#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <stdint.h>

#define BASE62 "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

// Convert a number to Base-62
void to_base62(uint64_t num, char *output, int length) {
    char buffer[16] = {0};  // Temporary storage
    int i = 0;
    
    while (num > 0 && i < sizeof(buffer) - 1) {
        buffer[i++] = BASE62[num % 62];
        num /= 62;
    }

    // Reverse the string to get the correct order
    int j = 0;
    while (i > 0) {
        output[j++] = buffer[--i];
    }

    // Ensure fixed length (pad with '0' if needed)
    while (j < length) {
        output[j++] = '0';
    }
    
    output[j] = '\0';  // Null-terminate the string
}

// Generate the UID
void generate_uid(char *uid) {
    struct timespec ts;
    clock_gettime(CLOCK_REALTIME, &ts);

    uint64_t epoch_2020 = 1577836800000ULL;  // 2020-01-01 00:00:00 UTC in milliseconds
    uint64_t now = (uint64_t)ts.tv_sec * 1000 + ts.tv_nsec / 1000000;  // Current time in ms
    uint64_t timestamp = (now - epoch_2020) % 1000000000000ULL;  // Keep only 12 digits

    uint64_t random_num = rand() % 100;  // Random 2-digit number (00-99)
    uint64_t final_num = timestamp * 100 + random_num;

    // Convert to Base-62 and ensure 8-character output
    to_base62(final_num, uid, 8);
}

int main() {
    srand(time(NULL));  // Seed random number generator

    char uid[9];  // 8 characters + null terminator
    generate_uid(uid);

    printf("Generated UID: %s\n", uid);
    return 0;
}