Add floating reroutes (#773)

### Floating reroutes

Native reroutes can now be kept in a disconnected state.

Link chains may be kept provided they are connected to _either_ an input
or an output. By design, reroutes will be automatically removed if both
sides are disconnected.

src/LLink.ts

@@ -104,12 +104,12 @@ export class LLink implements LinkSegment, Serialisable<SerialisableLLink> {
   }
 
   /**
-   * Gets all reroutes from the output slot to this segment.  If this segment is a reroute, it will be the last element.
+   * Gets all reroutes from the output slot to this segment.  If this segment is a reroute, it will not be included.
    * @returns An ordered array of all reroutes from the node output to
    * this reroute or the reroute before it.  Otherwise, an empty array.
    */
   static getReroutes(
-    network: ReadonlyLinkNetwork,
+    network: Pick<ReadonlyLinkNetwork, "reroutes">,
     linkSegment: LinkSegment,
   ): Reroute[] {
     if (!linkSegment.parentId) return []
@@ -119,7 +119,7 @@ export class LLink implements LinkSegment, Serialisable<SerialisableLLink> {
   }
 
   static getFirstReroute(
-    network: LinkNetwork,
+    network: Pick<ReadonlyLinkNetwork, "reroutes">,
     linkSegment: LinkSegment,
   ): Reroute | undefined {
     return LLink.getReroutes(network, linkSegment).at(0)
@@ -166,15 +166,44 @@ export class LLink implements LinkSegment, Serialisable<SerialisableLLink> {
   /**
    * Disconnects a link and removes it from the graph, cleaning up any reroutes that are no longer used
    * @param network The container (LGraph) where reroutes should be updated
-   * @param keepReroutes If `true`, reroutes will not be garbage collected.
+   * @param keepReroutes If `undefined`, reroutes will be automatically removed if no links remain.
+   * If `input` or `output`, reroutes will not be automatically removed, and retain a connection to the input or output, respectively.
    */
-  disconnect(network: LinkNetwork, keepReroutes?: boolean): void {
+  disconnect(network: LinkNetwork, keepReroutes?: "input" | "output"): void {
     const reroutes = LLink.getReroutes(network, this)
 
+    const lastReroute = reroutes.at(-1)
+
+    // When floating from output, 1-to-1 ratio of floating link to final reroute (tree-like)
+    const outputFloating = keepReroutes === "output" &&
+      lastReroute?.linkIds.size === 1 &&
+      lastReroute.floatingLinkIds.size === 0
+
+    // When floating from inputs, the final (input side) reroute may have many floating links
+    if (outputFloating || (keepReroutes === "input" && lastReroute)) {
+      const newLink = LLink.create(this)
+      newLink.id = -1
+
+      if (keepReroutes === "input") {
+        newLink.origin_id = -1
+        newLink.origin_slot = -1
+
+        lastReroute.floating = { slotType: "input" }
+      } else {
+        newLink.target_id = -1
+        newLink.target_slot = -1
+
+        lastReroute.floating = { slotType: "output" }
+      }
+
+      network.addFloatingLink(newLink)
+    }
+
     for (const reroute of reroutes) {
       reroute.linkIds.delete(this.id)
-      if (!keepReroutes && !reroute.linkIds.size)
+      if (!keepReroutes && !reroute.linkIds.size && !reroute.floatingLinkIds.size) {
         network.reroutes.delete(reroute.id)
+      }
     }
     network.links.delete(this.id)
   }