在near_sdk_rust中对UnorderedSet进行分页

[dependencies]
near-sdk = "2.0"

#[derive(Serialize, Deserialize)]
pub struct PaginatedResult<T> {
    pub items: Vec<T>,
    pub next_page: Option<String>,
}

#[near_bindgen]
impl Contract {
    pub fn get_paginated_items(&self, page_size: u64, start_after: Option<String>) -> PaginatedResult<String> {
        let mut items = Vec::new();
        let mut next_page = None;

        let unordered_set = self.unordered_set.borrow();
        let start_after_index = match start_after {
            Some(start_after) => unordered_set.get_index(&start_after).unwrap_or(0) + 1,
            None => 0,
        };

        for i in start_after_index..unordered_set.len() {
            items.push(unordered_set.get_index(i).unwrap());
            if items.len() >= page_size as usize {
                next_page = Some(unordered_set.get_index(i + 1).unwrap().clone());
                break;
            }
        }

        PaginatedResult {
            items,
            next_page,
        }
    }
}

#[near_bindgen]
impl Contract {
    pub fn get_first_page(&self, page_size: u64) -> PaginatedResult<String> {
        self.get_paginated_items(page_size, None)
    }

    pub fn get_next_page(&self, page_size: u64, start_after: String) -> PaginatedResult<String> {
        self.get_paginated_items(page_size, Some(start_after))
    }
}