const { numItems, cursor: cursorString } = paginationOpts;
const numItemsToFetch = numItems + 1;

let query = ctx.db.query("products");

const sortFieldMapping = {
  "by_price": "currentPrice",
  "by_popularity": "likes",
  "by_date": "updateTime" // Corrected to match the schema field name
};
const sortFieldJsName = sortFieldMapping[sort.field];

if (cursorString) {
  try {
    const parsedCursor = JSON.parse(cursorString) as { cursorValue: any; cursorId: Id<"products"> };
    const { cursorValue, cursorId } = parsedCursor;

    if (cursorValue === undefined || !cursorId) {
      // Log and proceed without cursor if it's malformed
      console.warn("Invalid cursor structure received:", cursorString);
    } else {
      query = query.filter(q => {
        // The type assertion `as any` is used because sortFieldJsName is dynamic.
        // Ensure `cursorValue` type matches the field's type.
        const docSortValue = q.field(sortFieldJsName as any);
        const docId = q.field("_id");

        if (sort.direction === "asc") {
          return q.or(
            q.gt(docSortValue, cursorValue),
            q.and(q.eq(docSortValue, cursorValue), q.gt(docId, cursorId))
          );
        } else { // desc
          return q.or(
            q.lt(docSortValue, cursorValue),
            q.and(q.eq(docSortValue, cursorValue), q.lt(docId, cursorId))
          );
        }
      });
    }
  } catch (e) {
    console.error("Failed to parse cursor string, fetching first page:", cursorString, e);
    // Invalid cursor string, effectively ignore it and fetch the first page.
  }
}

// dbProducts will hold raw product data from the database query
const dbProducts: any[] = await query.take(numItemsToFetch);

const hasMore = dbProducts.length > numItems;
const pageProducts = hasMore ? dbProducts.slice(0, numItems) : dbProducts;

let newContinueCursor: string | null = null;
if (hasMore) {
  const lastProductOnPage = pageProducts[pageProducts.length - 1];
  if (lastProductOnPage) {
    // Accessing field dynamically. Ensure Product type has these fields or handle potential undefined.
    const sortVal = (lastProductOnPage as any)[sortFieldJsName];
    if (sortVal === undefined) {
      console.warn(`Sort field '${sortFieldJsName}' is undefined for product '${lastProductOnPage._id}'. Cursor may be incorrect.`);
    }
    newContinueCursor = JSON.stringify({
      cursorValue: sortVal,
      cursorId: lastProductOnPage._id
    });
  }
}


return {
  page: pageProducts,
  isDone: !hasMore,
  continueCursor: newContinueCursor || "",
};