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use crate::page::Page;
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use serde::Deserialize;
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/// Abstracts away the `next_page` logic into a single stream of items
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#[derive(Debug, Clone)]
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pub struct ItemsIter<'a, T: Clone + for<'de> Deserialize<'de>> {
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page: Page<'a, T>,
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buffer: Vec<T>,
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cur_idx: usize,
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use_initial: bool,
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}
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impl<'a, T: Clone + for<'de> Deserialize<'de>> ItemsIter<'a, T> {
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pub(crate) fn new(page: Page<'a, T>) -> ItemsIter<'a, T> {
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ItemsIter {
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page,
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buffer: vec![],
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cur_idx: 0,
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use_initial: true,
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}
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}
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fn need_next_page(&self) -> bool {
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self.buffer.is_empty() || self.cur_idx == self.buffer.len()
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}
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async fn fill_next_page(&mut self) -> Option<()> {
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let items = if let Ok(items) = self.page.next_page().await {
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items
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} else {
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return None;
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};
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if let Some(items) = items {
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if items.is_empty() {
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return None;
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}
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self.buffer = items;
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self.cur_idx = 0;
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Some(())
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} else {
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None
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}
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}
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pub async fn next_item(&mut self) -> Option<T> {
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if self.use_initial {
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if self.page.initial_items.is_empty() || self.cur_idx == self.page.initial_items.len() {
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return None;
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}
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let idx = self.cur_idx;
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if self.cur_idx == self.page.initial_items.len() - 1 {
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self.cur_idx = 0;
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self.use_initial = false;
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} else {
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self.cur_idx += 1;
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}
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Some(self.page.initial_items[idx].clone())
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} else {
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if self.need_next_page() && self.fill_next_page().await.is_none() {
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return None;
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}
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let idx = self.cur_idx;
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self.cur_idx += 1;
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Some(self.buffer[idx].clone())
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}
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}
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}
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