Simplify graph vertex updates and add tests

eclair-core/src/main/scala/fr/acinq/eclair/router/Graph.scala

@@ -624,7 +624,15 @@ object Graph {
       }
     }
 
-    case class Vertex(features: Features[NodeFeature], incomingEdges: Map[ChannelDesc, GraphEdge])
+    case class Vertex(features: Features[NodeFeature], incomingEdges: Map[ChannelDesc, GraphEdge]) {
+      def update(desc: ChannelDesc, newShortChannelId: RealShortChannelId, newCapacity: Satoshi): Vertex =
+        incomingEdges.get(desc) match {
+          case None => this
+          case Some(edge) =>
+            val updatedEdge = edge.copy(desc = desc.copy(shortChannelId = newShortChannelId), capacity = newCapacity)
+            copy(incomingEdges = incomingEdges - desc + (desc.copy(shortChannelId = newShortChannelId) -> updatedEdge))
+        }
+    }
 
     /** A graph data structure that uses an adjacency list, stores the incoming edges of the neighbors */
     case class DirectedGraph(private val vertices: Map[PublicKey, Vertex]) {
@@ -688,14 +696,10 @@ object Graph {
        * @return a new graph with updated vertexes
        */
       def updateChannel(desc: ChannelDesc, newShortChannelId: RealShortChannelId, newCapacity: Satoshi): DirectedGraph = {
-        val newDesc = desc.copy(shortChannelId = newShortChannelId)
-        val updatedVertices =
-          vertices
-            .updatedWith(desc.b)(_.map(vertexB => vertexB.copy(incomingEdges = vertexB.incomingEdges - desc +
-              (newDesc -> vertexB.incomingEdges(desc).copy(desc = newDesc, capacity = newCapacity)))))
-            .updatedWith(desc.a)(_.map(vertexA => vertexA.copy(incomingEdges = vertexA.incomingEdges - desc.reversed +
-              (newDesc.reversed -> vertexA.incomingEdges(desc.reversed).copy(desc = newDesc.reversed, capacity = newCapacity)))))
-        DirectedGraph(updatedVertices)
+        DirectedGraph(vertices
+          .updatedWith(desc.b)(_.map(_.update(desc, newShortChannelId, newCapacity)))
+          .updatedWith(desc.a)(_.map(_.update(desc.reversed, newShortChannelId, newCapacity)))
+        )
       }
 
       /**

eclair-core/src/test/scala/fr/acinq/eclair/router/BalanceEstimateSpec.scala

@@ -98,8 +98,7 @@ class BalanceEstimateSpec extends AnyFunSuite {
       .couldSend(60_000 msat, TimestampSecond.now())
 
     // a splice-in that increases channel capacity increases high but not low bounds
-    val balance1 = balance
-      .updateEdge(a.desc, RealShortChannelId(5), 250 sat)
+    val balance1 = balance.updateEdge(a.desc, RealShortChannelId(5), 250 sat)
     assert(balance1.maxCapacity == 250.sat)
     assert(balance1.low == 60_000.msat)
     assert(balance1.high == 190_000.msat)

eclair-core/src/test/scala/fr/acinq/eclair/router/GraphSpec.scala

@@ -461,4 +461,25 @@ class GraphSpec extends AnyFunSuite {
       assert(MessagePath.dijkstraMessagePath(graph, a, f, Set.empty, boundaries, BlockHeight(793397), wr).isEmpty)
     }
   }
+
+  test("a channel update only changes the scid and capacity of one edge") {
+    // A --> B has two edges with different short channel ids.
+    val edge = makeEdge(7, a, b, 1 msat, 1)
+    val g = makeTestGraph().addEdge(edge)
+
+    val g1 = g.updateChannel(ChannelDesc(ShortChannelId(7), a, b), RealShortChannelId(10), 99 sat)
+    val edge1 = g1.getEdge(ChannelDesc(ShortChannelId(10), a, b)).get
+    assert(edge1.capacity == 99.sat)
+    assert(g1.getEdge(ChannelDesc(ShortChannelId(7), a, b)).isEmpty)
+
+    // Only the scid and capacity of one edge changes.
+    assert(g1 == makeTestGraph().addEdge(edge1))
+
+    // Updates are symmetric.
+    assert(g1 == g.updateChannel(ChannelDesc(ShortChannelId(7), b, a), RealShortChannelId(10), 99 sat))
+
+    // Updates to an unknown channel do not change the graph.
+    assert(g == g.updateChannel(ChannelDesc(ShortChannelId(1), randomKey().publicKey, b), RealShortChannelId(10), 99 sat))
+  }
+
 }