macro-examples/src/case_study.rs

use std::net::Ipv4Addr;
use chrono::{DateTime, Utc};
use uuid::Uuid;

pub struct Event<T> {
    pub time: DateTime<Utc>,
    pub id: Uuid,
    pub event: T,
}

pub struct Pending{
    pub recipient: Ipv4Addr,
}

#[derive(Default)]
pub struct Sending {
    pub payload: Vec<u8>,
    pub bytes_sent: usize,
    pub prev: Event<Pending>,
}

#[derive(Default)]
pub struct Sent {
    pub ack_req: bool,
    pub prev: Event<Sending>,
}

#[derive(Default)]
pub struct Ack {
    pub data: Vec<u8>,
    pub prev: Event<Sent>,
}

#[derive(Default)]
pub struct Finished<T> {
    pub prev: Event<T>,
}

pub enum Active {
    Pending(Event<Pending>),
    Sending(Event<Sending>),
    Sent(Event<Sent>),
    Acked(Event<Ack>),
    FinishedNoAck(Event<Finished<Sent>>),
    FinishedAcked(Event<Finished<Ack>>),
}

pub trait Timestamped {
    fn time(&self) -> DateTime<Utc>;
}

pub trait Chronological {
    type Prev;
    type Next;

    fn prev(&self) -> Self::Prev;
    fn next(&self) -> Self::Next;
}

pub trait Elapsed<P, N>: Chronological<Prev = P, Next = N> {
    fn elapsed(&self) -> chrono::Duration;
}

impl<T> Timestamped for Event<T> {
    fn time(&self) -> DateTime<Utc> { self.time }
}

impl<P, N, T> Elapsed<P, N> for T
    where T: Chronological<Prev = P, Next = N>,
          P: Timestamped,
          N: Timestamped
{
    fn elapsed(&self) -> chrono::Duration {
        self.next().time().signed_duration_since(self.prev().time())
    }
}

impl<N, T> Elapsed<(), N> for T
    where T: Chronological<Prev = (), Next = N>
{
    fn elapsed(&self) -> chrono::Duration {
        chrono::Duration::seconds(0)
    }
}

/*
impl Timestamped for Active {
    fn time(&self) -> DateTime<Utc> {
        use Active::*;
        match self {
            Pending(event) => event.time,
            Sending(event) => event.time,
            Sent(event) => event.time,
            Acked(event) => event.time,
            FinishedNoAck(event) => event.time,
            FinishedAcked(event) => event.time,
        }
    }
}
*/

macro_rules! event_attr {
    ($method:ident, $t:ty, $attr:ident) => {
        fn $method(&self) -> $t {
            use Active::*;
            match self {
                Pending(event) => event.$attr,
                Sending(event) => event.$attr,
                Sent(event) => event.$attr,
                Acked(event) => event.$attr,
                FinishedNoAck(event) => event.$attr,
                FinishedAcked(event) => event.$attr,
            }
        }
    }
}

impl Timestamped for Active {
    event_attr!(time, DateTime<Utc>, time);
}

macro_rules! optionally_public_event_attr {

    // note: `vis` is automatically optional, doesn't need 
    // this will work as-is if there is nothing there
    
    ($pub:vis $method:ident, $t:ident, $attr:ident) => {
        $pub fn $method(&self) -> $t {
            use Active::*;
            match self {
                Pending(event) => event.$attr,
                Sending(event) => event.$attr,
                Sent(event) => event.$attr,
                Acked(event) => event.$attr,
                FinishedNoAck(event) => event.$attr,
                FinishedAcked(event) => event.$attr,
            }
        }
    }
}

impl Active {
    optionally_public_event_attr!(pub id, Uuid, id);
}

impl From<Event<Pending>> for Active {
    fn from(pending: Event<Pending>) -> Active {
        Active::Pending(pending)
    }
}

macro_rules! from_event {
    ($t:ty, $variant:ident) => {
        impl From<Event<$t>> for Active {
            fn from(event: Event<$t>) -> Active {
                Active::$variant(event)
            }
        }
    }
}

//from_event!(Pending, Pending);
from_event!(Sending, Sending);
from_event!(Sent, Sent);
from_event!(Ack, Acked);
from_event!(Finished<Sent>, FinishedNoAck);
from_event!(Finished<Ack>, FinishedAcked);

macro_rules! variant_check {
    ($f:ident, $variant:ident) => {
        impl Active {
            pub fn $f(&self) -> bool {
                match self {
                    Active::$variant(..) => true,
                    _ => false,
                }
            }
        }
    }
}

variant_check!(is_pending, Pending);
variant_check!(is_sending, Sending);
variant_check!(is_sent, Sent);
variant_check!(is_acked, Acked);
variant_check!(is_finished_noack, FinishedNoAck);
variant_check!(is_finished_acked, FinishedAcked);

macro_rules! multiple_variant_check {
    ($f:ident; $($variant:ident),*) => {
        impl Active {
            pub fn $f(&self) -> bool {
                match self {
                    $( Active::$variant(..) => { true } )*

                    _ => false,
                }
            }
        }
    }
}

multiple_variant_check!(is_finished; FinishedNoAck, FinishedAcked);
multiple_variant_check!(is_still_unfinished; Pending, Sending, Sent, Acked);
multiple_variant_check!(anything_but_sent; Pending, Sending, Acked, FinishedNoAck, FinishedAcked);

// needed because Ipv4Addr does not implement Default
// other event type structs derive Default instead
impl Default for Pending {
    fn default() -> Self {
        Self { recipient: Ipv4Addr::new(127, 0, 0, 1) }
    }
}

impl<T> Default for Event<T>
    where T: Default
{
    fn default() -> Self {
        Self {
            time: Utc::now(),
            id: Uuid::new_v4(),
            event: T::default(),
        }
    }
}

impl Default for Active {
    fn default() -> Self {
        Active::Pending(Default::default())
    }
}


macro_rules! new_with_default {
    ($f:ident, $t:ty) => {
        impl Active {
            pub fn $f() -> Self {
                let inner: Event<$t> = Default::default();
                Self::from(inner)
            }
        }
    }
}

new_with_default!(new_pending, Pending);
new_with_default!(new_sending, Sending);
new_with_default!(new_sent, Sent);
new_with_default!(new_acked, Ack);
new_with_default!(new_finished_noack, Finished<Sent>);
new_with_default!(new_finished_acked, Finished<Ack>);

#[allow(unused)]
#[cfg(test)]
mod tests {
    use super::*;
    use std::str::FromStr;

    #[test]
    fn event_attr_accessors_work() {
        let pending = Pending { recipient: "0.0.0.0".parse().unwrap() };
        let now = Utc::now();
        let id = Uuid::new_v4();
        let pending_event = Event {
            time: now,
            id,
            event: pending,
        };
        let pending_active = Active::Pending(pending_event);
        assert_eq!(pending_active.time(), now);
        assert_eq!(pending_active.id(), id);
    }

    #[test]
    fn check_generated_methods_for_pending() {
        let active = Active::new_pending();
        assert!(active.is_pending());
        assert!(active.is_still_unfinished());
    }

    #[test]
    fn generated_method_check_for_variant() {
        macro_rules! check_for_variant {
            ($new:ident, $single:ident, $multiple:ident, $not:ident) => {
                let active = Active::$new();
                assert!(active.$single());
                assert!(active.$multiple());
                assert!( ! active.$not());
            }
        }

        check_for_variant!(new_pending, is_pending, is_still_unfinished, is_sent);
        check_for_variant!(new_sending, is_sending, is_still_unfinished, is_acked);
        check_for_variant!(new_sent, is_sent, is_still_unfinished, is_finished_noack);
        check_for_variant!(new_acked, is_acked, is_still_unfinished, is_pending);
        check_for_variant!(new_finished_noack, is_finished_noack, is_finished, is_still_unfinished);
        check_for_variant!(new_finished_acked, is_finished_acked, is_finished, is_still_unfinished);
    }

    #[test]
    fn active_impls_timestamped() {
        fn tm_plus_42min<T: Timestamped>(x: &T) -> DateTime<Utc> {
            x.time() + chrono::Duration::minutes(42)
        }

        let active = Active::new_sent();
        let t2 = tm_plus_42min(&active);
        assert_eq!(active.time() + chrono::Duration::minutes(42), t2);
    }

    #[test]
    fn check_that_vis_can_handle_all_three_possibilities_for_visibility() {
        pub struct A {
            x: i32,
            y: DateTime<Utc>,
            z: f32,
        }

        macro_rules! a_attr {
            ($pub:vis $method:ident, $t:ty, $attr:ident) => {
                impl A {
                    $pub fn $method(&self) -> $t {
                        self.$attr
                    }
                }
            }
        }

        a_attr!(get_x, i32, x);
        a_attr!(pub(crate) get_y, DateTime<Utc>, y);
        a_attr!(pub get_z, f32, z);

        let a = A { x: 0i32, y: Utc::now(), z: 1.234f32 };

        assert_eq!(a.get_x(), a.x);
        assert_eq!(a.get_y(), a.y);
        assert_eq!(a.get_z(), a.z);
    }

    #[test]
    fn usage_of_variant_check_example() {
        let pending = Pending { recipient: Ipv4Addr::new(127, 0, 0, 1) };
        let event = Event { time: Utc::now(), id: Uuid::new_v4(), event: pending };
        let active = Active::from(event);
        assert_eq!(active.is_pending(), true);
    }
}