From 0e8eb4e568dd02c91af7127f596d727ebc20d7fe Mon Sep 17 00:00:00 2001
From: Paul Woolcock <paul@woolcock.us>
Date: Sun, 5 Aug 2018 11:03:48 -0400
Subject: [PATCH] Add `PageIter<T>` to abstract over iterating over pages

---
 src/entities/mod.rs      |  2 +
 src/entities/pageiter.rs | 94 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 src/entities/pageiter.rs

diff --git a/src/entities/mod.rs b/src/entities/mod.rs
index c82ae5a..e45057c 100644
--- a/src/entities/mod.rs
+++ b/src/entities/mod.rs
@@ -6,6 +6,7 @@ pub mod instance;
 pub mod list;
 pub mod mention;
 pub mod notification;
+pub mod pageiter;
 pub mod relationship;
 pub mod report;
 pub mod search_result;
@@ -27,6 +28,7 @@ pub mod prelude {
     pub use super::list::List;
     pub use super::mention::Mention;
     pub use super::notification::Notification;
+    pub use super::pageiter::PageIter;
     pub use super::relationship::Relationship;
     pub use super::report::Report;
     pub use super::search_result::SearchResult;
diff --git a/src/entities/pageiter.rs b/src/entities/pageiter.rs
new file mode 100644
index 0000000..52c92dc
--- /dev/null
+++ b/src/entities/pageiter.rs
@@ -0,0 +1,94 @@
+use page::Page;
+use entities::{
+    account::Account,
+    notification::Notification,
+    relationship::Relationship,
+    report::Report,
+    status::{Emoji, Status}
+};
+use serde::Deserialize;
+
+macro_rules! into_pageiter {
+    ($typ:ty) => {
+        impl<'a> IntoIterator for Page<'a, $typ> {
+            type Item = $typ;
+            type IntoIter = PageIter<'a, $typ>;
+
+            fn into_iter(self) -> PageIter<'a, $typ> {
+                PageIter::new(self)
+            }
+        }
+    }
+}
+
+into_pageiter!(Status);
+into_pageiter!(Account);
+into_pageiter!(String);
+into_pageiter!(Emoji);
+into_pageiter!(Notification);
+into_pageiter!(Report);
+into_pageiter!(Relationship);
+
+pub struct PageIter<'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>> PageIter<'a, T> {
+    fn new(page: Page<'a, T>) -> PageIter<'a, T> {
+        PageIter {
+            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 PageIter<'a, T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.use_initial {
+            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())
+        }
+    }
+}