Create page with next/prev url

api/src/models/utils/keyset-paginate.ts

@@ -3,6 +3,10 @@ import { eq, or, type Column, and, gt, lt } from "drizzle-orm";
 
 type Table<Name extends string> = Record<Name, Column>;
 
+type After = Record<string, string | number | boolean | undefined> & {
+	reverse?: boolean;
+};
+
 // Create a filter (where) expression on the query to skip everything before/after the referenceID.
 // The generalized expression for this in pseudocode is:
 //   (x > a) OR
@@ -27,7 +31,7 @@ export const keysetPaginate = <
 	sort: Sort<T, Remap>;
 }) => {
 	if (!after) return undefined;
-	const cursor: Record<string, string | number> = JSON.parse(
+	const { reverse, ...cursor }: After = JSON.parse(
 		Buffer.from(after, "base64").toString("utf-8"),
 	);
 
@@ -36,7 +40,7 @@ export const keysetPaginate = <
 	let where = undefined;
 	let previous = undefined;
 	for (const by of [...sort, { key: "pk" as const, desc: false }]) {
-		const cmp = by.desc ? lt : gt;
+		const cmp = by.desc !== reverse ? lt : gt;
 		where = or(where, and(previous, cmp(table[by.key], cursor[by.key])));
 		previous = and(previous, eq(table[by.key], cursor[by.key]));
 	}
@@ -44,4 +48,14 @@ export const keysetPaginate = <
 	return where;
 };
 
-
+export const generateAfter = (
+	cursor: any,
+	sort: Sort<any, any>,
+	reverse?: boolean,
+) => {
+	const ret: After = { reverse };
+	for (const by of sort) {
+		ret[by.key] = cursor[by.key];
+	}
+	return Buffer.from(JSON.stringify(ret), "utf-8").toString("base64");
+};

api/src/models/utils/page.ts

@@ -1,13 +1,34 @@
 import type { ObjectOptions } from "@sinclair/typebox";
 import { t, type TSchema } from "elysia";
+import type { Sort } from "./sort";
+import { generateAfter } from "./keyset-paginate";
 
 export const Page = <T extends TSchema>(schema: T, options?: ObjectOptions) =>
 	t.Object(
 		{
 			items: t.Array(schema),
 			this: t.String({ format: "uri" }),
-			prev: t.String({ format: "uri" }),
-			next: t.String({ format: "uri" }),
+			prev: t.Nullable(t.String({ format: "uri" })),
+			next: t.Nullable(t.String({ format: "uri" })),
 		},
 		options,
 	);
+
+export const createPage = <T>(
+	items: T[],
+	{ url, sort }: { url: string; sort: Sort<any, any> },
+) => {
+	let prev: string | null = null;
+	let next: string | null = null;
+	const uri = new URL(url);
+
+	if (uri.searchParams.has("after")) {
+		uri.searchParams.set("after", generateAfter(items[0], sort, true));
+		prev = uri.toString();
+	}
+	if (items.length) {
+		uri.searchParams.set("after", generateAfter(items[items.length - 1], sort));
+		next = uri.toString();
+	}
+	return { items, this: url, prev, next };
+};