blockchain.py

import hashlib
import time

class Block:
    def __init__(self, index, previous_hash, timestamp, data, nonce=0):
        self.index = index
        self.previous_hash = previous_hash
        self.timestamp = timestamp
        self.data = data
        self.nonce = nonce
        self.hash = self.calculate_hash()

    def calculate_hash(self):
        block_string = f"{self.index}{self.previous_hash}{self.timestamp}{self.data}{self.nonce}"
        return hashlib.sha256(block_string.encode()).hexdigest()

class Blockchain:
    def __init__(self):
        self.chain = [self.create_genesis_block()]

    def create_genesis_block(self):
        return Block(0, "0", time.time(), "Genesis Block")

    def get_latest_block(self):
        return self.chain[-1]

    def add_block(self, new_data):
        last_block = self.get_latest_block()
        new_index = last_block.index + 1
        new_timestamp = time.time()
        new_block = Block(new_index, last_block.hash, new_timestamp, new_data)
        mined_block = self.proof_of_work(new_block)
        self.chain.append(mined_block)

    def proof_of_work(self, block, difficulty=4):
        prefix = '0' * difficulty
        while not block.hash.startswith(prefix):
            block.nonce += 1
            block.hash = block.calculate_hash()
        return block

    def is_chain_valid(self):
        for i in range(1, len(self.chain)):
            current = self.chain[i]
            prev = self.chain[i - 1]

            if current.hash != current.calculate_hash():
                return False
            if current.previous_hash != prev.hash:
                return False
        return True