/* --------------------------------------------------- */
/* ---              Obracanie riadkov              --- */
/* --------------------------------------------------- */

/* ---------------------------------------------------
          zapocet z C pre 3MI december 1996
   ---------------------------------------------------
   
   Uloha c.1:
   ----------
     - upravte program tak, aby v pripade ak mu boli 
       z prikazoveho riadku zadane neuplne udaje, si
       dalsie informacie sam od uzivatela ziskal
       (problemovy pripad: bol zadany iba jeden subor) 
      
   Uloha c.2:
   ----------
     - upravte program tak, aby pri reverzii riadkov 
       nepouzival rekurziu
     - co by ste zmenili aby program obracal len 
       jednotlive slova vo vstupnom riadku

   --------------------------------------------------- */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* ---  maximalna dlzka vstupneho riadku  --- */
#define	MAX_LEN	1024

/* --- vrati "revertovany" retazec k retazcu 'str' --- */
char * reverse(char * str);
/* ---  pomocna funkcia  --- */
char * reverse_buffer(char * in, char * out);

int main(int argc, char * argv[]) {
	/* ---  Deklaracia premmenych  --- */
	char buffer[MAX_LEN + 1];
	FILE * input, * output;
	
	if (argc <= 1) {
		/* --- 
		   ak nemame dost zadanych argumentov budeme
		   citat zo standardneho vstupu a pisat na 
		   standardny vystup
		   --- */
		input = stdin;
		output = stdout;
	} else if (argc <= 2) { /* a sucasne nie je <= 1*/
		printf("Chcem bud dva argumenty: vstupny_subor vystupny_subor\n");
		printf("alebo ziaden argument (potom citam zo stdin a pisem na stdout)\n");
		return 0;
	} else {
		/* ---
		   otvor subor zadany z prikazoveho riadku na citanie
		   --- */
		argc--;
		argv++;
		input = fopen(argv[0], "r");
		if (!input) {
			printf("Nemozem nasjst, alebo otvorit vstupny subor !\n");
			return -1;
		}

		output = fopen(argv[1], "w");
		if (!output) {
			printf("Nemozem nasjst, alebo otvorit vystupny subor !\n");
			return -1;
		}
	}
	
	for (;;) {
		/* --- nacitaj dalsi riadok do buffra --- */
		fgets(buffer, sizeof(buffer) -1, input);
		/* --- kontrola --- */
		if (ferror(input)) {
			printf("Chyba pri citani zo suboru !\n");
			if (input != stdin)
				fclose(input);
			return -1;
		}
		/* --- treba otestovat koniec vstupu --- */
		if (feof(input))
			break;
		/* --- odstranit koncovy 'EOL' --- */
		buffer[strlen(buffer) -1] = 0;
		/* --- vystup --- */
		fprintf(output, "%s\n", reverse(buffer));
	}

	/* ---
	   ak bol vstup citany zo suboru treba ho zavriet
	   --- */
	if (input != stdin)
		fclose(input);

	/* ---
	   treba vratit vysledok cinnosti programu 
	   --- */
	return 0;
}

/* ---  pomocna funkcia  --- */
char * reverse_buffer(char * in, char * out) {
	if (*in) {
		*out = *in;
		out --;
		in ++;
		return reverse_buffer(in, out);
	} else
		return out +1;
}

/* --- vrati "revertovany" retazec k retazcu 'str' --- */
char * reverse(char * str) {
	char buffer[MAX_LEN +1];
	int len = strlen(str);
	memset(buffer, 0, sizeof(buffer));
	return reverse_buffer(str, &buffer[len -1]);
}