@inward/context/src/value-promise.ts

LoopBack's container for Inversion of Control

// Copyright IBM Corp. 2018,2020. All Rights Reserved.
// Node module: @inward/context
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT

/**
 * This module contains types for values and/or promises as well as a set of
 * utility methods to handle values and/or promises.
 */

import {v4 as uuidv4} from 'uuid';
/**
 * A class constructor accepting arbitrary arguments.
 */
export type Constructor<T> =
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  new (...args: any[]) => T;

// eslint-disable-next-line @typescript-eslint/no-explicit-any
export type BoundValue = any;

/**
 * Representing a value or promise. This type is used to represent results of
 * synchronous/asynchronous resolution of values.
 *
 * Note that we are using PromiseLike instead of native Promise to describe
 * the asynchronous variant. This allows producers of async values to use
 * any Promise implementation (e.g. Bluebird) instead of native Promises
 * provided by JavaScript runtime.
 */
export type ValueOrPromise<T> = T | PromiseLike<T>;

export type MapObject<T> = Record<string, T>;

/**
 * Check whether a value is a Promise-like instance.
 * Recognizes both native promises and third-party promise libraries.
 *
 * @param value - The value to check.
 */
export function isPromiseLike<T>(
  value: T | PromiseLike<T> | undefined,
): value is PromiseLike<T> {
  if (!value) return false;
  if (typeof value !== 'object' && typeof value !== 'function') return false;
  return typeof (value as PromiseLike<T>).then === 'function';
}

/**
 * Get nested properties of an object by path
 * @param value - Value of the source object
 * @param path - Path to the property
 */
export function getDeepProperty<OUT = BoundValue, IN = BoundValue>(
  value: IN,
  path: string,
): OUT | undefined {
  let result: BoundValue = value;
  const props = path.split('.').filter(Boolean);
  for (const p of props) {
    if (result == null) {
      return undefined;
    }
    result = result[p];
  }
  return <OUT>result;
}

/**
 * Resolve entries of an object into a new object with the same keys. If one or
 * more entries of the source object are resolved to a promise by the `resolver`
 * function, this method returns a promise which will be resolved to the new
 * object with fully resolved entries.
 *
 * @example
 *
 * - Example 1: resolve all entries synchronously
 * ```ts
 * const result = resolveMap({a: 'x', b: 'y'}, v => v.toUpperCase());
 * ```
 * The `result` will be `{a: 'X', b: 'Y'}`.
 *
 * - Example 2: resolve one or more entries asynchronously
 * ```ts
 * const result = resolveMap({a: 'x', b: 'y'}, v =>
 *   Promise.resolve(v.toUpperCase()),
 * );
 * ```
 * The `result` will be a promise of `{a: 'X', b: 'Y'}`.
 *
 * @param map - The original object containing the source entries
 * @param resolver - A function resolves an entry to a value or promise. It will
 * be invoked with the property value, the property name, and the source object.
 */
export function resolveMap<T, V>(
  map: MapObject<T>,
  resolver: (val: T, key: string, map: MapObject<T>) => ValueOrPromise<V>,
): ValueOrPromise<MapObject<V>> {
  const result: MapObject<V> = {};
  let asyncResolvers: PromiseLike<void>[] | undefined = undefined;

  const setter = (key: string) => (val: V) => {
    if (val !== undefined) {
      // Only set the value if it's not undefined so that the default value
      // for a key will be honored
      result[key] = val;
    }
  };

  for (const key in map) {
    const valueOrPromise = resolver(map[key], key, map);
    if (isPromiseLike(valueOrPromise)) {
      if (!asyncResolvers) asyncResolvers = [];
      asyncResolvers.push(valueOrPromise.then(setter(key)));
    } else {
      if (valueOrPromise !== undefined) {
        // Only set the value if it's not undefined so that the default value
        // for a key will be honored
        result[key] = valueOrPromise;
      }
    }
  }

  if (asyncResolvers) {
    return Promise.all(asyncResolvers).then(() => result);
  } else {
    return result;
  }
}

/**
 * Resolve entries of an array into a new array with the same indexes. If one or
 * more entries of the source array are resolved to a promise by the `resolver`
 * function, this method returns a promise which will be resolved to the new
 * array with fully resolved entries.
 *
 * @example
 *
 * - Example 1: resolve all entries synchronously
 * ```ts
 * const result = resolveList(['a', 'b'], v => v.toUpperCase());
 * ```
 * The `result` will be `['A', 'B']`.
 *
 * - Example 2: resolve one or more entries asynchronously
 * ```ts
 * const result = resolveList(['a', 'b'], v =>
 *   Promise.resolve(v.toUpperCase()),
 * );
 * ```
 * The `result` will be a promise of `['A', 'B']`.
 *
 * @param list - The original array containing the source entries
 * @param resolver - A function resolves an entry to a value or promise. It will
 * be invoked with the property value, the property index, and the source array.
 */
export function resolveList<T, V>(
  list: T[],
  resolver: (val: T, index: number, list: T[]) => ValueOrPromise<V>,
): ValueOrPromise<V[]> {
  const result: V[] = new Array<V>(list.length);
  let asyncResolvers: PromiseLike<void>[] | undefined = undefined;

  const setter = (index: number) => (val: V) => {
    result[index] = val;
  };

  for (let ix = 0; ix < list.length; ix++) {
    const valueOrPromise = resolver(list[ix], ix, list);
    if (isPromiseLike(valueOrPromise)) {
      if (!asyncResolvers) asyncResolvers = [];
      asyncResolvers.push(valueOrPromise.then(setter(ix)));
    } else {
      result[ix] = valueOrPromise;
    }
  }

  if (asyncResolvers) {
    return Promise.all(asyncResolvers).then(() => result);
  } else {
    return result;
  }
}

/**
 * Try to run an action that returns a promise or a value
 * @param action - A function that returns a promise or a value
 * @param finalAction - A function to be called once the action
 * is fulfilled or rejected (synchronously or asynchronously)
 */
export function tryWithFinally<T>(
  action: () => ValueOrPromise<T>,
  finalAction: () => void,
): ValueOrPromise<T> {
  let result: ValueOrPromise<T>;
  try {
    result = action();
  } catch (err) {
    finalAction();
    throw err;
  }
  if (isPromiseLike(result)) {
    // Once (promise.finally)[https://github.com/tc39/proposal-promise-finally
    // is supported, the following can be simplifed as
    // `result = result.finally(finalAction);`
    result = result.then(
      val => {
        finalAction();
        return val;
      },
      err => {
        finalAction();
        throw err;
      },
    );
  } else {
    finalAction();
  }
  return result;
}

/**
 * Resolve an iterator of source values into a result until the evaluator
 * returns `true`
 * @param source - The iterator of source values
 * @param resolver - The resolve function that maps the source value to a result
 * @param evaluator - The evaluate function that decides when to stop
 */
export function resolveUntil<T, V>(
  source: Iterator<T>,
  resolver: (sourceVal: T) => ValueOrPromise<V | undefined>,
  evaluator: (sourceVal: T, targetVal: V | undefined) => boolean,
): ValueOrPromise<V | undefined> {
  // Do iteration in loop for synchronous values to avoid stack overflow
  // eslint-disable-next-line no-constant-condition
  while (true) {
    const next = source.next();
    if (next.done) return undefined; // End of the iterator
    const sourceVal = next.value;
    const valueOrPromise = resolver(sourceVal);
    if (isPromiseLike(valueOrPromise)) {
      return valueOrPromise.then(v => {
        if (evaluator(sourceVal, v)) {
          return v;
        } else {
          return resolveUntil(source, resolver, evaluator);
        }
      });
    } else {
      if (evaluator(sourceVal, valueOrPromise)) {
        return valueOrPromise;
      }
      // Continue with the while loop
    }
  }
}

/**
 * Transform a value or promise with a function that produces a new value or
 * promise
 * @param valueOrPromise - The value or promise
 * @param transformer - A function that maps the source value to a value or promise
 */
export function transformValueOrPromise<T, V>(
  valueOrPromise: ValueOrPromise<T>,
  transformer: (val: T) => ValueOrPromise<V>,
): ValueOrPromise<V> {
  if (isPromiseLike(valueOrPromise)) {
    return valueOrPromise.then(transformer);
  } else {
    return transformer(valueOrPromise);
  }
}

/**
 * A utility to generate uuid v4
 */
export function uuid() {
  return uuidv4();
}

/**
 * A regular expression for testing uuid v4 PATTERN
 */
export const UUID_PATTERN = /[0-9A-F]{8}-[0-9A-F]{4}-[4][0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}/i;