#include "utf8.hpp"

size_t utf8_codepoint_size(char32_t codepoint) {
  if (0 == ((char32_t)0xffffff80 & codepoint)) {
    return 1;
  } else if (0 == ((char32_t)0xfffff800 & codepoint)) {
    return 2;
  } else if (0 == ((char32_t)0xffff0000 & codepoint)) {
    return 3;
  } else {
    return 4;
  }
}

char *utf8_write_codepoint(char *str, char32_t codepoint) {
  if (0 == ((char32_t)0xffffff80 & codepoint)) {
    /* 1-byte/7-bit ascii
     * (0b0xxxxxxx) */
    str[0] = (char)codepoint;
    str += 1;
  } else if (0 == ((char32_t)0xfffff800 & codepoint)) {
    /* 2-byte/11-bit utf8 code point
     * (0b110xxxxx 0b10xxxxxx) */
    str[0] = (char)(0xc0 | (char)((codepoint >> 6) & 0x1f));
    str[1] = (char)(0x80 | (char)(codepoint & 0x3f));
    str += 2;
  } else if (0 == ((char32_t)0xffff0000 & codepoint)) {
    /* 3-byte/16-bit utf8 code point
     * (0b1110xxxx 0b10xxxxxx 0b10xxxxxx) */
    str[0] = (char)(0xe0 | (char)((codepoint >> 12) & 0x0f));
    str[1] = (char)(0x80 | (char)((codepoint >> 6) & 0x3f));
    str[2] = (char)(0x80 | (char)(codepoint & 0x3f));
    str += 3;
  } else { /* if (0 == ((int)0xffe00000 & chr)) { */
    str[0] = (char)(0xf0 | (char)((codepoint >> 18) & 0x07));
    str[1] = (char)(0x80 | (char)((codepoint >> 12) & 0x3f));
    str[2] = (char)(0x80 | (char)((codepoint >> 6) & 0x3f));
    str[3] = (char)(0x80 | (char)(codepoint & 0x3f));
    str += 4;
  }

  return str;
}