import time, hashlib, json

"""

Created by trustgeek on 2017-10-23 (11:04).

"""

class Block:

def __init__(self, index, timestamp, data, previous_hash):

self._index = index

self._timestamp = timestamp

self._data = data

self._previous_hash = previous_hash

self._nounce = None

self._hash = self.hash()

def valid_hash(self, the_hash):

return the_hash.startswith('0000')

def mined(self):

return self._nounce is not None

def mine(self):

start_time = time.time()

the_nounce = self._nounce or 0

while True:

the_hash = self.hash(nonce=the_nounce)

if self.valid_hash(the_hash):

self._hash = the_hash

self._nounce = the_nounce

end_time = time.time()

time_taken = end_time - start_time

print("----- Mine time: %s -----" % time_taken)

return

else:

the_nounce += 1

def hash(self, nonce=None):

self._nounce = nonce or self._nounce

block_json = {'index': self._index, 'timestamp': self._timestamp, 'data': self._data,

'previous_hash': self._previous_hash, 'nounce': self._nounce}

return hashlib.sha256(json.dumps(block_json).encode('utf-8')).hexdigest()

def __str__(self):

return json.dumps(

{'index': self._index, 'timestamp': self._timestamp, 'data': self._data,

'previous_hash': self._previous_hash,

'hash': self._hash, 'nounce': self._nounce})

# genesis block is the first block in the blockchain

def genesis_block():

return Block(0, time.time(), "This is genesis block", '0')

# create next block for blockchain

def next_block(_previous_block, data):

_new_index = _previous_block._index + 1

_new_timestamp = time.time()

_previous_hash = _previous_block._hash

return Block(_new_index, _new_timestamp, data, _previous_hash)

blockchain = [genesis_block()]

# first block for blockchain

previous_block = blockchain[0]

num_of_blocks = 20

# iteratively adding block to blockchain

for i in range(0, num_of_blocks):

transaction = {'from': '0x12345' + str(i), 'to': '0x54321' + str(i * 3), 'amount': 100}

new_block = next_block(previous_block, transaction)

new_block.mine()

blockchain.append(new_block)

previous_block = new_block

print("Block added to blockchain")

print(new_block)