export const tutorialProgressKey = campaignId => `hex-trails-tutorial-v1-${campaignId}`;

function tutorialCount(count) {
  return Number.isInteger(count) && count > 0 ? count : 0;
}

function normalizeProgress(value, count) {
  const valid = index => Number.isInteger(index) && index >= 0 && index < count;
  return {
    current: valid(value?.current) ? value.current : 0,
    completed: [...new Set(Array.isArray(value?.completed) ? value.completed.filter(valid) : [])],
  };
}

export function readTutorialProgress(storage, campaignId, count) {
  count = tutorialCount(count);
  let value;
  if (count) {
    try { value = JSON.parse(storage?.getItem(tutorialProgressKey(campaignId)) ?? '{}'); } catch {}
  }
  return normalizeProgress(value, count);
}

export function writeTutorialProgress(storage, campaignId, count, progress) {
  count = tutorialCount(count);
  if (!count || !storage) return false;
  try {
    storage.setItem(tutorialProgressKey(campaignId), JSON.stringify(normalizeProgress(progress, count)));
    return true;
  } catch { return false; }
}

export function tutorialLaunch(search, count, progress, campaignProgress) {
  count = tutorialCount(count);
  if (!count) return null;
  const params = new URLSearchParams(search);
  const requested = params.get('tutorial');
  if (/^\d+$/.test(requested ?? '')) {
    const index = Number(requested) - 1;
    if (Number.isInteger(index) && index >= 0 && index < count) return index;
  }
  // Existing level links keep their destination, including links to level 1.
  if (params.has('level')) return null;
  if ((Number.isInteger(campaignProgress?.current) && campaignProgress.current > 0)
    || (Array.isArray(campaignProgress?.completed) && campaignProgress.completed.length > 0)) return null;

  const normalized = normalizeProgress(progress, count);
  const completed = new Set(normalized.completed);
  for (let offset = 0; offset < count; offset += 1) {
    const index = (normalized.current + offset) % count;
    if (!completed.has(index)) return index;
  }
  return null;
}