const test = require('node:test');
const assert = require('node:assert/strict');
const { initialState, mergeState } = require('../state');

test('initialState has the expected shape', () => {
  assert.deepEqual(initialState, {
    title: '',
    artist: '',
    album: '',
    albumArt: '',
    isPlaying: false,
    progress: 0,
    duration: 0,
  });
});

test('mergeState applies a single field update', () => {
  const next = mergeState(initialState, { title: 'Foo' });
  assert.equal(next.title, 'Foo');
});

test('mergeState preserves fields not present in the update', () => {
  const current = { ...initialState, title: 'Old', artist: 'Bar' };
  const next = mergeState(current, { title: 'New' });
  assert.equal(next.artist, 'Bar');
});

test('mergeState treats undefined fields as no-change', () => {
  const current = { ...initialState, isPlaying: true };
  const next = mergeState(current, { isPlaying: undefined });
  assert.equal(next.isPlaying, true);
});

test('mergeState applies false as a real value (not a no-change)', () => {
  const current = { ...initialState, isPlaying: true };
  const next = mergeState(current, { isPlaying: false });
  assert.equal(next.isPlaying, false);
});

test('mergeState does not mutate inputs', () => {
  const current = { ...initialState };
  const update = { title: 'X' };
  const before = { ...current };
  mergeState(current, update);
  assert.deepEqual(current, before);
  assert.deepEqual(update, { title: 'X' });
});

test('mergeState treats null fields as no-change', () => {
  const current = { ...initialState, title: 'Previous' };
  const next = mergeState(current, { title: null });
  assert.equal(next.title, 'Previous');
});

test('mergeState applies 0 as a real value (not a no-change)', () => {
  const current = { ...initialState, progress: 42 };
  const next = mergeState(current, { progress: 0 });
  assert.equal(next.progress, 0);
});