toTree.ts

type Trace = string | { open: true } | { open: false };

type TraceTree = Array<string | TraceTree>;

const toTree = (trace: Array<Trace>): TraceTree => {
  let currentBranch: TraceTree = [];
  const path: TraceTree[] = [currentBranch];

  const closeBranch = () => {
    const closedBranch = path.pop()!;
    currentBranch = path[path.length - 1];
    currentBranch.push(closedBranch);
  };

  trace.forEach((item, i, all) => {
    if (typeof item === 'string') {
      currentBranch.push(item);
    } else if (item.open === true) {
      currentBranch = [];
      path.push(currentBranch);
    } else if (item.open === false) {
      closeBranch();
    }
    // close all remaining open branches
    if (i === all.length - 1) {
      while (path.length > 1) {
        closeBranch();
      }
    }
  });

  return currentBranch;
};

test('toTree', () => {
  expect(toTree([])).toEqual([]);
  expect(toTree(['foo'])).toEqual(['foo']);
  expect(
    toTree(['foo', { open: true }, 'bar', { open: false }, 'baz'])
  ).toEqual(['foo', ['bar'], 'baz']);
  expect(
    toTree([
      '1',
      { open: true },
      '2',
      { open: true },
      '3',
      '4',
      { open: false },
      '5',
      { open: false },
      '6',
      { open: true },
      '7',
      { open: false }
    ])
  ).toEqual(['1', ['2', ['3', '4'], '5'], '6', ['7']]);
});

test('toTree unclosed', () => {
  expect(toTree(['1', { open: true }, '2', { open: true }, '3', '4'])).toEqual([
    '1',
    ['2', ['3', '4']]
  ]);
});