/*
 *  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 libcore.net;

import java.io.ByteArrayOutputStream;
import java.net.URISyntaxException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

/**
 * Encodes and decodes {@code application/x-www-form-urlencoded} content.
 * Subclasses define exactly which characters are legal.
 *
 * <p>By default, UTF-8 is used to encode escaped characters. A single input
 * character like "\u0080" may be encoded to multiple octets like %C2%80.
 */
public abstract class UriCodec {

    /**
     * Returns true if {@code c} does not need to be escaped.
     */
    protected abstract boolean isRetained(char c);

    /**
     * Throws if {@code s} is invalid according to this encoder.
     */
    public final String validate(String uri, int start, int end, String name)
            throws URISyntaxException {
        for (int i = start; i < end; ) {
            char ch = uri.charAt(i);
            if ((ch >= 'a' && ch <= 'z')
                    || (ch >= 'A' && ch <= 'Z')
                    || (ch >= '0' && ch <= '9')
                    || isRetained(ch)) {
                i++;
            } else if (ch == '%') {
                if (i + 2 >= end) {
                    throw new URISyntaxException(uri, "Incomplete % sequence in " + name, i);
                }
                int d1 = hexToInt(uri.charAt(i + 1));
                int d2 = hexToInt(uri.charAt(i + 2));
                if (d1 == -1 || d2 == -1) {
                    throw new URISyntaxException(uri, "Invalid % sequence: "
                            + uri.substring(i, i + 3) + " in " + name, i);
                }
                i += 3;
            } else {
                throw new URISyntaxException(uri, "Illegal character in " + name, i);
            }
        }
        return uri.substring(start, end);
    }

    /**
     * Throws if {@code s} contains characters that are not letters, digits or
     * in {@code legal}.
     */
    public static void validateSimple(String s, String legal)
            throws URISyntaxException {
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (!((ch >= 'a' && ch <= 'z')
                    || (ch >= 'A' && ch <= 'Z')
                    || (ch >= '0' && ch <= '9')
                    || legal.indexOf(ch) > -1)) {
                throw new URISyntaxException(s, "Illegal character", i);
            }
        }
    }

    /**
     * Encodes {@code s} and appends the result to {@code builder}.
     *
     * @param isPartiallyEncoded true to fix input that has already been
     *     partially or fully encoded. For example, input of "hello%20world" is
     *     unchanged with isPartiallyEncoded=true but would be double-escaped to
     *     "hello%2520world" otherwise.
     */
    private void appendEncoded(StringBuilder builder, String s, Charset charset,
            boolean isPartiallyEncoded) {
        if (s == null) {
            throw new NullPointerException("s == null");
        }

        int escapeStart = -1;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if ((c >= 'a' && c <= 'z')
                    || (c >= 'A' && c <= 'Z')
                    || (c >= '0' && c <= '9')
                    || isRetained(c)
                    || (c == '%' && isPartiallyEncoded)) {
                if (escapeStart != -1) {
                    appendHex(builder, s.substring(escapeStart, i), charset);
                    escapeStart = -1;
                }
                if (c == '%' && isPartiallyEncoded) {
                    // this is an encoded 3-character sequence like "%20"
                    builder.append(s, i, Math.min(i + 3, s.length()));
                    i += 2;
                } else if (c == ' ') {
                    builder.append('+');
                } else {
                    builder.append(c);
                }
            } else if (escapeStart == -1) {
                escapeStart = i;
            }
        }
        if (escapeStart != -1) {
            appendHex(builder, s.substring(escapeStart, s.length()), charset);
        }
    }

    public final String encode(String s, Charset charset) {
        // Guess a bit larger for encoded form
        StringBuilder builder = new StringBuilder(s.length() + 16);
        appendEncoded(builder, s, charset, false);
        return builder.toString();
    }

    public final void appendEncoded(StringBuilder builder, String s) {
        appendEncoded(builder, s, StandardCharsets.UTF_8, false);
    }

    public final void appendPartiallyEncoded(StringBuilder builder, String s) {
        appendEncoded(builder, s, StandardCharsets.UTF_8, true);
    }

    /**
     * @param convertPlus true to convert '+' to ' '.
     * @param throwOnFailure true to throw an IllegalArgumentException on
     *     invalid escape sequences; false to replace them with the replacement
     *     character (U+fffd).
     */
    public static String decode(String s, boolean convertPlus, Charset charset,
            boolean throwOnFailure) {
        if (s.indexOf('%') == -1 && (!convertPlus || s.indexOf('+') == -1)) {
            return s;
        }

        StringBuilder result = new StringBuilder(s.length());
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        for (int i = 0; i < s.length();) {
            char c = s.charAt(i);
            if (c == '%') {
                do {
                    int d1, d2;
                    if (i + 2 < s.length()
                            && (d1 = hexToInt(s.charAt(i + 1))) != -1
                            && (d2 = hexToInt(s.charAt(i + 2))) != -1) {
                        out.write((byte) ((d1 << 4) + d2));
                    } else if (throwOnFailure) {
                        throw new IllegalArgumentException("Invalid % sequence at " + i + ": " + s);
                    } else {
                        byte[] replacement = "\ufffd".getBytes(charset);
                        out.write(replacement, 0, replacement.length);
                    }
                    i += 3;
                } while (i < s.length() && s.charAt(i) == '%');
                result.append(new String(out.toByteArray(), charset));
                out.reset();
            } else {
                if (convertPlus && c == '+') {
                    c = ' ';
                }
                result.append(c);
                i++;
            }
        }
        return result.toString();
    }

    /**
     * Like {@link Character#digit}, but without support for non-ASCII
     * characters.
     */
    private static int hexToInt(char c) {
        if ('0' <= c && c <= '9') {
            return c - '0';
        } else if ('a' <= c && c <= 'f') {
            return 10 + (c - 'a');
        } else if ('A' <= c && c <= 'F') {
            return 10 + (c - 'A');
        } else {
            return -1;
        }
    }

    public static String decode(String s) {
        return decode(s, false, StandardCharsets.UTF_8, true);
    }

    private static void appendHex(StringBuilder builder, String s, Charset charset) {
        for (byte b : s.getBytes(charset)) {
            appendHex(builder, b);
        }
    }

    private static void appendHex(StringBuilder sb, byte b) {
        sb.append('%');
        sb.append(Byte.toHexString(b, true));
    }
}
