string_to_base64

def string_to_base64(input_string):
    """
    Convert a string to its Base64 representation without using external packages.

    Args:
        input_string (str): The input string to be converted.

    Returns:
        str: The Base64-encoded representation of the input string.
    """
    # Define the Base64 character mapping
    base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

    # Filter out non-alphanumeric characters and whitespace
    filtered_string = ''.join(char for char in input_string if char.isalnum() or char.isspace())

    # Initialize variables
    result = []
    current_bits = 0
    num_bits = 0

    # Convert the filtered input string to bytes
    bytes_data = filtered_string.encode('utf-8')

    # Iterate through each byte in the filtered input data
    for byte in bytes_data:
        # Shift the current_bits left by 8 bits and add the new byte
        current_bits = (current_bits << 8) | byte
        num_bits += 8

        # While we have at least 6 bits, extract and encode them
        while num_bits >= 6:
            num_bits -= 6
            # Extract the top 6 bits
            index = (current_bits >> num_bits) & 0x3F
            result.append(base64_chars[index])

    # Handle any remaining bits (less than 6 bits)
    if num_bits > 0:
        # Pad with zeros to make a multiple of 6 bits
        current_bits <<= 6 - num_bits
        index = current_bits & 0x3F
        result.append(base64_chars[index])

    # Add padding '=' characters if necessary
    while len(result) % 4 != 0:
        result.append('=')

    # Join the Base64 characters to form the final encoded string
    base64_data = ''.join(result)

    return base64_data

# Example usage:
if __name__ == "__main__":
    input_string = "Hello, this is a string to be encoded in Base64. #$%^"
    base64_result = string_to_base64(input_string)
    print("Base64 Encoded String:", base64_result)