#include <stdio.h> /* fprintf(3), getc(3), putc(3) stderr, stdin, EOF */
#include <string.h> /* strchr(3) */
#include "ascii.h" /* ASCII_HEXADECIMAL_DIGITS_LOWER,
                    * ASCII_HEXADECIMAL_DIGITS_UPPER */
#include "libunicode.h" /* utf8(3) */

static struct {
	char *name;
	utf32_t (*f)(utf32_t);
}

static char *hex = ASCII_HEXADECIMAL_DIGITS_UPPER
	ASCII_HEXADECIMAL_DIGITS_LOWER;

int main(int argc, char *argv[]){
	int c;
	int i;
	int l; /* line counter */
	char *n;
	utf32_t codepoint;
	utf8_t encoded;

	l = 0;

init:	codepoint = 0;
	i = 0;
	++l;
	n = NULL;
	while((c = getc(stdin)) != EOF){
		if(c == '\n'){
			if(i < 2 && i > 0) /* empty lines are fine */
				fprintf(stderr, "%s: %s: Syntax error.\n",
					argv[0], l);
			else if(i >= 2){
				encoded = utf8(codepoint);
				for(i = 3; i >= 0; --i)
					if((encoded >> 8 * i) > 0 || i == 0)
						putc(encoded >> 8 * i, stdout);
			}
			goto init;
		}
		if(
				(i == 0 && c != 'U')
				|| (i == 1 && c != '+')
				|| i > 8 /* strlen("U+10FFFF") */
				|| (i > 1 && ((n = strchr(hex, c)) == NULL))
		){
				fprintf(stderr, "%s: %s: Syntax error.\n",
					argv[0], l);
				while((c = getc(stdin)) != '\n' && c != EOF);
				++l;
				continue;
		}
		if(n != NULL)
			codepoint = (codepoint << 4) + (n - hex) % 16;
		++i;
	}
}