#include "../../include/mgl/system/utf8.h"

static inline bool utf8_get_codepoint_length(unsigned char b, size_t *codepoint_length) {
    if((b & 0x80) == 0) {
        *codepoint_length = 1;
        return true;
    } else if((b & 0xE0) == 0xC0) {
        *codepoint_length = 2;
        return true;
    } else if((b & 0xF0) == 0xE0) {
        *codepoint_length = 3;
        return true;
    } else if((b & 0xF8) == 0xF0) {
        *codepoint_length = 4;
        return true;
    } else {
        return false;
    }
}

/* TODO: Optimize (remove branching, etc) */
bool mgl_utf8_decode(const unsigned char *str, size_t size, uint32_t *decoded_codepoint, size_t *codepoint_length) {
    if(size == 0)
        return false;

    size_t clen;
    if(!utf8_get_codepoint_length(str[0], &clen))
        return false;

    if(size < clen)
        return false;

    for(size_t i = 1; i < clen; ++i) {
        if((str[i] & 0xC0) != 0x80)
            return false;
    }

    uint32_t codepoint;
    switch(clen) {
        case 1:
            codepoint =  (uint32_t)(str[0] & 0x7F);
            break;
        case 2:
            codepoint = ((uint32_t)(str[0] & 0x1F) << 6);
            codepoint |= (uint32_t)(str[1] & 0x3F);
            break;
        case 3:
            codepoint =  ((uint32_t)(str[0] & 0x0F) << 12);
            codepoint |= ((uint32_t)(str[1] & 0x3F) << 6);
            codepoint |=  (uint32_t)(str[2] & 0x3F);
            break;
        case 4:
            codepoint =  ((uint32_t)(str[0] & 0x07) << 18);
            codepoint |= ((uint32_t)(str[1] & 0x3F) << 12);
            codepoint |= ((uint32_t)(str[2] & 0x3F) << 6);
            codepoint |=  (uint32_t)(str[3] & 0x3F);
            break;
    }

    *codepoint_length = clen;
    *decoded_codepoint = codepoint;
    return true;
}