From bab98a3a230bcc2161254e5796ec97e1391b4907 Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Sun, 3 Sep 2023 17:50:46 -0700
Subject: [PATCH] Encode time in time-logger's format

This is not a good format.  It looses timezone information during daylight
savings time changes -- it cannot distinguish between the first 01:30
and the second 01:30 during the fall transition.
---
 common.c         | 13 +++++++++++++
 common.h         |  4 ++++
 tl-append-test.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+)

diff --git a/common.c b/common.c
index ffa4b5a..1bc1102 100644
--- a/common.c
+++ b/common.c
@@ -1,3 +1,6 @@
+#define _POSIX_C_SOURCE 2
+#include "common.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -13,3 +16,13 @@ void die_err(const char *message) {
   perror(message);
   exit(1);
 }
+
+const char *encode_time(time_t t) {
+  struct tm tm;
+  localtime_r(&t, &tm);
+  const size_t size = 20;
+  char *out = (char *)malloc(size);
+  if (strftime(out, size, "%Y %m %d %H %M %S", &tm) != size - 1)
+    die("Couldn't format time");
+  return out;
+}
diff --git a/common.h b/common.h
index e442b2c..8d40a78 100644
--- a/common.h
+++ b/common.h
@@ -1,5 +1,9 @@
+#include <time.h>
+
 extern const char *FILENAME;
 
 void die(const char *message);
 
 void die_err(const char *message);
+
+const char *encode_time(time_t t);
diff --git a/tl-append-test.c b/tl-append-test.c
index 6d037cb..7e8455d 100644
--- a/tl-append-test.c
+++ b/tl-append-test.c
@@ -1,4 +1,7 @@
 #define _POSIX_C_SOURCE 2
+#define _XOPEN_SOURCE
+#include <assert.h>
+#include <ctype.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -68,6 +71,45 @@ static void verify_log_contents(ex_t exps[]) {
     die_err("Error closing log file");
 }
 
+static void test_encode_time() {
+  /* localtime_r to set tm's timezone */
+  time_t now_time = time(NULL);
+  struct tm tm;
+  if (localtime_r(&now_time, &tm) == NULL)
+    die_err("Can't unpack current time?");
+
+  const char *strptime_result = strptime("2011-12-13 14:15:16", "%F %T", &tm);
+  if (strptime_result == NULL || *strptime_result != '\0')
+    die("Couldn't parse time?");
+  time_t tt = mktime(&tm);
+  if (tt == (time_t)-1)
+    die_err("Can't pack time?");
+
+  const char *encoded = encode_time(tt);
+  /* Loose check to allow for daylight savings time changes between the current
+   * time and the target time.  :( */
+  assert(encoded[0] == '2');
+  assert(encoded[1] == '0');
+  assert(encoded[2] == '1');
+  assert(encoded[3] == '1');
+  assert(encoded[4] == ' ');
+  assert(encoded[5] == '1');
+  assert(encoded[6] == '2');
+  assert(encoded[7] == ' ');
+  assert(encoded[8] == '1');
+  assert(encoded[9] == '3');
+  assert(encoded[10] == ' ');
+  assert(encoded[11] == '1');
+  assert(isdigit(encoded[12]));
+  assert(encoded[13] == ' ');
+  assert(isdigit(encoded[14]));
+  assert(isdigit(encoded[15]));
+  assert(encoded[16] == ' ');
+  assert(encoded[17] == '1');
+  assert(encoded[18] == '6');
+  assert(encoded[19] == '\0');
+}
+
 static void write_and_read_line() {
   remove_logfile();
   ex_t e = write_to_tl_append("foo\n");
@@ -82,6 +124,7 @@ static void write_and_read_two_lines() {
 }
 
 int main() {
+  test_encode_time();
   write_and_read_line();
   write_and_read_two_lines();
 }
-- 
2.44.1