#!/usr/bin/env python

import sys, hashlib
from electrum import Interface

"""validate a transaction (SPV)"""


Hash = lambda x: hashlib.sha256(hashlib.sha256(x).digest()).digest()

def rev_hex(s):
    return s.decode('hex')[::-1].encode('hex')

def int_to_hex(i, length=1):
    s = hex(i)[2:].rstrip('L')
    s = "0"*(2*length - len(s)) + s
    return rev_hex(s)


i = Interface({'server':'ecdsa.org:50002:s'})
i.start()


def get_header(i, block_height):
    i.send([('blockchain.block.get_header',[block_height])])
    while True:
        r = i.responses.get(True, 100000000000)
        method = r.get('method') 
        if method == 'blockchain.block.get_header':
            break
    return r.get('result')



def get_merkle(i, tx_hash):

    i.send([('blockchain.transaction.get_merkle',[tx_hash])])
    while True:
        r = i.responses.get(True, 100000000000)
        method = r.get('method') 
        if method == 'blockchain.transaction.get_merkle':
            break

    return r.get('result')


def merkle_root(merkle):

    merkle = map (lambda tx_hash: tx_hash.decode('hex')[::-1], merkle)
    while len(merkle) != 1:
        if len(merkle)%2: merkle.append( merkle[-1] )
        n = []
        while merkle:
            n.append( Hash( merkle[0] + merkle[1] ) )
            merkle = merkle[2:]

        merkle = n
            
    return merkle[0][::-1].encode('hex')


def hash_header(res):
    header = int_to_hex(res.get('version'),4) \
        + rev_hex(res.get('prev_block_hash')) \
        + rev_hex(res.get('merkle_root')) \
        + int_to_hex(int(res.get('timestamp')),4) \
        + int_to_hex(int(res.get('bits')),4) \
        + int_to_hex(int(res.get('nonce')),4)
    return rev_hex(Hash(header.decode('hex')).encode('hex'))


def verify_tx(tx_hash):
    res = get_merkle(i, tx_hash)
    assert res.get('merkle_root') == merkle_root(res['merkle'])
    block_height = res.get('block_height')
    _hash = None
    for height in range(block_height-10,block_height+10):
        header = get_header(i, height)
        if _hash: assert _hash == header.get('prev_block_hash')
        _hash = hash_header(header)
        #print _hash
        if height==block_height:
            assert header.get('merkle_root') == res.get('merkle_root')
        


try:
    tx = sys.argv[1]
except:
    tx = '587430e52af2cec98b3fd543083469ffa7a5f5dd2bd569898a7897a64e2eb031'

verify_tx(tx)