feat(sim): world, contact trace, SimTransport

tines-sim/src/trace.rs

@@ -0,0 +1,68 @@
+//! Contact traces: a timeline of which nodes are within range of each other.
+
+/// A single contact window between two nodes.
+///
+/// Nodes `a` and `b` are in contact during the half-open interval
+/// `[start_ms, end_ms)`. Contacts are symmetric: a contact recorded as
+/// `(a, b)` is equivalent to `(b, a)`.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Contact {
+    pub start_ms: u64,
+    pub end_ms: u64,
+    pub a: usize,
+    pub b: usize,
+}
+
+/// An ordered list of contact windows, as produced by the contact simulator.
+#[derive(Clone, Debug, Default)]
+pub struct ContactTrace {
+    pub contacts: Vec<Contact>,
+}
+
+impl ContactTrace {
+    /// Whether `a` and `b` are in contact at time `t`, for any contact
+    /// involving the pair in either order.
+    ///
+    /// A contact counts during its half-open window: `start_ms <= t < end_ms`.
+    pub fn in_contact(&self, a: usize, b: usize, t: u64) -> bool {
+        self.contacts
+            .iter()
+            .any(|c| is_contact_pair(c, a, b) && in_window(c, t))
+    }
+
+    /// The last time any contact ends, or `0` if there are no contacts.
+    pub fn end(&self) -> u64 {
+        self.contacts.iter().map(|c| c.end_ms).max().unwrap_or(0)
+    }
+}
+
+/// True when `c` links `a` and `b` in either order.
+fn is_contact_pair(c: &Contact, a: usize, b: usize) -> bool {
+    (c.a == a && c.b == b) || (c.a == b && c.b == a)
+}
+
+/// True when `t` falls inside the half-open window `[start, end)`.
+fn in_window(c: &Contact, t: u64) -> bool {
+    c.start_ms <= t && t < c.end_ms
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Contact, ContactTrace};
+
+    #[test]
+    fn in_contact_matches_both_orders() {
+        let mut trace = ContactTrace::default();
+        trace.contacts.push(Contact { start_ms: 100, end_ms: 200, a: 3, b: 7 });
+        assert!(!trace.in_contact(3, 7, 50)); // before the window
+        assert!(trace.in_contact(3, 7, 100)); // at the start edge
+        assert!(trace.in_contact(7, 3, 150)); // mid-window, either order
+        assert!(!trace.in_contact(3, 7, 200)); // at the end edge (half-open)
+        assert!(!trace.in_contact(3, 7, 300)); // after the window
+    }
+
+    #[test]
+    fn end_is_zero_when_empty() {
+        assert_eq!(ContactTrace::default().end(), 0);
+    }
+}