blockchain.py

import hashlib
import json
from textwrap import dedent
from time import time
from uuid import uuid4

from flask import Flask, jsonify, request

'''Creat the blockchain class'''
class Blockchain(object):
    def __init__(self):
        self.chain = []
        self.current_transactions = []

        #Creat the genesis block
        self.new_block(previous_hash=1,proof=100)
        
    def new_block(self,proof,previous_hash=None):
        """
        Creat a new Block in the Blockchain
        :param proof: <int> The proof given by the proof of Work algorithm
        :param previous_hash: (Optional) <str> Hash of previous Block
        :return: <dict> New Block
        """
        # Creates a new Block and adds it to the chain
        block = {
            'index': len(self.chain) + 1,
            'timestamp': time(),
            'transactions': self.current_transactions,
            'proof': proof,
            'previous_hash': previous_hash or self.hash(self.chain[-1]),
        }

        #reset the current list of transactions
        self.current_transactions = []

        self.chain.append(block)
        return block
    
    def new_transaction(self, sender, recipient, amount):
        """
        Creats a new transaction to go into the next mined Block
        :param sender: <str> Address of the Sender
        :param recipient: <str> Address of the Recipient
        :param amount: <int> Amount
        :return: <int> The index of the Block that will hold this transaction
        """
        # Adds a new transaction to the list of transactions
        self.current_transactions.append({
            'sender': sender,
            'recipient': recipient,
            'amount': amount
        })

        return self.last_block['index'] + 1
    
    @staticmethod
    def hash(block):
        """
        Creat a SHA-256 hash of a Block
        :param block: <dict> Block
        :return: <str>
        """

        #We must make sure that the Dictionary is Ordered
        #Or we'll have inconsistent hashes
        block_string = json.dumps(block,sort_keys=True).encode()
        return hashlib.sha256(block_string).hexdigest()

    @property
    def last_block(self):
        # Returns the last Block in the chain
        return self.chain[-1]
    
    def proof_of_work(self,last_proof):
        """
        Simple Proof of Work Algorithm:
         - Find a number p' such that hash(pp') contains leading 4 zeros,
           where p is the prvious p'
         - p is the previous proof,and p' is the new proof
         :param last_proof: <int>
         :return: <int>
        """

        proof = 0
        while self.valid_proof(last_proof,proof) is False:
            proof += 1

        return proof
    
    @staticmethod
    def valid_proof(last_proof, proof):
        """
        Validates the Proof: Does hash(last_proof, proof) conrain 4 leading zeroes?
        :param lase_proof: <int> Previous Proof
        :param proof: <int> Current Proof
        :return: <bool> True if correct, False if not.
        """

        guess = f'{last_proof}{proof}'.encode()
        guess_hash = hashlib.sha256(guess).hexdigest()
        return guess_hash[:4] == "0000"


#Instantiate our Node
app = Flask(__name__)

#Generate a globally unique address for this node
node_identifier = str(uuid4()).replace('-', '')

#Instantiate the Blockchain
blockchain = Blockchain()
'''
@app.route('/mine', methods=['GET'])
def mine():
    return "We'll mine a new Block"

@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    return "We'll add a new transaction"
'''

#The APIs can be used in Postman app

@app.route('/mine', methods=['GET'])
def mine():
    #We run the proof of work algorithm to get the next proof...
    last_block = blockchain.last_block
    last_proof = last_block['proof']
    proof = blockchain.proof_of_work(last_proof)

    #We must receive a reward for finding the proof.
    #The sender is '0' to signify that this node has mined a new coin
    blockchain.new_transaction(
        sender="0",
        recipient=node_identifier,
        amount=1,
    )

    #Forge the new Block by adding it to the chain
    block = blockchain.new_block(proof)

    response = {
        'message': "New Block Forge",
        'index': block['index'],
        'transactions': block['transactions'],
        'proof': block['proof'],
        'previous_hash': block['previous_hash']
    }
    return jsonify(response),200

@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json()

    #Check that the required fields are in the POST'ed data
    required = ['sender', 'recipient', 'amount']
    if not all(k in values for k in required):
        return 'Missing valuse', 400
    
    #Creat a new Transaction
    index = blockchain.new_transaction(values['sender'], values['recipient'], values['amount'])

    response = {'message': f'Transaction will be added to Block {index}'}
    return jsonify(response), 201

@app.route('/chain', methods=['GET'])
def full_chain():
    response = {
        'chain': blockchain.chain,
        'length': len(blockchain.chain),
    }
    return jsonify(response),200

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)