
# Module 2 - Creating CryptoCurrency DjukaCoin

# =======================
# This client is Dennis Rodman
# =======================

# To be installed:
# Flask == 0.12.2: pip install Flask==0.12.2
# Postman: https://www.getpostman.com/
# requests: requests==2.18.4: pip install requests==2.18.4

import datetime
import hashlib
import json
from flask import Flask, jsonify, request
import requests
from uuid import uuid4
from urllib.parse import urlparse


class Blockchain:

    def __init__(self):
        self.chain = []
        # -- Create a list of transactions
        self.transactions = []
        # -- Add genesis block
        self.create_block(proof=1, previous_hash='0')
        self.nodes = set()

    def create_block(self, proof, previous_hash):
        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,
                 'previous_hash': previous_hash,
                 'transactions': self.transactions
                 }
        self.transactions = []
        self.chain.append(block)
        return block

    def get_previous_block(self):
        return self.chain[-1]

    # Create a problem that is hard to find but easy to verify
    # This will be needed for the create block function
    def proof_of_work(self, previous_proof):
        new_proof = 1
        check_proof = False
        while check_proof is False:
            # The problem that miners have to solve
            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 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 += 1
        return True

    def add_transaction(self, sender, receiver, amount):
        self.transactions.append({'sender': sender,
                                  'receiver': receiver,
                                  'amound': amount})
        previous_block = self.get_previous_block()
        return previous_block['index'] + 1

    def add_node(self, address):
        # -- Parse address of the node
        parsed_url = urlparse(address)
        self.nodes.add(parsed_url.netloc)

    def replace_chain(self):
        # -- Looking for longest chain
        network = self.nodes
        longest_chain = None
        max_length = len(self.chain)
        for node in network:
            # -- Call api for this nodes netloc
            response = requests.get(f'http://{node}/get-chain')
            # -- Do other stuff if the response is 200 OK
            if response.status_code == 200:
                length = response.json()['length']
                chain = response.json()['chain']
                if length > max_length and self.is_chain_valid(chain):
                    max_length = length
                    longest_chain = chain
        # -- If the longest chain is not None that means that it was replaced
        if longest_chain:
            self.chain = longest_chain
            return True
        return False

# Creating a web app
app = Flask(__name__)

# Part 2 - Mining our Blockchain
blockchain = Blockchain()

# -- Create address for the node on Port 5000
node_address = str(uuid4()).replace('-', '')

# Mining a new block
@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)
    blockchain.add_transaction(sender=node_address, receiver='Dennis Rodman', amount=1)
    block = blockchain.create_block(proof, previous_hash)
    response = {'message': 'Congrats! You just mined a block!',
                'index': block['index'],
                'timestamp': block['timestamp'],
                'proof': block['proof'],
                'previous_hash': block['previous_hash'],
                'transactions': block['transactions']}
    return jsonify(response), 200


# Getting the full Blockchain
@app.route('/get-chain', methods=['GET'])
def get_chain():
    response = {'chain': blockchain.chain,
                'length': len(blockchain.chain)}
    return jsonify(response), 200


# Checking if the Blockchain is valid
@app.route('/check-chain-valid', methods=['GET'])
def check_chain_valid():
    response = {'is-chain-valid': blockchain.is_chain_valid(blockchain.chain)}
    return jsonify(response), 200


# -- Adding transaction to blockchain
@app.route('/add-transaction', methods=['POST'])
def add_transaction():
    json = request.get_json()
    transaction_keys = ['sender', 'receiver', 'amount']
    if not all(key in json for key in transaction_keys):
        return 'Some elements of the transaction are missing!', 400
    index = blockchain.add_transaction(json['sender'], json['receiver'], json['amount'])
    response = {'message': f'This transaction will be added to Block {index}'}
    return jsonify(response), 201


# -- Connecting new nodes
@app.route('/connect-node', methods=['POST'])
def connect_node():
    json = request.get_json()
    nodes = json.get('nodes')
    if nodes is None:
        return 'No nodes!', 400
    for node in nodes:
        blockchain.add_node(node)
    response = {
        'message': f'All nodes are now connected. The DjukaCoin now contains the following nodes:',
        'total-nodes': list(blockchain.nodes)
    }
    return jsonify(response), 201


# Replacing the chain by the longest chain if needed
@app.route('/replace-chain', methods=['GET'])
def replace_chain():
    is_chain_replaced = blockchain.replace_chain()
    if is_chain_replaced:
        response = {'message': f'The nodes had different chains so the chain was replaced by the longest one',
                    'new-chain': blockchain.chain}
    else:
        response = {'message': f'All good the chain is the longest one.',
                    'actual-chain': blockchain.chain}
    return jsonify(response), 200


# Running the app
app.run(host='0.0.0.0', port=5003)

