def encode_compact_size(i):
 """Encodes an integer into Bitcoin's CompactSize format."""
 if i < 253:
 return i.to_bytes(1, 'little')
 elif i <= 0xFFFF:
 return b'\xfd' + i.to_bytes(2, 'little')
 elif i <= 0xFFFFFFFF:
 return b'\xfe' + i.to_bytes(4, 'little')
 else:
 return b'\xff' + i.to_bytes(8, 'little')

def decode_compact_size(data):
 """Decodes a CompactSize byte string and returns (value, bytes_read)."""
 first = data[0]
 if first < 253:
 return first, 1
 elif first == 253:
 return int.from_bytes(data[1:3], 'little'), 3
 elif first == 254:
 return int.from_bytes(data[1:5], 'little'), 5
 else:
 return int.from_bytes(data[1:9], 'little'), 9

# --- Simulation ---

test_values = [10, 252, 253, 1000, 70000, 5000000000]

print("--- CompactSize (VarInt) Audit ---")
for val in test_values:
 encoded = encode_compact_size(val)
 decoded, size = decode_compact_size(encoded)

 print(f"[*] Value: {val:<12} | Hex: {encoded.hex(' '):<20} | Bytes: {size}")

 if val != decoded:
 print(f" [X] ERROR: Decode mismatch!")

# Scenario: Parsing a mock Input Count
print("\nScenario: Parsing Input Count from Raw Hex")
raw_data = bytes.fromhex("fd0002") # 512 in Little Endian with FD marker
count, s = decode_compact_size(raw_data)
print(f"[*] Parsed Count: {count} inputs (Read {s} bytes)")