/*
 * Copyright (C) 2022 The Android Open Source Project
 *
 * 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 com.android.modules.utils;

import java.io.UTFDataFormatException;

public class ModifiedUtf8 {
    /**
     * Decodes a byte array containing <i>modified UTF-8</i> bytes into a string.
     *
     * <p>Note that although this method decodes the (supposedly impossible) zero byte to U+0000,
     * that's what the RI does too.
     */
    public static String decode(byte[] in, char[] out, int offset, int utfSize)
            throws UTFDataFormatException {
        int count = 0, s = 0, a;
        while (count < utfSize) {
            if ((out[s] = (char) in[offset + count++]) < '\u0080') {
                s++;
            } else if (((a = out[s]) & 0xe0) == 0xc0) {
                if (count >= utfSize) {
                    throw new UTFDataFormatException("bad second byte at " + count);
                }
                int b = in[offset + count++];
                if ((b & 0xC0) != 0x80) {
                    throw new UTFDataFormatException("bad second byte at " + (count - 1));
                }
                out[s++] = (char) (((a & 0x1F) << 6) | (b & 0x3F));
            } else if ((a & 0xf0) == 0xe0) {
                if (count + 1 >= utfSize) {
                    throw new UTFDataFormatException("bad third byte at " + (count + 1));
                }
                int b = in[offset + count++];
                int c = in[offset + count++];
                if (((b & 0xC0) != 0x80) || ((c & 0xC0) != 0x80)) {
                    throw new UTFDataFormatException("bad second or third byte at " + (count - 2));
                }
                out[s++] = (char) (((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F));
            } else {
                throw new UTFDataFormatException("bad byte at " + (count - 1));
            }
        }
        return new String(out, 0, s);
    }

    /**
     * Returns the number of bytes the modified UTF-8 representation of 's' would take. Note
     * that this is just the space for the bytes representing the characters, not the length
     * which precedes those bytes, because different callers represent the length differently,
     * as two, four, or even eight bytes. If {@code shortLength} is true, we'll throw an
     * exception if the string is too long for its length to be represented by a short.
     */
    public static long countBytes(String s, boolean shortLength) throws UTFDataFormatException {
        long result = 0;
        final int length = s.length();
        for (int i = 0; i < length; ++i) {
            char ch = s.charAt(i);
            if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
                ++result;
            } else if (ch <= 2047) {
                result += 2;
            } else {
                result += 3;
            }
            if (shortLength && result > 65535) {
                throw new UTFDataFormatException("String more than 65535 UTF bytes long");
            }
        }
        return result;
    }

    /**
     * Encodes the <i>modified UTF-8</i> bytes corresponding to string {@code s} into the
     * byte array {@code dst}, starting at the given {@code offset}.
     */
    public static void encode(byte[] dst, int offset, String s) {
        final int length = s.length();
        for (int i = 0; i < length; i++) {
            char ch = s.charAt(i);
            if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
                dst[offset++] = (byte) ch;
            } else if (ch <= 2047) {
                dst[offset++] = (byte) (0xc0 | (0x1f & (ch >> 6)));
                dst[offset++] = (byte) (0x80 | (0x3f & ch));
            } else {
                dst[offset++] = (byte) (0xe0 | (0x0f & (ch >> 12)));
                dst[offset++] = (byte) (0x80 | (0x3f & (ch >> 6)));
                dst[offset++] = (byte) (0x80 | (0x3f & ch));
            }
        }
    }

    private ModifiedUtf8() {
    }
}