blockchain.py

import hashlib
import json
import os
from time import time

BLOCKCHAIN_DIR = os.curdir + "/blocks/"


def check_blocks_integrity():
    result = []
    cur_proof = -1
    for i in range(2, int(get_next_block())):
        prev_index = str(i - 1)
        cur_index = str(i)
        tmp = {"block": "", "result": "", "proof": ""}
        try:
            file_dict = json.load(open(f"{BLOCKCHAIN_DIR}{cur_index}.json"))
            cur_hash = file_dict["prev_hash"]
            cur_proof = file_dict["proof"]
        except Exception as e:
            print(e)

        try:
            prev_hash = hashlib.sha256(
                open(BLOCKCHAIN_DIR + prev_index + ".json", "rb").read()
            ).hexdigest()
        except Exception as e:
            print(e)

        tmp["block"] = prev_index
        tmp["proof"] = cur_proof
        if cur_hash == prev_hash:
            tmp["result"] = "ok"
        else:
            tmp["result"] = "error"
        result.append(tmp)
    return result


def check_block(index):
    cur_index = str(index)
    prev_index = str(int(index) - 1)
    cur_proof = -1
    cur_hash = 0
    prev_hash = 0
    tmp = {"block": "", "result": "", "proof": ""}
    try:
        file_dict = json.load(open(BLOCKCHAIN_DIR + cur_index + ".json"))
        cur_hash = file_dict["prev_hash"]
        cur_proof = file_dict["proof"]
    except Exception as e:
        print(e)
    try:
        prev_hash = hashlib.sha256(
            open(BLOCKCHAIN_DIR + prev_index + ".json", "rb").read()
        ).hexdigest()
    except Exception as e:
        print(e)
    tmp["block"] = prev_index
    tmp["proof"] = cur_proof
    if cur_hash == prev_hash:
        tmp["result"] = "ok"
    else:
        tmp["result"] = "error"
    return tmp


def get_hash(file_name):
    file_name = str(file_name)
    if not file_name.endswith(".json"):
        file_name += ".json"
    try:
        with open(BLOCKCHAIN_DIR + file_name, "rb") as file:
            return hashlib.sha256(file.read()).hexdigest()
    except Exception:
        print(f"File {file_name} is not found")
        raise


def get_next_block():
    files = os.listdir(BLOCKCHAIN_DIR)
    index_list = [int(file.split(".")[0]) for file in files]
    cur_index = sorted(index_list)[-1]
    next_index = cur_index + 1
    return str(next_index)


def is_valid_proof(last_proof, proof, difficulty):
    guess = f"{last_proof}{proof}".encode()
    guess_hash = hashlib.sha256(guess).hexdigest()
    return guess_hash[:difficulty] == "0" * difficulty


def get_POW(file_name, difficulty=1):
    # POW - proof of work
    file_name = str(file_name)
    if file_name.endswith(".json"):
        file_name = int(file_name.split(".")[0])
    else:
        file_name = int(file_name)

    last_proof = json.load(open(BLOCKCHAIN_DIR + str(file_name - 1) + ".json"))["proof"]
    proof = 0
    while is_valid_proof(last_proof, proof, difficulty) is False:
        proof += 1
    cur_block = json.load(open(BLOCKCHAIN_DIR + str(file_name) + ".json"))
    cur_block["proof"] = proof
    cur_block["prev_hash"] = get_hash(str(file_name - 1))
    with open(BLOCKCHAIN_DIR + str(file_name) + ".json", "w") as file:
        json.dump(cur_block, file, indent=4, ensure_ascii=False)


def write_block(text, make_proof=False):
    cur_index = get_next_block()
    prev_index = str(int(cur_index) - 1)
    prev_block_hash = get_hash(prev_index)
    data = {
        "text": text,
        "prev_hash": prev_block_hash,
        "timestamp": time(),
        "proof": -1,
        "index": cur_index,
    }

    with open(f"{BLOCKCHAIN_DIR}{cur_index}.json", "w") as file:
        json.dump(data, file, indent=4, ensure_ascii=False)
    if make_proof:
        get_POW(str(cur_index))


if __name__ == "__main__":
    for data in range(10):
        write_block(str(data), True)
    for data in range(2, 10):
        print(check_block(str(data)))
    print(check_blocks_integrity())