From f7d077a1d71d51139ce7386be0538dcdd29c08e1 Mon Sep 17 00:00:00 2001
From: John Walley <john@walley.org.uk>
Date: Sun, 10 Apr 2022 17:03:05 +0100
Subject: [PATCH] feat: avoid unmounting pane with same key which changes
 position (#226)

---
 package.json                 |  2 ++
 src/allotment.tsx            | 30 ++++++++++++++++++++++++++++++
 src/split-view/split-view.ts | 32 ++++++++++++++++++++++++++++++++
 yarn.lock                    | 12 ++++++++++++
 4 files changed, 76 insertions(+)

diff --git a/package.json b/package.json
index f8c2037d..8232363c 100644
--- a/package.json
+++ b/package.json
@@ -28,6 +28,7 @@
     "eventemitter3": "^4.0.0",
     "lodash.clamp": "^4.0.0",
     "lodash.debounce": "^4.0.0",
+    "lodash.isequal": "^4.5.0",
     "use-resize-observer": "^8.0.0"
   },
   "devDependencies": {
@@ -50,6 +51,7 @@
     "@types/jest": "27.4.1",
     "@types/lodash.clamp": "4.0.6",
     "@types/lodash.debounce": "4.0.6",
+    "@types/lodash.isequal": "4.5.5",
     "@typescript-eslint/parser": "5.18.0",
     "@vscode/codicons": "0.0.29",
     "babel-jest": "27.5.1",
diff --git a/src/allotment.tsx b/src/allotment.tsx
index 837a3f31..58526347 100644
--- a/src/allotment.tsx
+++ b/src/allotment.tsx
@@ -1,5 +1,6 @@
 import classNames from "classnames";
 import clamp from "lodash.clamp";
+import isEqual from "lodash.isequal";
 import React, {
   forwardRef,
   useCallback,
@@ -260,6 +261,7 @@ const Allotment = forwardRef<AllotmentHandle, AllotmentProps>(
     useEffect(() => {
       if (dimensionsInitialized) {
         const keys = childrenArray.map((child) => child.key as string);
+        const panes = [...previousKeys.current];
 
         const enter = keys.filter((key) => !previousKeys.current.includes(key));
         const update = keys.filter((key) => previousKeys.current.includes(key));
@@ -268,6 +270,7 @@ const Allotment = forwardRef<AllotmentHandle, AllotmentProps>(
         exit.forEach((flag, index) => {
           if (flag) {
             splitViewRef.current?.removeView(index);
+            panes.splice(index, 1);
             views.current.splice(index, 1);
           }
         });
@@ -292,6 +295,12 @@ const Allotment = forwardRef<AllotmentHandle, AllotmentProps>(
             keys.findIndex((key) => key === enterKey)
           );
 
+          panes.splice(
+            keys.findIndex((key) => key === enterKey),
+            0,
+            enterKey
+          );
+
           views.current.splice(
             keys.findIndex((key) => key === enterKey),
             0,
@@ -299,6 +308,27 @@ const Allotment = forwardRef<AllotmentHandle, AllotmentProps>(
           );
         }
 
+        // Move panes if order has changed
+        while (!isEqual(keys, panes)) {
+          for (const [i, key] of keys.entries()) {
+            const index = panes.findIndex((pane) => pane === key);
+
+            if (index !== i) {
+              splitViewRef.current?.moveView(
+                splitViewViewRef.current.get(key) as HTMLElement,
+                index,
+                i
+              );
+
+              const tempKey = panes[index];
+              panes.splice(index, 1);
+              panes.splice(i, 0, tempKey);
+
+              break;
+            }
+          }
+        }
+
         for (const enterKey of enter) {
           const index = keys.findIndex((key) => key === enterKey);
 
diff --git a/src/split-view/split-view.ts b/src/split-view/split-view.ts
index 2d75f973..2ddbdc25 100644
--- a/src/split-view/split-view.ts
+++ b/src/split-view/split-view.ts
@@ -565,6 +565,38 @@ export class SplitView extends EventEmitter implements Disposable {
     return view;
   }
 
+  /**
+   * Move a {@link View view} to a different index.
+   *
+   * @param from The source index.
+   * @param to The target index.
+   */
+  public moveView(container: HTMLElement, from: number, to: number): void {
+    const cachedVisibleSize = this.getViewCachedVisibleSize(from);
+
+    const sizing =
+      typeof cachedVisibleSize === "undefined"
+        ? this.getViewSize(from)
+        : Sizing.Invisible(cachedVisibleSize);
+
+    const view = this.removeView(from);
+    this.addView(container, view, sizing, to);
+  }
+
+  /**
+   * Returns the {@link View view}'s size previously to being hidden.
+   *
+   * @param index The {@link View view} index.
+   */
+  private getViewCachedVisibleSize(index: number): number | undefined {
+    if (index < 0 || index >= this.viewItems.length) {
+      throw new Error("Index out of bounds");
+    }
+
+    const viewItem = this.viewItems[index];
+    return viewItem.cachedVisibleSize;
+  }
+
   /**
    * Layout the {@link SplitView}.
    *
diff --git a/yarn.lock b/yarn.lock
index 9cc179a1..f70776d9 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3779,6 +3779,13 @@
   dependencies:
     "@types/lodash" "*"
 
+"@types/lodash.isequal@4.5.5":
+  version "4.5.5"
+  resolved "https://registry.yarnpkg.com/@types/lodash.isequal/-/lodash.isequal-4.5.5.tgz#4fed1b1b00bef79e305de0352d797e9bb816c8ff"
+  integrity sha512-4IKbinG7MGP131wRfceK6W4E/Qt3qssEFLF30LnJbjYiSfHGGRU/Io8YxXrZX109ir+iDETC8hw8QsDijukUVg==
+  dependencies:
+    "@types/lodash" "*"
+
 "@types/lodash@*":
   version "4.14.175"
   resolved "https://registry.yarnpkg.com/@types/lodash/-/lodash-4.14.175.tgz#b78dfa959192b01fae0ad90e166478769b215f45"
@@ -9479,6 +9486,11 @@ lodash.debounce@^4.0.0, lodash.debounce@^4.0.8:
   resolved "https://registry.yarnpkg.com/lodash.debounce/-/lodash.debounce-4.0.8.tgz#82d79bff30a67c4005ffd5e2515300ad9ca4d7af"
   integrity sha1-gteb/zCmfEAF/9XiUVMArZyk168=
 
+lodash.isequal@^4.5.0:
+  version "4.5.0"
+  resolved "https://registry.yarnpkg.com/lodash.isequal/-/lodash.isequal-4.5.0.tgz#415c4478f2bcc30120c22ce10ed3226f7d3e18e0"
+  integrity sha1-QVxEePK8wwEgwizhDtMib30+GOA=
+
 lodash.ismatch@^4.4.0:
   version "4.4.0"
   resolved "https://registry.yarnpkg.com/lodash.ismatch/-/lodash.ismatch-4.4.0.tgz#756cb5150ca3ba6f11085a78849645f188f85f37"