import machine
import utime
utime.sleep(0.1)  # Wait for USB to become ready

# Message related constants
MESSAGE_START = "S"
MESSAGE_END = "Z"

def parse_message(fmessage):
    identifier_indices = []

    # Check the start byte
    if len(fmessage) == 0 or fmessage[0].upper() != MESSAGE_START:
        print("Error! Start Byte Missing!")
        return []

    # Check the stop byte
    if fmessage[-1].upper() != MESSAGE_END:
        print("Error! Stop Byte Missing!")
        return []

    # Iterate through the message to process characters
    for i in range(1, len(fmessage) - 1):  # Exclude start and end bytes
        if fmessage[i].isalpha():
            # Add indices of alphabetic characters
            identifier_indices.append(i)

    return identifier_indices

def read_command(fmessage, fidentifier_indices):
    command_list = []
    num_identifiers = len(fidentifier_indices)

    for i in range(num_identifiers):
        start_index = fidentifier_indices[i] + 1
        if i + 1 < num_identifiers:
            end_index = fidentifier_indices[i + 1]
        else:
            end_index = -1  # Up to the character before 'Z'
        
        # Extract substring based on indices
        package = fmessage[start_index:end_index]
        
        if not package.isdigit():
            raise ValueError(f"Error! Data field empty or invalid for identifier '{fmessage[fidentifier_indices[i]]}'!")

        command_list.append(int(package))

    return command_list

def main():
    # Main loop
    while True:
        # Prompt the user for input
        message = input("What is your command? (type 'exit' to quit): ").strip()

        # Exit condition
        if message.lower() == "exit":
            print("Exiting program. Goodbye!")
            break

        # Parse the message
        identifier_indices = parse_message(message)

        if not identifier_indices:
            print("No valid command identifiers found. Please try again.")
            continue

        # Debugging (optional): Display the identifier indices
        print("Identifier Indices:", identifier_indices)

        # Process the commands
        command_list = read_command(message, identifier_indices)
        if not command_list:
            # Error message already printed in read_command
            continue

        print("Command List:", command_list)
        # You can add code here to handle the commands as needed

# this ensures the main() loop runs only when the file is executed directly
# In another Python script 
# import script  # The main() function will NOT run
if __name__ == "__main__":
    main()