wallet-core/src/util/helpers.ts

/*
 This file is part of TALER
 (C) 2016 GNUnet e.V.

 TALER is free software; you can redistribute it and/or modify it under the
 terms of the GNU General Public License as published by the Free Software
 Foundation; either version 3, or (at your option) any later version.

 TALER is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

 You should have received a copy of the GNU General Public License along with
 TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
 */

/**
 * Small helper functions that don't fit anywhere else.
 */

/**
 * Imports.
 */
import { AmountJson } from "./amounts";
import * as Amounts from "./amounts";

/**
 * Show an amount in a form suitable for the user.
 * FIXME:  In the future, this should consider currency-specific
 * settings such as significant digits or currency symbols.
 */
export function amountToPretty(amount: AmountJson): string {
  const x = amount.value + amount.fraction / Amounts.fractionalBase;
  return `${x} ${amount.currency}`;
}


/**
 * Canonicalize a base url, typically for the exchange.
 *
 * See http://api.taler.net/wallet.html#general
 */
export function canonicalizeBaseUrl(url: string) {
  if (!url.startsWith("http") && !url.startsWith("https")) {
    url = "https://" + url;
  }
  const x = new URL(url);
  if (!x.pathname.endsWith("/")) {
    x.pathname = x.pathname + "/";
  }
  x.search = "";
  x.hash = "";
  return x.href;
}


/**
 * Convert object to JSON with canonical ordering of keys
 * and whitespace omitted.
 */
export function canonicalJson(obj: any): string {
  // Check for cycles, etc.
  JSON.stringify(obj);
  if (typeof obj === "string" || typeof obj === "number" || obj === null) {
    return JSON.stringify(obj);
  }
  if (Array.isArray(obj)) {
    const objs: string[] = obj.map((e) => canonicalJson(e));
    return `[${objs.join(",")}]`;
  }
  const keys: string[] = [];
  for (const key in obj) {
    keys.push(key);
  }
  keys.sort();
  let s = "{";
  for (let i = 0; i < keys.length; i++) {
    const key = keys[i];
    s += JSON.stringify(key) + ":" + canonicalJson(obj[key]);
    if (i !== keys.length - 1) {
      s += ",";
    }
  }
  return s + "}";
}


/**
 * Check for deep equality of two objects.
 * Only arrays, objects and primitives are supported.
 */
export function deepEquals(x: any, y: any): boolean {
  if (x === y) {
    return true;
  }

  if (Array.isArray(x) && x.length !== y.length) {
    return false;
  }

  const p = Object.keys(x);
  return Object.keys(y).every((i) => p.indexOf(i) !== -1) &&
    p.every((i) => deepEquals(x[i], y[i]));
}


/**
 * Map from a collection to a list or results and then
 * concatenate the results.
 */
export function flatMap<T, U>(xs: T[], f: (x: T) => U[]): U[] {
  return xs.reduce((acc: U[], next: T) => [...f(next), ...acc], []);
}

/**
 * Compute the hash function of a JSON object.
 */
export function hash(val: any): number {
  const str = canonicalJson(val);
  // https://github.com/darkskyapp/string-hash
  let h = 5381;
  let i = str.length;
  while (i) {
    h = (h * 33) ^ str.charCodeAt(--i);
  }

  /* JavaScript does bitwise operations (like XOR, above) on 32-bit signed
  * integers. Since we want the results to be always positive, convert the
  * signed int to an unsigned by doing an unsigned bitshift. */
  return h >>> 0;
}


/**
 * Lexically compare two strings.
 */
export function strcmp(s1: string, s2: string): number {
  if (s1 < s2) {
    return -1;
  }
  if (s1 > s2) {
    return 1;
  }
  return 0;
}

/**
 * Run a function and return its result.
 * 
 * Used as a nicer-looking way to do immediately invoked function
 * expressions (IFFEs).
 */
export function runBlock<T>(f: () => T) {
  return f();
}