/*
 * Copyright © 2012 Intel Corporation
 * Copyright © 2014 Ran Benita <ran234@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Author: Rob Bradford <rob@linux.intel.com>
 */

#include <stddef.h>
#include <stdbool.h>
#include <inttypes.h>

#include "utf8.h"

int
utf32_to_utf8(uint32_t unichar, char *buffer)
{
    int count, shift, length;
    uint8_t head;

    if (unichar <= 0x007f) {
        buffer[0] = unichar;
        buffer[1] = '\0';
        return 2;
    }
    else if (unichar <= 0x07FF) {
        length = 2;
        head = 0xc0;
    }
    else if (unichar <= 0xffff) {
        length = 3;
        head = 0xe0;
    }
    else if (unichar <= 0x1fffff) {
        length = 4;
        head = 0xf0;
    }
    else if (unichar <= 0x3ffffff) {
        length = 5;
        head = 0xf8;
    }
    else {
        length = 6;
        head = 0xfc;
    }

    for (count = length - 1, shift = 0; count > 0; count--, shift += 6)
        buffer[count] = 0x80 | ((unichar >> shift) & 0x3f);

    buffer[0] = head | ((unichar >> shift) & 0x3f);
    buffer[length] = '\0';

    return length + 1;
}

bool
is_valid_utf8(const char *ss, size_t len)
{
    size_t i = 0;
    size_t tail_bytes = 0;
    const uint8_t *s = (const uint8_t *) ss;

    /* This beauty is from:
     *  The Unicode Standard Version 6.2 - Core Specification, Table 3.7
     *  http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf#G7404
     * We can optimize if needed. */
    while (i < len)
    {
        if (s[i] <= 0x7F) {
            tail_bytes = 0;
        }
        else if (s[i] >= 0xC2 && s[i] <= 0xDF) {
            tail_bytes = 1;
        }
        else if (s[i] == 0xE0) {
            i++;
            if (i >= len || !(s[i] >= 0xA0 && s[i] <= 0xBF))
                return false;
            tail_bytes = 1;
        }
        else if (s[i] >= 0xE1 && s[i] <= 0xEC) {
            tail_bytes = 2;
        }
        else if (s[i] == 0xED) {
            i++;
            if (i >= len || !(s[i] >= 0x80 && s[i] <= 0x9F))
                return false;
            tail_bytes = 1;
        }
        else if (s[i] >= 0xEE && s[i] <= 0xEF) {
            tail_bytes = 2;
        }
        else if (s[i] == 0xF0) {
            i++;
            if (i >= len || !(s[i] >= 0x90 && s[i] <= 0xBF))
                return false;
            tail_bytes = 2;
        }
        else if (s[i] >= 0xF1 && s[i] <= 0xF3) {
            tail_bytes = 3;
        }
        else if (s[i] == 0xF4) {
            i++;
            if (i >= len || !(s[i] >= 0x80 && s[i] <= 0x8F))
                return false;
            tail_bytes = 2;
        }
        else {
            return false;
        }

        i++;

        while (i < len && tail_bytes > 0 && s[i] >= 0x80 && s[i] <= 0xBF) {
            i++;
            tail_bytes--;
        }

        if (tail_bytes != 0)
            return false;
    }

    return true;
}