From 0dce0832b9f389f9a3d2bf815963fd72e41659d1 Mon Sep 17 00:00:00 2001
From: Matthias Beyer <mail@beyermatthias.de>
Date: Sun, 4 Apr 2021 14:23:43 +0200
Subject: Add AsyncDag::merge() function

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
---
 src/async_dag.rs | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

(limited to 'src')

diff --git a/src/async_dag.rs b/src/async_dag.rs
index 75e56fc..9faf1e6 100644
--- a/src/async_dag.rs
+++ b/src/async_dag.rs
@@ -121,6 +121,19 @@ impl<Id, N, Backend> AsyncDag<Id, N, Backend>
             _node: std::marker::PhantomData,
         }
     }
+
+    /// Merge another AsyncDag into this one
+    ///
+    /// Use the `merger` function to merge the two head IDs and generate a new Node instance for
+    /// the new HEAD of `self`.
+    pub async fn merge<Merger>(&mut self, other: AsyncDag<Id, N, Backend>, merger: Merger) -> Result<Id>
+        where Merger: FnOnce(Id, Id) -> Result<N>
+    {
+        let node = merger(self.head.clone(), other.head)?;
+        let id = self.backend.put(node).await?;
+        self.head = id.clone();
+        Ok(id)
+    }
 }
 
 
@@ -353,5 +366,69 @@ mod tests {
         assert_eq!(branched.head, test::Id(0));
     }
 
+    #[test]
+    fn test_merging() {
+        let mut dag = {
+            let head = test::Node {
+                id: test::Id(0),
+                parents: vec![],
+                data: 42,
+            };
+            let b = test::Backend::new(vec![Some(head.clone())]);
+            let dag = tokio_test::block_on(AsyncDag::new(b, head));
+            assert!(dag.is_ok());
+            dag.unwrap()
+        };
+
+        let mut branched = dag.branch();
+
+        {
+            assert_eq!(dag.backend.0.read().unwrap().len(), 1);
+            assert_eq!(dag.head, test::Id(0));
+            let new_head = test::Node {
+                id: test::Id(1),
+                parents: vec![test::Id(0)],
+                data: 43,
+            };
+
+            let id = tokio_test::block_on(dag.update_head(new_head));
+            assert!(id.is_ok());
+            let id = id.unwrap();
+
+            assert_eq!(dag.backend.0.read().unwrap().len(), 2);
+            assert_eq!(dag.head, test::Id(1));
+        }
+
+        {
+            assert_eq!(branched.backend.0.read().unwrap().len(), 2);
+            assert_eq!(branched.head, test::Id(0));
+            let new_head = test::Node {
+                id: test::Id(2),
+                parents: vec![test::Id(0)],
+                data: 44,
+            };
+
+            let id = tokio_test::block_on(branched.update_head(new_head));
+            assert!(id.is_ok());
+            let id = id.unwrap();
+
+            assert_eq!(branched.backend.0.read().unwrap().len(), 3);
+            assert_eq!(branched.head, test::Id(2));
+        }
+
+        let merge = tokio_test::block_on(dag.merge(branched, |left, right| {
+            Ok(test::Node {
+                id: test::Id(3),
+                parents: vec![left, right],
+                data: 45,
+            })
+        }));
+        assert!(merge.is_ok());
+        let merge = merge.unwrap();
+
+        assert_eq!(dag.backend.0.read().unwrap().len(), 4);
+        assert_eq!(dag.head, test::Id(3));
+    }
+
 }
 
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