/*
 * 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.
 */

#include "config.h"

#include "unicode.h"

#include <stddef.h>

size_t guac_utf8_charsize(unsigned char c) {

    /* Determine size in bytes of character */
    if ((c | 0x7F) == 0x7F) return 1;
    if ((c | 0x1F) == 0xDF) return 2;
    if ((c | 0x0F) == 0xEF) return 3;
    if ((c | 0x07) == 0xF7) return 4;

    /* Default to one character */
    return 1;

}

size_t guac_utf8_strlen(const char* str) {

    /* The current length of the string */
    int length = 0;

    /* Number of characters before start of next character */
    int skip = 0;

    while (*str != 0) {

        /* If skipping, then skip */
        if (skip > 0) skip--;

        /* Otherwise, determine next skip value, and increment length */
        else {

            /* Get next character */
            unsigned char c = (unsigned char) *str;

            /* Determine skip value (size in bytes of rest of character) */
            skip = guac_utf8_charsize(c) - 1;

            length++;
        }

        str++;
    }

    return length;

}

int guac_utf8_write(int codepoint, char* utf8, int length) {

    int i;
    int mask, bytes;

    /* If not even one byte, cannot write */
    if (length <= 0)
        return 0;

    /* Determine size and initial byte mask */
    if (codepoint <= 0x007F) {
        mask  = 0x00;
        bytes = 1;
    }
    else if (codepoint <= 0x7FF) {
        mask  = 0xC0;
        bytes = 2;
    }
    else if (codepoint <= 0xFFFF) {
        mask  = 0xE0;
        bytes = 3;
    }
    else if (codepoint <= 0x1FFFFF) {
        mask  = 0xF0;
        bytes = 4;
    }

    /* Otherwise, invalid codepoint */
    else {
        *(utf8++) = '?';
        return 1;
    }

    /* If not enough room, don't write anything */
    if (bytes > length)
        return 0;

    /* Offset buffer by size */
    utf8 += bytes - 1;

    /* Add trailing bytes, if any */
    for (i=1; i<bytes; i++) {
        *(utf8--) = 0x80 | (codepoint & 0x3F);
        codepoint >>= 6;
    }

    /* Set initial byte */
    *utf8 = mask | codepoint;

    /* Done */
    return bytes;

}

int guac_utf8_read(const char* utf8, int length, int* codepoint) {

    unsigned char initial;
    int bytes;
    int result;
    int i;

    /* If not even one byte, cannot read */
    if (length <= 0)
        return 0;

    /* Read initial byte */
    initial = (unsigned char) *(utf8++);

    /* 0xxxxxxx */
    if ((initial | 0x7F) == 0x7F) {
        result = initial;
        bytes  = 1;
    }

    /* 110xxxxx 10xxxxxx */
    else if ((initial | 0x1F) == 0xDF) {
        result = initial & 0x1F;
        bytes  = 2;
    }

    /* 1110xxxx 10xxxxxx 10xxxxxx */
    else if ((initial | 0x0F) == 0xEF) {
        result = initial & 0x0F;
        bytes  = 3;
    }

    /* 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx */
    else if ((initial | 0x07) == 0xF7) {
        result = initial & 0x07;
        bytes  = 4;
    }

    /* Otherwise, invalid codepoint */
    else {
        *codepoint = 0xFFFD; /* Replacement character */
        return 1;
    }

    /* If not enough room, don't read anything */
    if (bytes > length)
        return 0;

    /* Read trailing bytes, if any */
    for (i=1; i<bytes; i++) {
        result <<= 6;
        result |= *(utf8++) & 0x3F;
    }

    *codepoint = result;
    return bytes;

}