move PduEvent from services to core

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/pdu/count.rs

@@ -0,0 +1,51 @@
+use std::cmp::Ordering;
+
+use ruma::api::client::error::ErrorKind;
+
+use crate::{Error, Result};
+
+#[derive(Hash, PartialEq, Eq, Clone, Copy, Debug)]
+pub enum PduCount {
+	Backfilled(u64),
+	Normal(u64),
+}
+
+impl PduCount {
+	#[must_use]
+	pub fn min() -> Self { Self::Backfilled(u64::MAX) }
+
+	#[must_use]
+	pub fn max() -> Self { Self::Normal(u64::MAX) }
+
+	pub fn try_from_string(token: &str) -> Result<Self> {
+		if let Some(stripped_token) = token.strip_prefix('-') {
+			stripped_token.parse().map(PduCount::Backfilled)
+		} else {
+			token.parse().map(PduCount::Normal)
+		}
+		.map_err(|_| Error::BadRequest(ErrorKind::InvalidParam, "Invalid pagination token."))
+	}
+
+	#[must_use]
+	pub fn stringify(&self) -> String {
+		match self {
+			Self::Backfilled(x) => format!("-{x}"),
+			Self::Normal(x) => x.to_string(),
+		}
+	}
+}
+
+impl PartialOrd for PduCount {
+	fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) }
+}
+
+impl Ord for PduCount {
+	fn cmp(&self, other: &Self) -> Ordering {
+		match (self, other) {
+			(Self::Normal(s), Self::Normal(o)) => s.cmp(o),
+			(Self::Backfilled(s), Self::Backfilled(o)) => o.cmp(s),
+			(Self::Normal(_), Self::Backfilled(_)) => Ordering::Greater,
+			(Self::Backfilled(_), Self::Normal(_)) => Ordering::Less,
+		}
+	}
+}