From 97643fbbfa5bbcaaf5e14f82e1880dd0359f9429 Mon Sep 17 00:00:00 2001
From: Josh Wooding <12938082+joshwooding@users.noreply.github.com>
Date: Tue, 8 Oct 2024 16:18:30 +0100
Subject: [PATCH] Further improve CB performance (#4251)

---
 .../core/src/list-control/ListControlState.ts | 44 +++++++++++----
 .../stories/combo-box/combo-box.stories.tsx   | 53 +++++++++++++++++--
 2 files changed, 81 insertions(+), 16 deletions(-)

diff --git a/packages/core/src/list-control/ListControlState.ts b/packages/core/src/list-control/ListControlState.ts
index 4d045b5863..4464aa1f0f 100644
--- a/packages/core/src/list-control/ListControlState.ts
+++ b/packages/core/src/list-control/ListControlState.ts
@@ -58,28 +58,51 @@ function findElementPosition(
   element: HTMLElement,
 ) {
   if (elements.length === 0) {
-    return 0;
+    return [0, false] as const;
   }
 
   if (
     element.compareDocumentPosition(elements[elements.length - 1].element) &
     Node.DOCUMENT_POSITION_PRECEDING
   ) {
-    return -1;
+    return [-1, false] as const;
   }
 
   if (
     element.compareDocumentPosition(elements[0].element) &
     Node.DOCUMENT_POSITION_FOLLOWING
   ) {
-    return 0;
+    return [0, false] as const;
   }
 
-  return elements.findIndex(
-    (option) =>
-      option.element.compareDocumentPosition(element) &
-      Node.DOCUMENT_POSITION_PRECEDING,
-  );
+  let left = 0;
+  let right = elements.length;
+  let leftLast = 0;
+  let rightLast = right;
+
+  let exists = false;
+
+  while (left < right) {
+    const inPos = Math.floor((right + left) / 2);
+    const compared = element.compareDocumentPosition(elements[inPos].element);
+    if (compared & Node.DOCUMENT_POSITION_PRECEDING) {
+      left = inPos;
+    } else if (compared & Node.DOCUMENT_POSITION_FOLLOWING) {
+      right = inPos;
+    } else {
+      right = inPos;
+      left = inPos;
+      exists = true;
+    }
+    // nothing has changed, must have found limits. insert between.
+    if (leftLast === left && rightLast === right) {
+      break;
+    }
+    leftLast = left;
+    rightLast = right;
+  }
+
+  return [right, exists] as const;
 }
 
 export function defaultValueToString<Item>(item: Item): string {
@@ -193,10 +216,9 @@ export function useListControl<Item>(props: ListControlProps<Item>) {
   const register = useCallback(
     (optionValue: OptionValue<Item>, element: HTMLElement) => {
       const { id } = optionValue;
-      const option = optionsRef.current.find((item) => item.data.id === id);
-      const index = findElementPosition(optionsRef.current, element);
+      const [index, exists] = findElementPosition(optionsRef.current, element);
 
-      if (!option) {
+      if (!exists) {
         if (index === -1) {
           optionsRef.current.push({ data: optionValue, element });
         } else {
diff --git a/packages/core/stories/combo-box/combo-box.stories.tsx b/packages/core/stories/combo-box/combo-box.stories.tsx
index 63521e5657..d0467c84b7 100644
--- a/packages/core/stories/combo-box/combo-box.stories.tsx
+++ b/packages/core/stories/combo-box/combo-box.stories.tsx
@@ -912,12 +912,55 @@ export const Bordered = () => {
   );
 };
 
-export const PerformanceTest = () => {
+const hugeArray = Array.from({ length: 10000 }).map(
+  (_, index) => `Option ${index}`,
+);
+
+export const PerformanceTest: StoryFn<ComboBoxProps> = (args) => {
+  const [value, setValue] = useState(getTemplateDefaultValue(args));
+
+  const handleChange = (event: ChangeEvent<HTMLInputElement>) => {
+    // React 16 backwards compatibility
+    event.persist();
+
+    const value = event.target.value;
+    setValue(value);
+  };
+
+  const handleSelectionChange = (
+    event: SyntheticEvent,
+    newSelected: string[],
+  ) => {
+    // React 16 backwards compatibility
+    event.persist();
+
+    args.onSelectionChange?.(event, newSelected);
+
+    if (args.multiselect) {
+      setValue("");
+      return;
+    }
+
+    if (newSelected.length === 1) {
+      setValue(newSelected[0]);
+    } else {
+      setValue("");
+    }
+  };
+
+  const filteredItems = hugeArray.filter((item) =>
+    item.toLowerCase().includes(value.trim().toLowerCase()),
+  );
+
   return (
-    <ComboBox>
-      {Array.from({ length: 10000 }).map((_, index) => (
-        <Option key={index} value={`option-${index}`}>
-          Option {index + 1}
+    <ComboBox
+      value={value}
+      onChange={handleChange}
+      onSelectionChange={handleSelectionChange}
+    >
+      {filteredItems.map((item) => (
+        <Option key={item} value={item}>
+          {item}
         </Option>
       ))}
     </ComboBox>