/*
 * utf8.c
 * Copyright © 2016 David A. Baer
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the organization nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY David A. Baer ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL David A. Baer BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 */

#include <stdlib.h>
#include <string.h>
#include "utf8.h"

utf8iterator*
utf8NewIterator(const char* txt) {
    utf8iterator* result = malloc(sizeof(utf8iterator));
    memset(result, 0, sizeof(utf8iterator));
    result->txt = txt;
    return result;
}

uint32_t utf8CharAt(const utf8iterator* iter) {
    int byteIndex = iter->byteIndex;
    if ((iter->txt[byteIndex] & 0x80) == 0) {
        return iter->txt[byteIndex];
    } else if (((iter->txt[byteIndex] & 0xe0) == 0xc0) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80)) {
        return (uint32_t)(iter->txt[byteIndex + 1] & 0x3f) |
               ((uint32_t)(iter->txt[byteIndex] & 0x1f) << 6);
    } else if (((iter->txt[byteIndex] & 0xf0) == 0xe0) && 
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) && 
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80)) {
        return (uint32_t)(iter->txt[byteIndex + 2] & 0x3f) |
               ((uint32_t)(iter->txt[byteIndex + 1] & 0x3f) << 6) |
               ((uint32_t)(iter->txt[byteIndex] & 0xf) << 12);
    } else if (((iter->txt[byteIndex] & 0xf8) == 0xf0) && 
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) && 
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80)) {
        return (uint32_t)(iter->txt[byteIndex + 3] & 0x3f) |
               ((uint32_t)(iter->txt[byteIndex + 2] & 0x3f) << 6) |
               ((uint32_t)(iter->txt[byteIndex + 1] & 0x3f) << 12) |
               ((uint32_t)(iter->txt[byteIndex] & 0x07) << 18);
    } else if (((iter->txt[byteIndex] & 0xfc) == 0xf8) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 4] & 0xc0) == 0x80)) {
        return (uint32_t)(iter->txt[byteIndex + 4] & 0x3f) |
               ((uint32_t)(iter->txt[byteIndex + 3] & 0x3f) << 6) |
               ((uint32_t)(iter->txt[byteIndex + 2] & 0x3f) << 12) |
               ((uint32_t)(iter->txt[byteIndex + 1] & 0x3f) << 18) |
               ((uint32_t)(iter->txt[byteIndex] & 0x03) << 24);

    } else if (((iter->txt[byteIndex] & 0xf7) == 0xfc) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 4] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 5] & 0xc0) == 0x80)) {
        return (uint32_t)(iter->txt[byteIndex + 5] & 0x3f) |
               ((uint32_t)(iter->txt[byteIndex + 4] & 0x3f) << 6) |
               ((uint32_t)(iter->txt[byteIndex + 3] & 0x3f) << 12) |
               ((uint32_t)(iter->txt[byteIndex + 2] & 0x3f) << 18) |
               ((uint32_t)(iter->txt[byteIndex + 1] & 0x3f) << 24) |
               ((uint32_t)(iter->txt[byteIndex] & 0x01) << 30);
    }
    return 0;
}

static int
_next_offset(const utf8iterator* iter) {
    int byteIndex = iter->byteIndex;
    if ((iter->txt[byteIndex] & 0x80) == 0) {
        return 1;
    } else if (((iter->txt[byteIndex] & 0xe0) == 0xc0) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80)) {
        return 2;
    } else if (((iter->txt[byteIndex] & 0xf0) == 0xe0) && 
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) && 
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80)) {
        return 3;
    } else if (((iter->txt[byteIndex] & 0xf8) == 0xf0) && 
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) && 
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80)) {
        return 4;
    } else if (((iter->txt[byteIndex] & 0xfc) == 0xf8) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 4] & 0xc0) == 0x80)) {
        return 5;
    } else if (((iter->txt[byteIndex] & 0xf7) == 0xfc) &&
               ((iter->txt[byteIndex + 1] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 2] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 3] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 4] & 0xc0) == 0x80) &&
               ((iter->txt[byteIndex + 5] & 0xc0) == 0x80)) {
        return 6;
    } else return -1;
}

int
utf8Advance(utf8iterator* iter) {
    int next_offset = _next_offset(iter);
    if (next_offset > 0) {
        iter->byteIndex += next_offset;
        return ++iter->logicalIndex;
    } else return -1;
}

int
utf8CopyEncodedCharAt(const utf8iterator* iter, size_t bufsize, char* dest) {
    size_t sz = _next_offset(iter);
    if (sz + 1 > bufsize) {
        return 0;
    } else {
        memset(dest, 0, bufsize);
        memcpy(dest, iter->txt + iter->byteIndex, sz);
        return 1;
    }
}

void
utf8ResetIterator(utf8iterator* iter) {
    iter->logicalIndex = iter->byteIndex = 0;
}

void
utf8FreeIterator(utf8iterator* iter) {
    free(iter);
}