Add lempel ziv compression (#2107)

* Added lempel-ziv compression algorithm implementation

* Added lempel-ziv decompression algorithm implementation

* Reformatted lempel-ziv compress/decompress files using black

* Added type hints and some other modifications (Doctests coming up)

* Shortened several lines to comply with the standards

compression/lempel_ziv.py

@@ -0,0 +1,125 @@
+"""
+    One of the several implementations of Lempel–Ziv–Welch compression algorithm
+    https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
+"""
+
+import math
+import os
+import sys
+
+
+def read_file_binary(file_path: str) -> str:
+    """
+    Reads given file as bytes and returns them as a long string
+    """
+    result = ""
+    try:
+        with open(file_path, "rb") as binary_file:
+            data = binary_file.read()
+        for dat in data:
+            curr_byte = "{0:08b}".format(dat)
+            result += curr_byte
+        return result
+    except IOError:
+        print("File not accessible")
+        sys.exit()
+
+
+def add_key_to_lexicon(
+    lexicon: dict, curr_string: str, index: int, last_match_id: int
+) -> None:
+    """
+    Adds new strings (curr_string + "0",  curr_string + "1") to the lexicon
+    """
+    lexicon.pop(curr_string)
+    lexicon[curr_string + "0"] = last_match_id
+
+    if math.log2(index).is_integer():
+        for curr_key in lexicon:
+            lexicon[curr_key] = "0" + lexicon[curr_key]
+
+    lexicon[curr_string + "1"] = bin(index)[2:]
+
+
+def compress_data(data_bits: str) -> str:
+    """
+    Compresses given data_bits using Lempel–Ziv–Welch compression algorithm
+    and returns the result as a string
+    """
+    lexicon = {"0": "0", "1": "1"}
+    result, curr_string = "", ""
+    index = len(lexicon)
+
+    for i in range(len(data_bits)):
+        curr_string += data_bits[i]
+        if curr_string not in lexicon:
+            continue
+
+        last_match_id = lexicon[curr_string]
+        result += last_match_id
+        add_key_to_lexicon(lexicon, curr_string, index, last_match_id)
+        index += 1
+        curr_string = ""
+
+    while curr_string != "" and curr_string not in lexicon:
+        curr_string += "0"
+
+    if curr_string != "":
+        last_match_id = lexicon[curr_string]
+        result += last_match_id
+
+    return result
+
+
+def add_file_length(source_path: str, compressed: str) -> str:
+    """
+    Adds given file's length in front (using Elias  gamma coding) of the compressed
+    string
+    """
+    file_length = os.path.getsize(source_path)
+    file_length_binary = bin(file_length)[2:]
+    length_length = len(file_length_binary)
+
+    return "0" * (length_length - 1) + file_length_binary + compressed
+
+
+def write_file_binary(file_path: str, to_write: str) -> None:
+    """
+    Writes given to_write string (should only consist of 0's and 1's) as bytes in the
+    file
+    """
+    byte_length = 8
+    try:
+        with open(file_path, "wb") as opened_file:
+            result_byte_array = [
+                to_write[i : i + byte_length]
+                for i in range(0, len(to_write), byte_length)
+            ]
+
+            if len(result_byte_array[-1]) % byte_length == 0:
+                result_byte_array.append("10000000")
+            else:
+                result_byte_array[-1] += "1" + "0" * (
+                    byte_length - len(result_byte_array[-1]) - 1
+                )
+
+            for elem in result_byte_array:
+                opened_file.write(int(elem, 2).to_bytes(1, byteorder="big"))
+    except IOError:
+        print("File not accessible")
+        sys.exit()
+
+
+def compress(source_path, destination_path: str) -> None:
+    """
+    Reads source file, compresses it and writes the compressed result in destination
+    file
+    """
+    data_bits = read_file_binary(source_path)
+    compressed = compress_data(data_bits)
+    compressed = add_file_length(source_path, compressed)
+    write_file_binary(destination_path, compressed)
+
+
+if __name__ == "__main__":
+    compress(sys.argv[1], sys.argv[2])

compression/lempel_ziv_decompress.py

@@ -0,0 +1,111 @@
+"""
+    One of the several implementations of Lempel–Ziv–Welch decompression algorithm
+    https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
+"""
+
+import math
+import sys
+
+
+def read_file_binary(file_path: str) -> str:
+    """
+    Reads given file as bytes and returns them as a long string
+    """
+    result = ""
+    try:
+        with open(file_path, "rb") as binary_file:
+            data = binary_file.read()
+        for dat in data:
+            curr_byte = "{0:08b}".format(dat)
+            result += curr_byte
+        return result
+    except IOError:
+        print("File not accessible")
+        sys.exit()
+
+
+def decompress_data(data_bits: str) -> str:
+    """
+    Decompresses given data_bits using Lempel–Ziv–Welch compression algorithm
+    and returns the result as a string
+    """
+    lexicon = {"0": "0", "1": "1"}
+    result, curr_string = "", ""
+    index = len(lexicon)
+
+    for i in range(len(data_bits)):
+        curr_string += data_bits[i]
+        if curr_string not in lexicon:
+            continue
+
+        last_match_id = lexicon[curr_string]
+        result += last_match_id
+        lexicon[curr_string] = last_match_id + "0"
+
+        if math.log2(index).is_integer():
+            newLex = {}
+            for curr_key in list(lexicon):
+                newLex["0" + curr_key] = lexicon.pop(curr_key)
+            lexicon = newLex
+
+        lexicon[bin(index)[2:]] = last_match_id + "1"
+        index += 1
+        curr_string = ""
+    return result
+
+
+def write_file_binary(file_path: str, to_write: str) -> None:
+    """
+    Writes given to_write string (should only consist of 0's and 1's) as bytes in the
+    file
+    """
+    byte_length = 8
+    try:
+        with open(file_path, "wb") as opened_file:
+            result_byte_array = [
+                to_write[i : i + byte_length]
+                for i in range(0, len(to_write), byte_length)
+            ]
+
+            if len(result_byte_array[-1]) % byte_length == 0:
+                result_byte_array.append("10000000")
+            else:
+                result_byte_array[-1] += "1" + "0" * (
+                    byte_length - len(result_byte_array[-1]) - 1
+                )
+
+            for elem in result_byte_array[:-1]:
+                opened_file.write(int(elem, 2).to_bytes(1, byteorder="big"))
+    except IOError:
+        print("File not accessible")
+        sys.exit()
+
+
+def remove_prefix(data_bits: str) -> str:
+    """
+    Removes size prefix, that compressed file should have
+    Returns the result
+    """
+    counter = 0
+    for letter in data_bits:
+        if letter == "1":
+            break
+        counter += 1
+
+    data_bits = data_bits[counter:]
+    data_bits = data_bits[counter + 1 :]
+    return data_bits
+
+
+def compress(source_path: str, destination_path: str) -> None:
+    """
+    Reads source file, decompresses it and writes the result in destination file
+    """
+    data_bits = read_file_binary(source_path)
+    data_bits = remove_prefix(data_bits)
+    decompressed = decompress_data(data_bits)
+    write_file_binary(destination_path, decompressed)
+
+
+if __name__ == "__main__":
+    compress(sys.argv[1], sys.argv[2])