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'use strict';
const Assert = require('./assert'); const Clone = require('./clone'); const Merge = require('./merge'); const Reach = require('./reach');
const internals = {};
module.exports = function (defaults, source, options = {}) {
Assert(defaults && typeof defaults === 'object', 'Invalid defaults value: must be an object'); Assert(!source || source === true || typeof source === 'object', 'Invalid source value: must be true, falsy or an object'); Assert(typeof options === 'object', 'Invalid options: must be an object');
if (!source) { // If no source, return null
return null; }
if (options.shallow) { return internals.applyToDefaultsWithShallow(defaults, source, options); }
const copy = Clone(defaults);
if (source === true) { // If source is set to true, use defaults
return copy; }
const nullOverride = options.nullOverride !== undefined ? options.nullOverride : false; return Merge(copy, source, { nullOverride, mergeArrays: false }); };
internals.applyToDefaultsWithShallow = function (defaults, source, options) {
const keys = options.shallow; Assert(Array.isArray(keys), 'Invalid keys');
const seen = new Map(); const merge = source === true ? null : new Set();
for (let key of keys) { key = Array.isArray(key) ? key : key.split('.'); // Pre-split optimization
const ref = Reach(defaults, key); if (ref && typeof ref === 'object') {
seen.set(ref, merge && Reach(source, key) || ref); } else if (merge) { merge.add(key); } }
const copy = Clone(defaults, {}, seen);
if (!merge) { return copy; }
for (const key of merge) { internals.reachCopy(copy, source, key); }
const nullOverride = options.nullOverride !== undefined ? options.nullOverride : false; return Merge(copy, source, { nullOverride, mergeArrays: false }); };
internals.reachCopy = function (dst, src, path) {
for (const segment of path) { if (!(segment in src)) { return; }
const val = src[segment];
if (typeof val !== 'object' || val === null) { return; }
src = val; }
const value = src; let ref = dst; for (let i = 0; i < path.length - 1; ++i) { const segment = path[i]; if (typeof ref[segment] !== 'object') { ref[segment] = {}; }
ref = ref[segment]; }
ref[path[path.length - 1]] = value; };
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