116 lines
2.2 KiB
TypeScript
116 lines
2.2 KiB
TypeScript
import { NotFoundError } from './error/NotFoundError';
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import { PredicateC1 } from './Predicate';
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/**
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* Unset value.
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*
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* @public
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*/
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/* eslint-disable-next-line @typescript-eslint/ban-types */
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export type Nil = null | undefined;
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/**
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* Value that may be nil.
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*
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* @public
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*/
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export type Optional<T> = T | Nil;
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/**
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* Check if a value is nil.
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*
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* @public
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*/
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/* eslint-disable-next-line @typescript-eslint/ban-types */
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export function isNil<T>(val: Optional<T>): val is Nil {
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/* eslint-disable-next-line no-null/no-null */
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return val === null || val === undefined;
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}
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/**
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* Calculate the "length" of an array or value.
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*
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* Arrays return their length, single values return 1, and nil values return 0.
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* This counts the number of elements that setOrPush would add.
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*
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* @public
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*/
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export function countOf(val: unknown): number {
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if (Array.isArray(val)) {
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return val.length;
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}
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if (doesExist(val)) {
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return 1;
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}
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return 0;
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}
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/**
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* Remove any null or undefined items from the list.
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*
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* @public
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*/
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export function filterNil<TItem>(list: ArrayLike<Optional<TItem>>): Array<TItem> {
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return Array.from(list).filter(doesExist);
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}
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/**
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* Find a value matching the given predicate or throw.
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*
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* @public
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*/
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export function mustFind<TVal>(list: Array<Optional<TVal>>, predicate: PredicateC1<TVal>): TVal {
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const val = filterNil(list).find(predicate);
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return mustExist(val);
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}
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/**
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* Check if a variable is not nil.
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*
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* @public
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*/
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export function doesExist<T>(val: Optional<T>): val is T {
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return !isNil(val);
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}
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/**
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* Assert that a variable is not nil and return the value.
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*
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* @throws NotFoundError
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* @returns val
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*
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* @public
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*/
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export function mustExist<T>(val: Optional<T>): T {
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if (isNil(val)) {
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throw new NotFoundError();
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}
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return val;
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}
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/**
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* Return the first value that is not nil.
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*
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* @public
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* @todo: rename to mustDefault
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*/
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export function mustCoalesce<T>(...values: Array<Optional<T>>): T {
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return mustFind(values, doesExist);
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}
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/**
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* Return the first element when `condition` is true and the second element when `condition` is false.
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*
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* @public
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*/
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export function defaultWhen<TVal>(condition: boolean, ...items: Array<TVal>): TVal {
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if (condition) {
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return items[0];
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} else {
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return items[1];
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}
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}
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