/// Types for the BLK_BOX NOW priv protocol

#ifndef _BBNOW_PRIV_H
#define _BBNOW_PRIV_H

#include <stdint.h>
#include <vector>
#include <optional>
#include <span>
#include <variant>

#include "bb_expantions.hpp"

///////////////////////////////////////
// ACK                              //
/////////////////////////////////////
/// The data associated with the `ACK` type.
struct BBNowPrivAckData {
};

///////////////////////////////////////
// DISCOVERY RESPONSE               //
/////////////////////////////////////
/// The data associated with the `DISCOVERY_RESPONSE` type.
struct BBNowPrivDiscoveryResponseData {
    BlkBoxExpantion expantion_type{};
};

///////////////////////////////////////
// EXPANDER MESSAGE                 //
/////////////////////////////////////
/// The data associated with the `EXPANDER_MESSAGE` type.
struct BBNowPrivExpanderMessageData {
    // TODO: this should get flattened into a concrete type, an enum over the expander types.
    std::vector<uint8_t> data;
};

///////////////////////////////////////
// INFO QUERY                       //
/////////////////////////////////////
/// The data associated with the `INFO_QUERY` type.
struct BBNowPrivInfoQueryData {
    uint8_t battery_percentage;
    // TODO: add other status fields that may be useful to query.
};

///////////////////////////////////////
// PRIV PACKET                      //
/////////////////////////////////////
/// The packet type for `BBNowPrivPacket`s.
enum class BBNowPrivPacketType: uint16_t {
    NONE = 0,
    ACK = 1,
    // TODO: we will need to add more here for handshaking in the future.
    DISCOVERY_RESPONSE = 2,
    EXPANDER_MESSAGE = 3,
    INFO_QUERY = 4,
    MAX = 4,
};

/// The data field for the packet.
using BBNowPrivPacketData = std::variant<
    std::monostate,
    BBNowPrivAckData,
    BBNowPrivDiscoveryResponseData,
    BBNowPrivExpanderMessageData,
    BBNowPrivInfoQueryData
>;

struct BBNowPrivPacket {
    /// ACK packet size.
    const static size_t ACK_PACKET_SIZE = 4;
    static_assert(
        ACK_PACKET_SIZE == sizeof(BBNowPrivPacketType) + sizeof(uint16_t),
        "ACK packet size should match it's data size"
    );

    /// Discovery response packet size.
    const static size_t DISCOVERY_RESPONSE_PACKET_SIZE = 6;
    static_assert(
        DISCOVERY_RESPONSE_PACKET_SIZE == sizeof(BBNowPrivPacketType) +
        sizeof(uint16_t) +
        sizeof(BBNowPrivDiscoveryResponseData),
        "Discovery response packet size should match it's data size"
    );

    /// Info query packet size.
    const static size_t INFO_QUERY_PACKET_SIZE = 5;
    static_assert(
        INFO_QUERY_PACKET_SIZE ==
            sizeof(BBNowPrivPacketType) +
            sizeof(uint16_t) +
            sizeof(BBNowPrivInfoQueryData),
        "Info query packet size should match its data size"
    );

    /// The type of packet this is.
    BBNowPrivPacketType packet_type{};

    /// Sequence number associated with this packet.
    uint16_t sequence{};

    /// The data held by the packet.
    BBNowPrivPacketData packet_data{};

    /// The size of the serialized packet (in bytes).
    size_t serialize_size() const;

    /// Serializes the packet to a vector.
    std::vector<uint8_t> serialize() const;

    /// Serializes the packet into the given vector.
    ///
    /// Returns the number of bytes written into the buffer.
    size_t serialize_into(std::vector<uint8_t>& buf) const;

    /// Deserializes a packet from the given bytes.
    static std::optional<BBNowPrivPacket>
    deserialize(std::span<const uint8_t> bytes);

    /// Constructs an empty packet.
    BBNowPrivPacket() = default;

    /// Constructs a new `ACK` packet.
    static BBNowPrivPacket new_ack(uint16_t sequence);

    /// Constructs a new `DISCOVERY_RESPONSE` packet.
    static BBNowPrivPacket new_discovery_response(
        uint16_t sequence,
        BBNowPrivDiscoveryResponseData data
    );

    /// Constructs a new `EXPANDER_MESSAGE` packet.
    static BBNowPrivPacket new_expander_message(
        uint16_t sequence,
        BBNowPrivExpanderMessageData data
    );

    /// Constructs a new `INFO_QUERY` packet.
    static BBNowPrivPacket new_info_query(
        uint16_t sequence, 
        BBNowPrivInfoQueryData data
    );
};

#endif /* _BBNOW_PRIV_H */