/* See LICENSE file for copyright and license details. */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include "util.h"

#define CLAMP(x, l, h) MIN(h, MAX(l, x))

static void printline(int, char *);
static char *nextline(char *, int, FILE *, char *);
static void finish(int, FILE *, char *);

static int show = 0x07;

static void
usage(void)
{
	eprintf("usage: %s [-123] file1 file2\n", argv0);
}

int
main(int argc, char *argv[])
{
	int i, dif = 0;
	FILE *fp[2];
	char lines[2][LINE_MAX+1];

	ARGBEGIN {
	case '1':
	case '2':
	case '3':
		show &= 0x07 ^ (1 << (ARGC() - '1'));
		break;
	default:
		usage();
	} ARGEND;

	if(argc != 2)
		usage();

	for(i = 0; i < LEN(fp); i++) {
		if(!(fp[i] = fopen(argv[i], "r")))
			eprintf("comm: '%s':", argv[i]);
	}

	for(;;) {
		if(dif <= 0) {
			if(!nextline(lines[0], sizeof(lines[0]),
						fp[0], argv[0])) {
				finish(1, fp[1], argv[1]);
			}
		}
		if(dif >= 0) {
			if(!nextline(lines[1], sizeof(lines[1]),
						fp[1], argv[1])) {
				finish(0, fp[0], argv[0]);
			}
		}
		dif = strcmp(lines[0], lines[1]);
		dif = CLAMP(dif, -1, 1);
		printline((2-dif) % 3, lines[MAX(0, dif)]);
	}

	return 0;
}

void
printline(int pos, char *line)
{
	int i;

	if(!(show & (0x1 << pos)))
		return;

	for(i = 0; i < pos; i++) {
		if(show & (0x1 << i))
			putchar('\t');
	}
	printf("%s", line);
}

char *
nextline(char *buf, int n, FILE *f, char *name)
{
	buf = fgets(buf, n, f);
	if(!buf && !feof(f))
		eprintf("comm: '%s':", name);
	if(buf && !strchr(buf, '\n'))
		eprintf("comm: '%s': line too long.\n", name);

	return buf;
}

void
finish(int pos, FILE *f, char *name)
{
	char buf[LINE_MAX+1];

	while(nextline(buf, sizeof(buf), f, name))
		printline(pos, buf);

	exit(1);
}