104 lines
2.8 KiB
TypeScript
104 lines
2.8 KiB
TypeScript
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import { NotFoundError } from "backend/src/error/not-found-error";
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import { Metadata } from "./types/metadata";
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type FetchItemsFunction<T> = (fetchItems: FetchItems) => Promise<T[]>;
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export class Pagination<T> {
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private itemsPerPage: number = 0;
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private totalItems: number = 0;
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private items: T[] | null = null; // Optional array to hold set items
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/**
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* Sets the number of items per page.
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* @param itemsPerPage - The number of items per page.
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* @returns the pagination
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*/
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setItemsPerPage(itemsPerPage: number): Pagination<T> {
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this.itemsPerPage = itemsPerPage;
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return this;
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}
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/**
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* Sets the items to paginate.
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* @param items - The items to paginate.
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* @returns the pagination
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*/
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setItems(items: T[]): Pagination<T> {
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this.items = items;
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this.totalItems = items.length;
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return this;
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}
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/**
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* Sets the total number of items.
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* @param totalItems - Total number of items.
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* @returns the pagination
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*/
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setTotalItems(totalItems: number): Pagination<T> {
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this.totalItems = totalItems;
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return this;
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}
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/**
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* Gets a page of items, using either static items or a dynamic fetchItems callback.
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* @param page - The page number to retrieve.
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* @param fetchItems - The async function to fetch items if setItems was not used.
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* @returns A promise resolving to the page of items.
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* @throws throws an error if the page number is invalid.
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*/
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async getPage(page: number, fetchItems?: FetchItemsFunction<T>): Promise<Page<T>> {
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const totalPages = Math.ceil(this.totalItems / this.itemsPerPage);
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if (page < 1 || page > totalPages) {
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throw new NotFoundError("Invalid page number");
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}
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// Calculate the range of items to fetch for the current page
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const start = (page - 1) * this.itemsPerPage;
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const end = start + this.itemsPerPage;
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let pageItems: T[];
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// Use set items if they are present, otherwise use fetchItems callback
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if (this.items) {
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pageItems = this.items.slice(start, end);
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} else if (fetchItems) {
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pageItems = await fetchItems(new FetchItems(start, end));
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} else {
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throw new Error("Items function is not set and no fetchItems callback provided");
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}
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return new Page<T>(pageItems, new Metadata(totalPages, this.totalItems, page, this.itemsPerPage));
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}
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}
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class FetchItems {
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readonly start: number;
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readonly end: number;
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constructor(start: number, end: number) {
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this.start = start;
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this.end = end;
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}
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}
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export class Page<T> {
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readonly items: T[];
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readonly metadata: Metadata;
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constructor(items: T[], metadata: Metadata) {
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this.items = items;
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this.metadata = metadata;
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}
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/**
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* Converts the page to a JSON object.
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*/
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toJSON() {
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return {
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items: this.items,
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metadata: this.metadata,
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};
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}
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}
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