/**
 * Compares two values for shallow equality, only 1 level deep.
 */
export const shallowEqual = (a: any, b: any): boolean => {
  if (a === b) {
    return true;
  }

  if (a && b && typeof a === "object" && typeof b === "object") {
    if (a.constructor !== b.constructor) {
      return false;
    }

    let i: number | [any, any];
    let length: number;
    if (Array.isArray(a)) {
      length = a.length;
      if (length !== b.length) {
        return false;
      }
      for (i = length; i-- !== 0;) {
        if (a[i] !== b[i]) {
          return false;
        }
      }
      return true;
    }

    if (a instanceof Map && b instanceof Map) {
      if (a.size !== b.size) {
        return false;
      }
      for (i of a.entries()) {
        if (!b.has(i[0])) {
          return false;
        }
      }
      for (i of a.entries()) {
        if (i[1] !== b.get(i[0])) {
          return false;
        }
      }
      return true;
    }

    if (a instanceof Set && b instanceof Set) {
      if (a.size !== b.size) {
        return false;
      }
      for (i of a.entries()) {
        if (!b.has(i[0])) {
          return false;
        }
      }
      return true;
    }

    if (ArrayBuffer.isView(a) && ArrayBuffer.isView(b)) {
      // @ts-ignore
      length = a.length;
      // @ts-ignore
      if (length !== b.length) {
        return false;
      }
      for (i = length; i-- !== 0;) {
        if (a[i] !== b[i]) {
          return false;
        }
      }
      return true;
    }

    if (a.constructor === RegExp) {
      return a.source === b.source && a.flags === b.flags;
    }
    if (a.valueOf !== Object.prototype.valueOf) {
      return a.valueOf() === b.valueOf();
    }
    if (a.toString !== Object.prototype.toString) {
      return a.toString() === b.toString();
    }

    const keys = Object.keys(a);
    length = keys.length;
    if (length !== Object.keys(b).length) {
      return false;
    }
    for (i = length; i-- !== 0;) {
      if (!Object.prototype.hasOwnProperty.call(b, keys[i])) {
        return false;
      }
    }

    for (i = length; i-- !== 0;) {
      const key = keys[i];

      if (a[key] !== b[key]) {
        return false;
      }
    }

    return true;
  }

  // true if both NaN, false otherwise
  // eslint-disable-next-line no-self-compare
  return a !== a && b !== b;
};
