alexion
6081e3e325
Imported as a linear vendor commit so forge rebases do not replay the upstream root tree. git-subtree-dir: third_party/pi git-subtree-split: 71023aec1546d6d677a65669c5665c0927ce0dd0
41 lines
1.7 KiB
TypeScript
41 lines
1.7 KiB
TypeScript
import { StorageRequestError } from "../errors.ts";
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import type { Id, ScanOrder } from "../types.ts";
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/** Where a built-in storage scan starts: its order and the last ID a previous page returned. */
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export type ScanStart = {
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readonly order: ScanOrder;
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readonly after: number | undefined;
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};
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/**
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* Resolve a scan's order and position. A cursor continues in the order it was created with, whether the query repeats
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* that order or omits it; a different `order` throws. A cursor without an order, written before scans had one,
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* continues in the scan's default order.
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*/
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export function scanStart(
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requested: ScanOrder | undefined,
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cursor: Readonly<Record<string, unknown>> | undefined,
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fallback: ScanOrder,
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): ScanStart {
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if (requested !== undefined && requested !== "ascending" && requested !== "descending") {
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throw new StorageRequestError(`Invalid scan order: ${String(requested)}`);
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}
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if (cursor === undefined) return { order: requested ?? fallback, after: undefined };
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const { after, order: stored } = cursor;
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if (typeof after !== "number" || !Number.isSafeInteger(after))
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throw new StorageRequestError("Invalid storage cursor");
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if (stored !== undefined && stored !== "ascending" && stored !== "descending") {
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throw new StorageRequestError("Invalid storage cursor");
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}
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const order = stored ?? fallback;
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if (requested !== undefined && requested !== order) {
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throw new StorageRequestError(`The cursor continues a ${order} scan; the query asks for ${requested}`);
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}
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return { order, after };
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}
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/** The continuation of a scan whose last returned item has `id`. */
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export function nextCursor(id: Id<string>, order: ScanOrder): { readonly after: number; readonly order: ScanOrder } {
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return { after: id, order };
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}
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