'use strict';


export function create(obj, proto=Object.prototype) {
  const props = Object.keys(obj)
    .map((key) => [ key, { value: obj[key], enumerable: true } ])
    .reduce((acc, [ key, value ]) => ({ ...acc, [key]: value }), {});

  return Object.create(proto, props);
};


export function random_choice(collection, r=Math.random()) {
  const idx = Math.floor(collection.length * r);
  return collection[idx];
}


export function pairs(arr1, arr2) {
  return arr1
    .map((x, i) => arr2.map(y => [x, y]))
    .flat();
}


export function deepEqual(a, b, debug=false) {
  if (typeof(a) === 'object') {
    if (typeof(b) === 'object') {
      // do deep equality
      return [...new Set(Object.keys(a).concat(Object.keys(b)))].reduce(
        (acc, key) => {
          return acc && deepEqual(a[key], b[key]);
        },
        true 
      );
    } else {
      // one object, one non-object
      return false;
    }
  } else {
    return a === b;
  }
}


export function apply(f, n, x0) {
  if (n == 0) {
    return x0;
  } else {
    return f(apply(f, n-1, x0));
  }
}