//
// Created by bruno on 4/29/25.
//

#include <string.h>
#include <stdio.h>
#include <stdint-gcc.h>
#include <malloc.h>
#include "base.h"

static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                                'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                                'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
                                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
                                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                                '4', '5', '6', '7', '8', '9', '+', '/'};
static char *decoding_table = NULL;

void build_decoding_table() {

    decoding_table = malloc(256);

    for (int i = 0; i < 64; i++)
        decoding_table[(unsigned char) encoding_table[i]] = i;
}


unsigned char *base64_decode(const char *data, size_t input_length, size_t *output_length) {

    if (decoding_table == NULL) build_decoding_table();

    if (input_length % 4 != 0) {
        printf("babbaba %zu\n", input_length);
        return NULL;
    }

    *output_length = input_length / 4 * 3;
    if (data[input_length - 1] == '=') (*output_length)--;
    if (data[input_length - 2] == '=') (*output_length)--;

    unsigned char *decoded_data = malloc(*output_length);
    if (decoded_data == NULL) {
        printf("fefefefeg\n");
        return NULL;
    }

    for (int i = 0, j = 0; i < input_length;) {

        uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];

        uint32_t triple = (sextet_a << 3 * 6)
                          + (sextet_b << 2 * 6)
                          + (sextet_c << 1 * 6)
                          + (sextet_d << 0 * 6);

        if (j < *output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }

    return decoded_data;
}


void hex_dump(const unsigned char *data, size_t len) {
    for (size_t i = 0; i < len; i++) {
        printf("%02X ", data[i]);
        if ((i + 1) % 16 == 0)
            printf("\n");
    }
    printf("\n");
}

static uint32_t crc32_table[256];

// Call this once before computing CRCs
void init_crc32_table(void) {
    uint32_t poly = 0xEDB88320;  // reversed polynomial of 0x04C11DB7
    for (uint32_t i = 0; i < 256; i++) {
        uint32_t crc = i;
        for (uint8_t j = 0; j < 8; j++) {
            if (crc & 1)
                crc = (crc >> 1) ^ poly;
            else
                crc >>= 1;
        }
        crc32_table[i] = crc;
    }
}

uint32_t crc32_le(uint32_t crc, const uint8_t *buf, size_t len) {
    crc = ~crc;
    while (len--) {
        crc = crc32_table[(crc ^ *buf++) & 0xFF] ^ (crc >> 8);
    }
    return ~crc;
}