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#include "encoding.h"
#include <queue>
map<int, int> buildFrequencyTable(istream& input) {
map<int, int> freq_table;
while (true) {
int c = input.get();
if (input.eof()) {
break;
}
if (!freq_table.count(c)) {
freq_table[c] = 0;
}
freq_table[c] += 1;
}
freq_table[PSEUDO_EOF] = 1;
return freq_table;
}
HuffmanNode* buildEncodingTree(const map<int, int>& freq_table) {
std::priority_queue<HuffmanNode> nodes;
for (const auto& freq_element : freq_table) {
nodes.push(HuffmanNode(freq_element.first, freq_element.second));
}
while (nodes.size() > 1) {
HuffmanNode* node_left = new HuffmanNode(nodes.top());
nodes.pop();
HuffmanNode* node_right = new HuffmanNode(nodes.top());
nodes.pop();
HuffmanNode merged_node = HuffmanNode();
merged_node.count = node_left->count + node_right->count;
merged_node.zero = node_left;
merged_node.one = node_right;
nodes.push(merged_node);
}
HuffmanNode* root = new HuffmanNode(nodes.top());
return root;
}
template <typename T, typename U>
void merge_map(map<T, U>& into, const map<T, U>& from) {
for (const auto& element : from) {
into[element.first] = element.second;
}
}
map<int, string> encoding_map_helper(HuffmanNode *encoding_tree, const string& cur_string) {
map<int, string> encoding_map;
if (encoding_tree) {
if (encoding_tree->isLeaf()) {
encoding_map[encoding_tree->character] = cur_string;
} else {
encoding_map = encoding_map_helper(encoding_tree->zero,
cur_string + "0");
merge_map(encoding_map, encoding_map_helper(encoding_tree->one,
cur_string + "1"));
}
}
return encoding_map;
}
map<int, string> buildEncodingMap(HuffmanNode* encoding_tree) {
return encoding_map_helper(encoding_tree, "");
}
void encode_char(int c, const map<int, string>& encoding_map, obitstream& output) {
for (const auto& bit : encoding_map.at(c)) {
output.writeBit(bit == '0' ? 0 : 1);
}
}
void encodeData(istream& input, const map<int, string>& encoding_map, obitstream& output) {
while (true) {
int c = input.get();
if (input.eof()) {
break;
}
encode_char(c, encoding_map, output);
}
encode_char(PSEUDO_EOF, encoding_map, output);
}
int read_char(ibitstream& input, HuffmanNode* encoding_tree) {
if (encoding_tree->isLeaf()) {
return encoding_tree->character;
} else {
int bit = input.readBit();
if (bit == 0) {
return read_char(input, encoding_tree->zero);
} else {
return read_char(input, encoding_tree->one);
}
}
}
void decodeData(ibitstream& input, HuffmanNode* encoding_tree, ostream& output) {
while (true) {
int next_char = read_char(input, encoding_tree);
if (next_char == PSEUDO_EOF) {
break;
}
char c = (char)next_char;
output.write(&c, 1);
}
}
void encodeHeader(const map<int, int>& freq_table, obitstream& output) {
output.write("{", 1);
int i = 0;
for (const auto& encode : freq_table) {
string char_num_str = to_string(encode.first);
string char_freq_str = to_string(encode.second);
output.write(char_num_str.c_str(), char_num_str.length());
output.write(":", 1);
output.write(char_freq_str.c_str(), char_freq_str.length());
if (i != freq_table.size() - 1) {
output.write(", ", 2);
}
i++;
}
output.write("}", 1);
}
void compress(istream& input, obitstream& output) {
map<int, int> freq_table = buildFrequencyTable(input);
HuffmanNode* encoding_tree = buildEncodingTree(freq_table);
map<int, string> encoding_map = buildEncodingMap(encoding_tree);
encodeHeader(freq_table, output);
input.clear();
input.seekg(0, ios::beg);
encodeData(input, encoding_map, output);
freeTree(encoding_tree);
}
int read_int(istream& input, int *next_char = nullptr) {
string str;
while (true) {
int c = input.get();
if (c < '0' || c > '9') {
if (next_char) {
*next_char = c;
}
return stoi(str);
} else {
str = str + (char)c;
}
}
}
map<int, int> decodeHeader(istream& input) {
map<int, int> freq_table;
if (input.get() != '{') {
cerr << "Broken huffman header, expected '{' as first byte" << endl;
return freq_table;
}
while (true) {
int next_input, next_char_val, next_char_freq;
next_char_val = read_int(input);
next_char_freq = read_int(input, &next_input);
freq_table[next_char_val] = next_char_freq;
if (next_input == '}') {
break;
}
input.get(); // read space, ',' was read by read_int
}
return freq_table;
}
void decompress(ibitstream& input, ostream& output) {
map<int, int> freq_table = decodeHeader(input);
HuffmanNode* encoding_tree = buildEncodingTree(freq_table);
decodeData(input, encoding_tree, output);
freeTree(encoding_tree);
}
void freeTree(HuffmanNode* node) {
if (node) {
if (!node->isLeaf()) {
freeTree(node->zero);
freeTree(node->one);
}
delete node;
} else {
cerr << "Tried to free null tree" << endl;
}
}
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