From 1c19a195cc83e4a4e9b16555d8170f421ef0c6ab Mon Sep 17 00:00:00 2001
From: Andrey Okonetchnikov <andrey@okonet.dev>
Date: Tue, 20 Sep 2022 12:42:48 +0200
Subject: [PATCH] Improve Combobox behavior by rendering the selectedItem in
 the prefix as text

---
 .../src/components/combobox.stories.tsx       | 12 ++-
 .../design-system/src/components/combobox.tsx | 99 +++++++++++++------
 2 files changed, 77 insertions(+), 34 deletions(-)

diff --git a/packages/design-system/src/components/combobox.stories.tsx b/packages/design-system/src/components/combobox.stories.tsx
index b55a30a339..5ae0eff1c1 100644
--- a/packages/design-system/src/components/combobox.stories.tsx
+++ b/packages/design-system/src/components/combobox.stories.tsx
@@ -8,8 +8,12 @@ export default {
 };
 
 export const Simple: ComponentStory<typeof Combobox> = () => {
-  const items = [{ label: "Apple" }, { label: "Banana" }, { label: "Orange" }];
-  const [value, setValue] = React.useState(items[0]);
+  const items = [
+    { label: "Apple" },
+    { label: "Banana" },
+    { label: "Orange" },
+  ] as const;
+  const [value, setValue] = React.useState<typeof items[number] | undefined>();
   return (
     <Combobox
       name="fruit"
@@ -26,7 +30,9 @@ export const CustomInput: ComponentStory<typeof Combobox> = () => {
     { label: "Banana", value: "banana" },
     { label: "Orange", value: "orange" },
   ];
-  const [value, setValue] = React.useState(items[0]);
+  const [value, setValue] = React.useState<typeof items[0] | undefined>(
+    items[0]
+  );
 
   return (
     <Combobox
diff --git a/packages/design-system/src/components/combobox.tsx b/packages/design-system/src/components/combobox.tsx
index 90691c8bab..c6529c232c 100644
--- a/packages/design-system/src/components/combobox.tsx
+++ b/packages/design-system/src/components/combobox.tsx
@@ -1,7 +1,7 @@
 import {
   useState,
   forwardRef,
-  useEffect,
+  useCallback,
   type ComponentProps,
   type ForwardRefRenderFunction,
 } from "react";
@@ -64,7 +64,7 @@ const ListboxItem = styled("li", itemCss, {
 
 type ListProps<Item> = {
   containerProps: ComponentProps<typeof Listbox>;
-  items: Array<Item>;
+  items: ReadonlyArray<Item>;
   getItemProps: (
     options: UseComboboxGetItemPropsOptions<Item>
   ) => ComponentProps<typeof ListboxItem>;
@@ -113,11 +113,11 @@ export const ComboboxPopperContent = PopperContent;
 type ComboboxProps<Item> = {
   name: string;
   label?: string;
-  items: Array<Item>;
+  items: ReadonlyArray<Item>;
   value?: Item;
-  onItemSelect?: (value: Item) => void;
+  onItemSelect?: (value?: Item) => void;
   onItemHighlight?: (value?: Item) => void;
-  itemToString?: (item: Item | null) => string;
+  itemToString?: (item?: Item | null) => string;
   renderTextField?: (
     props: ComponentProps<typeof ComboboxTextField>
   ) => JSX.Element;
@@ -132,9 +132,7 @@ export const Combobox = <Item extends BaseItem>({
   value,
   name,
   itemToString = (item) =>
-    typeof item === "object" && item !== null && "label" in item
-      ? item.label
-      : item ?? "",
+    item != null && "label" in item ? item.label : item ?? "",
   onItemSelect,
   onItemHighlight,
   renderTextField = (props) => <ComboboxTextField {...props} />,
@@ -143,6 +141,39 @@ export const Combobox = <Item extends BaseItem>({
   renderPopperContent = (props) => <ComboboxPopperContent {...props} />,
 }: ComboboxProps<Item>) => {
   const [foundItems, setFoundItems] = useState(items);
+  const stateReducer = useCallback((state, actionAndChanges) => {
+    const { type, changes } = actionAndChanges;
+    switch (type) {
+      // on item selection.
+      case useCombobox.stateChangeTypes.ItemClick:
+      case useCombobox.stateChangeTypes.InputKeyDownEnter:
+      case useCombobox.stateChangeTypes.InputBlur:
+      case useCombobox.stateChangeTypes.ControlledPropUpdatedSelectedItem:
+        return {
+          ...changes,
+          // if we had an item selected.
+          ...(changes.selectedItem && {
+            // we will set the input value to be empty since we display it using prefix
+            inputValue: "",
+          }),
+        };
+      // Clear input value on escape
+      case useCombobox.stateChangeTypes.InputKeyDownEscape:
+        return {
+          ...changes,
+          inputValue: "",
+          selectedItem: null,
+        };
+      // Reset selectedItem when there is selection and we type something
+      case useCombobox.stateChangeTypes.InputChange:
+        return {
+          ...changes,
+          selectedItem: null,
+        };
+      default:
+        return changes; // otherwise business as usual.
+    }
+  }, []);
   const {
     isOpen,
     getToggleButtonProps,
@@ -154,23 +185,20 @@ export const Combobox = <Item extends BaseItem>({
     getItemProps,
     selectedItem,
   } = useCombobox({
-    onInputValueChange({ inputValue }) {
-      if (inputValue) {
-        const options =
-          typeof items[0] === "object" && "label" in items[0]
-            ? { keys: ["label"] }
-            : undefined;
-        const foundItems = matchSorter(items, inputValue, options);
-        setFoundItems(foundItems);
-      }
-    },
-    items: foundItems,
-    selectedItem: value,
+    items: foundItems as Item[],
+    selectedItem: value ?? null, // Avoid downshift warning about switching controlled mode
+    stateReducer,
     itemToString,
+    onInputValueChange({ inputValue }) {
+      const options =
+        typeof items[0] === "object" && "label" in items[0]
+          ? { keys: ["label"] }
+          : undefined;
+      const foundItems = matchSorter(items, inputValue ?? "", options);
+      setFoundItems(foundItems);
+    },
     onSelectedItemChange({ selectedItem }) {
-      if (selectedItem) {
-        onItemSelect?.(selectedItem);
-      }
+      onItemSelect?.(selectedItem ?? undefined);
     },
     onHighlightedIndexChange({ highlightedIndex }) {
       if (highlightedIndex !== undefined) {
@@ -179,13 +207,18 @@ export const Combobox = <Item extends BaseItem>({
     },
   });
 
-  useEffect(() => {
-    if (isOpen === false) {
-      setFoundItems(items);
-    }
-  }, [isOpen, items]);
-
-  const inputProps: Record<string, unknown> = getInputProps({ name });
+  const inputProps: Record<string, unknown> = getInputProps({
+    name,
+    onKeyDown: (event) => {
+      // When we press Backspace and the input is empty,
+      // we should to clear the selection
+      // @todo: it would be much better to handle this in reducer but downshift doesn't handle this event
+      if (event.key === "Backspace" && selectedItem !== null) {
+        onItemSelect?.(undefined);
+      }
+    },
+    prefix: itemToString?.(selectedItem ?? undefined),
+  });
   const toggleProps: Record<string, unknown> = getToggleButtonProps();
   const comboboxProps: Record<string, unknown> = getComboboxProps();
   const menuProps: Record<string, unknown> = getMenuProps();
@@ -195,7 +228,11 @@ export const Combobox = <Item extends BaseItem>({
     <Popper>
       <Box {...comboboxProps}>
         <PopperAnchor>
-          {renderTextField({ inputProps, toggleProps, highlightedItem })}
+          {renderTextField({
+            inputProps,
+            toggleProps,
+            highlightedItem,
+          })}
         </PopperAnchor>
         {renderPopperContent({
           style: { zIndex: 1 },