app.py

import pickle
import hashlib
import time
import plyvel
import struct
from typing import List
from hashlib import sha256
import streamlit as st

# Global constant for target bits
TARGET_BITS = 24

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

    def serialize(self):
        """Serialize the Block object to a byte stream."""
        return pickle.dumps(self.__dict__)

    @staticmethod
    def deserialize(serialized_block):
        """Deserialize a byte stream into a Block object."""
        block_dict = pickle.loads(serialized_block)
        return Block(**block_dict)

    def __repr__(self):
        return (f"Block(index={self.index}, "
                f"timestamp={self.timestamp}, "
                f"data={self.data.decode('utf-8')}, "
                f"prev_block_hash={self.previous_hash.hex()}, "
                f"hash={self.hash.hex()}, "
                f"nonce={self.nonce})")

class ProofOfWork:
    def __init__(self, block: Block):
        self.block = block
        self.target = 1 << (256 - TARGET_BITS)

    def prepare_data(self, nonce: int) -> bytes:
        """Prepare the data to be hashed."""
        return b''.join([
            self.block.previous_hash,
            self.block.data,
            struct.pack('>I', int(self.block.timestamp)),  # Convert timestamp to int
            struct.pack('>I', TARGET_BITS),
            struct.pack('>I', nonce)
        ])

    def run(self) -> (int, bytes):
        """Run the Proof of Work algorithm."""
        nonce = 0
        st.write(f"Mining the block containing \"{self.block.data.decode('utf-8')}\"")
        while nonce < 2**32:  # maxNonce
            data = self.prepare_data(nonce)
            hash = sha256(data).digest()
            st.write(f"\r{hash.hex()}", end="")

            hash_int = int.from_bytes(hash, byteorder='big')
            if hash_int < self.target:
                break
            else:
                nonce += 1
        st.write("\n\n")
        return nonce, hash

    def validate(self) -> bool:
        """Validate the Proof of Work."""
        data = self.prepare_data(self.block.nonce)
        hash = sha256(data).digest()
        hash_int = int.from_bytes(hash, byteorder='big')
        return hash_int < self.target

def new_genesis_block():
    return Block(index=0, previous_hash=b'0'*64, timestamp=time.time(), data='Genesis Block'.encode('utf-8'), nonce=0, hash=b'genesis_hash')

class Blockchain:
    def __init__(self):
        self.db = plyvel.DB('blockchain.db', create_if_missing=True)
        self.tip = self._init_blockchain()

    def _init_blockchain(self):
        """Initialize the blockchain or load the existing one."""
        blocks_bucket = self.db.prefixed_db(b'blocks')
        if blocks_bucket.get(b'l') is None:
            genesis = new_genesis_block()
            blocks_bucket.put(genesis.hash, genesis.serialize())
            blocks_bucket.put(b'l', genesis.hash)
            return genesis.hash
        else:
            return blocks_bucket.get(b'l')

    def add_block(self, data):
        """Add a new block to the blockchain."""
        blocks_bucket = self.db.prefixed_db(b'blocks')
        last_hash = blocks_bucket.get(b'l')

        new_block = Block(index=self.get_block_count(), previous_hash=last_hash, timestamp=time.time(), data=data.encode('utf-8'), nonce=0, hash=b'')
        pow = ProofOfWork(new_block)
        nonce, hash = pow.run()

        new_block.hash = hash
        new_block.nonce = nonce

        blocks_bucket.put(new_block.hash, new_block.serialize())
        blocks_bucket.put(b'l', new_block.hash)
        self.tip = new_block.hash

    def get_block_count(self):
        """Get the number of blocks in the blockchain."""
        blocks_bucket = self.db.prefixed_db(b'blocks')
        return len(list(blocks_bucket))

    def get_last_block_hash(self):
        """Get the hash of the last block in the chain."""
        blocks_bucket = self.db.prefixed_db(b'blocks')
        return blocks_bucket.get(b'l')

    def get_block(self, block_hash):
        """Retrieve a block from the BoltDB by its hash."""
        blocks_bucket = self.db.prefixed_db(b'blocks')
        serialized_block = blocks_bucket.get(block_hash)
        if serialized_block:
            return Block.deserialize(serialized_block)
        return None

    def close(self):
        """Close the database connection."""
        self.db.close()

def print_blockchain(bc):
    last_hash = bc.get_last_block_hash()
    while last_hash:
        block = bc.get_block(last_hash)
        if block is None:
            st.write("Block not found for hash:", last_hash.hex())
            break
        st.write(f"Prev. hash: {block.previous_hash.hex()}")
        st.write(f"Data: {block.data.decode('utf-8')}")
        st.write(f"Hash: {block.hash.hex()}")
        st.write(f"Nonce: {block.nonce}")
        pow = ProofOfWork(block)
        st.write(f"PoW: {pow.validate()}")
        st.write()
        # Stop iterating when we reach the genesis block
        if block.previous_hash == b'0'*64:
            break
        last_hash = block.previous_hash

# Initialize the blockchain
try:
    bc = Blockchain()
except IOError as e:
    st.write(f"Error initializing blockchain: {e}")
    bc = None

if bc:
    try:
        # Add a new block with the Starbucks reusable Holiday cup data
        starbucks_data = "Pay 0.0001 BTC for a Starbucks reusable Holiday cup coffee ($9.20 USD)"
        bc.add_block(starbucks_data)

        # Print the entire blockchain
        print_blockchain(bc)

    finally:
        # Ensure the database is closed properly
        bc.close()

# Streamlit App
st.title("Blockchain Prototype 4")
st.image('Starbucks BTC Model 1.jpeg', caption='Starbucks BTC Model 1')
st.image('Starbucks BTC Model 2.jpeg', caption='Starbucks BTC Model 2')