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import hashlib
import struct

####http://python-bitcoinlib.readthedocs.org/en/latest/_modules/bitcoin/core/serialize.html
def uint256_from_str(s):
    """Convert bytes to uint256"""
    r = 0
    t = struct.unpack(b"<IIIIIIII", s[:32])
    for i in range(8):
        r += t[i] << (i * 32)
    return r

def uint256_from_compact(c):
    """Convert compact encoding to uint256
    Used for the nBits compact encoding of the target in the block header. """
    nbytes = (c >> 24) & 0xFF
    v = (c & 0xFFFFFF) << (8 * (nbytes - 3))
    return v 
####

def reverse_byte_order(data):
    return data[::-1]

def get_merkle_parents(data):
    if len(data) % 2:
        data.append(data[-1])
    hashes = []
    half = len(data) / 2
    for i in range(half):
        hashes.append((dsha256(data[i * 2] + data[i * 2 + 1])))
    if len(hashes) == 1:
        return hashes
    return hashes + get_merkle_parents(hashes)

def get_merkle_tree(txs_data):
    """hex in, hex out"""
    if len(txs_data) == 0:
        return 0
    if len(txs_data) == 1:
        #return dsha256(txs_data[0])
        return [txs_data[0]]
    txs_data_rev = []
    for t in txs_data:
        txs_data_rev.append(reverse_byte_order(t.decode("hex")))
    treeHashed = get_merkle_parents(txs_data_rev)
    tree = []
    for t in treeHashed:
        tree.append(reverse_byte_order(t).encode("hex"))
    tree = txs_data + tree
    return tree

def get_merkle_root(txs_data):    
    return get_merkle_tree(txs_data)[-1]

def dsha256(data):
    return hashlib.sha256(hashlib.sha256(data).digest()).digest()

def hash_block(B):
    blkheader = ""
    blkheader += struct.pack('<I', B['version'])
    blkheader += B['previousblockhash'].decode("hex")[::-1]
    blkheader += B["merkleroot"].decode("hex")[::-1]
    blkheader += struct.pack('<I', B['time'])
    blkheader += struct.pack('<I', B['bits'])
    blkheader += struct.pack('<I', B['nonce'])
    h = dsha256(blkheader)[::-1]
    return h.encode("hex")

def check_pow(blockHash, bits):
    target = uint256_from_compact(bits)

    if len(blockHash) == 64:
        blockHash = blockHash.decode("hex")
    assert(len(blockHash) == 32)
    
    blockHash = reverse_byte_order(blockHash)  # why?
    nHash = uint256_from_str(blockHash)

    #print "target:", target
    #print "nHash:", nHash

    return nHash <= target

if __name__ == "__main__":
    # block data as from client
    b10001 = {u'merkleroot': u'41183c608fc0cac556f219330c418cf0381c178d3f25db5b254af204340aa4b8', ...
    b19199 = {u'merkleroot': u'0f8e8a23da3c8e53f9ef1f6722d0667e228b9275cd61e9a1460d717763d89894', ...
    b200000 = {u'merkleroot': u'ca714d4f72d212bbbb3521886ff2561f54506cdbb2515acb2d26842005fe7744', ...

    for b in [b10001, b19199, b200000]:
        print "block height:", b["height"]
        print "original block hash:", b["hash"]
        print "hashed block ok:", hash_block(b) == b["hash"]
        print "calculated merkle root ok:", get_merkle_root(b["tx"]) == b["merkleroot"]
        print "pow check:", check_pow(b["hash"], b["bits"])
        print