// A user's synced display preferences: theme, default Reader translation, verse layout, the
// commentary they last chose, and where they left off in the Reader. Each preference carries
// its own timestamp ({ v, at }) so the most recent change to each one wins, device by device.
const ENUMS = {
  theme: ['paper', 'sepia', 'dark'],
  translation: ['BSB', 'ESV', 'NLT', 'CSB', 'NASB', 'NET'],
  layout: ['flow', 'verses'],
  startPage: ['studies', 'reader', 'plans'], // where the app opens and where Home buttons go
  planTranslation: ['same', 'BSB', 'ESV', 'NLT', 'CSB', 'NASB', 'NET'], // which Bible new reading plans start in
  commentarySource: ['matthew-henry', 'john-gill', 'jamieson-fausset-brown', 'tyndale', 'adam-clarke', 'john-calvin', 'keil-delitzsch'],
};
const DAY_MS = 86_400_000;
const COLOR = /^#[0-9a-fA-F]{3,8}$/;

// A cleaned value, or undefined when it isn't acceptable for that preference.
export function cleanPrefValue(key, value) {
  if (ENUMS[key]) return ENUMS[key].includes(value) ? value : undefined;
  if (key === 'colorLabels') {
    // What each highlight colour means to the reader: { "#fef08a": "Promises", ... }
    if (!value || typeof value !== 'object' || Array.isArray(value)) return undefined;
    const out = {};
    for (const [color, label] of Object.entries(value).slice(0, 12)) {
      if (COLOR.test(color) && typeof label === 'string' && label.trim()) out[color] = label.trim().slice(0, 30);
    }
    return out;
  }
  if (key === 'studyTemplates') {
    // The person's own study templates: prompts for the note boxes and scaffold text to start each chunk with
    if (!Array.isArray(value)) return undefined;
    const text = (v, max) => (typeof v === 'string' ? v.slice(0, max) : '');
    const fields = (o, names, max) => {
      const out = {};
      for (const n of names) { const t = text(o?.[n], max); if (t.trim()) out[n] = t; }
      return out;
    };
    return value.slice(0, 12).filter((t) => t && typeof t.id === 'string' && /^user-[\w-]{1,40}$/.test(t.id) && typeof t.name === 'string' && t.name.trim()).map((t) => {
      const prompts = fields(t.prompts, ['observation', 'interpretation', 'application'], 800);
      const starters = fields(t.starters, ['generalNotes', 'observation', 'interpretation', 'application'], 2000);
      return { id: t.id, name: text(t.name, 40).trim(), description: text(t.description, 120), ...(Object.keys(prompts).length ? { prompts } : {}), ...(Object.keys(starters).length ? { starters } : {}) };
    });
  }
  if (key === 'position') {
    if (!value || typeof value !== 'object') return undefined;
    const book = String(value.book ?? '').toUpperCase();
    if (!/^[1-3A-Z]{3}$/.test(book) || !Number.isInteger(value.chapter) || value.chapter < 1 || value.chapter > 200) return undefined;
    return { book, chapter: value.chapter };
  }
  return undefined;
}

// Body -> { key: { v, at } } with only known keys, valid values and sane timestamps.
export function cleanPrefsPatch(body, now = Date.now()) {
  const out = {};
  const prefs = body?.prefs;
  if (!prefs || typeof prefs !== 'object' || Array.isArray(prefs)) return out;
  for (const [key, entry] of Object.entries(prefs)) {
    const v = cleanPrefValue(key, entry?.v);
    const at = entry?.at;
    if (v === undefined || !Number.isFinite(at) || at < 0 || at > now + DAY_MS) continue;
    out[key] = { v, at };
  }
  return out;
}

// Per key, the entry with the newer timestamp wins (the stored one on a tie).
export function mergePrefs(existing = {}, patch = {}) {
  const merged = { ...existing };
  for (const [key, entry] of Object.entries(patch)) {
    if (!merged[key] || entry.at > merged[key].at) merged[key] = entry;
  }
  return merged;
}