input: Write a function to port a Java code snippet to Python 3. The function should take in a Java class as input and return the equivalent Python 3 code. Ensure that the function handles the conversion of class definitions and method signatures properly.
  assert port_java_to_python("public class Foo { public int foo( int a, int b ) { return a + b; } }") == "def foo(a, b):\n return a + b"
  assert port_java_to_python("public class Bar { public int bar( int x ) { return x * 2; } }") == "def bar(x):\n return x * 2"
  assert port_java_to_python("public class Test { public int test( int y, int z ) { return y - z; } }") == "def test(y, z):\n return y - z"
  assert port_java_to_python("public class Empty {}") == "pass"
  assert port_java_to_python("") == "Invalid input"
output: def port_java_to_python(java_code):
      if not java_code.strip():
          return "Invalid input"
      
      if "public class" not in java_code:
          return "Invalid input"
      
      class_name = java_code.split("public class")[1].split("{")[0].strip()
      method_match = re.search(r"public\s+\w+\s+(\w+)\s*\(([^)]*)\)\s*\{([^}]*)\}", java_code)
      
      if not method_match:
          return "pass"
      
      method_name = method_match.group(1)
      params = method_match.group(2).replace("int", "").replace(" ", "").split(",")
      body = method_match.group(3).strip()
      
      if body.startswith("return"):
          body = body.replace("return", "").strip()
      
      param_str = ", ".join(params)
      return f"def {method_name}({param_str}):\n return {body}"