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

#define VERSION "1.1.1"

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

int parse_arguments(const int argc, const char *const *const argv,
                    price_t *const price, wattage_t *const wattage, interval_t *const interval);

inline interval_t interval_to_seconds(const char *const interval);
inline price_t    price_kwh_to_wattsecond(const price_t price);

inline void print_version();
inline void print_usage();

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

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

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

    return 0;
}

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 (argv[i][1] == 'h' || argv[i][2] == 'h')
                return 1;
            else if (argv[i][1] == 'v' || argv[i][2] == 'v')
                return 2;
            else
                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_t)atof(argv[2]);
            ++pos;
        } else
            *interval += interval_to_seconds(argv[i]);

    return 0;
}

inline 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;
    }
}

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

inline void print_version() {
    fputs("kwh-cost Ver. " VERSION "\n"
         "Copyright (C) 2021-2023 Alexander \"Arav\" Andreev <me@arav.su>. All rights reserved.\n"
         "This program is distributed under the terms of MIT+NIGGER licence.\n"
         "You can see a license for this program in /usr/share/licenses/kwh-cost/LICENSE.\n", stderr);
}

inline void print_usage() {
    fputs("Usage: kwh-cost [OPTIONS] price wattage interval [interval ...]\n"
         "Options:\n"
         "  --help, -h     display this usage information.\n"
         "  --version, -v  display program version.\n"
         "Arguments:\n"
         "  price     price per kWh.\n"
         "  wattage   power usage in Watts.\n"
         "  interval  time interval in seconds during which\n"
         "            this much power to be constantly used.\n"
         "            You may specify other time units such as:\n"
         "            m'inute, h'our, d'ay. Example: 5d 3h.\n"
         "            All given intervals will be summed up.\n", stderr);
}