def transaction_chain_is_valid(chain):
"""
This section deals with enforcing rules of a chain made up
of blocks of transactions. The following must apply:
- Each transaction must only appear once in the chain.
- There can only be one mining reward per block.
- Each transaction must be valid.
"""
transaction_ids = set()
for i in range(len(chain)):
block = chain[i]
has_mining_reward = False
for transaction_json in block.data:
transaction = SystemTransactions.convert_transaction_data_from_json(transaction_json)
if transaction.id in transaction_ids:
raise Exception(f'Transaction {transaction.id} is not unique')
transaction_ids.add(transaction.id)
if transaction.transaction_input == INPUT_FOR_MINING_REWARD:
if has_mining_reward:
raise Exception(
'There can only be one mining reward given per block.'\
f'Check block with the hash: {block.hash}'
)
has_mining_reward = True
else:
historic_blockchain = Blockchain()
historic_blockchain.chain = chain[0:i]
historic_balance = Wallet.wallet_balance_calculation(
historic_blockchain,
transaction.transaction_input['address']
)
if historic_balance != transaction.transaction_input['amount']:
raise Exception(
f'Transaction {transaction.id} has an invalid '\
'input amount'
)
SystemTransactions.positively_validate_transaction(transaction)
