base64_urlsafe kinda roughly. for the recoverable filenames.

base64_urlsafe.c

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

static inline void process_triplet(const char *input, size_t i, uint32_t *triplet) {
    *triplet = (input[i] << 16) | (i + 1 < strlen(input) ? input[i + 1] << 8 : 0) | (i + 2 < strlen(input) ? input[i + 2] : 0);
}

static inline void process_quartet(const char *input, size_t i, uint32_t *quartet, int *k, const char *base64_urlsafe_table) {
    *quartet = 0;
    for (*k = 0; *k < 4; (*k)++) {
        char c = input[i + *k];
        if (c == '=') break;
        char* pos = strchr(base64_urlsafe_table, c);
        if (!pos) { *quartet = UINT32_MAX; break; }
        *quartet = (*quartet << 6) | (pos - base64_urlsafe_table);
    }
    *quartet <<= 6 * (4 - *k);
}

static char* encode_triplets(const char *input, size_t len) {
    static const char base64_urlsafe_table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
    size_t output_len = 4 * ((len + 2) / 3);
    char *output = (char*)malloc(output_len + 1);
    if (!output) return NULL;

    int i, j;
    for (i = 0, j = 0; i < len; i += 3) {
        uint32_t triplet;
        process_triplet(input, i, &triplet);
        output[j++] = base64_urlsafe_table[(triplet >> 18) & 0x3F];
        output[j++] = base64_urlsafe_table[(triplet >> 12) & 0x3F];
        output[j++] = i + 1 < len ? base64_urlsafe_table[(triplet >> 6) & 0x3F] : '=';
        output[j++] = i + 2 < len ? base64_urlsafe_table[triplet & 0x3F] : '=';
    }
    output[output_len] = '\0';

    return output;
}

static char* decode_quartets(const char *input, size_t len) {
    static const char base64_urlsafe_table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
    if (len % 4 != 0) return NULL;

    size_t output_len = len / 4 * 3;
    if (input[len - 1] == '=') output_len--;
    if (input[len - 2] == '=') output_len--;

    char* output = (char*)malloc(output_len + 1);
    if (!output) return NULL;

    int i, j;
    for (i = 0, j = 0; i < len; i += 4) {
        uint32_t quartet;
        int k;
        process_quartet(input, i, &quartet, &k, base64_urlsafe_table);
        if (quartet == UINT32_MAX) { free(output); output = NULL; break; }
        if (k > 1) output[j++] = (quartet >> 16) & 0xFF;
        if (k > 2) output[j++] = (quartet >> 8) & 0xFF;
        if (k > 3) output[j++] = quartet & 0xFF;
    }
    if (output) output[output_len] = '\0';

    return output;
}

// ----------------------------------------------------------------------------
// borrowed utilities
long time_in_ms() {
    struct timespec time;
    clock_gettime(CLOCK_REALTIME, &time);
    return time.tv_sec * 1000 + time.tv_nsec / 1000000;
}

int main() {
	
 // for saving files
    time_t t = time(NULL);
    struct tm *tm_info = localtime(&t);
    char timestamp[26];
    strftime(timestamp, 26, "%Y%m%d%H%M%S", tm_info);

    char dirname[] = "inbox";
    // Check if directory exists
    if (_access(dirname, 0) == -1) {
        printf("Directory %s does not exist. Attempting to create it.\n", dirname);
        // If directory doesn't exist, create it
        if (_mkdir(dirname) == -1) {
            printf("Unable to create directory %s!\n", dirname);
            return 1;
        }
    }	

	char filename[150];
	char *prompt = "This could be a prompt";
	snprintf(filename, 150, "inbox/%s_?_%s.txt", timestamp, prompt);
    FILE *output_file = NULL; // Declare output_file outside the if statement
	
	//const char* original_string = filename;
    char* encoded_string = encode_triplets(filename, strlen(filename));

	output_file = fopen(encoded_string, "w");
	if (!output_file) {
		printf("Unable to open the inbox file %s!\n", encoded_string);
		return 1;
	}
	    
    char* decoded_string = decode_quartets(encoded_string, strlen(encoded_string));

    printf("Original: %s\n", filename);
    printf("Encoded: %s\n", encoded_string);
    printf("Decoded: %s\n", decoded_string);
    free(encoded_string);
    free(decoded_string);

    return 0;
}