//! V2X Transmission Utilities

use alloc::vec::Vec;

use c_its_parser::gn as geonetworking;

pub mod gn;

/// Interface for ITS Payloads inside a Geonetworking header
pub trait GnItsPayload {
    // common GN parameters
    const LIFETIME_MILLIS: u32 = 60_000; // itsGnDefaultPacketLifetime is 60 seconds according to ETSI EN 302 636-4-1 V1.4.1

    // ---------------------------------------------
    // methods to build a GN packet with ITS payload
    // ---------------------------------------------

    /// Builds the [`geonetworking::en302636_4_1::ExtendedHeader`] and additional information for the ITS message
    ///
    /// Output:
    /// - Extended header
    /// - Area type (when using GAC or GBC)
    /// - hop limit
    ///
    /// Note: Make sure to increase the sequence number on multi-hop packets.
    ///
    /// # Errors
    /// Returns a human-readable error description if values are out of range
    fn make_eh(
        &self,
        address: [u8; 6],
        own_position: &crate::PosVel,
        time: chrono::DateTime<chrono::Utc>,
        seq_no: &mut u16,
    ) -> Result<
        (
            geonetworking::en302636_4_1::ExtendedHeader,
            Option<geonetworking::en302636_4_1::AreaType>,
            u8,
        ),
        alloc::string::String,
    >;

    /// Creates the ITS payload (without BTP header)
    ///
    /// # Errors
    /// Returns a human-readable error description if values are out of range
    fn make_payload(
        &self,
    ) -> Result<(Vec<u8>, c_its_parser::standards::extensions::ItsMessageId), alloc::string::String>;

    // ---------------------------------------------
    // common methods (with implementation)
    // ---------------------------------------------

    /// Encodes the GN packet
    ///
    /// # Errors
    /// Returns a human-readable error description if values are out of range
    fn encode_packet(
        &self,
        address: [u8; 6],
        own_position: &crate::PosVel,
        time: chrono::DateTime<chrono::Utc>,
        is_mobile: bool,
        seq_no: &mut u16,
    ) -> Result<Vec<u8>, alloc::string::String> {
        use geonetworking::Encode as _;

        // Build payload (including BTP header)
        let (mut its_payload, msg_type) = self.make_payload()?;
        let mut payload = make_btp_b(msg_type).encode()?;

        payload.append(&mut its_payload);

        #[allow(clippy::cast_possible_truncation)]
        let payload_length = (payload.len()) as u16;

        // get extended header (depending on message type and sometimes content as well)
        let (eh, area_type, maximum_hop_limit) =
            self.make_eh(address, own_position, time, seq_no)?;

        // Build GN headers
        let traffic_class = geonetworking::en302636_4_1::TrafficClass::try_new(
            false,
            false,
            make_traffic_class(msg_type),
        )
        .map_err(|err| alloc::format!("Failed to create TrafficClass: {err:?}"))?;
        let common = geonetworking::en302636_4_1::CommonHeader::from_values(
            geonetworking::en302636_4_1::NextAfterCommon::BTPB,
            geonetworking::en302636_4_1::HeaderType::new_from(&eh, area_type)?,
            traffic_class,
            is_mobile,
            payload_length,
            maximum_hop_limit,
        );

        let remaining_hop_limit = maximum_hop_limit;
        let basic = geonetworking::en302636_4_1::BasicHeader::try_new(
            1,
            geonetworking::en302636_4_1::NextAfterBasic::CommonHeader,
            geonetworking::en302636_4_1::Lifetime::from_milliseconds(Self::LIFETIME_MILLIS),
            remaining_hop_limit,
        )
        .map_err(|err| alloc::format!("Failed to create BasicHeader: {err}"))?;

        // Assemble and encode packet
        let packet = geonetworking::Packet::Unsecured {
            basic,
            common,
            extended: Some(eh),
            payload: &payload,
        };

        packet
            .encode_to_vec()
            .map_err(|err| alloc::format!("Failed to encode GN packet: {err:?}"))
    }
}

/// Creates a BTP-B header based on the ITS message ID (message type)
///
/// Port numbers and destination port info according to ETSI TS 103 248
fn make_btp_b(
    msg_type: c_its_parser::standards::extensions::ItsMessageId,
) -> c_its_parser::transport::TransportHeader {
    let (destination_port, destination_port_info) = match msg_type {
        c_its_parser::standards::extensions::ItsMessageId::Denm => (2002, 0),
        c_its_parser::standards::extensions::ItsMessageId::Cam => (2001, 0),
        c_its_parser::standards::extensions::ItsMessageId::Mapem => (2003, 0),
        c_its_parser::standards::extensions::ItsMessageId::Spatem => (2004, 0),
        c_its_parser::standards::extensions::ItsMessageId::Saem => (2005, 0),
        c_its_parser::standards::extensions::ItsMessageId::Ivim => (2006, 0),
        c_its_parser::standards::extensions::ItsMessageId::Srem => (2007, 0),
        c_its_parser::standards::extensions::ItsMessageId::Ssem => (2008, 0),
        c_its_parser::standards::extensions::ItsMessageId::Cpm => (2009, 0),
        c_its_parser::standards::extensions::ItsMessageId::Poi => (2010, 0),
        c_its_parser::standards::extensions::ItsMessageId::EvRsr => (2012, 0),
        c_its_parser::standards::extensions::ItsMessageId::Rtcmem => (2013, 0),
        _ => (0, 0), // no information found for the subsequent types
    };

    c_its_parser::transport::TransportHeader::BtpB(c_its_parser::transport::BasicTransportBHeader {
        destination_port,
        destination_port_info,
    })
}

/// Creates a traffic class ID based on the ITS message ID (message type)
fn make_traffic_class(msg_type: c_its_parser::standards::extensions::ItsMessageId) -> u8 {
    #[allow(clippy::match_same_arms)]
    match msg_type {
        c_its_parser::standards::extensions::ItsMessageId::Denm => 1,
        c_its_parser::standards::extensions::ItsMessageId::Cam => 2,
        c_its_parser::standards::extensions::ItsMessageId::Mapem => 3, // from C-Roads RS_RSP_063(1)
        c_its_parser::standards::extensions::ItsMessageId::Spatem => 3, // from C-Roads RS_RSP_063(1)
        c_its_parser::standards::extensions::ItsMessageId::Ivim => 3, // from C-Roads RS_RSP_063(1)
        c_its_parser::standards::extensions::ItsMessageId::Srem => 2, // from C-Roads RS_RSP_063(1)
        c_its_parser::standards::extensions::ItsMessageId::Ssem => 2, // from C-Roads RS_RSP_063(1)
        c_its_parser::standards::extensions::ItsMessageId::Rtcmem => 3, // CSP_MaxPrio=252 -> 3
        _ => 3, // fall-back to lowest priority
    }
}