1 files changed, 121 insertions, 0 deletions
diff --git a/frontend/src/lib/selection/Selection.svelte.ts b/frontend/src/lib/selection/Selection.svelte.ts
new file mode 100644
index 0000000..dc294d0
--- /dev/null
+++ b/frontend/src/lib/selection/Selection.svelte.ts
@@ -0,0 +1,121 @@
+import { getContext, setContext } from 'svelte';
+import { SvelteSet } from 'svelte/reactivity';
+import { range } from '../Utils';
+
+interface Selectable {
+	id: number;
+}
+
+export function initSelectionContext<T extends Selectable>(
+	typename: string,
+	toName: (item: T) => string,
+	selectable?: (item: T) => boolean
+) {
+	return setContext('selection', new ItemSelection(typename, toName, selectable));
+}
+
+export function getSelectionContext<T extends Selectable>() {
+	return getContext<ItemSelection<T>>('selection');
+}
+
+export class ItemSelection<T extends Selectable> {
+	active = $state(false);
+	view: T[] = $state([]);
+
+	#ids = $state(new SvelteSet<number>());
+	#masked = $derived(new SvelteSet([...this.#ids].filter((i) => this.#indexOf(i) >= 0)));
+
+	typename: string;
+	#toName: (item: T) => string;
+	selectable: (item: T) => boolean;
+
+	constructor(
+		typename: string,
+		toName: (item: T) => string,
+		selectable: (item: T) => boolean = () => true
+	) {
+		this.typename = typename;
+		this.#toName = toName;
+		this.selectable = selectable;
+	}
+
+	#indexOf = (id: number) => this.view.findIndex((v) => v.id === id);
+
+	update = (index: number, shift: boolean) => {
+		const id = this.view[index].id;
+
+		const selectableRange = (first: number, last: number) =>
+			range(first, last)
+				.filter((i) => this.selectable(this.view[i]))
+				.map((i) => this.view[i].id);
+
+		if (shift) {
+			const indices = this.indices;
+
+			const first = indices.at(0);
+			const last = indices.at(-1);
+
+			if (first === undefined || last === undefined) {
+				this.#ids.add(id);
+			} else if (index === first || index === last) {
+				this.#ids.clear();
+			} else if (index > last) {
+				this.#ids = new SvelteSet([...this.#ids, ...selectableRange(last, index)]);
+			} else if (index < last) {
+				this.#ids = new SvelteSet([...this.#ids, ...selectableRange(index, last)]);
+			}
+		} else {
+			if (this.#ids.has(id)) {
+				this.#ids.delete(id);
+			} else {
+				this.#ids.add(id);
+			}
+		}
+	};
+
+	toggle = () => {
+		this.active = !this.active;
+
+		if (!this.active) {
+			this.none();
+		}
+	};
+
+	all = () => {
+		this.#ids = new SvelteSet(this.view.filter(this.selectable).map((i) => i.id));
+	};
+
+	none = () => {
+		this.#ids.clear();
+		this.#masked.clear();
+	};
+
+	clear = () => {
+		this.active = false;
+		this.none();
+	};
+
+	contains(id: number) {
+		return this.#masked.has(id);
+	}
+
+	get ids() {
+		return [...this.#masked];
+	}
+
+	get size() {
+		return this.#masked.size;
+	}
+
+	get indices() {
+		return [...this.#ids].map(this.#indexOf).filter((i) => i >= 0);
+	}
+
+	get items() {
+		return this.indices.map((i) => this.view[i]);
+	}
+
+	get names() {
+		return this.items.map(this.#toName);
+	}
+}