cob: Start testing history permutations

Signed-off-by: Alexis Sellier <self@cloudhead.io>

radicle/src/cob/op.rs

@@ -62,6 +62,18 @@ pub struct Op<A> {
     pub timestamp: clock::Physical,
 }
 
+impl<A: Eq> PartialOrd for Op<A> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        self.id().partial_cmp(&other.id())
+    }
+}
+
+impl<A: Eq> Ord for Op<A> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.id().cmp(&other.id())
+    }
+}
+
 impl<A: Serialize> Op<A> {
     pub fn new(
         action: A,

radicle/src/cob/store.rs

@@ -54,6 +54,15 @@ pub trait FromHistory: Sized + Default {
 
         Ok((obj, history.clock().into()))
     }
+
+    /// Create an object from individual operations.
+    /// Returns an error if any of the operations fails to apply.
+    fn from_ops(ops: impl IntoIterator<Item = Op<Self::Action>>) -> Result<Self, Self::Error> {
+        let mut state = Self::default();
+        state.apply(ops)?;
+
+        Ok(state)
+    }
 }
 
 /// Store error.

radicle/src/cob/test.rs

@@ -1,25 +1,31 @@
+use std::collections::BTreeSet;
 use std::marker::PhantomData;
-use std::ops::Deref;
+use std::ops::{ControlFlow, Deref};
 
 use nonempty::NonEmpty;
 use serde::Serialize;
 
-use crate::cob::op::Op;
+use crate::cob::op::{Op, Ops};
 use crate::cob::store::encoding;
 use crate::cob::History;
 use crate::git::Oid;
 use crate::test::arbitrary;
 
+use super::store::FromHistory;
+
 /// Convenience type for building histories.
 #[derive(Debug, Clone)]
-pub struct HistoryBuilder<A> {
+pub struct HistoryBuilder<T> {
     history: History,
-    witness: PhantomData<A>,
     resource: Oid,
+    witness: PhantomData<T>,
 }
 
-impl<A: Serialize> HistoryBuilder<A> {
-    pub fn new(op: &Op<A>) -> HistoryBuilder<A> {
+impl<T: FromHistory> HistoryBuilder<T>
+where
+    T::Action: Serialize + Eq,
+{
+    pub fn new(op: &Op<T::Action>) -> HistoryBuilder<T> {
         let entry = arbitrary::oid();
         let resource = arbitrary::oid();
         let contents = encoding::encode(&op.action).unwrap();
@@ -37,7 +43,7 @@ impl<A: Serialize> HistoryBuilder<A> {
         }
     }
 
-    pub fn append(&mut self, op: &Op<A>) -> &mut Self {
+    pub fn append(&mut self, op: &Op<T::Action>) -> &mut Self {
         self.history.extend(
             arbitrary::oid(),
             op.author,
@@ -51,6 +57,27 @@ impl<A: Serialize> HistoryBuilder<A> {
     pub fn merge(&mut self, other: Self) {
         self.history.merge(other.history);
     }
+
+    /// Return a sorted list of operations by traversing the history in topological order.
+    pub fn sorted(&self) -> Vec<Op<T::Action>> {
+        self.history.traverse(Vec::new(), |mut acc, entry| {
+            let Ops(ops) =
+                Ops::try_from(entry).expect("HistoryBuilder::sorted: operations must be valid");
+            acc.extend(ops);
+
+            ControlFlow::Continue(acc)
+        })
+    }
+
+    /// Return `n` permutations of the topological ordering of operations.
+    /// *This function will never return if less than `n` permutations exist.*
+    pub fn permutations(&self, n: usize) -> impl IntoIterator<Item = Vec<Op<T::Action>>> {
+        let mut permutations = BTreeSet::new();
+        while permutations.len() < n {
+            permutations.insert(self.sorted());
+        }
+        permutations.into_iter()
+    }
 }
 
 impl<A> Deref for HistoryBuilder<A> {
@@ -62,6 +89,9 @@ impl<A> Deref for HistoryBuilder<A> {
 }
 
 /// Create a new test history.
-pub fn history<A: Serialize>(op: &Op<A>) -> HistoryBuilder<A> {
+pub fn history<T: FromHistory>(op: &Op<T::Action>) -> HistoryBuilder<T>
+where
+    T::Action: Serialize + Eq,
+{
     HistoryBuilder::new(op)
 }

radicle/src/cob/thread.rs

@@ -373,6 +373,7 @@ mod tests {
     use super::*;
     use crate as radicle;
     use crate::cob::store::FromHistory;
+    use crate::cob::test;
     use crate::crypto::test::signer::MockSigner;
 
     #[derive(Clone)]
@@ -641,6 +642,33 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_histories() {
+        let mut alice = Actor::<MockSigner>::default();
+        let mut bob = Actor::<MockSigner>::default();
+        let mut eve = Actor::<MockSigner>::default();
+
+        let a0 = alice.comment("Alice's comment", None);
+        let b0 = bob.comment("Bob's reply", Some(a0.id())); // Bob and Eve's replies are concurrent.
+        let e0 = eve.comment("Eve's reply", Some(a0.id()));
+
+        let mut a = test::history::<Thread>(&a0);
+        let mut b = a.clone();
+        let mut e = a.clone();
+
+        b.append(&b0);
+        e.append(&e0);
+
+        a.merge(b);
+        a.merge(e);
+
+        let (expected, _) = Thread::from_history(&a).unwrap();
+        for permutation in a.permutations(2) {
+            let actual = Thread::from_ops(permutation).unwrap();
+            assert_eq!(actual, expected);
+        }
+    }
+
     #[test]
     fn prop_invariants() {
         fn property(log: Changes<3>) -> TestResult {