From 06a0b4d1ec8ee10736565eda0c4a5e3c885c73c6 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Tue, 31 Aug 2021 16:13:03 -0400
Subject: main: Handle options

---
diff --git a/configure.ac b/configure.ac
index 12dc4cf..cb2f4da 100644
--- a/configure.ac
+++ b/configure.ac
@@ -43,6 +43,12 @@ AC_CHECK_FUNCS(
 	],
 	[],
 	[funcs_missing=true])
+AC_CHECK_FUNCS(
+	[getopt_long],
+	[],
+	[
+		AC_CHECK_FUNCS([getopt], [], [funcs_missing=true])
+	])
 if ${funcs_missing}; then
 	AC_MSG_ERROR([required functions are missing])
 fi
diff --git a/src/main.c b/src/main.c
index b5f518b..81096a5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -24,10 +24,67 @@
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
+#include "config.h"
 #include "datetime.h"
 
+#if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
+#include <getopt.h>
+#endif
+
+extern const char *PACKAGE_VERSION_GIT;
+
+#if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
+struct option LONGOPTS_[] = {
+	{
+		.name    = "help",
+		.has_arg = 0,
+		.flag    = NULL,
+		.val     = 'h',
+	},
+	{
+		.name    = "version",
+		.has_arg = 0,
+		.flag    = NULL,
+		.val     = 'V',
+	},
+};
+#endif
+
+static void
+_print_usage(FILE *stream, const char *program_name)
+{
+	fprintf(stream, "Usage: %s [date]time\n", program_name);
+}
+
+static void
+_print_help(const char *program_name)
+{
+	_print_usage(stdout, program_name);
+	puts("Options:");
+#if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
+	puts("\t-h, --help     Show this help information");
+	puts("\t-V, --version  Show version information");
+#else
+	puts("\t-h  Show this help information");
+	puts("\t-V  Show version information");
+#endif
+}
+
+static void
+_print_version(void)
+{
+	printf("@ (atsign) %s%s\n", PACKAGE_VERSION, PACKAGE_VERSION_GIT);
+	puts("Copyright (C) 2021  P. J. McDermott");
+	puts("License GPLv3+: GNU GPL version 3 or later "
+			"<http://gnu.org/licenses/gpl.html>.");
+	puts("This is free software: you are free to change and redistribute "
+			"it.");
+	puts("There is NO WARRANTY, to the extent permitted by law.\n");
+	printf("Please report bugs to <%s>.\n", PACKAGE_BUGREPORT);
+}
+
 static char *
-_concat_args(int argc, const char *argv[])
+_concat_args(int argc, char * const argv[])
 {
 	int   buf_l;
 	int   i;
@@ -60,14 +117,44 @@ _concat_args(int argc, const char *argv[])
 }
 
 int
-main(int argc, const char *argv[])
+main(int argc, char * const argv[])
 {
+	int     opt;
 	char   *buf;
 	time_t  arg;
 	time_t  now;
 	time_t  dif;
 
-	buf = _concat_args(argc - 1, argv + 1);
+	optind = 1;
+	opterr = 0;
+#if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
+	while ((opt = getopt_long(argc, argv, "hV", LONGOPTS_, NULL)) > 0) {
+#else
+	while ((opt = getopt(argc, argv, "hV")) > 0) {
+#endif
+		switch (opt) {
+			case 'h':
+				_print_help(argv[0]);
+				return EXIT_SUCCESS;
+			case 'V':
+				_print_version();
+				return EXIT_SUCCESS;
+			default:
+				_print_usage(stderr, argv[0]);
+#if defined(HAVE_GETOPT_LONG) && HAVE_GETOPT_LONG
+				fprintf(stderr, "Try '%s --help' for more "
+						"information.\n", argv[0]);
+#else
+				fprintf(stderr, "Try '%s -h' for more "
+						"information.\n", argv[0]);
+#endif
+				return EXIT_FAILURE;
+		}
+	}
+	argc -= optind;
+	argv += optind;
+
+	buf = _concat_args(argc, argv);
 	if (buf == NULL) {
 		return EXIT_FAILURE;
 	}
--
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