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import type {
SelectionKey,
UseSelectionOptions,
UseSelectionReturn,
} from "./types";
/**
* Manage multi- or single-selection state for a list or table, backed by a
* `Set` of keys.
*
* The `Set` stores **keys** (see the `getKey` option), never the items
* themselves, so a selection survives new object identities across renders —
* rebuilding the `items` array every render will not lose the selection as long
* as `getKey` maps the same logical item to the same key. Every item-facing
* value (`selected`, `isAllSelected`, `isPartiallySelected`, …) is **derived
* from the current `items`**, so removing a selected row from `items` makes it
* disappear from `selected` and recomputes the aggregate flags automatically —
* no manual reconciliation needed.
*
* Features:
* - `Set`-backed, immutable updates (a fresh `Set` on every change)
* - No-op skipping — `selectAll` when all are already selected, and `clear`
* when already empty, bail out without a re-render
* - Single-selection mode (`multiple: false`) that replaces the selection
* - Stable action identities (`toggle`/`select`/`deselect`/`selectAll`/`clear`
* and `isSelected`) — safe as effect dependencies
* - `isPartiallySelected` for a header checkbox's indeterminate state
* - SSR-safe (pure state) and StrictMode/concurrent-safe (no mutation of prior
* state, callbacks never fire from inside a `setState` updater)
*
* @template T - The item type.
* @param items - The current list of items the selection is scoped to.
* @param options - {@link UseSelectionOptions} (`getKey`, `multiple`).
* @returns {@link UseSelectionReturn}
*
* @example
* ```tsx
* type User = { id: number; name: string };
*
* function UserTable({ users }: { users: User[] }) {
* const {
* selected,
* isSelected,
* toggle,
* selectAll,
* clear,
* isAllSelected,
* isPartiallySelected,
* } = useSelection(users, { getKey: (u) => u.id });
*
* return (
* <table>
* <thead>
* <tr>
* <th>
* <input
* type="checkbox"
* checked={isAllSelected}
* ref={(el) => {
* if (el) el.indeterminate = isPartiallySelected;
* }}
* onChange={() => (isAllSelected ? clear() : selectAll())}
* />
* </th>
* <th>Name ({selected.length} selected)</th>
* </tr>
* </thead>
* <tbody>
* {users.map((user) => (
* <tr key={user.id}>
* <td>
* <input
* type="checkbox"
* checked={isSelected(user)}
* onChange={() => toggle(user)}
* />
* </td>
* <td>{user.name}</td>
* </tr>
* ))}
* </tbody>
* </table>
* );
* }
* ```
*
* @example
* ```tsx
* // Single-selection mode (radio-like): selecting replaces the previous choice.
* const { selected, isSelected, select } = useSelection(options, {
* multiple: false,
* });
* ```
*/
export function useSelection<T>(
items: T[],
options: UseSelectionOptions<T> = {}
): UseSelectionReturn<T> {
const { multiple = true } = options;
const [selectedKeys, setSelectedKeys] = useState<Set<SelectionKey>>(
() => new Set()
);
// Mirror the latest inputs so the stable actions can read fresh values
// without being recreated each render.
const getKeyOptionRef = useRef(options.getKey);
getKeyOptionRef.current = options.getKey;
const itemsRef = useRef(items);
itemsRef.current = items;
const multipleRef = useRef(multiple);
multipleRef.current = multiple;
const selectedKeysRef = useRef(selectedKeys);
selectedKeysRef.current = selectedKeys;
// A stable key resolver that always uses the latest `getKey`. Falls back to
// identity (works for primitive items) when no `getKey` is provided.
const getKey = useCallback((item: T): SelectionKey => {
const fn = getKeyOptionRef.current;
return fn ? fn(item) : (item as unknown as SelectionKey);
}, []);
const select = useCallback(
(item: T) => {
const key = getKey(item);
setSelectedKeys((prev) => {
if (multipleRef.current) {
if (prev.has(key)) {
return prev; // already selected — no-op
}
const next = new Set(prev);
next.add(key);
return next;
}
// single-selection: replace with just this key
if (prev.size === 1 && prev.has(key)) {
return prev; // already the sole selection — no-op
}
return new Set<SelectionKey>([key]);
});
},
[getKey]
);
const deselect = useCallback(
(item: T) => {
const key = getKey(item);
setSelectedKeys((prev) => {
if (!prev.has(key)) {
return prev; // not selected — no-op
}
const next = new Set(prev);
next.delete(key);
return next;
});
},
[getKey]
);
const toggle = useCallback(
(item: T) => {
const key = getKey(item);
setSelectedKeys((prev) => {
if (prev.has(key)) {
const next = new Set(prev);
next.delete(key);
return next;
}
if (multipleRef.current) {
const next = new Set(prev);
next.add(key);
return next;
}
// single-selection: replace with just this key
return new Set<SelectionKey>([key]);
});
},
[getKey]
);
const selectAll = useCallback(() => {
// Selecting "all" is a multi-selection concept.
if (!multipleRef.current) {
return;
}
setSelectedKeys((prev) => {
const currentItems = itemsRef.current;
if (currentItems.length === 0) {
return prev; // nothing to select — no-op
}
let changed = false;
const next = new Set(prev);
for (const item of currentItems) {
const key = getKey(item);
if (!next.has(key)) {
next.add(key);
changed = true;
}
}
return changed ? next : prev; // no-op when all already selected
});
}, [getKey]);
const clear = useCallback(() => {
setSelectedKeys((prev) =>
prev.size === 0 ? prev : new Set<SelectionKey>()
);
}, []);
const isSelected = useCallback(
(item: T) => selectedKeysRef.current.has(getKey(item)),
[getKey]
);
// Derive item-facing values from the current items ∩ selected keys. This is
// what drops stale keys and keeps the aggregate flags in sync when `items`
// changes. `getKey` is stable, so this recomputes only when `items` or the
// selection changes.
const { selected, isAllSelected, isPartiallySelected, isNoneSelected } =
useMemo(() => {
const sel: T[] = [];
for (const item of items) {
if (selectedKeys.has(getKey(item))) {
sel.push(item);
}
}
const count = sel.length;
const total = items.length;
return {
selected: sel,
isAllSelected: total > 0 && count === total,
isPartiallySelected: count > 0 && count < total,
isNoneSelected: count === 0,
};
}, [items, selectedKeys, getKey]);
return {
selected,
selectedKeys,
isSelected,
toggle,
select,
deselect,
selectAll,
clear,
isAllSelected,
isPartiallySelected,
isNoneSelected,
};
}
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