/*
 * Copyright (c) 2023 Emma Tebibyte
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * This file is part of YAC coreutils.
 *
 * YAC coreutils is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Affero General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 * 
 * YAC coreutils is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see https://www.gnu.org/licenses/.
 */

#include <errno.h>
#include <sysexits.h>
#include <sys/stat.h>
#include <stdbool.h>
#include <stdio.h>
#include <unistd.h>

void cat(FILE *file, bool u) {
	int byte = 0; /* variable for storing bytes as they are read */
	int p = 0; /* index counter for bytes in buffered reading */
	char buf[4096]; /* buffer for buffered reading */

	if (u) {
		while (byte != EOF) {
			byte = fgetc(file);
			putchar(byte);
		}
	} else {
		while (byte != EOF) {
			byte = fgetc(file);
			if (p > sizeof(buf)) {
				fputs(buf, stdout);
				p = 0;
			} else {
				buf[p] = byte;
				p += 1;
			}
		}

		fwrite(buf, 1, p, stdout);
		fflush(stdout);
	}
}

int main(int argc, char *argv[]) {
	bool u = false;
	int opt;
	int i;

	extern int optind;
	while ((opt = getopt(argc, argv, "u")) != -1) {
		switch (opt) {
			/*
			 * From cat(1p):
			 *
			 * -u        Write bytes from the input file to the standard output
			 *           without delay as each is read.
			 */
			case 'u':
				u = true;
				break;
			default:
				fprintf(stderr, "Usage: %s (-u) file...\n", argv[0]);
				return EX_USAGE;
		}
	}

	/*
	 * From cat(1p):
	 *
	 * file      A pathname of an input file. If no file operands are
	 *           specified, the standard input shall be used. If a file is
	 *           '-', the cat utility shall read from the standard input at
	 *           that point in the sequence. The cat utility shall not close
	 *           and reopen standard input when it is referenced in this way,
	 *           but shall accept multiple occurrences of '-' as a file
	 *           operand.
	 */

	if (optind == argc) {
		cat(stdin, u);
		return 0;
	}
	
	FILE *file;
	struct stat stats;

	for (i = optind; i < argc; i++) {
		if (argv[i][0] == '-') {
			switch (argv[i][1]) {
				case '\0':
					file = stdin;
					break;
				default:
					continue;
			}
		} else if (stat(argv[i], &stats) == 0 && S_ISDIR(stats.st_mode)) {
			fprintf(stderr, "%s: %s: Is a directory.\n", argv[0], argv[i]);
			return EX_NOINPUT;
		} else if ((file = fopen(argv[i], "r")) == NULL) {
			switch (errno) {
				case EACCES:
					fprintf(stderr, "%s: %s: Permission denied.\n", argv[0], argv[i]);
					return EX_NOINPUT;
				case EISDIR:
					fprintf(stderr, "%s: %s: Is a directory.\n", argv[0], argv[i]);
					return EX_NOINPUT;
				case ELOOP:
					fprintf(stderr, "%s: %s: Is a symbolic link loop.\n", argv[0], argv[i]);
					return EX_UNAVAILABLE;
				case EMFILE:
					fprintf(stderr, "%s: Internal error.\n", argv[0]);
					return EX_SOFTWARE;
				case ENOENT: case ENOTDIR: case ENXIO:
					fprintf(stderr, "%s: %s: No such file or directory.\n", argv[0], argv[i]);
					return EX_NOINPUT;
				default:
					fprintf(stderr, "%s: Unknown error.\n", argv[0]);
					return EX_UNAVAILABLE;
			}
		}

		cat(file, u);
		if (file != stdin) { fclose(file); }
	}

	return EX_OK;
}