From 28226fed7a52114efbd43860ef1ff7794ce88931 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Sat, 28 Aug 2021 17:53:27 -0400
Subject: datetime: WIP

---
diff --git a/src/datetime.c b/src/datetime.c
new file mode 100644
index 0000000..f39f80c
--- /dev/null
+++ b/src/datetime.c
@@ -0,0 +1,104 @@
+#define _XOPEN_SOURCE
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include "datetime.h"
+
+static const char *DATETIME_FMTS_[] = {
+	"%H:%M:%S",
+	"%I:%M:%S %p",
+	"%H:%M",
+	"%Y-%m-%dT%H:%M:%S",
+	"%Y-%m-%d %H:%M:%S",
+	"%A %B %d, %Y %H:%M:%S",
+	NULL
+};
+
+static char *
+datetime_normalize_spacing(int argc, const char *argv[])
+{
+	int   buf_l;
+	int   i;
+	int   l;
+	bool  was_space;
+	int   j;
+	char *buf;
+	int   buf_i;
+
+	buf_l = 0;
+	for (i = 0; i < argc; ++i) {
+		l = strlen(argv[i]);
+		was_space = true;
+		for (j = 0; j < l; ++j) {
+			if (isspace(argv[i][j]) != 0) {
+				if (was_space == false) {
+					buf_l++;
+					was_space = true;
+				}
+			} else {
+				buf_l++;
+				was_space = false;
+			}
+		}
+		++buf_l;
+	}
+
+	buf = calloc(buf_l, sizeof(*buf));
+	if (buf == NULL) {
+		fprintf(stderr, "Failed to allocate buffer: %s\n",
+				strerror(errno));
+		return NULL;
+	}
+
+	buf_i = 0;
+	for (i = 0; i < argc; ++i) {
+		l = strlen(argv[i]);
+		was_space = true;
+		for (j = 0; j < l; ++j) {
+			if (isspace(argv[i][j]) != 0) {
+				if (was_space == false) {
+					buf[buf_i++] = ' ';
+					was_space = true;
+				}
+			} else {
+				buf[buf_i++] = argv[i][j];
+				was_space = false;
+			}
+		}
+		buf[buf_i++] = ' ';
+	}
+	buf[--buf_i] = '\0';
+
+	return buf;
+}
+
+int
+datetime_parse(int argc, const char *argv[], struct tm *tm)
+{
+	int   e   = -1;
+	char *buf;
+	int   i;
+	char *end;
+
+	buf = datetime_normalize_spacing(argc, argv);
+	if (buf == NULL) {
+		return -1;
+	}
+
+	for (i = 0; DATETIME_FMTS_[i] != NULL; ++i) {
+		printf("%s =~ %s\n", buf, DATETIME_FMTS_[i]);
+		end = strptime(buf, DATETIME_FMTS_[i], tm);
+		if (end != NULL && *end == '\0') {
+			e = 0;
+			break;
+		}
+	}
+
+	free(buf);
+	return e;
+}
diff --git a/src/datetime.h b/src/datetime.h
new file mode 100644
index 0000000..562b377
--- /dev/null
+++ b/src/datetime.h
@@ -0,0 +1,4 @@
+
+int
+datetime_parse(int argc, const char *argv[], struct tm *tm);
+
diff --git a/src/local.mk b/src/local.mk
index 51037fb..0882580 100644
--- a/src/local.mk
+++ b/src/local.mk
@@ -1,2 +1,4 @@
 @_SOURCES += \
+	%reldir%/datetime.c \
+	%reldir%/datetime.h \
 	%reldir%/main.c
diff --git a/src/main.c b/src/main.c
index 71f0d9b..62e00dd 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,5 +1,16 @@
+#include <stdio.h>
+#include <time.h>
+#include "datetime.h"
+
 int
 main(int argc, char *argv[])
 {
+	struct tm tm;
+
+	datetime_parse(argc - 1, argv + 1, &tm);
+	printf("%d-%02d-%02dT%02d:%02d:%02d\n",
+			tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+			tm.tm_hour, tm.tm_min, tm.tm_sec);
+
 	return 0;
 }
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