/* Copyright (C) 2008  Emmanuel Varoquaux

   This file is part of XOS.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>. */

#include "common.h"

#include <getopt.h>
#include <error.h>
#include <stdlib.h>
#include <time.h>
#include <stdio.h>
#include <errno.h>

static void print_date(const char *format, const struct tm *tm)
{
  char buf[4096];

  if (!strftime(buf, sizeof buf, format, tm))
    error(EXIT_FAILURE, 0, "output too big");
  printf("%s\n", buf + 1);
}

static void __attribute__ ((noreturn)) die_bad_usage()
{
  fprintf(stderr, "Try `%s --help' for more information.\n", program_invocation_name);
  exit(EXIT_FAILURE);
}

static void print_help()
{
  printf("Usage: %s [OPTION]... [+FORMAT]\n", program_invocation_name);
  puts("Display the current time in the given FORMAT, or set the system date.");
  putchar('\n');
  puts("  -u, --utc, --universal  print Coordinated Universal Time");
  puts("  -h, --help              display this help and exit");
}

int main(int argc, char **argv)
{
  static const struct option longopts[] = {
    {"utc", no_argument, NULL, 'u'},
    {"universal", no_argument, NULL, 'u'},
    {"help", no_argument, NULL, 'h'},
    {NULL, 0, NULL, 0}
  };

  char c;
  int utc;
  const char *format;
  time_t current_time;
  const struct tm *date;

  atexit(close_stdout);

  utc = 0;
  while ((c = getopt_long(argc, argv, "uh", longopts, NULL)) != -1)
    switch (c) {
    case 'u':
      utc = 1;
      break;
    case 'h':
      print_help();
      return EXIT_SUCCESS;
    case '?':
      die_bad_usage();
    }

  if (argc > optind + 1) {
    error(0, 0, "extra operand `%s'", argv[optind + 1]);
    die_bad_usage();
  }

  if (optind < argc) {
    if (argv[optind][0] != '+')
      error(EXIT_FAILURE, 0, "the argument %s lacks a leading `+'", argv[optind]);
    format = argv[optind];
  }
  else
    format = "+%a %b %e %H:%M:%S %Z %Y";

  if (time(&current_time) == (time_t)-1)
    error(EXIT_FAILURE, errno, "cannot get system date");
  if (utc)
    if (setenv("TZ", "UTC", 1) == -1)
      error(EXIT_FAILURE, errno, "setenv");
  if (!(date = localtime(&current_time)))
    error(EXIT_FAILURE, errno, "localtime");
  print_date(format, date);
  return EXIT_SUCCESS;
}