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

class Blockchain:
   def __init__(self):
       self.chain = []
       self.create_blockchain(proof=1, previous_hash='0')

   def create_blockchain(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):
       last_block = self.chain[-1]
       return last_block
   def proof_of_work(self, previous_proof):
       # miners proof submitted
       new_proof = 1
       # status of proof of work
       check_proof = False
       while check_proof is False:
           # problem and algorithm based off the previous proof and new proof
           hash_operation = hashlib.sha256(str(new_proof ** 2 - previous_proof ** 2).encode()).hexdigest()
           # check miners solution to problem, by using miners proof in cryptographic encryption
           # if miners proof results in 4 leading zero's in the hash operation, then:
           if hash_operation[:4] == '0000':
               check_proof = True
           else:
               # if miners solution is wrong, give mine another chance until correct
               new_proof += 1
       return new_proof
   # generate a hash of an entire block
   def hash(self, block):
       encoded_block = json.dumps(block, sort_keys=True).encode()
       return hashlib.sha256(encoded_block).hexdigest()

   # check if the blockchain is valid
   def is_chain_valid(self, chain):
       # get the first block in the chain and it serves as the previous block
       previous_block = chain[0]
       # an index of the blocks in the chain for iteration
       block_index = 1
       while block_index < len(chain):
           # get the current block
           block = chain[block_index]
           # check if the current block link to previous block has is the same as the hash of the previous block
           if block["previous_hash"] != self.hash(previous_block):
               return False

           # get the previous proof from the previous block
           previous_proof = previous_block['proof']

           # get the current proof from the current block
           current_proof = block['proof']

           # run the proof data through the algorithm
           hash_operation = hashlib.sha256(str(current_proof ** 2 - previous_proof ** 2).encode()).hexdigest()
           # check if hash operation is invalid
           if hash_operation[:4] != '0000':
               return False
           # set the previous block to the current block after running validation on current block
           previous_block = block
           block_index += 1
       return True


app = Flask(__name__)
blockchain = Blockchain()

@app.route('/')


@app.route('/mine_block', methods=['GET'])
def mine_block():
   # get the data we need to create a 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_blockchain(proof, previous_hash)
   response = {'message': 'Block mined!',
               '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.run(host='0.0.0.0', port=5000)