use serde::Deserialize;
use crate::page::Page;
pub(crate) struct ItemsIter<'a, T: Clone + for<'de> Deserialize<'de>> {
page: Page<'a, T>,
buffer: Vec<T>,
cur_idx: usize,
use_initial: bool,
}
impl<'a, T: Clone + for<'de> Deserialize<'de>> ItemsIter<'a, T> {
pub(crate) fn new(page: Page<'a, T>) -> ItemsIter<'a, T> {
ItemsIter {
page: page,
buffer: vec![],
cur_idx: 0,
use_initial: true,
}
}
fn need_next_page(&self) -> bool {
self.buffer.is_empty() ||
self.cur_idx == self.buffer.len()
}
fn fill_next_page(&mut self) -> Option<()> {
let items = if let Ok(items) = self.page.next_page() {
items
} else {
return None;
};
if let Some(items) = items {
self.buffer = items;
self.cur_idx = 0;
Some(())
} else {
None
}
}
}
impl<'a, T: Clone+ for<'de> Deserialize<'de>> Iterator for ItemsIter<'a, T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
if self.use_initial {
if self.page.initial_items.is_empty() {
return None;
}
let idx = self.cur_idx;
if self.cur_idx == self.page.initial_items.len() - 1 {
self.cur_idx = 0;
self.use_initial = false;
} else {
self.cur_idx += 1;
}
Some(self.page.initial_items[idx].clone())
} else {
if self.need_next_page() {
if self.fill_next_page().is_none() {
return None;
}
}
let idx = self.cur_idx;
self.cur_idx += 1;
Some(self.buffer[idx].clone())
}
}
}