/// (C) 2010, Andrew Polar under GPL ver. 3.
//   LICENSE
//
//   This program is free software; you can redistribute it and/or
//   modify it under the terms of the GNU General Public License as
//   published by the Free Software Foundation; either version 3 of
//   the License, or (at your option) any later version.
//
//   This program is distributed in the hope that it will be useful, but
//   WITHOUT ANY WARRANTY; without even the implied warranty of
//   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//   General Public License for more details at
//   Visit <http://www.gnu.org/copyleft/gpl.html>.
//
// This is skeleton of iROLZ algorithm

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <memory.h>
#include <math.h>
#include <string.h>

#define PREFIX_SIZE             2   //must be 1, 2 or 3
#define HISTORY_BUFFER_BITLEN   16  //trade between time and compression ratio
#define LONGEST_COUNT           255 //must be one byte
#define SUFFICIENT_MATCH        63  //does not make big difference
#define MAX_STEPS               127 //must be some limit
#define MINIMUM_MATCH           2   //must be 1 or larger, the larger the limit the more literals

unsigned short* g_buffer = 0;
int current_byte;
int number_of_literals, number_of_couples;
double estimated_compression_ratio;

///////auxiliary functions///////////////////////////////
template <class T>
double calculate_entropy(T* data, int data_size) {
	
	int min, max, counter, buffer_size;
	int* buffer;
	double entropy;
	double log2 = log(2.0);
	double prob;

	min = data[0];
	max = data[0];
	for (counter=0; counter<data_size; ++counter) {
		if (data[counter] < min)
			min = data[counter];
		if (data[counter] > max)
			max = data[counter];
	}

	buffer_size = max - min + 1;
	buffer = (int*)malloc(buffer_size * sizeof(int));
	memset(buffer, 0x00, buffer_size * sizeof(int));
	for (counter=0; counter<data_size; ++counter) {
		++buffer[data[counter]-min];
	}

	entropy = 0.0;
	for (counter=0; counter<buffer_size; ++counter) {
		if (buffer[counter] > 0) {
			prob = (double)buffer[counter];
			prob /= (double)data_size;
			entropy += log(prob)/log2*prob;
		}
	}
	entropy *= -1.0;

	if (buffer)
		free(buffer);

	return  entropy;
}

int getFileSize(char* fileName) {
	FILE* f;
	if ((f = fopen(fileName, "rb")) == NULL)
		return -1;
	fseek(f, 0, SEEK_END);
	int bytes = ftell(f);
	fclose(f);
	return bytes;
}
//////end auxiliary functions list//////////////////

//this is reversible reducer of entropy for executables of Ilya Muraviev
//source: http://balz.sourceforge.net/
void exetransform(int mode, unsigned char* data, int size) {
	const int end = size - 8;
	int i = 0;
	while ((reinterpret_cast<int&>(data[i]) != 0x4550) && (++i < end));
	// perform call/jmp address translation
	while (i < end) {
		if ((data[i++] & 254) == 0xe8) {
			int &addr = reinterpret_cast<int&>(data[i]);
			if (mode) {
				if ((addr >= -i) && (addr<(size - i))) {
					addr += i;
				}
				else {
					if ((addr > 0) && (addr < size)) addr -= size;
				}
			}
			else {
				if (addr < 0) {
					if ((addr + i) >= 0) addr += size;
				}
				else {
					if (addr < size) addr -= i;
				}
			}
			i += 4;
		}
	}
}

class Dictionary {
public:
	Dictionary(int PrefixSize, int OffsetLen);
	~Dictionary();
	void updateDictionary(unsigned char byte);
	int  getNextPosition(int position);
private:
	int* m_last_position_lookup;
	int* m_self_addressed_dictionary;
	int m_prefix_mask, m_buffer_mask, m_context, m_index;
};

Dictionary::Dictionary(int PrefixSize, int OffsetLen) {
	if (PrefixSize == 1) m_prefix_mask = 0xff;
	else if (PrefixSize == 2) m_prefix_mask = 0xffff;
	else m_prefix_mask = 0xffffff;
	m_last_position_lookup = (int*)malloc((m_prefix_mask + 1) * sizeof(int));
	memset(m_last_position_lookup, 0x00, (m_prefix_mask + 1) * sizeof(int));
	m_buffer_mask = (1<<OffsetLen) - 1;
	m_self_addressed_dictionary = (int*)malloc((m_buffer_mask + 1) * sizeof(int));
	memset(m_self_addressed_dictionary, 0x00, (m_buffer_mask + 1) * sizeof(int));
	m_context = m_index = 0;
}

Dictionary::~Dictionary() {
	if (m_self_addressed_dictionary) free(m_self_addressed_dictionary);
	if (m_last_position_lookup)      free(m_last_position_lookup);
}

void Dictionary::updateDictionary(unsigned char byte) {
	m_context <<= 8;
	m_context |= byte;
	m_context &= m_prefix_mask;
	m_self_addressed_dictionary[m_index & m_buffer_mask] = m_last_position_lookup[m_context];
	m_last_position_lookup[m_context] = m_index;
	++m_index;
}

int Dictionary::getNextPosition(int position) {
	return m_self_addressed_dictionary[position & m_buffer_mask];
}

inline int getLongestMatch(Dictionary* dictionary, const unsigned char* data, int index, int data_size, int& nsteps) {
	if (index + MINIMUM_MATCH >= data_size) return 0;
	int max_count, max_step, step, position, count;
	position = index;
	max_count = max_step = step = 0;
	while (true) {
		int new_position = dictionary->getNextPosition(position);
		if (new_position >= position) break;
		if (data[index + MINIMUM_MATCH] == data[new_position + MINIMUM_MATCH]) { //quick test
			count = 0;
			while (true) {
				if (index + 1 + count >= data_size) break;
				if (data[index + 1 + count] == data[new_position + 1 + count]) {
					++count;
				}
				else break;
				if (count >= LONGEST_COUNT) break;
			}
			if (count > max_count) {
				max_count = count;
				max_step  = step;
			}
			if (max_count > SUFFICIENT_MATCH) break;
		}
		if (step++ >= MAX_STEPS) break;
		position = new_position;
	} 
	nsteps = max_step;
	return max_count;
}

bool irolz_compress(const unsigned char* data, const int data_size) {
	Dictionary* dictionary = new Dictionary(PREFIX_SIZE, HISTORY_BUFFER_BITLEN);
	int max_count, max_step;
	int index = 0;
	do {
		dictionary->updateDictionary(data[index]);
		//save literal
		g_buffer[current_byte++] = data[index];
		while (true) {
			max_count = getLongestMatch(dictionary, data, index, data_size, max_step);
			if (max_count >= MINIMUM_MATCH ) { 
				//save <offset, lenght>
				g_buffer[current_byte++] = 256 + max_count;
				g_buffer[current_byte++] = max_step;
				for (int k=0; k<max_count; ++k) {
					++index;
					dictionary->updateDictionary(data[index]);
				}
			}
			else {
				break;
			}
		}
		++index;
	} while (index < data_size);
	delete dictionary;
	return true;
}

void irolz_decompress(unsigned char* data, int& size, int data_size) {
	//this is for statistics only
	int* literals_and_leng = (int*)malloc(data_size * sizeof(int));
	int* index             = (int*)malloc(data_size * sizeof(int));
	int index_cnt = 0;
	int literals_and_leng_cnt = 0;
	///////////////////////////////////////////////////////////////

	number_of_literals = number_of_couples = 0;
	Dictionary* dictionary = new Dictionary(PREFIX_SIZE, HISTORY_BUFFER_BITLEN);
	int counter = 0;
	for (int i=0; i<current_byte; ++i) {
		if (g_buffer[i] < 256) {
			literals_and_leng[literals_and_leng_cnt++] = g_buffer[i]; //statistics
			data[counter] = (unsigned char)g_buffer[i];
			dictionary->updateDictionary(data[counter]);
			++counter;
			++number_of_literals;
		}
		else {
			literals_and_leng[literals_and_leng_cnt++] = g_buffer[i]; //statistics
			int length = g_buffer[i] - 256;
			++i;
			int step = g_buffer[i];
			index[index_cnt++] = g_buffer[i];

			int offset = 0; 
			int position = counter - 1;
			for (int k=0; k<=step; ++k) {
				position = dictionary->getNextPosition(position);
				if (position < 0) {
					printf("Error: misformatted data\n");
					return;
				}
			}
			offset = counter - 1 - position;
			for (int k=0; k<length; ++k) {
				data[counter] = data[counter - offset];
				dictionary->updateDictionary(data[counter]);
				++counter;
			}
			++number_of_couples;
		}
	}
	size = counter;
	delete dictionary;
	
	//rough approximate estimation of compression ratio, this estimation is for lowest compression,
	//it must be better when context modelling is applied. 
	double entropy_literals_and_leng = calculate_entropy(literals_and_leng, literals_and_leng_cnt);
	double entropy_index = calculate_entropy(index, index_cnt);
	double bits = entropy_literals_and_leng * double(literals_and_leng_cnt);
	bits += entropy_index * double(index_cnt);
	estimated_compression_ratio = bits/8.0/double(data_size);

	if (index) free(index);
	if (literals_and_leng) free(literals_and_leng);
	///////////////////////////////////////////////
}

int main() {
	char fileName[] = "C:\\Users\\apolar\\projects\\files\\ohs.doc";
	//char fileName[] = "C:\\\Users\\apolar\\projects\\files\\calgary\\bib";
	int data_size = getFileSize(fileName);
	if (data_size < 0) {
		printf("File not found\n");
		return -1;
	}

	unsigned char* data = (unsigned char*)malloc(data_size * sizeof(*data));
	FILE* f = fopen(fileName, "rb");
	fread(data, 1, data_size, f);
	fclose(f);

	g_buffer = (unsigned short*)malloc((data_size + data_size/2)*sizeof(unsigned short));

	//preprocessing to provide better compression of exe and dll
	//if applied should be reversed by exetransform(0, data, data_size)
	//to restore original.
	exetransform(1, data, data_size);

	printf("Andrew Polar under GPL ver. 3. LICENSE\n");
	clock_t start = clock();
	current_byte = 0;
	irolz_compress(data, data_size);
	clock_t end = clock();
	printf("Encoding time    %2.3f s.\n", (double)(end - start)/CLOCKS_PER_SEC);
	int compressed_array_size = current_byte;

	start = clock();
	unsigned char* test = (unsigned char*)malloc((data_size + data_size/2));
	int size = 0;
	irolz_decompress(test, size, data_size);
	end = clock();
	printf("Decoding time    %2.3f s.\n", (double)(end - start)/CLOCKS_PER_SEC);

	bool isOK = true;
	if (size != data_size) {
		printf("Size mismatch\n");
		isOK = false;
	}
	else {
		for (int i=0; i<data_size; ++i) {
			if (test[i] != data[i]) {
				printf("Data mismatch %d\n", i);
				isOK = false;
				break;
			}
		}
	}
	if (isOK) printf("Round trip is OK.\n");

	printf("Original and compressed data sizes          %d %d\n", data_size, compressed_array_size);
	printf("Approximate ratio relative to original size %f\n", estimated_compression_ratio);
	printf("This compression ratio is calculated without applying context modelling.\n");
	printf("We can expect additional improvement on 10 to 15 percent if apply it.\n");
	printf("Number of literals                          %d\n", number_of_literals);
	printf("Number of couples                           %d\n", number_of_couples);
	if (test) free(test);
	if (g_buffer) free(g_buffer);
	return 0;
}