text: # Electrum - Lightweight Bitcoin Client
  # Copyright (c) 2012 Thomas Voegtlin
  #
  # Permission is hereby granted, free of charge, to any person
  # obtaining a copy of this software and associated documentation files
  # (the "Software"), to deal in the Software without restriction,
  # including without limitation the rights to use, copy, modify, merge,
  # publish, distribute, sublicense, and/or sell copies of the Software,
  # and to permit persons to whom the Software is furnished to do so,
  # subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be
  # included in all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  # NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  # BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  # ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  from .util import ThreadJob
  from .bitcoin import *
  
  
  class SPV(ThreadJob):
      """ Simple Payment Verification """
  
      def __init__(self, network, wallet):
          self.wallet = wallet
          self.network = network
          self.blockchain = network.blockchain()
          # Keyed by tx hash.  Value is None if the merkle branch was
          # requested, and the merkle root once it has been verified
          self.merkle_roots = {}
  
      def run(self):
          lh = self.network.get_local_height()
          unverified = self.wallet.get_unverified_txs()
          for tx_hash, tx_height in unverified.items():
              # do not request merkle branch before headers are available
              if (tx_height > 0) and (tx_hash not in self.merkle_roots) and (tx_height <= lh):
                  request = ('blockchain.transaction.get_merkle',
                             [tx_hash, tx_height])
                  self.network.send([request], self.verify_merkle)
                  self.print_error('requested merkle', tx_hash)
                  self.merkle_roots[tx_hash] = None
  
          #if self.network.blockchain != self.blockchain:
          #    self.blockchain = self.network.blockchain
          #    self.undo_verifications()
  
      def verify_merkle(self, r):
          if r.get('error'):
              self.print_error('received an error:', r)
              return
          params = r['params']
          merkle = r['result']
          # Verify the hash of the server-provided merkle branch to a
          # transaction matches the merkle root of its block
          tx_hash = params[0]
          tx_height = merkle.get('block_height')
          pos = merkle.get('pos')
          merkle_root = self.hash_merkle_root(merkle['merkle'], tx_hash, pos)
          header = self.network.blockchain().read_header(tx_height)
          if not header or header.get('merkle_root') != merkle_root:
              # FIXME: we should make a fresh connection to a server to
              # recover from this, as this TX will now never verify
              self.print_error("merkle verification failed for", tx_hash)
              return
          # we passed all the tests
          self.merkle_roots[tx_hash] = merkle_root
          self.print_error("verified %s" % tx_hash)
          self.wallet.add_verified_tx(tx_hash, (tx_height, header.get('timestamp'), pos))
  
      def hash_merkle_root(self, merkle_s, target_hash, pos):
          h = hash_decode(target_hash)
          for i in range(len(merkle_s)):
              item = merkle_s[i]
              h = Hash(hash_decode(item) + h) if ((pos >> i) & 1) else Hash(h + hash_decode(item))
          return hash_encode(h)
  
      def undo_verifications(self):
          height = self.blockchain.get_checkpoint()
          tx_hashes = self.wallet.undo_verifications(self.blockchain, height)
          for tx_hash in tx_hashes:
              self.print_error("redoing", tx_hash)
              self.merkle_roots.pop(tx_hash, None)
  