77 lines
2.1 KiB
TypeScript
77 lines
2.1 KiB
TypeScript
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import { generateKeyBetween, generateNKeysBetween } from "fractional-indexing";
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export interface Ordered {
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readonly id: string;
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readonly order: string;
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}
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export function compareOrdered(a: Ordered, b: Ordered): number {
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if (a.order !== b.order) {
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return a.order < b.order ? -1 : 1;
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}
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return a.id < b.id ? -1 : a.id > b.id ? 1 : 0;
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}
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/** Where `item` sorts into `sorted`: its own index when present, else its insertion index. */
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export function rankOf(sorted: readonly Ordered[], item: Ordered): number {
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let low = 0;
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let high = sorted.length;
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while (low < high) {
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const middle = (low + high) >>> 1;
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if (compareOrdered(sorted[middle]!, item) < 0) {
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low = middle + 1;
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} else {
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high = middle;
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}
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}
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return low;
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}
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/** A key after every item in `sorted`. */
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export function appendKey(sorted: readonly Ordered[]): string {
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return (
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between(sorted[sorted.length - 1]?.order ?? null, null) ??
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generateKeyBetween(null, null)
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);
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}
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/** Keys that put `sorted[from]` at `index` among the other items; `repairs` re-key those only when no key fits between its new neighbours. */
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export function placeAt(
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sorted: readonly Ordered[],
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from: number,
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index: number,
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): { key: string; repairs: Array<{ id: string; order: string }> } {
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const other = (at: number) => sorted[at < from ? at : at + 1];
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const key = between(
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other(index - 1)?.order ?? null,
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other(index)?.order ?? null,
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);
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if (key !== undefined) {
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return { key, repairs: [] };
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}
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const keys = generateNKeysBetween(null, null, sorted.length);
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return {
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key: keys[index]!,
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repairs: sorted
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.filter((_, at) => at !== from)
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.map((item, at) => ({
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id: item.id,
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order: keys[at < index ? at : at + 1]!,
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})),
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};
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}
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/** The index of `item` in `sorted`, or -1. */
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export function indexOf(sorted: readonly Ordered[], item: Ordered): number {
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const rank = rankOf(sorted, item);
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return sorted[rank] === item ? rank : -1;
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}
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function between(a: string | null, b: string | null): string | undefined {
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try {
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return generateKeyBetween(a, b);
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} catch {
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return undefined;
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}
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}
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