#include <cstring>

static unsigned char str_byte_next(const char **ptr)
{
		unsigned char byte_value = **ptr;
			(*ptr)++;
				return byte_value;
}

static void str_byte_rewind(const char **ptr)
{
		(*ptr)--;
}

int str_length(const char *str)
{
	return (int)strlen(str);
}


int str_utf8_decode(const char **ptr)
{
	// As per https://encoding.spec.whatwg.org/#utf-8-decoder.
	unsigned char utf8_lower_boundary = 0x80;
	unsigned char utf8_upper_boundary = 0xBF;
	int utf8_code_point = 0;
	int utf8_bytes_seen = 0;
	int utf8_bytes_needed = 0;
	while(true)
	{
		unsigned char byte_value = str_byte_next(ptr);
		if(utf8_bytes_needed == 0)
		{
			if(byte_value <= 0x7F)
			{
				return byte_value;
			}
			else if(0xC2 <= byte_value && byte_value <= 0xDF)
			{
				utf8_bytes_needed = 1;
				utf8_code_point = byte_value - 0xC0;
			}
			else if(0xE0 <= byte_value && byte_value <= 0xEF)
			{
				if(byte_value == 0xE0)
					utf8_lower_boundary = 0xA0;
				if(byte_value == 0xED)
					utf8_upper_boundary = 0x9F;
				utf8_bytes_needed = 2;
				utf8_code_point = byte_value - 0xE0;
			}
			else if(0xF0 <= byte_value && byte_value <= 0xF4)
			{
				if(byte_value == 0xF0)
					utf8_lower_boundary = 0x90;
				if(byte_value == 0xF4)
					utf8_upper_boundary = 0x8F;
				utf8_bytes_needed = 3;
				utf8_code_point = byte_value - 0xF0;
			}
			else
			{
				return -1; // Error.
			}
			utf8_code_point = utf8_code_point << (6 * utf8_bytes_needed);
			continue;
		}
		if(!(utf8_lower_boundary <= byte_value && byte_value <= utf8_upper_boundary))
		{
			// Resetting variables not necessary, will be done when
			// the function is called again.
			str_byte_rewind(ptr);
			return -1;
		}
		utf8_lower_boundary = 0x80;
		utf8_upper_boundary = 0xBF;
		utf8_bytes_seen += 1;
		utf8_code_point = utf8_code_point + ((byte_value - 0x80) << (6 * (utf8_bytes_needed - utf8_bytes_seen)));
		if(utf8_bytes_seen != utf8_bytes_needed)
		{
			continue;
		}
		// Resetting variables not necessary, see above.
		return utf8_code_point;
	}
}

int str_utf8_isstart(char c)
{
	if((c & 0xC0) == 0x80) /* 10xxxxxx */
		return 0;
	return 1;
}

int str_utf8_rewind(const char *str, int cursor)
{
	while(cursor)
	{
		cursor--;
		if(str_utf8_isstart(*(str + cursor)))
			break;
	}
	return cursor;
}

int str_utf8_fix_truncation(char *str)
{
	int len = str_length(str);
	if(len > 0)
	{
		int last_char_index = str_utf8_rewind(str, len);
		const char *last_char = str + last_char_index;
		// Fix truncated UTF-8.
		if(str_utf8_decode(&last_char) == -1)
		{
			str[last_char_index] = 0;
			return last_char_index;
		}
	}
	return len;
}

int str_copy(char *dst, const char *src, int dst_size)
{
	dst[0] = '\0';
	strncat(dst, src, dst_size - 1);
	return str_utf8_fix_truncation(dst);
}

template<int N>
void str_copy(char (&dst)[N], const char *src)
{
	str_copy(dst, src, N);
}	

int main()
{
	enum
	{
		MAX_LINES = 25,
		MAX_LINE_LENGTH = 256
	};
	char m_aaLastChatMessages[MAX_LINES][MAX_LINE_LENGTH];
	for(int i = MAX_LINES; i > 0; i--)
	{
		str_copy(m_aaLastChatMessages[i], m_aaLastChatMessages[i - 1]);
	}
}