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


# Building a Blockchain
class Blockchain:
    def __init__(self):
        """
        Create Blockchain and a genesis block
        """
        self.chain = []
        self.create_block(proof=1, previous_hash='0')

    def create_block(self, proof, previous_hash):
        """
        :param proof: Proof of new block
        :param previous_hash: hash of the previous block in Blockchain
        :return: newly created block
        """
        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: Last block of Blockchain
        """
        return self.chain[-1]

    def proof_of_work(self, previous_proof):
        """
        :param previous_proof: hash of the previous block in Blockchain
        :return: proof on new block
        """
        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):
        """
        :param block: A block in a Blockchain
        :return: hash of the block
        """
        encoded_block = json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(encoded_block).hexdigest()

    def is_chain_valid(self, chain):
        """
        :param chain: list of blocks in Blockchain
        :return: True if chain is valid, otherwise False
        """
        block_index = 1
        previous_block = chain[0]

        while block_index < len(chain):
            block = chain[block_index]
            # Checks if previous_hash of current block is equal to hash of previous block
            if block['previous_hash'] != self.hash(previous_block):
                return False

            # Check if proof of current block satisfies the 4 zeroes condition or not
            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 a web app
app = Flask(__name__)

# Creating a Blockchain
blockchain = Blockchain()


# 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)

    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


# 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('/is_valid', methods=['GET'])
def is_valid():
    if blockchain.is_chain_valid(blockchain.chain):
        response = {'message': 'All good. The Blockchain is valid.'}
    else:
        response = {'message': 'We have a problem. The Blockchain is not valid'}
    return jsonify(response), 200


# Running the app
app.run(host='0.0.0.0', port=1710)
