/* file: pbs-or.c		G. Moody		25 February 2012

Read N sorted files, write lines in any of them (logical "or")
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LMAX 128

char **line, *pline;
FILE **ifile;
int n;

/* cleanup: close input files, free allocated memory, and quit. */
void cleanup()
{
    while (n-- > 0) {
	fclose(ifile[n]);
	free(line[n]);
    }
    free(line);
    free(ifile);
    exit(0);
}

/* init: open input files and read the first line of each. Ignore unreadable
   and empty files, since they will not contribute to the output. */
void init(int argc, char **argv)
{
    if (argc < 3)
	exit(1);

    argc--; argv++;	/* skip argv[0] */
    ifile = (FILE **)calloc(argc, sizeof(FILE *));
    line = (char **)calloc(argc, sizeof(char *));
    for (n = 0; n < argc; n++) {
	if ((ifile[n] = fopen(argv[n], "r")) == NULL) {
	    argc--; argv++; n--; continue;
	}
	line[n] = (char *)calloc(LMAX, sizeof(char));
	if (fgets(line[n], LMAX, ifile[n]) == NULL) {
	    argc--; argv++; fclose(ifile[n--]); continue;
	}
    }
    pline = (char *)calloc(LMAX, sizeof(char));
}

main(int argc, char **argv)
{
    init(argc, argv);

    while (n > 0) {
	int i, j;

	for (i = 0, j = 1; j < n; j++)
	    if (strcmp(line[i], line[j]) > 0) i = j;
	/* line[i] is the (lexicographically) smallest input line remaining */
	if (strcmp(line[i], pline)) {	/* output only if not already written */
	    fputs(line[i], stdout);
	    strcpy(pline, line[i]);
	}
	/* get the next line from ifile[i] */
	if (fgets(line[i], LMAX, ifile[i]) == NULL) {
	    /* if there is nothing left in ifile[i], close it */
	    fclose(ifile[i]);
	    free(line[i]);
	    /* move the last open input into the slot just vacated */
	    if (i < --n) {
		ifile[i] = ifile[n];
		line[i] = line[n];
	    }
	}
    }

    /* when there are no more open inputs, we're done! */
    cleanup();
}