1 files changed, 141 insertions, 0 deletions
diff --git a/frontend/src/lib/Selection.ts b/frontend/src/lib/Selection.ts
new file mode 100644
index 0000000..0ea85cc
--- /dev/null
+++ b/frontend/src/lib/Selection.ts
@@ -0,0 +1,141 @@
+import { getContext, hasContext, setContext } from 'svelte';
+import { writable, type Writable } from 'svelte/store';
+import { range } from './Utils';
+
+interface Item {
+	id: number;
+}
+
+export const hasSelectionContext = () => hasContext('selection');
+
+export function getSelectionContext<T extends Item>() {
+	return getContext<Writable<ItemSelection<T>>>('selection');
+}
+
+export function initSelectionContext<T extends Item>(
+	typename?: string,
+	toName?: (item: T) => string
+) {
+	return setContext<Writable<ItemSelection<T>>>(
+		'selection',
+		writable(new ItemSelection(typename, toName))
+	);
+}
+
+export class ItemSelection<T extends Item> {
+	active = false;
+	typename: string;
+	#toName: (item: T) => string;
+
+	#view: T[] = [];
+	selectable: (item: T) => boolean = () => true;
+
+	#ids = new Set<number>();
+	#masked = new Set<number>();
+
+	constructor(typename?: string, toName?: (item: T) => string) {
+		this.typename = typename ?? 'unknown';
+		this.#toName = toName ?? (() => 'unknown');
+	}
+
+	set view(view: T[]) {
+		this.#view = view;
+		this.#updateMasked();
+	}
+
+	#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 Set([...this.#ids, ...selectableRange(last, index)]);
+			} else if (index < last) {
+				this.#ids = new Set([...this.#ids, ...selectableRange(index, last)]);
+			}
+		} else {
+			if (this.#ids.has(id)) {
+				this.#ids.delete(id);
+			} else {
+				this.#ids.add(id);
+			}
+		}
+
+		this.#updateMasked();
+
+		return this;
+	}
+
+	toggle() {
+		this.active = !this.active;
+
+		if (!this.active) {
+			return this.none();
+		}
+
+		return this;
+	}
+
+	all() {
+		this.#ids = new Set(this.#view.filter(this.selectable).map((i) => i.id));
+		this.#updateMasked();
+
+		return this;
+	}
+
+	none() {
+		this.#ids.clear();
+		this.#masked.clear();
+
+		return this;
+	}
+
+	clear() {
+		this.active = false;
+
+		return this.none();
+	}
+
+	contains(id: number) {
+		return this.#masked.has(id);
+	}
+
+	#updateMasked() {
+		this.#masked = new Set([...this.#ids].filter((i) => this.#indexOf(i) >= 0));
+	}
+
+	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);
+	}
+}