/******************************************************************************
 * This program converts a Base64 back into the original binary file.
 * 
 * Copyright © 2021 Richard Lesh.  All rights reserved.
 *****************************************************************************/

#undef NDEBUG

#include "Utils.hpp"
#include <cctype>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace Utils;
using namespace std;

static string BASE64_CODES = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

vector<int> decode_base64(const vector<int> input_bytes) noexcept {
    vector<int> sextets(4);
    vector<int> output_bytes(3);
    for (auto i = 0; i < 4; ++i) {
        sextets[i] = BASE64_CODES.find(input_bytes[i]);
    }
    output_bytes[0] = (sextets[0] << 2) | (sextets[1] >> 4);
    output_bytes[1] = ((sextets[1] << 4) | (sextets[2] >> 2)) & 0xFF;
    output_bytes[2] = ((sextets[2] << 6) | (sextets[3])) & 0xFF;
    return output_bytes;
}

void convert_from_base64(string from_filespec, string to_filespec) {
    ifstream ifh(filesystem::path(from_filespec).c_str());
    ofstream ofh(filesystem::path(to_filespec).c_str(), ios_base::binary);
    if (!ifh.good()) {
        throw ios_base::failure("Problem opening input file!");
    }
    if (!ofh.good()) {
        throw ios_base::failure("Problem opening output file!");
    }
    int c;
    int count = 0;
    vector<int> input_bytes(4);
    vector<int> output_bytes = {};
    while ((c = ifh.get()) != EOF) {
        if (!(isspace(c))) {
            input_bytes[count % 4] = c;
            ++count;
            if (count % 4 == 0) {
                output_bytes = decode_base64(input_bytes);
                int max = 3;
                if (input_bytes[3] == 0x3D) {
                    --max;
                }
                if (input_bytes[2] == 0x3D) {
                    --max;
                }
                for (auto i = 0; i < max; ++i) {
                    ofh.put(output_bytes[i]);
                }
            }
        }
    }
    ifh.close();
    ofh.close();
}

int main(int argc, char **argv) {
    if (argc != 3) {
        cout << "Syntax: " << argv[0] << " {fromFilespec} {toFilespec}" << endl;
        exit(1);
    }
    string from_filespec(argv[1]);
    string to_filespec(argv[2]);
    try {
        convert_from_base64(from_filespec, to_filespec);
    } catch (ios_base::failure ex) {
        cout << "Error: " << Utils::exceptionMessage<char>(ex) << endl;
    }
    return 0;
}