#!/usr/bin/env python
# example of proof-of-work algorithm

import hashlib
import time

try:
    long        # Python 2
    xrange
except NameError:
    long = int  # Python 3
    xrange = range

max_nonce = 2 ** 32  # 4 billion


def proof_of_work(header, difficulty_bits):
    # calculate the difficulty target
    target = 2 ** (256 - difficulty_bits)

    for nonce in xrange(max_nonce):
        hash_result = hashlib.sha256(str(header) + str(nonce)).hexdigest()

        # check if this is a valid result, below the target
        if long(hash_result, 16) < target:
            print("Success with nonce %d" % nonce)
            print("Hash is %s" % hash_result)
            return (hash_result, nonce)

    print("Failed after %d (max_nonce) tries" % nonce)
    return nonce


if __name__ == '__main__':
    nonce = 0
    hash_result = ''

    # difficulty from 0 to 31 bits
    for difficulty_bits in xrange(32):
        difficulty = 2 ** difficulty_bits
        print("Difficulty: %ld (%d bits)" % (difficulty, difficulty_bits))
        print("Starting search...")

        # checkpoint the current time
        start_time = time.time()

        # make a new block which includes the hash from the previous block
        # we fake a block of transactions - just a string
        new_block = 'test block with transactions' + hash_result

        # find a valid nonce for the new block
        (hash_result, nonce) = proof_of_work(new_block, difficulty_bits)

        # checkpoint how long it took to find a result
        end_time = time.time()

        elapsed_time = end_time - start_time
        print("Elapsed Time: %.4f seconds" % elapsed_time)

        if elapsed_time > 0:

            # estimate the hashes per second
            hash_power = float(long(nonce) / elapsed_time)
            print("Hashing Power: %ld hashes per second" % hash_power)
