src/savedBookshelf.js

export const SAVED_BOOKS_STORAGE_KEY = "world-citybook-saved-books";

export function normalizeSavedBookRecords(value) {
  const items = Array.isArray(value) ? value : [];
  const records = [];
  const byId = new Map();

  items.forEach((item) => {
    const bookId = typeof item === "string" ? item.trim() : String(item?.bookId || "").trim();
    if (!bookId) return;

    const savedAt = typeof item === "object" && item?.savedAt ? String(item.savedAt) : "";
    if (byId.has(bookId)) {
      const existing = byId.get(bookId);
      existing.savedAt = latestTimestamp(existing.savedAt, savedAt);
      return;
    }

    const record = { bookId, savedAt };
    byId.set(bookId, record);
    records.push(record);
  });

  return records;
}

export function savedBookIds(records) {
  return normalizeSavedBookRecords(records).map((record) => record.bookId);
}

export function paginateShelfItems(items, options = {}) {
  const source = Array.isArray(items) ? items : [];
  const pageSize = Math.max(1, Math.floor(Number(options.pageSize) || 1));
  const totalPages = Math.max(1, Math.ceil(source.length / pageSize));
  const page = clampInteger(options.page, 0, totalPages - 1);
  const start = page * pageSize;

  return {
    page,
    pageSize,
    totalPages,
    items: source.slice(start, start + pageSize),
  };
}

export function buildFixedShelfRows(items, options = {}) {
  const source = Array.isArray(items) ? items : [];
  const rowSize = Math.max(1, Math.floor(Number(options.rowSize) || 1));
  const rowCount = Math.max(1, Math.floor(Number(options.rowCount) || 1));

  return Array.from({ length: rowCount }, (_, rowIndex) => {
    const start = rowIndex * rowSize;
    return source.slice(start, start + rowSize);
  });
}

export function upsertSavedBook(records, bookId, savedAt = new Date().toISOString()) {
  const normalizedBookId = String(bookId || "").trim();
  if (!normalizedBookId) return normalizeSavedBookRecords(records);

  const next = normalizeSavedBookRecords(records).filter((record) => record.bookId !== normalizedBookId);
  return [{ bookId: normalizedBookId, savedAt }, ...next];
}

export function removeSavedBook(records, bookId) {
  const normalizedBookId = String(bookId || "").trim();
  return normalizeSavedBookRecords(records).filter((record) => record.bookId !== normalizedBookId);
}

function latestTimestamp(left, right) {
  if (!left) return right || "";
  if (!right) return left;
  return right > left ? right : left;
}

function clampInteger(value, min, max) {
  const number = Math.floor(Number(value) || 0);
  return Math.min(Math.max(number, min), max);
}