93 lines
2.4 KiB
TypeScript
93 lines
2.4 KiB
TypeScript
// Copyright 2021 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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/* eslint-disable max-classes-per-file */
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export function isIterable(value: unknown): value is Iterable<unknown> {
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return (
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(typeof value === 'object' && value !== null && Symbol.iterator in value) ||
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typeof value === 'string'
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);
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}
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export function size(iterable: Iterable<unknown>): number {
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// We check for common types as an optimization.
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if (typeof iterable === 'string' || Array.isArray(iterable)) {
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return iterable.length;
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}
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if (iterable instanceof Set || iterable instanceof Map) {
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return iterable.size;
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}
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const iterator = iterable[Symbol.iterator]();
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let result = -1;
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for (let done = false; !done; result += 1) {
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done = Boolean(iterator.next().done);
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}
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return result;
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}
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export function map<T, ResultT>(
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iterable: Iterable<T>,
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fn: (value: T) => ResultT
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): Iterable<ResultT> {
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return new MapIterable(iterable, fn);
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}
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class MapIterable<T, ResultT> implements Iterable<ResultT> {
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constructor(
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private readonly iterable: Iterable<T>,
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private readonly fn: (value: T) => ResultT
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) {}
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[Symbol.iterator](): Iterator<ResultT> {
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return new MapIterator(this.iterable[Symbol.iterator](), this.fn);
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}
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}
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class MapIterator<T, ResultT> implements Iterator<ResultT> {
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constructor(
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private readonly iterator: Iterator<T>,
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private readonly fn: (value: T) => ResultT
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) {}
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next(): IteratorResult<ResultT> {
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const nextIteration = this.iterator.next();
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if (nextIteration.done) {
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return nextIteration;
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}
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return {
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done: false,
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value: this.fn(nextIteration.value),
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};
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}
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}
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export function take<T>(iterable: Iterable<T>, amount: number): Iterable<T> {
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return new TakeIterable(iterable, amount);
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}
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class TakeIterable<T> implements Iterable<T> {
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constructor(
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private readonly iterable: Iterable<T>,
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private readonly amount: number
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) {}
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[Symbol.iterator](): Iterator<T> {
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return new TakeIterator(this.iterable[Symbol.iterator](), this.amount);
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}
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}
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class TakeIterator<T> implements Iterator<T> {
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constructor(private readonly iterator: Iterator<T>, private amount: number) {}
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next(): IteratorResult<T> {
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const nextIteration = this.iterator.next();
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if (nextIteration.done || this.amount === 0) {
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return { done: true, value: undefined };
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}
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this.amount -= 1;
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return nextIteration;
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}
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}
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