/*
 * 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
 *
 *      https://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.commons.codec.net;

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.BitSet;

import org.apache.commons.codec.BinaryDecoder;
import org.apache.commons.codec.BinaryEncoder;
import org.apache.commons.codec.CharEncoding;
import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.EncoderException;
import org.apache.commons.codec.StringDecoder;
import org.apache.commons.codec.StringEncoder;
import org.apache.commons.codec.binary.StringUtils;

/**
 * Implements the 'www-form-urlencoded' encoding scheme, also misleadingly known as URL encoding.
 * <p>
 * This codec is meant to be a replacement for standard Java classes {@link URLEncoder} and
 * {@link URLDecoder} on older Java platforms, as these classes in Java versions below
 * 1.4 rely on the platform's default charset encoding.
 * </p>
 * <p>
 * This class is thread-safe as of 1.11
 * </p>
 *
 * @see <a href="https://www.w3.org/TR/html4/interact/forms.html#h-17.13.4.1">Chapter 17.13.4 Form content types</a>
 *           of the <a href="https://www.w3.org/TR/html4/">HTML 4.01 Specification</a>
 *
 * @since 1.2
 */
public class URLCodec implements BinaryEncoder, BinaryDecoder, StringEncoder, StringDecoder {

    /**
     * Release 1.5 made this field final.
     */
    protected static final byte ESCAPE_CHAR = '%';

    private static final byte PLUS_CHAR = '+';

    /**
     * BitSet of www-form-url safe characters.
     * This is a copy of the internal BitSet which is now used for the conversion.
     * Changes to this field are ignored.
     *
     * @deprecated 1.11 Will be removed in 2.0 (CODEC-230)
     */
    @Deprecated
    protected static final BitSet WWW_FORM_URL;

    private static final BitSet WWW_FORM_URL_SAFE = new BitSet(256);

    // Static initializer for www_form_url
    static {
        // alpha characters
        for (int i = 'a'; i <= 'z'; i++) {
            WWW_FORM_URL_SAFE.set(i);
        }
        for (int i = 'A'; i <= 'Z'; i++) {
            WWW_FORM_URL_SAFE.set(i);
        }
        // numeric characters
        for (int i = '0'; i <= '9'; i++) {
            WWW_FORM_URL_SAFE.set(i);
        }
        // special chars
        WWW_FORM_URL_SAFE.set('-');
        WWW_FORM_URL_SAFE.set('_');
        WWW_FORM_URL_SAFE.set('.');
        WWW_FORM_URL_SAFE.set('*');
        // blank to be replaced with +
        WWW_FORM_URL_SAFE.set(' ');

        // Create a copy in case anyone (ab)uses it
        WWW_FORM_URL = (BitSet) WWW_FORM_URL_SAFE.clone();
    }

    /**
     * Decodes an array of bytes using the safe set supplied to {@link #encodeUrl(BitSet, byte[])}.
     * <p>
     * A percent sign marked safe is copied literally; otherwise it starts a two-digit hexadecimal escape. A plus sign marked safe is copied literally.
     * Otherwise, a plus sign becomes a space only if space is marked safe. All other bytes are copied unchanged. A {@code null} bitset selects the default
     * {@code www-form-urlencoded} safe set, giving the same behavior as {@link #decodeUrl(byte[])}.
     * </p>
     * <p>
     * Not every safe set permits a round trip. If both space and plus are marked safe, the encoder maps both to plus and this method preserves that plus. If
     * percent is marked safe, literal percent signs cannot be distinguished from generated escapes, so this method preserves all percent signs, including
     * generated escapes. Use a safe set that excludes percent and does not mark both space and plus safe when a round trip is required.
     * </p>
     *
     * @param urlsafe bitset of characters deemed URL safe during encoding, or {@code null} to use the default safe set.
     * @param bytes   array of encoded bytes, or {@code null}.
     * @return array of decoded bytes, or {@code null} if the input is {@code null}.
     * @throws DecoderException if percent is not marked safe and an escape is incomplete or contains invalid hexadecimal digits.
     * @since 1.23.0
     */
    public static final byte[] decodeUrl(BitSet urlsafe, final byte[] bytes) throws DecoderException {
        if (bytes == null) {
            return null;
        }
        if (urlsafe == null) {
            urlsafe = WWW_FORM_URL_SAFE;
        }
        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        for (int i = 0; i < bytes.length; i++) {
            final int b = bytes[i];
            if (b == PLUS_CHAR && !urlsafe.get(PLUS_CHAR) && urlsafe.get(' ')) {
                buffer.write(' ');
            } else if (b == ESCAPE_CHAR && !urlsafe.get(ESCAPE_CHAR)) {
                try {
                    final int u = Utils.digit16(bytes[++i]);
                    final int l = Utils.digit16(bytes[++i]);
                    buffer.write((char) ((u << 4) + l));
                } catch (final ArrayIndexOutOfBoundsException e) {
                    throw new DecoderException("Invalid URL encoding: ", e);
                }
            } else {
                buffer.write(b);
            }
        }
        return buffer.toByteArray();
    }

    /**
     * Decodes an array of URL safe 7-bit characters into an array of original bytes. Escaped characters are converted
     * back to their original representation.
     *
     * <p>
     * Decoding always follows {@code www-form-urlencoded} rules: {@code +} becomes a space and {@code %} starts a hexadecimal escape.
     * Output from {@link #encodeUrl(BitSet, byte[])} with a custom safe set may therefore not decode back to the original input and may cause a
     * {@link DecoderException}, depending on which characters were marked safe.
     * </p>
     *
     * @param bytes
     *            array of URL safe characters.
     * @return array of original bytes.
     * @throws DecoderException
     *             Thrown if URL decoding is unsuccessful.
     */
    public static final byte[] decodeUrl(final byte[] bytes) throws DecoderException {
        return decodeUrl(null, bytes);
    }

    /**
     * Encodes an array of bytes using the given set of URL safe characters.
     * <p>
     * Unsafe characters are percent-escaped. Characters marked safe are copied unchanged, except that a space marked safe is converted to {@code +}. A
     * {@code null} bitset selects the default {@code www-form-urlencoded} safe set, which escapes both {@code %} and {@code +}.
     * </p>
     * <p>
     * A custom bitset can produce output that {@link #decodeUrl(byte[])} and the {@code decode} methods cannot decode back to the original input. These
     * decoders always convert {@code +} to a space and interpret {@code %} as the start of a hexadecimal escape, regardless of the bitset used for encoding. If
     * the custom bitset marks either character safe, decoding can change the original data or throw {@link DecoderException}. Callers using a custom bitset
     * can use {@link #decodeUrl(BitSet, byte[])} with the same bitset, subject to its documented limitations for ambiguous safe sets.
     * </p>
     *
     * @param urlsafe bitset of characters deemed URL safe, or {@code null} to use the default {@code www-form-urlencoded} safe set.
     * @param bytes   array of bytes to convert to URL safe characters.
     * @return array of bytes containing URL safe characters.
     */
    public static final byte[] encodeUrl(BitSet urlsafe, final byte[] bytes) {
        if (bytes == null) {
            return null;
        }
        if (urlsafe == null) {
            urlsafe = WWW_FORM_URL_SAFE;
        }

        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        for (final byte c : bytes) {
            int b = c;
            if (b < 0) {
                b = 256 + b;
            }
            if (urlsafe.get(b)) {
                if (b == ' ') {
                    b = PLUS_CHAR;
                }
                buffer.write(b);
            } else {
                buffer.write(ESCAPE_CHAR);
                final char hex1 = Utils.hexChar(b >> 4);
                final char hex2 = Utils.hexChar(b);
                buffer.write(hex1);
                buffer.write(hex2);
            }
        }
        return buffer.toByteArray();
    }

    /**
     * The default charset used for string decoding and encoding.
     *
     * @deprecated TODO: This field will be changed to a private final Charset in 2.0. (CODEC-126)
     */
    @Deprecated
    protected volatile String charset; // added volatile: see CODEC-232

    /**
     * Default constructor.
     */
    public URLCodec() {
        this(CharEncoding.UTF_8);
    }

    /**
     * Constructs a new instance for the selection of a default charset.
     *
     * @param charset The default string charset to use.
     */
    public URLCodec(final String charset) {
        this.charset = charset;
    }

    /**
     * Decodes an array of URL safe 7-bit characters into an array of original bytes. Escaped characters are converted
     * back to their original representation.
     *
     * <p>
     * Decoding always follows {@code www-form-urlencoded} rules: {@code +} becomes a space and {@code %} starts a hexadecimal escape.
     * Output from {@link #encodeUrl(BitSet, byte[])} with a custom safe set may therefore not decode back to the original input and may cause a
     * {@link DecoderException}, depending on which characters were marked safe.
     * </p>
     *
     * @param bytes
     *            array of URL safe characters.
     * @return array of original bytes.
     * @throws DecoderException
     *             Thrown if URL decoding is unsuccessful.
     */
    @Override
    public byte[] decode(final byte[] bytes) throws DecoderException {
        return decodeUrl(bytes);
    }

    /**
     * Decodes a URL safe object into its original form. Escaped characters are converted back to their original
     * representation.
     *
     * <p>
     * Decoding always follows {@code www-form-urlencoded} rules: {@code +} becomes a space and {@code %} starts a hexadecimal escape.
     * Output from {@link #encodeUrl(BitSet, byte[])} with a custom safe set may therefore not decode back to the original input and may cause a
     * {@link DecoderException}, depending on which characters were marked safe.
     * </p>
     *
     * @param obj
     *            URL safe object to convert into its original form.
     * @return original object.
     * @throws DecoderException
     *             Thrown if the argument is not a {@code String} or {@code byte[]}. Thrown if a failure
     *             condition is encountered during the decode process.
     */
    @Override
    public Object decode(final Object obj) throws DecoderException {
        if (obj == null) {
            return null;
        }
        if (obj instanceof byte[]) {
            return decode((byte[]) obj);
        }
        if (obj instanceof String) {
            return decode((String) obj);
        }
        throw new DecoderException("Objects of type " + obj.getClass().getName() + " cannot be URL decoded");
    }

    /**
     * Decodes a URL safe string into its original form using the default string charset. Escaped characters are
     * converted back to their original representation.
     *
     * <p>
     * Decoding always follows {@code www-form-urlencoded} rules: {@code +} becomes a space and {@code %} starts a hexadecimal escape.
     * Output from {@link #encodeUrl(BitSet, byte[])} with a custom safe set may therefore not decode back to the original input and may cause a
     * {@link DecoderException}, depending on which characters were marked safe.
     * </p>
     *
     * @param str
     *            URL safe string to convert into its original form.
     * @return original string.
     * @throws DecoderException
     *             Thrown if URL decoding is unsuccessful.
     * @see #getDefaultCharset()
     */
    @Override
    public String decode(final String str) throws DecoderException {
        if (str == null) {
            return null;
        }
        try {
            return decode(str, getDefaultCharset());
        } catch (final UnsupportedEncodingException e) {
            throw new DecoderException(e.getMessage(), e);
        }
    }

    /**
     * Decodes a URL safe string into its original form using the specified encoding. Escaped characters are converted
     * back to their original representation.
     *
     * <p>
     * Decoding always follows {@code www-form-urlencoded} rules: {@code +} becomes a space and {@code %} starts a hexadecimal escape.
     * Output from {@link #encodeUrl(BitSet, byte[])} with a custom safe set may therefore not decode back to the original input and may cause a
     * {@link DecoderException}, depending on which characters were marked safe.
     * </p>
     *
     * @param str
     *            URL safe string to convert into its original form.
     * @param charsetName
     *            the original string charset.
     * @return original string.
     * @throws DecoderException
     *             Thrown if URL decoding is unsuccessful.
     * @throws UnsupportedEncodingException
     *             Thrown if charset is not supported.
     */
    public String decode(final String str, final String charsetName)
            throws DecoderException, UnsupportedEncodingException {
        if (str == null) {
            return null;
        }
        return new String(decode(StringUtils.getBytesUsAscii(str)), charsetName);
    }

    /**
     * Encodes an array of bytes into an array of URL safe 7-bit characters. Unsafe characters are escaped.
     *
     * @param bytes
     *            array of bytes to convert to URL safe characters.
     * @return array of bytes containing URL safe characters.
     */
    @Override
    public byte[] encode(final byte[] bytes) {
        return encodeUrl(WWW_FORM_URL_SAFE, bytes);
    }

    /**
     * Encodes an object into its URL safe form. Unsafe characters are escaped.
     *
     * @param obj
     *            string to convert to a URL safe form.
     * @return URL safe object.
     * @throws EncoderException
     *             Thrown if URL encoding is not applicable to objects of this type or if encoding is unsuccessful.
     */
    @Override
    public Object encode(final Object obj) throws EncoderException {
        if (obj == null) {
            return null;
        }
        if (obj instanceof byte[]) {
            return encode((byte[]) obj);
        }
        if (obj instanceof String) {
            return encode((String) obj);
        }
        throw new EncoderException("Objects of type " + obj.getClass().getName() + " cannot be URL encoded");
    }

    /**
     * Encodes a string into its URL safe form using the default string charset. Unsafe characters are escaped.
     *
     * @param str
     *            string to convert to a URL safe form.
     * @return URL safe string.
     * @throws EncoderException
     *             Thrown if URL encoding is unsuccessful.
     * @see #getDefaultCharset()
     */
    @Override
    public String encode(final String str) throws EncoderException {
        if (str == null) {
            return null;
        }
        try {
            return encode(str, getDefaultCharset());
        } catch (final UnsupportedEncodingException e) {
            throw new EncoderException(e.getMessage(), e);
        }
    }

    /**
     * Encodes a string into its URL safe form using the specified string charset. Unsafe characters are escaped.
     *
     * @param str
     *            string to convert to a URL safe form.
     * @param charsetName
     *            the charset for str.
     * @return URL safe string.
     * @throws UnsupportedEncodingException
     *             Thrown if charset is not supported.
     */
    public String encode(final String str, final String charsetName) throws UnsupportedEncodingException {
        if (str == null) {
            return null;
        }
        return StringUtils.newStringUsAscii(encode(str.getBytes(charsetName)));
    }

    /**
     * Gets the default charset used for string decoding and encoding.
     *
     * @return The default string charset.
     */
    public String getDefaultCharset() {
        return this.charset;
    }

    /**
     * Gets the {@code String} encoding used for decoding and encoding.
     *
     * @return The encoding.
     * @deprecated Use {@link #getDefaultCharset()}, will be removed in 2.0.
     */
    @Deprecated
    public String getEncoding() {
        return this.charset;
    }

}