#!/usr/bin/python
from time import ctime

def behex(x):
   "Converts the given little-endian slice of bytes into big-endian hex digits"
   return x[::-1].encode('hex')

def varint(x):
   """Converts the bytes-slice to a list: first number is the number of bytes"""
   """the varint takes up. Second number is the actual int value. Recommend"""
   """only passing 9 bytes to this function, but extras will be ignored"""
   a = int(x[0].encode('hex'), 16)
   if a < 253: return (1, a)
   elif a == 253: return (3, int(behex(x[1:3]), 16))
   elif a == 254: return (5, int(behex(x[1:5]), 16))
   elif a == 255: return (9, int(behex(x[1:9]), 16))

class TrInput:
   """A single input in a single transaction. We create it from a slice"""
	"""of bytes, but do NOT make assumptions about where it ends. We"""
	"""infer that from script length, and further bytes are ignored."""
	def __init__(self, data):
		self.hash = data[0:32] ; self.index = data[32:36]
		(off1, scrlen) = varint(data[36:45])
		off1 = off1 + 36 ; off2 = off1 + scrlen ; self.size = off2 + 4
		self.script = data[off1:off2] ; self.seqnum = data[off2:self.size]

class TrOutput:
	"""A single output in a single transaction. We create it from a slice"""
	"""of bytes, but do NOT make assumptions about where it ends. We """
	"""infer that from script length, and further bytes are ignored."""
	def __init__(self, data):
		self.satval = data[0:8] ; (offset, scrlen) = varint(data[8:17])
		offset = offset + 8 ;	self.size = offset + scrlen
		self.script = data[offset:self.size]

class Transaction:
	"""Data is a slice of bytes, should start with version"""
	"""but can end anywhere, excess bytes are ignored."""
	def __init__(self, data):
		self.version = int(behex(data[0:4]), 16)
		(off1, ninps) = varint(data[4:13]) ; off1 = off1 + 4 ; self.inp = []
		for i in range(ninps):
			self.inp.append(TrInput(data[off1:]))
			off1 = off1 + self.inp[i].size
		(off2, nouts) = varint(data[off1:off1+9])
		off2 = off2 + off1 ; self.out = []
		for i in range(nouts):
			self.out.append(TrOutput(data[off2:]))
			off2 = off2 + self.out[i].size
		self.size = off2 + 4 ; self.locktime = behex(data[off2:self.size])

class Block:
	def __init__(self, blkdata):
		self.size = len(blkdata) ;	self.version = int(behex(blkdata[0:4]), 16)
		self.prevhash = blkdata[4:36] ; self.merkle = blkdata[36:68]
		self.tstamp = int(behex(blkdata[68:72]), 16)
		self.target = behex(blkdata[72:76])
		self.nonce = behex(blkdata[76:80])
		(offset, self.ntrans) = varint(blkdata[80:89])
		offset = offset + 80 ; self.trans = []
		for i in range(self.ntrans):
			self.trans.append(Transaction(blkdata[offset:]))
			offset = offset + self.trans[i].size

def checkmagicbytes(fname):
	"Reads 4 bytes from current position in file, checks they're 'magic'"
	x = fname.read(4) # why can't I ';' these two lines? (and next two) 
	if len(x) == 0: return 0 # ???
	y = int(behex(x), 16)
	if y != 0xD9B4BEF9: return 0
	return 1

def target2diff(t):
	"Converts the target in 4-byte hexstring form into difficulty (float)"
	# MAY not agree with diff given in block explorer for high diffs - check!
	i1 = int(t, 16) ; i2 = float(2**(248 - i1/(2**21)))/(i1 % (2**24))
	return i2 * 65535/65536	# I THINK that fudge factor fixes things...
	
bn = 0 ; fn = 0 ; chain = []
while True:
	fname = "/home/chris/.bitcoin/blocks/blk{:0=5}.dat".format(fn)
	try: bcfile = open(fname,"rb")
	except IOError: break
	while checkmagicbytes(bcfile): # issue about two failure modes!
		bkdata = bcfile.read(int(behex(bcfile.read(4)),16))
		chain.append(Block(bkdata)) ; bn = bn + 1
		if bn > 100000: break # just for memory purposes for now
	fn = fn + 1 ;	bcfile.close()
	if bn > 100000: break # ditto

bn = bn - 1 ; fn = fn - 1 ; print "Chain ends: block", bn, "file", fn
opt = int(raw_input("Enter a block number:"))
while opt <= bn:
	print "Version:", chain[opt].version
	print "Prev hash:", behex(chain[opt].prevhash)
	print "Merkle root:", behex(chain[opt].merkle)
	print "Timestamp:", ctime(chain[opt].tstamp)
	print "Difficulty:", target2diff(chain[opt].target)
	print "Nonce:", chain[opt].nonce
	trs = chain[opt].trans ; n = chain[opt].ntrans
	print "# of transactions:", n, "size:", chain[opt].size
	for t in range(n):
		print "Transaction", t, "Version", trs[t].version,
		print "Locktime", trs[t].locktime ; ni = len(trs[t].inp)
		# input and output data still needs to be presented readably...
		for i in range(ni):
			inp = trs[t].inp[i]
			print "Input:", i
			print "Hash:", inp.hash
			print "Index:", inp.index
			print "Script:", inp.script
			print "Seqnum:", inp.seqnum
		no = len(trs[t].out)
		for o in range(no):
			out = trs[t].out[i]
			print "Output:", o
			print "Value:", out.satval
			print "Script:", out.script
	opt = int(raw_input("Enter another block number:"))