use crate::enums::{FunctionCode, MessageIdentifier};

#[expect(clippy::big_endian_bytes, reason="Function is needed for the Protocol 300")]
/// Calculate the checksum for a Protocol 300 message
/// 
/// The inputs are seperate as the function is needed without have a construced
/// `Protocol300Message` sometimes.
pub fn calculate_checksum(length: u8, message_identifier: MessageIdentifier, function_code: FunctionCode, address: u16, data_length: u8, data: &[u8]) -> u8 {
    let mut checksum: u8 = 0;
    let [addr_hi, addr_lo] = address.to_be_bytes();

    for byte in [length, message_identifier.into(), function_code.into(), data_length, addr_hi, addr_lo].iter().chain(data) {
        checksum = checksum.wrapping_add(*byte);
    }

    checksum
}


#[cfg(test)]
mod tests {
    use crate::{enums::{FunctionCode, MessageIdentifier}, message::Protocol300Message, utils::calculate_checksum};
    #[cfg(not(feature = "std"))]
    extern crate alloc;

    #[cfg(not(feature = "std"))]
    use alloc::vec;

    #[cfg(not(feature = "std"))]
    use alloc::vec::Vec;

    #[test]
    fn check_checksum_1() {
        let test_msg = Protocol300Message {
            data_address: 0x5525,
            telegram_length: 0x05,
            function_code: FunctionCode::VirtualREAD,
            message_identifier: MessageIdentifier::Request,
            data_length: 0x02,
            data: vec![],
            checksum: 0x82,
        };
        assert_eq!(calculate_checksum(test_msg.telegram_length, test_msg.message_identifier, test_msg.function_code, test_msg.data_address, test_msg.data_length, &test_msg.data), 0x82);
    }

        #[test]
    fn check_checksum_2() {
        let test_msg = Protocol300Message {
            data_address: 0x5525,
            telegram_length: 0x07,
            function_code: FunctionCode::VirtualREAD,
            message_identifier: MessageIdentifier::Response,
            data_length: 0x02,
            data: vec![0x07, 0x01],
            checksum: 0x8D,
        };
        assert_eq!(calculate_checksum(test_msg.telegram_length, test_msg.message_identifier, test_msg.function_code, test_msg.data_address, test_msg.data_length, &test_msg.data), 0x8D);
    }

    #[test]
    fn received_message_wrapping_add_from_bytes() {
        let checksum = calculate_checksum(0x06, MessageIdentifier::Request, FunctionCode::VirtualWRITE, 0x2323, 0x01, &[0xB6]);
        assert_eq!(checksum, 0x05);
    }
}