Implemented date

src/date/date.c

@@ -1,6 +1,119 @@
+#define _POSIX_C_SOURCE 200112L // for setenv
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdbool.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define NAME "date (canoutils)"
+#define VERSION "1.0.0"
+#define AUTHOR "Eike Flath"
+
+#include "version_info.h"
+
+#define INITIAL_BUF_SIZE 512
+
+static struct tm *get_time(void) {
+  time_t t;
+  if (time(&t) == -1) {
+    fprintf(stderr, "date: failed to retrieve time: %s\n", strerror(errno));
+    exit(EXIT_FAILURE);
+  }
+  return localtime(&t);
+}
+
+static int set_time(char *str) {
+  size_t n;
+  for (n = 0; str[n]; n++) {
+    if (!isdigit(str[n])) {
+      fprintf(stderr, "date: invalid date '%s'\n", str);
+      return EXIT_FAILURE;
+    }
+  }
+
+#define s(i) (str[i] - '0')
+  struct tm tm;
+  memcpy(&tm, get_time(), sizeof tm);
+  bool century_specified = false;
+  switch (n) {
+  case 12:
+    tm.tm_year = 100 * (10 * s(n - 4) + s(n - 3));
+    century_specified = true;
+    // fallthrough
+  case 10:
+    if (century_specified) {
+      tm.tm_year += 10 * s(n - 2) + s(n - 1);
+    } else {
+      int yy = 10 * s(n - 2) + s(n - 1);
+      int cc = yy >= 69 ? 19 : 20;
+      tm.tm_year = 100 * cc + yy;
+    }
+    tm.tm_year -= 1900;
+    // fallthrough
+  case 8:
+    tm.tm_mon = 10 * s(0) + s(1) - 1; // tm.tm_mon is in [0,11]
+    tm.tm_mday = 10 * s(2) + s(3);
+    tm.tm_hour = 10 * s(4) + s(5);
+    tm.tm_min = 10 * s(6) + s(7);
+    tm.tm_isdst = -1;
+    break;
+  default:
+    fprintf(stderr, "date: invalid date '%s'\n", str);
+    return EXIT_FAILURE;
+  }
+#undef s
+  time_t t = mktime(&tm);
+  if (t == -1) {
+    fprintf(stderr, "date: '%s' does not specify a valid time\n", str);
+    return EXIT_FAILURE;
+  }
+  struct timespec ts = {.tv_sec = t};
+  if (clock_settime(CLOCK_REALTIME, &ts)) {
+    fprintf(stderr, "date: cannot set date: %s\n", strerror(errno));
+    return EXIT_FAILURE;
+  }
+  return EXIT_SUCCESS;
+}
+
+int main(int argc, char **argv) {
+  char *operand = "+%a %b %e %H:%M:%S %Z %Y";
+  bool parse_options = true;
+  for (int i = 1; i < argc; i++) {
+    if (parse_options) {
+      if (!strcmp(argv[i], "--")) {
+        parse_options = false;
+        continue;
+      }
+      if (!strcmp(argv[i], "--version")) {
+        print_version();
+        return EXIT_SUCCESS;
+      }
+      if (!strcmp(argv[i], "-u")) {
+        if (setenv("TZ", "UTC", 1) == -1) {
+          fprintf(stderr, "date: cannot setenv TZ: %s\n", strerror(errno));
+          return EXIT_FAILURE;
+        }
+        continue;
+      }
+    }
+    operand = argv[i];
+  }
+
+  if (operand[0] != '+')
+    return set_time(operand);
+
+  struct tm *tm = get_time();
 
-int main(void) {
-  printf("Hello, World!\n");
-  return 0;
-}
+  size_t cap = INITIAL_BUF_SIZE;
+  char *buf = malloc(cap);
+  while (!strftime(buf, cap, &operand[1], tm)) {
+    cap *= 2;
+    buf = realloc(buf, cap);
+  }
+  printf("%s\n", buf);
+  free(buf);
+  return EXIT_SUCCESS;
+}