// Bookmarks ({ "JHN-3-16": "#fef08a" }) and text highlights ([{ id, book, chapter, verse,
// startOffset, endOffset, color }]) — helpers for keeping them in sync between devices.

export const emptyMarks = () => ({ bookmarks: {}, highlights: [] });

export const isEmptyMarks = (m) => Object.keys(m.bookmarks).length === 0 && m.highlights.length === 0;

// Forgiving read of whatever came from localStorage or the server.
export function normalizeMarks(raw) {
  const bookmarks = raw?.bookmarks && typeof raw.bookmarks === 'object' && !Array.isArray(raw.bookmarks) ? raw.bookmarks : {};
  const highlights = Array.isArray(raw?.highlights) ? raw.highlights.filter((h) => h && typeof h.id === 'string') : [];
  return { bookmarks, highlights };
}

const sameSpan = (a, b) => a.book === b.book && a.chapter === b.chapter && a.verse === b.verse
  && a.startOffset === b.startOffset && a.endOffset === b.endOffset;

// Union of two devices' marks. Used only when both changed since they last synced, or the
// first time a device meets the server's copy, so nothing made on either side is lost. Where the
// same bookmark has two colours, the server's wins.
export function mergeMarks(local, server) {
  const bookmarks = { ...local.bookmarks, ...server.bookmarks };
  const highlights = [...server.highlights];
  for (const h of local.highlights) {
    if (!highlights.some((s) => s.id === h.id || sameSpan(s, h))) highlights.push(h);
  }
  return { bookmarks, highlights };
}

export function marksEqual(a, b) {
  const ka = Object.keys(a.bookmarks);
  if (ka.length !== Object.keys(b.bookmarks).length) return false;
  if (ka.some((k) => a.bookmarks[k] !== b.bookmarks[k])) return false;
  if (a.highlights.length !== b.highlights.length) return false;
  const byId = new Map(b.highlights.map((h) => [h.id, h]));
  return a.highlights.every((h) => {
    const o = byId.get(h.id);
    return o && sameSpan(h, o) && h.color === o.color;
  });
}