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pub const MQTT: &[u8] = b"MQTT";
pub const MQTT_LEVEL_3: u8 = 4;
pub const MQTT_LEVEL_5: u8 = 5;
pub const WILL_QOS_SHIFT: u8 = 3;

/// Max possible packet size
pub const MAX_PACKET_SIZE: u32 = 0xF_FF_FF_FF;

prim_enum! {
    /// Quality of Service
    pub enum QoS {
        /// At most once delivery
        ///
        /// The message is delivered according to the capabilities of the underlying network.
        /// No response is sent by the receiver and no retry is performed by the sender.
        /// The message arrives at the receiver either once or not at all.
        AtMostOnce = 0,
        /// At least once delivery
        ///
        /// This quality of service ensures that the message arrives at the receiver at least once.
        /// A QoS 1 PUBLISH Packet has a Packet Identifier in its variable header
        /// and is acknowledged by a PUBACK Packet.
        AtLeastOnce = 1,
        /// Exactly once delivery
        ///
        /// This is the highest quality of service,
        /// for use when neither loss nor duplication of messages are acceptable.
        /// There is an increased overhead associated with this quality of service.
        ExactlyOnce = 2
    }
}

bitflags::bitflags! {
    pub struct ConnectFlags: u8 {
        const USERNAME    = 0b1000_0000;
        const PASSWORD    = 0b0100_0000;
        const WILL_RETAIN = 0b0010_0000;
        const WILL_QOS    = 0b0001_1000;
        const WILL        = 0b0000_0100;
        const CLEAN_START = 0b0000_0010;
    }
}

bitflags::bitflags! {
    pub struct ConnectAckFlags: u8 {
        const SESSION_PRESENT = 0b0000_0001;
    }
}

pub(super) mod packet_type {
    pub const CONNECT: u8 = 0b0001_0000;
    pub const CONNACK: u8 = 0b0010_0000;
    pub const PUBLISH_START: u8 = 0b0011_0000;
    pub const PUBLISH_END: u8 = 0b0011_1111;
    pub const PUBACK: u8 = 0b0100_0000;
    pub const PUBREC: u8 = 0b0101_0000;
    pub const PUBREL: u8 = 0b0110_0010;
    pub const PUBCOMP: u8 = 0b0111_0000;
    pub const SUBSCRIBE: u8 = 0b1000_0010;
    pub const SUBACK: u8 = 0b1001_0000;
    pub const UNSUBSCRIBE: u8 = 0b1010_0010;
    pub const UNSUBACK: u8 = 0b1011_0000;
    pub const PINGREQ: u8 = 0b1100_0000;
    pub const PINGRESP: u8 = 0b1101_0000;
    pub const DISCONNECT: u8 = 0b1110_0000;
    pub const AUTH: u8 = 0b1111_0000;
}

#[derive(Debug, PartialEq, Clone, Copy)]
pub(crate) struct FixedHeader {
    /// Fixed Header byte
    pub first_byte: u8,
    /// the number of bytes remaining within the current packet,
    /// including data in the variable header and the payload.
    pub remaining_length: u32,
}