3 Object.create / getPrototypeOf

'use strict';
// ---------------------------------------------------------------------
// PROTO-DOJO · Module 1 / Exercise 3 — Object.create / getPrototypeOf
//
// GOAL:    Build a zero-copy settings cascade (engine → profile → game)
//          in which every layer STORES only its own overrides and READS
//          the rest through its hidden link — then walk that link by
//          hand with Object.getPrototypeOf.
// CONCEPT: Object.create(proto) returns a brand-new object whose
//          [[Prototype]] is `proto`. Nothing gets copied: patch the
//          engine defaults later and every running game picks the
//          change up on its very next read. Object.getPrototypeOf
//          follows exactly one link; a.isPrototypeOf(b) asks "does `a`
//          appear ANYWHERE on b's chain?".
// HINT:    Own props are the ones YOU wrote onto the object
//          (Object.keys lists only own enumerable ones). Everything
//          else is found by lookup, never by storage.
// MIRRORS: Layered configuration in game engines and UI toolkits —
//          built-in defaults → the player's saved profile → per-match
//          settings. A deep-merge helper COPIES each layer into a
//          frozen snapshot; the prototype chain gives the same fallback
//          semantics with zero copies, which is why editing a merged
//          snapshot never flows back upstream while a chained read
//          always sees the newest upstream value.
//
// Run: node 03-object-create-settings-cascade.cjs
// ---------------------------------------------------------------------
const assert = require('node:assert');

const engineDefaults = {
  difficulty: 'normal',
  volume: 0.8,
  jumpKey: 'Space',
  fpsCap: 60,
};

// -- TODO 1 -----------------------------------------------------------
// Build profileSettings so it PROTOTYPE-CHAINS to engineDefaults (no spread, no
// Object.assign — the profile has to pick up future engine edits for
// free) and
// OWNS exactly one override: volume 0.5.
const profileSettings = null;

// -- TODO 2 -----------------------------------------------------------
// Build gameSettings chained to profileSettings, owning a single override:
// difficulty 'hard'.
const gameSettings = null;


// -- TODO 3 -----------------------------------------------------------
// Starting FROM gameSettings, climb the chain with Object.getPrototypeOf until
// you arrive at engineDefaults. Your expression may not mention the
// profileSettings / engineDefaults variables directly.
const climbedToEngine = null;

// -- checks -----------------------------------------------------------
assert.ok(profileSettings, 'TODO 1: build profileSettings with Object.create(...)');
assert.strictEqual(Object.getPrototypeOf(profileSettings), engineDefaults,
  'TODO 1: the hidden link of profileSettings must point at engineDefaults');
assert.deepStrictEqual(Object.keys(profileSettings), ['volume'],
  'TODO 1: only volume is OWN — everything else must be inherited, not copied');
assert.strictEqual(profileSettings.volume, 0.5, 'profile override');
assert.strictEqual(profileSettings.jumpKey, 'Space', 'jumpKey should fall through to the engine defaults');

assert.ok(gameSettings, 'TODO 2: build gameSettings with Object.create(...)');
assert.strictEqual(Object.getPrototypeOf(gameSettings), profileSettings,
  'TODO 2: gameSettings chains to profileSettings, not straight to the engine defaults');
assert.strictEqual(gameSettings.difficulty, 'hard', 'own override wins');
assert.strictEqual(gameSettings.volume, 0.5, 'one hop: the profile override beats the engine default');
assert.strictEqual(gameSettings.fpsCap, 60, 'two hops: falls all the way through to the engine defaults');
assert.ok(engineDefaults.isPrototypeOf(gameSettings),
  'engineDefaults must sit somewhere on gameSettings\'s chain');

// live cascade — the entire reason to chain instead of copy:
engineDefaults.fpsCap = 144;
assert.strictEqual(gameSettings.fpsCap, 144,
  'an engine edit must be visible through the chain instantly — if this fails, you copied instead of chained');

assert.strictEqual(climbedToEngine, engineDefaults,
  'TODO 3: two climbs — Object.getPrototypeOf(Object.getPrototypeOf(gameSettings))');

console.log('PASS — 03-object-create-settings-cascade: zero-copy fallback via the chain');