#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <sys/types.h>
#include <time.h>
#include <stdlib.h>
#include <ctype.h>
#include "tztable.h"

/*it's not case sensitive
returns the offset
returns -1 if it doesn't find it*/
int findintable(char *what){
    for(size_t i = 0; i < TZTABLE_LENGHT; i++){
        if((strcasecmp(what, tz_table[i].zn)) == 0){
        return tz_table[i].offset; 
        }
    }
return -1; 
}

/*parses H or H:M (24hs)
returns 0 on success, -1 if it's not a valid time*/
int strtimetoint(const char *whattimeisit, davidtime *out) {
    if (whattimeisit == NULL || out == NULL) return -1;

    char *end;
    long hour = strtol(whattimeisit, &end, 10);
    if (end == whattimeisit) return -1;

    long minutes = 0;
    if (*end == ':') {
        const char *mstart = end + 1;
        minutes = strtol(mstart, &end, 10);
        if (end == mstart) return -1;
    }
    if (*end != '\0') return -1;

    if (hour < 0 || hour > 23 || minutes < 0 || minutes > 59) return -1;

    out->hour = (int)hour;
    out->minutes = (int)minutes;
    return 0;
}

char* gethhmm(char* buffer, size_t max_size) {
    time_t raw_time;
    struct tm* time_info;

    time(&raw_time);
    time_info = localtime(&raw_time);

    strftime(buffer, max_size, "%H:%M", time_info);
    return buffer;
}

int gettimeandstuff(void){
    time_t rawtime = time(NULL);
    struct tm utc = *gmtime(&rawtime); /*copy, gmtime uses a static buffer*/
 
    utc.tm_isdst = -1;
    time_t gmt = mktime(&utc);
    return difftime(rawtime, gmt) / 60;
}


/*tozone = 0 time is in zone, print it as local time
tozone = 1 time is local time, print it in zone
returns 0 ok -1 zone not found and -2 if invalid time*/
int convert(char *timey, char *zone, int tozone){
    
    int offset = gettimeandstuff(); 

    //tmzn hour --> utc00 --> local time 
    int zntime = findintable(zone);
    if(zntime == -1)return -1; 

    davidtime eugh;
    if(strtimetoint(timey, &eugh) == -1) return -2;
    int mins = eugh.hour * 60 + eugh.minutes;
    int total = tozone ? mins - offset + zntime : mins - zntime + offset; //ok this is better yeah
    
    int day = 0;
    while (total < 0){
        total += 1440; day--; 
    }
    while (total >= 1440){
        total -= 1440; day++;
    }

    printf("%02d:%02d", total / 60, total % 60);
    if(day) printf(" %+dd", day);  
    printf("\n");
    return 0;
}

/*takes in a single argument
and returns whatever timezones allign with the input*/
int convert2(char *timey){
    /*it should fist get the offset between local time and input
    it should probably round up to ~5 minutes so multiples of 5
    input is like 7:32 rounds down to 7:30 
    finds the closest match, on many matches it just presents the first in the list*/ 
 
    int localoffset = gettimeandstuff(); 
    davidtime hi; 
    if(strtimetoint(timey, &hi) == -1) return -2;
 
    char nowstr[16];
    davidtime now;
    gethhmm(nowstr, sizeof(nowstr));
    strtimetoint(nowstr, &now);
 
    int inmins  = hi.hour * 60 + hi.minutes;
    int nowmins = now.hour * 60 + now.minutes;
    inmins  -= inmins % 5;   /*round down to multiples of 5*/
    nowmins -= nowmins % 5;
 
    //offset of the zone that has the input as its current time
    int target = localoffset + (inmins - nowmins);
 
    int best = -1, bestdist = 1441;
    for(size_t i = 0; i < TZTABLE_LENGHT; i++){
        //distance on the 24h clock so +13 and -11 count as the same time
        int d = ((tz_table[i].offset - target) % 1440 + 1440) % 1440;
        if(d > 720) d = 1440 - d;
        if(d < bestdist){ 
            bestdist = d;
            best = (int)i;
        }
    }
    if(best == -1) return -1;
 
    int off = tz_table[best].offset;
    printf("%s (UTC%c%02d:%02d)\n", tz_table[best].zn, off < 0 ? '-' : '+', abs(off) / 60, abs(off) % 60);
    return 0;
}

int main (int argc, char **argv){
 
    if((argc <= 1) || (argc > 3)){
        printf("%s: usage: %s [TIME (24hs)] [ZONE]\ne.g: %s 7:15 est\n\nalso get relative times like %s [ZONE]\ne.g: %s est\n\nor find which zone has a given time right now like %s [TIME (24hs)]\ne.g: %s 17:00\n", argv[0], argv[0], argv[0], argv[0], argv[0], argv[0], argv[0]);
        exit(1);
    }
 
    char timestr[16];
    gethhmm(timestr, sizeof(timestr));
    if (argc == 2) {
        if (isdigit((unsigned char)argv[1][0])) {
            int res2 = convert2(argv[1]);
            if (res2 == -2) {
                printf("%s: invalid time, use 24hs format like 7:15\n", argv[0]);
                return 1;
            }
            if (res2 == -1) {
                printf("%s: no time zones to match against\n", argv[0]);
                return 1;
            }
            return 0;
        }
        if (convert(timestr, argv[1], 1) == -1) {
            printf("%s: time zone not found, did you write it correctly?\n", argv[0]);
            return 1;
        }
        return 0;
    }

    int res = convert(argv[1], argv[2], 0);
    if (res == -1) {
        printf("%s: time zone not found, did you write it correctly?\n", argv[0]);
        return 1;
    }
    if (res == -2) {
        printf("%s: invalid time, use 24hs format like 7:15\n", argv[0]);
        return 1;
    }
    return 0;
}