#include <iostream>

#include <iostream>
#include <iomanip>
#include <fstream>
#include <cstdlib>
#include <ctime>

using namespace std;

char *generate_output_filename (char *filename);
void copy_file (ifstream &input_file, ofstream &output_file, int file_length);

int main()
{
	double BER;
	char RS, MPE_FEC;
	
	char *input_filename = new char[300];
	cout << "Enter filename (file must be in the same directory as exe): ";
	cin >> input_filename;
	cout << "Enter BER (e.g for a BER of 10^-6 enter 1e-6): ";
	cin >> BER;
	cout << "Using RS coding (y/n)?: ";
	cin >> RS;
	//cout << "Using MPE-FEC (y/n) (can't use both RS and MPE-FEC at same time)?: ";
	//cin >> MPE_FEC;

	MPE_FEC = 'n';

	int NUM_RS_CORRECTABLE_BYTES = 5;
	int RS_CODEWORD_LENGTH = 110;

	if (MPE_FEC == 'y')
	{
		NUM_RS_CORRECTABLE_BYTES = 64;
		RS_CODEWORD_LENGTH = 255;
	}

	char *output_filename = generate_output_filename (input_filename);
	
	ifstream input_file(input_filename, ios::binary);
	if (!input_file)
	{
		cerr << "Input file could not be opened" << endl;
		exit(1);
	}

	ofstream output_file(output_filename, ios::binary);
	if (!output_file)
	{
		cerr << "Output file could not be opened" << endl;
		exit(1);
	}

	ofstream data_file("changes made.txt", ios::out);
	if (!data_file)
	{
		cerr << "Data file could not be opened" << endl;
		exit(1);
	}

	input_file.seekg (0, ios::end);     
	int file_length = input_file.tellg();		
	input_file.seekg (0, ios::beg);

	cout << "File length = " << file_length << endl;

	copy_file (input_file, output_file, file_length);

	int i;
	int num_errors = (int)(file_length * 8 * BER);
	unsigned long *byte_number; 
	byte_number = new unsigned long[num_errors];
	int number_rs_packets = file_length / RS_CODEWORD_LENGTH;
	
	unsigned long *rs_packet;
	rs_packet = new unsigned long [number_rs_packets];
	for (i=0; i<number_rs_packets; i++)
		rs_packet[i] = 0;


	int bit_number;
	unsigned char c;
	int bit_value;

	srand(time(0));
	cout << endl << "Add errors" << endl;
	for (i=0; i<num_errors; i++)
	{
		byte_number[i] = ((RAND_MAX + 1)*(unsigned long)rand() + rand()) % file_length; 
		rs_packet[byte_number[i] / RS_CODEWORD_LENGTH]++;
	}

	data_file << "Number of errors = " << num_errors << endl;
	
	for (i=0; i<num_errors; i++)
	{
		bit_number = rand() % 8;

		input_file.seekg(byte_number[i]);
		output_file.seekp(byte_number[i]);

		c = (unsigned char)input_file.get();

		data_file << dec << (i+1) << endl;
		data_file << "byte before = " << hex << setw(2) << (unsigned int)c << " - byte_number = " << dec << byte_number[i] << " - bit_number = " << bit_number << endl;

		bit_value = c & (1 << bit_number);

		if (bit_value)
			c &= ~(1 << bit_number);	// reset bit
		else
			c |= (1 << bit_number);	// set bit
		
		data_file << "byte after  = " << setw(2) << hex << (unsigned int)c << endl << endl;

		if (RS != 'y' && MPE_FEC != 'y')
			output_file.put(c);

		// RS error correction - errors are corrected if less errors per codeword than RS code's correcting capability
		else if (rs_packet[byte_number[i] / RS_CODEWORD_LENGTH] > NUM_RS_CORRECTABLE_BYTES)	 
			output_file.put(c);
	}

	output_file.close();

	// check that number of bytes that don't match equals number of errors 
	// (if the number is slightly out then there is more than one error in certain bytes)

	ifstream output_file2(output_filename, ios::binary);
	if (!output_file2)
	{
		cerr << "Output file could not be opened for comparing with original" << endl;
		exit(1);
	}

	int counter = 0;
	input_file.seekg(0);
	output_file2.seekg(0);
	for (i=0; i<file_length; i++)
	{
		c = input_file.get();
		if (c != output_file2.get())
			counter++;
		if (i % 10000 == 0)
			cout << "Comparing files ... " << fixed << setprecision(1) << 100.0* i / file_length << "%\r";
	}
	cout << "Comparing files ... " << fixed << setprecision(1) << 100.0* i / file_length << "%\r";
	cout << endl << dec << "Calculated number of errors = " << num_errors << " - actual number of bytes changed = " << counter << endl;
	if (counter != num_errors && RS != 'y' && MPE_FEC != 'y')
		cout << "If calculated value does not equal the actual value that means that certain bytes have multiple errors" << endl;
		
	input_file.close();
	data_file.close();
	output_file2.close();

	cout << "Enter a character then press Enter to close" << endl;
	cin >> c;
		
	
	return 0;
}



char *generate_output_filename (char *filename)
{
	int length = strlen(filename);

	char *output_filename = new char[length+3];

	int pos = (int)strchr(filename, '.') - (int)filename;
	strncpy(output_filename, filename, pos);
	output_filename[pos] = '\0';
	strcat(output_filename, "_01");
	strcat(output_filename, strchr(filename, '.'));

	return output_filename;
}



void copy_file (ifstream &input_file, ofstream &output_file, int file_length)
{
	int i;
	const int RW_BUFFER_SIZE = 2048;
	char *rw_buf = new char[RW_BUFFER_SIZE];

	unsigned int num_read_cycles = file_length / RW_BUFFER_SIZE;

	for (i=0; i<num_read_cycles; i++)
	{
		input_file.read(rw_buf, RW_BUFFER_SIZE);
		output_file.write(rw_buf, RW_BUFFER_SIZE);

		//if (i % 5 == 0)
			cout << "Copying original file to new file ... " << fixed << setprecision(1) << 100.0 * i / num_read_cycles << "%\r";
	}

	input_file.read(rw_buf, file_length - (i * RW_BUFFER_SIZE));
	output_file.write(rw_buf, file_length - (i * RW_BUFFER_SIZE));
	cout << "Copying original file to new file ... " << fixed << setprecision(1) << 100.0 << "%\r";
}