blockchain.py

import datetime
import hashlib
import json
from flask import Flask, jsonify


class Blockchain:
    
    def __init__(self):
        self.chain = []
        self.create_block(proof = 1,previous_hash = '0')
        
    def create_block(self, proof, previous_hash):
        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,
                 'previous_hash': previous_hash,}
        self.chain.append(block)
        return block
    def get_previous_block(self):
        return self.chain[-1]
        
    def proof_of_work(self, previous_proof):
        new_proof = 1
        check_proof = False
        while check_proof is False:
            hash_operation = hashlib.sha256(str(new_proof**2 - previous_proof**2).encode()).hexdigest()
            if hash_operation[:4] == '0000' : 
                check_proof = True
            else:
                new_proof += 1
            return new_proof 
    
    def hash(self, block):
        encoded_block = json.dumps(block, sort_keys= True).encode()
        return hashlib.sha256(encoded_block).hexdigest()
    
    def is_chain_valid(self, chain):
        previous_block = chain[0]
        block_index = 1
        while bock_index < len(chain):
            block = chain[block_index]
            if block['previous_hash'] != self.hash(previous_block):
                return False
            previous_proof = previous_block['proof']
            proof = block['proof']
            hash_operation = hashlib.sha256(str(proof**2 - previous_proof**2).encode()).hexdigest()
            if hash_operation[:4] != '0000':
                return False
            previous_block = block
            block_index += 1
        return True
    

# Creating webapp
app = Flask(__name__)

#creating a block chain
blockchain = Blockchain()

#mining blockchain
@app.route('/mine_block', methods=['GET'])
def mine_block():
    previous_block = blockchain.get_previous_block()
    previous_proof = previous_block['proof']
    proof = blockchain.proof_of_work(previous_proof)
    previous_hash = blockchain.hash(previous_block)
    block = blockchain.create_block(proof, previous_hash)
    response = {'message': 'Congratulations, you just mined a block!',
                'index':block['index'],
                'timestamp': block['timestamp'],
                'proof': block['proof'],
                'previous_hash' : block['previous_hash']}
    return jsonify(response), 200

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

#running the app
app.run(host = '0.0.0.0', port = 5000)