Merge pull request #2 from KenLearnsCoding/Cryptochain

Cryptochain

Blockchain_2/Blockchain/blockchain.py

@@ -0,0 +1,183 @@
+# create a Blockchain. 
+# A blockchain is a chain of blocks that contain data or information.
+
+# To be installed: pip install Flask
+# Download Postman to test the API
+# Importing the libraries
+import datetime # to get the current time
+import hashlib # to hash the blocks
+import json # to encode the blocks before hashing
+from flask import Flask, jsonify # to create the web app
+
+# Part 1 - Building a Blockchain.  
+class Blockchain: 
+    # this init like a constructor
+    # Self is the object that we are going to create
+    def __init__(self):
+        # create a chain
+        self.chain = []
+        # create the block
+        self.create_block(
+            proof = 1, 
+            previous_hash='0'
+        )
+
+    def create_block(self, proof, previous_hash):
+        #create the block with its properties
+        block= {
+            'index': len(self.chain) + 1, 
+            'timestamp': str(datetime.datetime.now()),# get the timestamp
+            'proof': proof, # pass proof of work here  from postman
+            'previous_hash': previous_hash, # pass the previous hash from postman
+        }
+        # append the block to the chain
+        self.chain.append(block)
+
+        # return the block to where the create_block function is called
+        return block
+
+    # get the previous block in the chain
+    def get_previous_block(self):
+        # get the last block in the chain
+        return self.chain[-1]
+
+    # proof of work
+    def proof_of_work(self, previous_proof):
+        new_proof = 1 # start with 1
+        check_proof = False # check if the proof is valid
+        while check_proof is False: 
+            # create a hash operation
+            hash_operation = hashlib.sha256(str(new_proof**2 - previous_proof**2).encode()).hexdigest()
+
+            # check if the first 4 characters of the hash are 0000
+            if hash_operation[:4] == '0000':
+                check_proof = True
+            else: 
+                new_proof += 1
+
+        return new_proof
+
+    def hash(self, block):
+        # encode the block before hashing  into the right format
+        encode_block = json.dumps(block, sort_keys = True).encode()
+
+        # return the hash of the block
+        return hashlib.sha256(encode_block).hexdigest()
+
+    # check the chain is valid or not
+    def is_chain_valid(self, chain):
+        # start checking the first block in the chain
+        previous_block = chain[0]
+
+        # each block has a number of block
+        block_index = 1
+
+        # loop through the chain
+        while block_index < len(chain):  #check the first block in the chain till the last block
+
+            #get the current block
+            block = chain[block_index]
+
+            # check if the previous hash of the current block is equal to the hash of the previous block
+            if block['previous_hash'] != self.hash(previous_block):
+                return False
+
+            # check if the proof of the previous block is valid
+            previous_proof = previous_block['proof']
+
+            # get the proof of the current block
+            proof = block['proof']
+
+            # create a hash operation to check if the proof is valid with the previous proof or not
+            hash_operation = hashlib.sha256(str(proof**2 - previous_proof**2).encode()).hexdigest()
+
+            # check the first 4 characters of the hash are 0000 or not
+            if hash_operation[:4] != '0000':
+                return False
+
+            # save the current block as the previous block for the next loop
+            previous_block = block
+
+            # update the block index
+            block_index += 1
+
+        return True
+
+# Part 2 - Mining our Blockchain
+# creating a web app
+app = Flask(__name__)
+app.config['JSONIFY_PRETTYPRINT_REGULAR'] = False
+
+# Creating a Blockchain
+blockchain = Blockchain()
+
+# Mining a new block
+@app.route('/mine_block', methods = ['GET']) # define the route
+
+# creating the mine_block function
+def mine_block():
+    # assign the previous block to the previous_block variable
+    previous_block = blockchain.get_previous_block()
+
+    # assign the previous proof to the previous_proof variable
+    previous_proof = previous_block['proof']
+
+    # assign the proof of the current block to the proof variable
+    proof = blockchain.proof_of_work(previous_proof)
+
+    # assign the previous hash to the previous_hash variable
+    previous_hash = blockchain.hash(previous_block)
+
+    # assign the current block to the block variable
+    block = blockchain.create_block(proof, previous_hash)
+
+    # create a response to return to the user
+    response = {
+        'message': 'Congratulation! you just mined a block!',
+        'index': block['index'], 
+        'timestamp': block['timestamp'],
+        'proof': block['proof'],
+        'previous_hash': block['previous_hash']
+    }
+
+    return jsonify(response), 200 # return the response to the user
+
+# Getting the full Blockchain
+@app.route('/get_chain', methods = ['GET'])
+
+# creating the get_chain function to get the full chain
+def get_chain():
+    # create a response to return to the user
+    response = {
+        'chain': blockchain.chain,
+        'length': len(blockchain.chain)
+    }
+
+    return jsonify(response), 200
+
+# Getting the full Blockchain
+@app.route('/is_valid', methods = ['GET'])
+
+# creating the is_valid function to check if the chain is valid or not
+def is_valid():
+    # get the chain and assign it to the chain variable
+    is_valid = blockchain.is_chain_valid(blockchain.chain)
+
+    # check if the chain is valid or not and return the response to the user
+    if is_valid: 
+        response = {
+            'message': 'All good. The Blockchain is valid.'
+        }
+    else: 
+        response = {
+            'message': 'Houston, we have a problem. The Blockchain is not valid.'
+        }
+
+    return jsonify(response), 200
+
+
+
+
+# Running the app
+app.run(host = '0.0.0.0', port = 5001)
+