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_prev_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 = 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):
        block_index = 1
        previous_block = chain[0]
        while block_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 = block_index + 1
        return True
    
app = Flask(__name__)

blockchain = Blockchain()

@app.route('/mine_block',methods = ['GET'])
def mine_block():
    previous_block = blockchain.get_prev_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 have mined a block successfully',
                '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

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

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