feat(chain): add TxGraph::canonical_set method

This is an O(n) algorithm to determine the canonical set of txids.

crates/chain/src/tx_graph.rs

@@ -1054,6 +1054,135 @@ impl<A: Anchor> TxGraph<A> {
             .filter_map(Result::transpose)
     }
 
+    /// Get a canonical set of txids.
+    pub fn canoncial_set<C: ChainOracle>(
+        &self,
+        chain: &C,
+        chain_tip: BlockId,
+    ) -> Result<HashSet<Txid>, C::Error> {
+        let mut definitely_canonical = HashSet::<Txid>::new();
+        let mut definitely_not_canonical = HashSet::<Txid>::new();
+        let txid_by_last_seen = self
+            .last_seen
+            .iter()
+            .map(|(&txid, &last_seen)| (last_seen, txid))
+            .collect::<BTreeSet<_>>();
+        for (_, txid) in txid_by_last_seen {
+            self.canonicalize_by_traversing_up(
+                chain,
+                chain_tip,
+                &mut definitely_canonical,
+                &mut definitely_not_canonical,
+                txid,
+            )?;
+        }
+        Ok(definitely_canonical)
+    }
+
+    fn canonicalize_by_traversing_up<C: ChainOracle>(
+        &self,
+        chain: &C,
+        chain_tip: BlockId,
+        definitely_canonical: &mut HashSet<Txid>,
+        definitely_not_canonical: &mut HashSet<Txid>,
+        txid: Txid,
+    ) -> Result<(), C::Error> {
+        type TxWithId = (Txid, Arc<Transaction>);
+        let tx = match self.get_tx(txid) {
+            Some(tx) => tx,
+            None => return Ok(()),
+        };
+        let maybe_canonical = TxAncestors::new_include_root(
+            self,
+            tx,
+            |_: usize, tx: Arc<Transaction>| -> Option<Result<TxWithId, C::Error>> {
+                let txid = tx.compute_txid();
+                match self.is_definitely_canonical(
+                    chain,
+                    chain_tip,
+                    definitely_canonical,
+                    definitely_not_canonical,
+                    txid,
+                ) {
+                    Ok(None) => Some(Ok((txid, tx))),
+                    Ok(Some(_)) => None,
+                    Err(err) => Some(Err(err)),
+                }
+            },
+        )
+        .collect::<Result<Vec<_>, C::Error>>()?;
+        // TODO: Check if this is correct.
+        for (txid, tx) in maybe_canonical {
+            if !definitely_not_canonical.contains(&txid) {
+                self.mark_definitely_canonical(definitely_canonical, tx);
+            }
+        }
+        Ok(())
+    }
+
+    fn is_definitely_canonical<C: ChainOracle>(
+        &self,
+        chain: &C,
+        chain_tip: BlockId,
+        definitely_canonical: &mut HashSet<Txid>,
+        definitely_not_canonical: &mut HashSet<Txid>,
+        txid: Txid,
+    ) -> Result<Option<bool>, C::Error> {
+        if definitely_canonical.contains(&txid) {
+            return Ok(Some(true));
+        }
+        if definitely_not_canonical.contains(&txid) {
+            return Ok(Some(false));
+        }
+        let tx = match self.get_tx(txid) {
+            Some(tx) => tx,
+            None => return Ok(None),
+        };
+        for anchor in self.anchors.get(&txid).unwrap_or(&self.empty_anchors) {
+            if chain.is_block_in_chain(anchor.anchor_block(), chain_tip)? == Some(true) {
+                self.mark_definitely_canonical(definitely_canonical, tx);
+                return Ok(Some(true));
+            }
+        }
+        for (_, conflicting_txid) in self.direct_conflicts(&tx) {
+            if definitely_canonical.contains(&conflicting_txid) {
+                self.mark_definitely_not_canonical(definitely_not_canonical, txid);
+                return Ok(Some(false));
+            }
+        }
+        Ok(None)
+    }
+
+    fn mark_definitely_not_canonical(
+        &self,
+        definitely_not_canonical: &mut HashSet<Txid>,
+        txid: Txid,
+    ) {
+        TxDescendants::new_include_root(self, txid, |_: usize, txid: Txid| -> Option<()> {
+            if definitely_not_canonical.insert(txid) {
+                Some(())
+            } else {
+                None
+            }
+        })
+        .for_each(|_| {})
+    }
+
+    fn mark_definitely_canonical(
+        &self,
+        definitely_canonical: &mut HashSet<Txid>,
+        tx: Arc<Transaction>,
+    ) {
+        TxAncestors::new_include_root(self, tx, |_: usize, tx: Arc<Transaction>| -> Option<()> {
+            if definitely_canonical.insert(tx.compute_txid()) {
+                Some(())
+            } else {
+                None
+            }
+        })
+        .for_each(|_| {})
+    }
+
     /// Get a filtered list of outputs from the given `outpoints` that are in `chain` with
     /// `chain_tip`.
     ///