1 files changed, 90 insertions, 0 deletions
diff --git a/src/event/sequence.rs b/src/event/sequence.rs
new file mode 100644
index 0000000..fbe3711
--- /dev/null
+++ b/src/event/sequence.rs
@@ -0,0 +1,90 @@
+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,
+    Debug,
+    Eq,
+    Ord,
+    PartialEq,
+    PartialOrd,
+    serde::Deserialize,
+    serde::Serialize,
+    sqlx::Type,
+)]
+#[serde(transparent)]
+#[sqlx(transparent)]
+pub struct Sequence(i64);
+
+impl fmt::Display for Sequence {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self(value) = self;
+        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 fn merge<E>(a: &E, b: &E) -> bool
+    where
+        E: Sequenced,
+    {
+        a.sequence() < b.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()
+    }
+}