File: countdown.c
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 2020-2025 pacman64
   5 
   6 Permission is hereby granted, free of charge, to any person obtaining a copy of
   7 this software and associated documentation files (the “Software”), to deal
   8 in the Software without restriction, including without limitation the rights to
   9 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  10 of the Software, and to permit persons to whom the Software is furnished to do
  11 so, subject to the following conditions:
  12 
  13 The above copyright notice and this permission notice shall be included in all
  14 copies or substantial portions of the Software.
  15 
  16 THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22 SOFTWARE.
  23 */
  24 
  25 /*
  26 You can build this command-line app by running
  27 
  28 cc -Wall -s -O2 -o ./countdown ./countdown.c
  29 */
  30 
  31 #include <fcntl.h>
  32 #include <stdbool.h>
  33 #include <stddef.h>
  34 #include <stdint.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <time.h>
  39 #include <unistd.h>
  40 
  41 #ifdef _WIN32
  42 #include <windows.h>
  43 #endif
  44 
  45 // info is the message shown when this app is given any of its help options
  46 const char* info = ""
  47     "countdown [options...] [seconds/duration...]\n"
  48     "\n"
  49     "\n"
  50     "Count-down the number of seconds given, or 60 seconds by default.\n"
  51     "\n"
  52     "The duration can be either a number (of seconds) or a string with no\n"
  53     "spaces and numbered units `h`, `m`, `s`, which can be mixed together.\n"
  54     "\n"
  55     "Decimal dots and negative numbers aren't allowed."
  56     "\n"
  57     "\n"
  58     "Options, all of which can start with either 1 or 2 dashes:\n"
  59     "\n"
  60     "\n"
  61     "  -h          show this help message\n"
  62     "  -help       show this help message\n"
  63     "\n"
  64     "\n"
  65     "Examples"
  66     "\n"
  67     "\n"
  68     "  countdown 33 # 33 seconds\n"
  69     "  countdown 3h45m # 3 hours and 45 minutes\n"
  70     "  countdown 3h45s # 3 hours and 45 seconds\n"
  71     "  countdown 3h4m5s # 3 hours 4 minutes and 5 seconds\n"
  72     "";
  73 
  74 void countdown(int seconds) {
  75     struct timespec now;
  76     clock_gettime(CLOCK_REALTIME, &now);
  77     const int64_t ns2sec = 1e9;
  78     const int64_t end = ns2sec * (now.tv_sec + seconds) + now.tv_nsec;
  79 
  80     struct timespec delay;
  81     delay.tv_sec = 0;
  82     delay.tv_nsec = 100 * 1e6;
  83 
  84     int64_t t = ns2sec * now.tv_sec + now.tv_nsec;
  85     while (t < end) {
  86         const int64_t diff = end - t;
  87         const int64_t round_up = (diff % ns2sec) > (ns2sec / 5);
  88         const int64_t left = diff / ns2sec + round_up;
  89         const int h = left / 3600;
  90         const int m = (left / 60) % 60;
  91         const int s = left % 60;
  92         fprintf(stderr, "\r%02d:%02d:%02d", h, m, s);
  93 
  94         nanosleep(&delay, NULL);
  95         clock_gettime(CLOCK_REALTIME, &now);
  96         t = ns2sec * now.tv_sec + now.tv_nsec;
  97     }
  98 
  99     fputs("\r        \r", stderr);
 100 }
 101 
 102 // is_help_option simplifies control-flow for func main
 103 bool is_help_option(char* s) {
 104     return (s[0] == '-') && (
 105         strcmp(s, "-h") == 0 || strcmp(s, "-help") == 0 ||
 106         strcmp(s, "--h") == 0 || strcmp(s, "--help") == 0
 107     );
 108 }
 109 
 110 // bool parse_duration(char* s, int* seconds) {
 111 //     char* end;
 112 //     int v = strtol(argv[1], &end, 10);
 113 //     if (*end == 0) {
 114 //         *seconds = v;
 115 //         return true;
 116 //     }
 117 //     return false;
 118 // }
 119 
 120 bool parse_duration(char* s, int* seconds) {
 121     int total = 0;
 122     int accum = 0;
 123 
 124     for (; *s != 0; s++) {
 125         const int b = *s;
 126 
 127         if ('0' <= b && b <= '9') {
 128             accum *= 10;
 129             accum += b - '0';
 130             continue;
 131         }
 132 
 133         switch (b) {
 134             case 'h':
 135                 accum *= 3600;
 136                 total += accum;
 137                 accum = 0;
 138                 break;
 139 
 140             case 'm':
 141                 accum *= 60;
 142                 total += accum;
 143                 accum = 0;
 144                 break;
 145 
 146             case 's':
 147                 total += accum;
 148                 accum = 0;
 149                 break;
 150 
 151             default:
 152                 return false;
 153         }
 154     }
 155 
 156     total += accum;
 157     *seconds = total;
 158     return true;
 159 }
 160 
 161 int main(int argc, char** argv) {
 162 #ifdef _WIN32
 163     setmode(fileno(stdin), O_BINARY);
 164     // ensure output lines end in LF instead of CRLF on windows
 165     setmode(fileno(stdout), O_BINARY);
 166     setmode(fileno(stderr), O_BINARY);
 167 #endif
 168 
 169     // handle any of the help options, if given
 170     if (argc > 1 && is_help_option(argv[1])) {
 171         puts(info);
 172         return 0;
 173     }
 174 
 175     int seconds = 60;
 176     if (argc > 1) {
 177         if (!parse_duration(argv[1], &seconds)) {
 178             const char* fmt = "\x1b[31minvalid duration '%s'\x1b[0m\n";
 179             fprintf(stderr, fmt, argv[1]);
 180             return 1;
 181         }
 182     }
 183 
 184     if (seconds > 0) {
 185         countdown(seconds);
 186     }
 187 
 188     printf("done waiting for %d seconds\n", seconds);
 189     return 0;
 190 }