/* lib9p/utf8.h - Internal UTF-8 validation
 *
 * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#ifndef _LIB9P_UTF8_H_
#define _LIB9P_UTF8_H_

static inline bool _is_valid_utf8(uint8_t *str, size_t len, bool forbid_nul) {
	uint32_t ch;
	uint8_t chlen;
	assert(str);
	for (size_t pos = 0; pos < len;) {
		if      ((str[pos] & 0b10000000) == 0b00000000) { ch = str[pos] & 0b01111111; chlen = 1; }
		else if ((str[pos] & 0b11100000) == 0b11000000) { ch = str[pos] & 0b00011111; chlen = 2; }
		else if ((str[pos] & 0b11110000) == 0b11100000) { ch = str[pos] & 0b00001111; chlen = 3; }
		else if ((str[pos] & 0b11111000) == 0b11110000) { ch = str[pos] & 0b00000111; chlen = 4; }
		else return false;
		if ((ch == 0 && (chlen != 1 || forbid_nul)) || pos + chlen > len) return false;
		for (uint8_t i = 1; i < chlen; i++) {
			if ((str[pos+i] & 0b11000000) != 0b10000000) return false;
			ch = (ch << 6) | (str[pos+i] & 0b00111111);
		}
		if (ch > 0x10FFFF) return false;
		pos += chlen;
	}
	return true;
}

#define is_valid_utf8(str, len)                 _is_valid_utf8(str, len, false)
#define is_valid_utf8_without_nul(str, len)     _is_valid_utf8(str, len, true)

#endif /* _LIB9P_UTF8_H_ */