main.py

import os
import heapq


class HuffmanCoding:

    def __init__(self, path):
        self.path = path
        self.heap = []
        self.codes = {}
        self.reverse_mapping = {}

    class HeapNode:
        def __init__(self, char, freq):
            self.char = char
            self.freq = freq
            self.left = None
            self.right = None

        def __lt__(self, other):
            return self.freq < other.freq

        def __eq__(self, other):
            if(other == None):
                return False
            if(not isinstance(other, HeapNode)):
                return False
            return self.freq == other.freq


    def make_frequency_dict(self, text):
        # calc freq and return
        frequency = {}
        for character in text:
            if not character in frequency:
                frequency[character] = 0
            frequency[character] += 1
        return frequency

    def make_heap(self, frequency):
        # make priority queue

        for key in frequency:
            node = self.HeapNode(key, frequency[key])
            heapq.heappush(self.heap, node)

    def merge_nodes(self):
        # build huffman tree, save root node in heap

        while(len(self.heap) > 1):
            node1 = heapq.heappop(self.heap)
            node2 = heapq.heappop(self.heap)

            merged = self.HeapNode(None, node1.freq + node2.freq)
            merged.left = node1
            merged.right = node2

            heapq.heappush(self.heap, merged)


    def make_codes_helper(self, root, current_code):

        if(root == None):
            return
        if(root.char != None):
            self.codes[root.char] = current_code
            self.reverse_mapping[current_code] = root.char

        self.make_codes_helper(root.left, current_code + "0")
        self.make_codes_helper(root.right, current_code + "1")

    def make_codes(self):
        # make codes for characters and save
        root = heapq.heappop(self.heap)
        current_code = ""
        self.make_codes_helper(root, current_code)

    def get_encoded_text(self, text):
        # replace characters with code and return
        encoded_text = ""
        for character in text:
            encoded_text += self.codes[character]
        return encoded_text

    def pad_encoded_text(self, encoded_text):
        # pad encoded text and return
        extra_padding = 8 - len(encoded_text) % 8
        for i in range(extra_padding):
            encoded_text += "0"

        padded_info = "{0:08b}".format(extra_padding)
        encoded_text = padded_info + encoded_text
        return encoded_text


    def get_byte_array(self, padded_encoded_text):

        if(len(padded_encoded_text) % 8 != 0):
            print("Encoded text not padded properly")
            exit(0)
        # convert bits into bytes, return byte array
        b = bytearray()
        for i in range(0, len(padded_encoded_text), 8):
            byte = padded_encoded_text[i:i+8]
            b.append(int(byte, 2))

        return b


    def compress(self):
        filename, file_extension = os.path.splitext(self.path)
        output_path = filename + ".bin"

        with open(self.path, 'r+') as file, open(output_path, 'wb') as output:
            text = file.read()
            text = text.rstrip()

            frequency = self.make_frequency_dict(text)

            self.make_heap(frequency)
            self.merge_nodes()
            self.make_codes()

            encoded_text = self.get_encoded_text(text)
            padded_encoded_text = self.pad_encoded_text(encoded_text)

            b = self.get_byte_array(padded_encoded_text)
            output.write(bytes(b))

        print("Compressed")
        return output_path

    def remove_padding(self, bit_string):
        # remove padding and return
        padded_info = bit_string[:8]
        extra_padding = int(padded_info, 2)

        bit_string = bit_string[8:]
        encoded_text = bit_string[:-1 * extra_padding]

        return encoded_text

    def decode_text(self, encoded_text):
        # decode and return
        current_code = ""
        decoded_text = ""

        for bit in encoded_text:
            current_code += bit
            if(current_code in self.reverse_mapping):
                character = self.reverse_mapping[current_code]
                decoded_text += character
                current_code = ""

        return decoded_text



    def decompress(self, input_path):
        filename, file_extension = os.path.splitext(self.path)
        output_path = filename + "_decompress" + ".txt"

        with open(input_path, 'rb') as file, open(output_path, 'w') as output:
            bit_string = ""

            byte = file.read(1)
            while(len(byte) > 0):
                byte = ord(byte)
                bits = bin(byte)[2:].rjust(8, '0')
                bit_string += bits
                byte = file.read(1)

            encoded_text = self.remove_padding(bit_string)
            decoded_text = self.decode_text(encoded_text)

            output.write(decoded_text)

        print("Decompressed")
        return output_path

path = ('sample.txt')
H = HuffmanCoding(path)
H.compress()
H.decompress('sample.bin')

f = open("sample.bin", mode="rb")

# Reading file data with read() method
data = f.read()

# Knowing the Type of our data
print(type(data))

# Printing our byte sequenced data
print(data)

# Closing the opened file
f.close()
file1 = open('sample_decompress.txt', 'r')
Lines = file1.readlines()

count = 0
# Strips the newline character
for line in Lines:
    count += 1
    print("Line{}: {}".format(count, line.strip()))