diff --git a/.github/workflows/run_tests.yml b/.github/workflows/run_tests.yml
new file mode 100644
index 0000000..0695e93
--- /dev/null
+++ b/.github/workflows/run_tests.yml
@@ -0,0 +1,29 @@
+name: Python application
+
+on: [push]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.13
+      uses: actions/setup-python@v3
+      with:
+        python-version: "3.13"
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install ruff
+        pip install pytest
+    - name: Lint with ruff
+      run: |
+        ruff check --output-format=github
+    - name: Test with pytest
+      run: |
+        pytest
\ No newline at end of file
diff --git a/haffman_code/code/decoding.py b/haffman_code/code/decoding.py
new file mode 100644
index 0000000..63c2356
--- /dev/null
+++ b/haffman_code/code/decoding.py
@@ -0,0 +1,39 @@
+import pickle
+import struct
+
+def decode(encoding: str, dictionary: dict[str, str]) -> str:
+    reverse_dict = {value: key for key, value in dictionary.items()}
+    
+    decoded_letters = []
+    current_letter = ""
+    
+    for bit in encoding:
+        current_letter += bit
+        if current_letter in reverse_dict:
+            decoded_letters.append(reverse_dict[current_letter])
+            current_letter = ""
+    
+    return ''.join(decoded_letters)
+
+
+
+def decode_file(input_file: str, output_file: str):
+    with open(input_file, 'rb') as f:
+        padding = struct.unpack('B', f.read(1))[0]
+            
+        table_len = struct.unpack('I', f.read(4))[0]
+        table = f.read(table_len)
+        codes_table = pickle.loads(table)
+
+        encoded_bytes = f.read()
+        
+    code = ''.join(f'{byte:08b}' for byte in encoded_bytes)
+        
+    if padding > 0:
+        code = code[:-padding]
+        
+    decoded_text = decode(code, codes_table)
+        
+    with open(output_file, 'w', encoding="utf-8") as file:
+        file.write(decoded_text)
+
diff --git a/haffman_code/code/encoding.py b/haffman_code/code/encoding.py
new file mode 100644
index 0000000..a9fdf6a
--- /dev/null
+++ b/haffman_code/code/encoding.py
@@ -0,0 +1,78 @@
+import pickle
+import struct
+
+class TreeNode:
+    def __init__(self, value: str):
+        self.left: None | TreeNode = None
+        self.right: None | TreeNode = None
+        self.value = value
+
+def sorted_insert(lst: list, value, key):
+    target_idx = 0
+    for i in range(len(lst)):
+        target_idx = i
+        if key(lst[i]) > key(value):
+            break
+    lst.insert(target_idx, value)
+
+def encode(inp: str) -> tuple[str, dict[str, str]]:
+    output_string = ""
+    dictionary = {}
+
+    frequencies = {}
+    for chr in inp:
+        if chr in frequencies:
+            frequencies[chr] += 1
+        else:
+            frequencies[chr] = 1
+    srt = sorted(list(frequencies.items()), key=lambda x: x[1])
+    nodes = [(TreeNode(char), value) for (char, value) in srt]
+
+    while len(nodes) > 1:
+        s1, s2 = nodes.pop(0), nodes.pop(0)
+        node = TreeNode(s1[0].value + s2[0].value)
+        node.left = s1[0]
+        node.right = s2[0]
+        sorted_insert(nodes, (node, s1[1] + s2[1]), lambda x: x[1])
+
+    root = nodes[0][0]
+
+    def walk(node, acc):
+            if node.left is None and node.right is None:
+                dictionary[node.value] = acc
+            else:
+                if node.left is not None:
+                    walk(node.left, acc + "0")
+                if node.right is not None:
+                    walk(node.right, acc + "1")
+
+    walk(root, "")
+            
+    for ch in inp:
+        output_string += dictionary[ch]
+    
+    return (output_string, dictionary)
+
+def encode_file(input_file: str, output_file: str):
+    with open(input_file, "r", encoding="utf-8") as file:
+        text = file.read()
+
+    code, dictionary = encode(text)
+    padding = 8 - len(code) % 8
+    if padding == 8:
+        padding = 0
+    code += '0' * padding
+
+    encoded_bytes = bytearray()
+    for i in range(0, len(code), 8):
+        byte = code[i:i+8]
+        encoded_bytes.append(int(byte, 2))
+
+    with open(output_file, "wb") as file:
+        file.write(struct.pack("B", padding))
+        table = pickle.dumps(dictionary)
+        file.write(struct.pack("I", len(table)))
+        file.write(table)
+        file.write(encoded_bytes)
+
+
diff --git a/haffman_code/code/origin_file.txt b/haffman_code/code/origin_file.txt
new file mode 100644
index 0000000..5dd01c1
--- /dev/null
+++ b/haffman_code/code/origin_file.txt
@@ -0,0 +1 @@
+Hello, world!
\ No newline at end of file
diff --git a/haffman_code/code/test_coding.py b/haffman_code/code/test_coding.py
new file mode 100644
index 0000000..fdc9598
--- /dev/null
+++ b/haffman_code/code/test_coding.py
@@ -0,0 +1,14 @@
+from encoding import encode_file
+from decoding import decode_file
+
+def make_file(str):
+    with open(str, 'w', encoding = 'utf-8') as file:
+        file.write('Hello, World!')
+
+def test_unit():
+    make_file('origin_file.txt')
+    encode_file("origin_file.txt", "encoding_file.txt")
+    decode_file("encoding_file.txt", "decoding_file.txt")
+    origin_file = open('origin_file.txt').read()
+    decoding_file = open('decoding_file.txt').read()
+    assert origin_file == decoding_file
\ No newline at end of file