@difizen/mana-common/src/iterator.ts

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

export namespace Iterable {
  export function is<T = any>(thing: any): thing is IterableIterator<T> {
    return (
      thing && typeof thing === 'object' && typeof thing[Symbol.iterator] === 'function'
    );
  }

  const _empty: Iterable<any> = Object.freeze([]);
  export function empty<T = any>(): Iterable<T> {
    return _empty;
  }

  export function* single<T>(element: T): Iterable<T> {
    yield element;
  }

  export function from<T>(iterable: Iterable<T> | undefined | null): Iterable<T> {
    return iterable || _empty;
  }

  export function isEmpty<T>(iterable: Iterable<T> | undefined | null): boolean {
    return !iterable || iterable[Symbol.iterator]().next().done === true;
  }

  export function first<T>(iterable: Iterable<T>): T | undefined {
    return iterable[Symbol.iterator]().next().value;
  }

  export function some<T>(
    iterable: Iterable<T>,
    predicate: (t: T) => boolean,
  ): boolean {
    for (const element of iterable) {
      if (predicate(element)) {
        return true;
      }
    }
    return false;
  }

  export function find<T, R extends T>(
    iterable: Iterable<T>,
    predicate: (t: T) => t is R,
  ): T | undefined;
  export function find<T>(
    iterable: Iterable<T>,
    predicate: (t: T) => boolean,
  ): T | undefined;
  export function find<T>(
    iterable: Iterable<T>,
    predicate: (t: T) => boolean,
  ): T | undefined {
    for (const element of iterable) {
      if (predicate(element)) {
        return element;
      }
    }

    return undefined;
  }

  export function filter<T, R extends T>(
    iterable: Iterable<T>,
    predicate: (t: T) => t is R,
  ): Iterable<R>;
  export function filter<T>(
    iterable: Iterable<T>,
    predicate: (t: T) => boolean,
  ): Iterable<T>;
  export function* filter<T>(
    iterable: Iterable<T>,
    predicate: (t: T) => boolean,
  ): Iterable<T> {
    for (const element of iterable) {
      if (predicate(element)) {
        yield element;
      }
    }
  }

  export function* map<T, R>(iterable: Iterable<T>, fn: (t: T) => R): Iterable<R> {
    for (const element of iterable) {
      yield fn(element);
    }
  }

  export function* concat<T>(...iterables: Iterable<T>[]): Iterable<T> {
    for (const iterable of iterables) {
      for (const element of iterable) {
        yield element;
      }
    }
  }

  export function* concatNested<T>(iterables: Iterable<Iterable<T>>): Iterable<T> {
    for (const iterable of iterables) {
      for (const element of iterable) {
        yield element;
      }
    }
  }

  export function reduce<T, R>(
    iterable: Iterable<T>,
    reducer: (previousValue: R, currentValue: T) => R,
    initialValue: R,
  ): R {
    let value = initialValue;
    for (const element of iterable) {
      value = reducer(value, element);
    }
    return value;
  }

  /**
   * Returns an iterable slice of the array, with the same semantics as `array.slice()`.
   */
  // eslint-disable-next-line @typescript-eslint/no-shadow
  export function* slice<T>(
    arr: readonly T[],
    from: number,
    to = arr.length,
  ): Iterable<T> {
    if (from < 0) {
      from += arr.length;
    }

    if (to < 0) {
      to += arr.length;
    } else if (to > arr.length) {
      to = arr.length;
    }

    for (; from < to; from++) {
      yield arr[from];
    }
  }

  /**
   * Consumes `atMost` elements from iterable and returns the consumed elements,
   * and an iterable for the rest of the elements.
   */
  export function consume<T>(
    iterable: Iterable<T>,
    atMost: number = Number.POSITIVE_INFINITY,
  ): [T[], Iterable<T>] {
    const consumed: T[] = [];

    if (atMost === 0) {
      return [consumed, iterable];
    }

    const iterator = iterable[Symbol.iterator]();

    for (let i = 0; i < atMost; i++) {
      const next = iterator.next();

      if (next.done) {
        return [consumed, Iterable.empty()];
      }

      consumed.push(next.value);
    }

    return [
      consumed,
      {
        [Symbol.iterator]() {
          return iterator;
        },
      },
    ];
  }

  /**
   * Returns whether the iterables are the same length and all items are
   * equal using the comparator function.
   */
  export function equals<T>(
    a: Iterable<T>,
    b: Iterable<T>,
    comparator = (at: T, bt: T) => at === bt,
  ) {
    const ai = a[Symbol.iterator]();
    const bi = b[Symbol.iterator]();
    // eslint-disable-next-line no-constant-condition
    while (true) {
      const an = ai.next();
      const bn = bi.next();

      if (an.done !== bn.done) {
        return false;
      }
      if (an.done) {
        return true;
      }
      if (!comparator(an.value, bn.value)) {
        return false;
      }
    }
  }

  /**
   * return the max value using the comparator
   * @param iterable collection
   * @param comparator fn
   * @returns max item
   */
  export function max<T>(
    iterable: Iterable<T>,
    comparator: (first: T, second: T) => number,
  ): T | undefined {
    const firstValue = first(iterable);
    if (!firstValue) {
      return undefined;
    }
    return reduce<T, T>(
      iterable,
      (prev, curr) => (comparator(prev, curr) > 0 ? prev : curr),
      firstValue,
    );
  }
}