From ec804134c33aedb001c426c5f42f43f53c47848f Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Wed, 2 Oct 2024 12:25:36 -0400
Subject: Represent channels and messages using a split "History" and
 "Snapshot" model.

This separates the code that figures out what happened to an entity from the code that represents it to a user, and makes it easier to compute a snapshot at a point in time (for things like bootstrap). It also makes the internal logic a bit easier to follow, since it's easier to tell whether you're working with a point in time or with the whole recorded history.

This hefty.
---
 src/event/sequence.rs | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

(limited to 'src/event/sequence.rs')

diff --git a/src/event/sequence.rs b/src/event/sequence.rs
index 9ebddd7..c566156 100644
--- a/src/event/sequence.rs
+++ b/src/event/sequence.rs
@@ -1,5 +1,20 @@
 use std::fmt;
 
+use crate::clock::DateTime;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, serde::Serialize)]
+pub struct Instant {
+    pub at: DateTime,
+    #[serde(skip)]
+    pub sequence: Sequence,
+}
+
+impl From<Instant> for Sequence {
+    fn from(instant: Instant) -> Self {
+        instant.sequence
+    }
+}
+
 #[derive(
     Clone,
     Copy,
@@ -22,3 +37,47 @@ impl fmt::Display for Sequence {
         value.fmt(f)
     }
 }
+
+impl Sequence {
+    pub fn up_to<E>(resume_point: Option<Self>) -> impl for<'e> Fn(&'e E) -> bool
+    where
+        E: Sequenced,
+    {
+        move |event| resume_point.map_or(true, |resume_point| event.sequence() <= resume_point)
+    }
+
+    pub fn after<E>(resume_point: Option<Self>) -> impl for<'e> Fn(&'e E) -> bool
+    where
+        E: Sequenced,
+    {
+        move |event| resume_point < Some(event.sequence())
+    }
+
+    pub fn start_from<E>(resume_point: Self) -> impl for<'e> Fn(&'e E) -> bool
+    where
+        E: Sequenced,
+    {
+        move |event| resume_point <= event.sequence()
+    }
+}
+
+pub trait Sequenced {
+    fn instant(&self) -> Instant;
+
+    fn sequence(&self) -> Sequence {
+        self.instant().into()
+    }
+}
+
+impl<E> Sequenced for &E
+where
+    E: Sequenced,
+{
+    fn instant(&self) -> Instant {
+        (*self).instant()
+    }
+
+    fn sequence(&self) -> Sequence {
+        (*self).sequence()
+    }
+}
-- 
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