import assert from 'node:assert/strict';
import test from 'node:test';

// Keep in sync with src/utils/sessions.ts merge rules for regression coverage.
function pickNewerIsoTimestamp(left, right) {
  const leftTime = Date.parse(left ?? '');
  const rightTime = Date.parse(right ?? '');
  const leftValid = Number.isFinite(leftTime);
  const rightValid = Number.isFinite(rightTime);
  if (!leftValid && !rightValid) return left ?? right;
  if (!leftValid) return right;
  if (!rightValid) return left;
  return leftTime >= rightTime ? left : right;
}

function mergeSessionRecord(existing, incoming) {
  if (!existing) return incoming;
  const merged = { ...existing, ...incoming, id: incoming.id };
  return {
    ...merged,
    updated_at: pickNewerIsoTimestamp(existing.updated_at, incoming.updated_at),
    message_count: Math.max(Number(existing.message_count ?? 0), Number(incoming.message_count ?? 0)),
  };
}

test('mergeSessionRecord keeps the newer updated_at when refreshing stale server summaries', () => {
  const merged = mergeSessionRecord(
    {
      id: 'sess-1',
      name: 'New Chat',
      message_count: 4,
      updated_at: '2026-09-02T14:48:00.000Z',
    },
    {
      id: 'sess-1',
      name: 'New Chat',
      message_count: 3,
      updated_at: '2026-09-02T14:40:00.000Z',
    },
  );
  assert.equal(merged.updated_at, '2026-09-02T14:48:00.000Z');
  assert.equal(merged.message_count, 4);
});

test('mergeSessionRecord adopts newer server timestamps when local cache is older', () => {
  const merged = mergeSessionRecord(
    {
      id: 'sess-2',
      name: 'New Chat',
      message_count: 2,
      updated_at: '2026-09-02T14:30:00.000Z',
    },
    {
      id: 'sess-2',
      name: 'New Chat',
      message_count: 5,
      updated_at: '2026-09-02T14:48:00.000Z',
    },
  );
  assert.equal(merged.updated_at, '2026-09-02T14:48:00.000Z');
  assert.equal(merged.message_count, 5);
});