convert(ByteChunk, EncodedSolidusHandling, EncodedSolidusHandling)}
     */
    @Deprecated
    public void convert(ByteChunk mb, EncodedSolidusHandling encodedSolidusHandling) throws IOException {
        convert(mb, false, encodedSolidusHandling, EncodedSolidusHandling.DECODE);
    }


    /**
     * URLDecode, will modify the source. Assumes source bytes are encoded using a superset of US-ASCII as per RFC 7230.
     *
     * @param mb                            The URL encoded bytes
     * @param encodedSolidusHandling        How should the %2f sequence handled by the decoder? For query strings this
     *                                          parameter will be ignored and the %2f sequence will be decoded
     * @param encodedReverseSolidusHandling How should the %5c sequence handled by the decoder? For query strings this
     *                                          parameter will be ignored and the %5c sequence will be decoded
     *
     * @throws IOException Invalid %xx URL encoding
     */
    public void convert(ByteChunk mb, EncodedSolidusHandling encodedSolidusHandling,
            EncodedSolidusHandling encodedReverseSolidusHandling) throws IOException {
        convert(mb, false, encodedSolidusHandling, encodedReverseSolidusHandling);
    }


    private void convert(ByteChunk mb, boolean query, EncodedSolidusHandling encodedSolidusHandling,
            EncodedSolidusHandling encodedReverseSolidusHandling) throws IOException {

        int start = mb.getStart();
        byte[] buff = mb.getBytes();
        int end = mb.getEnd();

        int idx = ByteChunk.findByte(buff, start, end, (byte) '%');
        int idx2 = -1;
        if (query) {
            idx2 = ByteChunk.findByte(buff, start, (idx >= 0 ? idx : end), (byte) '+');
        }
        if (idx < 0 && idx2 < 0) {
            return;
        }

        // idx will be the smallest positive index ( first % or + )
        if ((idx2 >= 0 && idx2 < idx) || idx < 0) {
            idx = idx2;
        }

        for (int j = idx; j < end; j++, idx++) {
            if (buff[j] == '+' && query) {
                buff[idx] = (byte) ' ';
            } else if (buff[j] != '%') {
                buff[idx] = buff[j];
            } else {
                // read next 2 digits
                if (j + 2 >= end) {
                    throw EXCEPTION_EOF;
                }
                byte b1 = buff[j + 1];
                byte b2 = buff[j + 2];
                if (!isHexDigit(b1) || !isHexDigit(b2)) {
                    throw EXCEPTION_NOT_HEX_DIGIT;
                }

                j += 2;
                int res = x2c(b1, b2);
                if (res == '/') {
                    switch (encodedSolidusHandling) {
                        case DECODE: {
                            buff[idx] = (byte) res;
                            break;
                        }
                        case REJECT: {
                            throw EXCEPTION_SLASH;
                        }
                        case PASS_THROUGH: {
                            buff[idx++] = buff[j - 2];
                            buff[idx++] = buff[j - 1];
                            buff[idx] = buff[j];
                        }
                    }
                } else if (res == '\\') {
                    switch (encodedReverseSolidusHandling) {
                        case DECODE: {
                            buff[idx] = (byte) res;
                            break;
                        }
                        case REJECT: {
                            throw EXCEPTION_BACKSLASH;
                        }
                        case PASS_THROUGH: {
                            buff[idx++] = buff[j - 2];
                            buff[idx++] = buff[j - 1];
                            buff[idx] = buff[j];
                        }
                    }
                } else if (res == '%') {
                    /*
                     * If encoded '/' or '\' is going to be left encoded then so must be encoded '%' else the subsequent
                     * %nn decoding will either fail or corrupt the output.
                     */
                    if (encodedSolidusHandling.equals(EncodedSolidusHandling.PASS_THROUGH) ||
                            encodedReverseSolidusHandling.equals(EncodedSolidusHandling.PASS_THROUGH)) {
                        buff[idx++] = buff[j - 2];
                        buff[idx++] = buff[j - 1];
                        buff[idx] = buff[j];
                    } else {
                        buff[idx] = (byte) res;
                    }
                } else {
                    buff[idx] = (byte) res;
                }
            }
        }

        mb.setEnd(idx);
    }

    // -------------------- Additional methods --------------------

    /**
     * Decode and return the specified URL-encoded String. It is assumed the string is not a query string.
     *
     * @param str     The url-encoded string
     * @param charset The character encoding to use; if null, UTF-8 is used.
     *
     * @return the decoded string
     *
     * @exception IllegalArgumentException if a '%' character is not followed by a valid 2-digit hexadecimal number
     */
    public static String URLDecode(String str, Charset charset) {
        return URLDecode(str, charset, EncodedSolidusHandling.DECODE, EncodedSolidusHandling.DECODE);
    }


    /**
     * Decode and return the specified URL-encoded String. It is assumed the string is not a query string.
     *
     * @param str                           The url-encoded string
     * @param charset                       The character encoding to use; if null, UTF-8 is used.
     * @param encodedSolidusHandling        The required handling of encoded solidus (%2f - /)
     * @param encodedReverseSolidusHandling The required handling of encoded reverse solidus (%5c - \)
     *
     * @return the decoded string
     *
     * @exception IllegalArgumentException if a '%' character is not followed by a valid 2-digit hexadecimal number
     */
    public static String URLDecode(String str, Charset charset, EncodedSolidusHandling encodedSolidusHandling,
            EncodedSolidusHandling encodedReverseSolidusHandling) {
        if (str == null) {
            return null;
        }

        if (str.indexOf('%') == -1) {
            // No %nn sequences, so return string unchanged
            return str;
        }

        if (charset == null) {
            charset = StandardCharsets.UTF_8;
        }

        /*
         * Decoding is required.
         *
         * Potential complications:
         *
         * - The source String may be partially decoded so it is not valid to assume that the source String is ASCII.
         *
         * - Have to process as characters since there is no guarantee that the byte sequence for '%' is going to be the
         * same in all character sets.
         *
         * - We don't know how many '%nn' sequences are required for a single character. It varies between character
         * sets and some use a variable length.
         */

        // This isn't perfect, but it is a reasonable guess for the size of the
        // array required
        ByteArrayOutputStream baos = new ByteArrayOutputStream(str.length() * 2);

        OutputStreamWriter osw = new OutputStreamWriter(baos, charset);

        char[] sourceChars = str.toCharArray();
        int len = sourceChars.length;
        int ix = 0;

        try {
            while (ix < len) {
                char c = sourceChars[ix++];
                if (c == '%') {
                    osw.flush();
                    if (ix + 2 > len) {
                        throw new IllegalArgumentException(sm.getString("uDecoder.urlDecode.missingDigit", str));
                    }
                    char c1 = sourceChars[ix++];
                    char c2 = sourceChars[ix++];
                    if (isHexDigit(c1) && isHexDigit(c2)) {
                        int decoded = x2c(c1, c2);
                        switch (decoded) {
                            case '/': {
                                switch (encodedSolidusHandling) {
                                    case DECODE: {
                                        osw.append('/');
                                        break;
                                    }
                                    case PASS_THROUGH: {
                                        osw.append(c);
                                        osw.append(c1);
                                        osw.append(c2);
                                        break;
                                    }
                                    case REJECT: {
                                        throw new IllegalArgumentException(
                                                sm.getString("uDecoder.urlDecode.rejectEncodedSolidus", str));
                                    }
                                }
                                break;
                            }
                            case '\\': {
                                switch (encodedReverseSolidusHandling) {
                                    case DECODE: {
                                        osw.append('\\');
                                        break;
                                    }
                                    case PASS_THROUGH: {
                                        osw.append(c);
                                        osw.append(c1);
                                        osw.append(c2);
                                        break;
                                    }
                                    case REJECT: {
                                        throw new IllegalArgumentException(
                                                sm.getString("uDecoder.urlDecode.rejectEncodedReverseSolidus", str));
                                    }
                                }
                                break;
                            }
                            case '%': {
                                if (encodedReverseSolidusHandling == EncodedSolidusHandling.PASS_THROUGH ||
                                        encodedSolidusHandling == EncodedSolidusHandling.PASS_THROUGH) {
                                    osw.append(c);
                                    osw.append(c1);
                                    osw.append(c2);
                                } else {
                                    baos.write('%');
                                }
                                break;
                            }
                            default:
                                baos.write(decoded);
                        }
                    } else {
                        throw new IllegalArgumentException(sm.getString("uDecoder.urlDecode.missingDigit", str));
                    }
                } else {
                    osw.append(c);
                }
            }
            osw.flush();

            return baos.toString(charset);
        } catch (IOException ioe) {
            throw new IllegalArgumentException(sm.getString("uDecoder.urlDecode.conversionError", str, charset.name()),
                    ioe);
        }
    }


    private static boolean isHexDigit(int c) {
        return ((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F'));
    }


    private static int x2c(byte b1, byte b2) {
        int digit = (b1 >= 'A') ? ((b1 & 0xDF) - 'A') + 10 : (b1 - '0');
        digit *= 16;
        digit += (b2 >= 'A') ? ((b2 & 0xDF) - 'A') + 10 : (b2 - '0');
        return digit;
    }


    private static int x2c(char b1, char b2) {
        int digit = (b1 >= 'A') ? ((b1 & 0xDF) - 'A') + 10 : (b1 - '0');
        digit *= 16;
        digit += (b2 >= 'A') ? ((b2 & 0xDF) - 'A') + 10 : (b2 - '0');
        return digit;
    }
}