blockchain.py

import hashlib
import json
from time import time
from uuid import uuid4
from urllib.parse import urlparse
import requests

class Blockchain(object):

	def __init__(self):
		self.chain = []
		self.current_transactions = []
		self.new_block(previous_hash=1,proof=100)
		self.nodes = set()

	def register_node(self,address):
		parsed_url = urlparse(address)
		self.nodes.add(parsed_url.netloc)

	def valid_chain(self,chain):
		last_block = chain[0]
		current_index = 1
		while current_index < len(chain):
			block = chain[current_index]
			print(f"{last_block}")
			print(f"{block}")
			print("\n---------------------------------------------------------------------------------------------------\n")
			if block["previous_hash"] != self.hash(last_block):
				return False
			if not self.valid_proof(last_block["proof"],block["proof"]):
				return False
			last_block = block
			current_index+=1
		return True
	def resolve_conflicts(self):
		neighbors = self.nodes
		new_chain = None
		max_length = len(self.chain)
		for node in neighbors:
			response = requests.get(f'http://{node}/chain')
			if response.status_code == 200:
				length = response.json()["length"]
				chain = response.json()["chain"]

				if length > max_length and self.valid_chain(chain):
					max_length = length
					new_chain = chain
		if new_chain:
			self.chain = new_chain
			return True
		else:
			return False
	def proof_of_work(self,last_proof):
		proof = 0
		while self.valid_proof(last_proof,proof) is False:
			proof += 1
		return proof
	@staticmethod
	def valid_proof(last_proof,proof):
		guess = f"{last_proof}{proof}".encode()
		guess_hash = hashlib.sha256(guess).hexdigest()
		return guess_hash[:4] == "0000"
	def new_block(self,proof,previous_hash=None):
		block = {
		'index': len(self.chain) + 1,
		'timestamp': time(),
		'transactions': self.current_transactions,
		'proof': proof,
		'previous_hash': previous_hash or self.hash(self.chain[-1]),
		}
		self.current_transactions = []
		self.chain.append(block);
		return block
	def new_transaction(self,sender,recipient,amount):

		self.current_transactions.append({'sender':sender,'recipient':recipient,'amount':amount})
		return self.last_block['index'] + 1;
	@staticmethod
	def hash(block):
		block_string = json.dumps(block,sort_keys = True).encode()
		return hashlib.sha256(block_string).hexdigest()
	@property
	def last_block(self):
		return self.chain[-1]