/*
 * UNG's Not GNU
 *
 * Copyright (c) 2022, Jakob Kaivo <jkk@ung.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#define _XOPEN_SOURCE 700
#include <fcntl.h>
#include <errno.h>
#include <limits.h>
#include <locale.h>
#include <ftw.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#ifndef OPEN_MAX
#ifdef _XOPEN_MAX
#define OPEN_MAX _XOPEN_MAX
#else
#define OPEN_MAX _POSIX_OPEN_MAX
#endif
#endif

static int directory_fd[2];
static char *directory_path[2];
static int return_value = 0;
static int current_fd = 0;
static size_t directory_base = 0;
static int suppress = 0;
static int diff_output = 0;

static int compare(char *d1, char *d2, const char *path)
{
	char p1[PATH_MAX];
	char p2[PATH_MAX];

	snprintf(p1, sizeof(p1), "%s/%s", d1, path);
	snprintf(p2, sizeof(p2), "%s/%s", d2, path);

	if (diff_output) {
		/* run diff d1/path d2/path */
		return 0;
	}

	FILE *f1 = fopen(p1, "r");
	if (!f1) {
		fprintf(stderr, "dircmp: %s: %s\n", p1, strerror(errno));
		return 1;
	}

	FILE *f2 = fopen(p2, "r");
	if (!f2) {
		fprintf(stderr, "dircmp: %s: %s\n", p2, strerror(errno));
		fclose(f1);
		return 1;
	}

	for (;;) {
		int c1 = fgetc(f1);
		int c2 = fgetc(f2);
		if (c1 != c2) {
			printf("files differ: %s %s\n", p1, p2);
			break;
		}
		if (c1 == EOF) {
			if (!suppress) {
				printf("files match: %s %s\n", p1, p2);
			}
			break;
		}
	}

	fclose(f1);
	fclose(f2);
	
	return 0;
}

static int dircmp(const char *path, const struct stat *st, int type, struct FTW *ftw)
{
	(void)ftw; (void)type; (void)st;

	//int fd1 = directory_fd[current_fd];
	int fd2 = directory_fd[current_fd == 0 ? 1 : 0];
	char *d1 = directory_path[current_fd];
	char *d2 = directory_path[current_fd == 0 ? 1 : 0];

	path += directory_base;

	struct stat st2;
	if (fstatat(fd2, path, &st2, 0) != 0) {
		if (errno == ENOENT) {
			printf("only in %s: %s\n", d1, path);
			return 0;
		}
		fprintf(stderr, "dircmp: %s/%s: %s\n", d2, path, strerror(errno));
		return_value = 1;
		return 0;
	}

	/* common files have already been compared */
	if (current_fd == 1) {
		return 0;
	}

	return_value |= compare(d1, d2, path);
	return 0;
}

int main(int argc, char *argv[])
{
	setlocale(LC_ALL, "");

	int c;
	while ((c = getopt(argc, argv, "ds")) != EOF) {
		switch (c) {
		case 'd':	/** compare files as with `diff` **/
			diff_output = 1;
			break;

		case 's':	/** suppress identical files output **/
			suppress = 1;
			break;

		default:
			return 1;
		}
	}

	if (optind != argc - 2) {
		fprintf(stderr, "cmp: missing operand\n");
		return 1;
	}

	directory_path[0] = argv[optind];
	directory_path[1] = argv[optind];

	directory_fd[0] = open(directory_path[0], O_RDONLY | O_DIRECTORY);
	if (directory_fd[0] == -1) {
		fprintf(stderr, "dircmp: %s: %s\n", directory_path[0], strerror(errno));
		return 1;
	}

	directory_fd[1] = open(directory_path[0], O_RDONLY | O_DIRECTORY);
	if (directory_fd[1] == -1) {
		fprintf(stderr, "dircmp: %s: %s\n", directory_path[1], strerror(errno));
		return 1;
	}


	directory_base = strlen(directory_path[0]) + 1;
	nftw(directory_path[0], dircmp, OPEN_MAX, 0);

	current_fd = 1;
	directory_base = strlen(directory_path[1]) + 1;
	nftw(directory_path[1], dircmp, OPEN_MAX, 0);

	return return_value;
}