kwh-cost/kwh-cost.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define VERSION "1.2.0"

typedef long double   price_t;
typedef long double   wattage_t;
typedef unsigned long interval_t;

interval_t interval_to_seconds(const char *const interval) {
    interval_t intrvl = (interval_t)atol(interval);

    switch (interval[strlen(interval) - 1]) {
        case 'm':
        case 'M':
            return intrvl * 60;
        case 'h':
        case 'H':
            return intrvl * 60 * 60;
        case 'd':
        case 'D':
            return intrvl * 60 * 60 * 24;
        default:
            return intrvl;
    }
}

wattage_t wattage_to_watts(const char *const wattage) {
    wattage_t wattg = (wattage_t)atof(wattage);

    switch (wattage[strlen(wattage)-1]) {
        case 'm':
            return wattg / 1000.;
        case 'k':
        case 'K':
            return wattg * 1000.;
        case 'M':
            return wattg * 1000000.;
        case 'G':
            return wattg * 1000000000.;
        case 'T':
            return wattg * 1000000000000.;
        default:
            return wattg;
    }
}

price_t price_kwh_to_wattsecond(const price_t price) {
    return price / 1000.f / 3600.f;
}

int parse_arguments(const int argc, const char *const *const argv,
                    price_t *const price, wattage_t *const wattage, interval_t *const interval) {
    if (argc < 2) return 1;

    for (int i = 1, pos = 0; i < argc; ++i)
        if (argv[i][0] == '-') {
            if (strlen(argv[i]) < 2) return 99;
            switch (argv[i][1]) {
                case 'h': return 1;
                case 'v': return 2;
                default: return 99;
            }
        } else if (argc < 4) {
            return 1;
        } else if (pos == 0) {
            *price = price_kwh_to_wattsecond((price_t)atof(argv[i]));
            ++pos;
        } else if (pos == 1) {
            *wattage = wattage_to_watts(argv[2]);
            ++pos;
        } else
            *interval += interval_to_seconds(argv[i]);

    return 0;
}

void print_version(void) {
    fputs("kwh-cost Ver. " VERSION "\n"
         "Copyright (C) 2021-2024 Alexander \"Arav\" Andreev <me@arav.su>. All rights reserved.\n"
         "This program is distributed under the terms of MIT+NIGGER license.\n"
         "A license for this program is placed in /usr/share/licenses/kwh-cost/LICENSE.\n", stderr);
}

void print_usage(void) {
    fputs("Usage: kwh-cost [OPTIONS] price wattage interval [interval ...]\n"
         "Options:\n"
         "  -h        display this usage information.\n"
         "  -v        display program version.\n"
         "Arguments:\n"
         "  price     price per kWh.\n"
         "  wattage   power usage in Watts (m, K, M, G, T).\n"
         "  interval  time interval in seconds (m'inutes, h'ours, d'ays,\n"
         "            like 5d 3h) during which given power is constantly used.\n"
         "            All given intervals will be summed up.\n", stderr);
}

int main(const int argc, const char *const *const argv) {
    price_t price = 0;
    wattage_t wattage = 0;
    interval_t interval = 0;

    switch (parse_arguments(argc, argv, &price, &wattage, &interval)) {
        case 1: print_usage(); return 0;
        case 2: print_version(); return 0;
        case 99: fputs("Unknown flag provided.\n", stderr); print_usage(); return 1;
    }

    printf("%.2Lf\n", (price * wattage) * interval);

    return 0;
}