import hashlib

class Transaction:
    def __init__(self, sender, amount, metadata=""):
        self.sender = sender
        self.amount = amount
        self.metadata = metadata # New rule: must not be empty!

class Node:
    def __init__(self, name, enforce_new_rules=False):
        self.name = name
        self.enforce_new_rules = enforce_new_rules
        self.blockchain = []

    def validate_tx(self, tx):
        # Old nodes allow empty metadata
        # New nodes REJECT empty metadata (Rule Tightening)
        if self.enforce_new_rules and not tx.metadata:
            return False
        return True

    def receive_block(self, block):
        for tx in block:
            if not self.validate_tx(tx):
                print(f"[!] {self.name}: REJECTED block. TX with empty metadata is invalid!")
                return False

        self.blockchain.append(block)
        print(f"[+] {self.name}: ACCEPTED block with {len(block)} transactions.")
        return True

# --- Simulation ---

# 1. Initialize Nodes
old_node = Node("Old Node (v0.1)", enforce_new_rules=False)
new_node = Node("New Node (v0.2)", enforce_new_rules=True)

# 2. A miner produces a block following NEW RULES (stricter)
print("--- Round 1: Validating a 'Strict' Block ---")
strict_tx = Transaction("Alice", 1.0, metadata="SECURE_ID_123")
block1 = [strict_tx]

old_node.receive_block(block1)
new_node.receive_block(block1)

# 3. A miner produces a block following OLD RULES (loose)
print("\n--- Round 2: Validating a 'Loose' Block (Soft Fork Violation) ---")
loose_tx = Transaction("Bob", 2.0, metadata="") # Empty metadata
block2 = [loose_tx]

old_node.receive_block(block2) # This will be accepted (loose rules)
new_node.receive_block(block2) # This will be REJECTED (strict rules)

# 4. Summary
print("\n--- Final Status ---")
print(f"Old Node Chain Height: {len(old_node.blockchain)}")
print(f"New Node Chain Height: {len(new_node.blockchain)}")