From 25737d93772968c00664a5dc1efaa79db80f4c23 Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Wed, 21 Jun 2023 16:28:19 -0700
Subject: [PATCH] [glacier] Add an IntrusiveList container

---
 lib/glacier/container/intrusive_list.h | 102 +++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 lib/glacier/container/intrusive_list.h

diff --git a/lib/glacier/container/intrusive_list.h b/lib/glacier/container/intrusive_list.h
new file mode 100644
index 0000000..8957a32
--- /dev/null
+++ b/lib/glacier/container/intrusive_list.h
@@ -0,0 +1,102 @@
+#pragma once
+
+#include <glacier/memory/ref_ptr.h>
+#include <stdint.h>
+
+namespace glcr {
+
+template <typename T>
+class IntrusiveListNode {
+ public:
+  RefPtr<T> next_;
+  RefPtr<T> prev_;
+};
+
+template <typename T>
+class IntrusiveList {
+ public:
+  IntrusiveList() : front_(nullptr), back_(nullptr) {}
+
+  void PushFront(const RefPtr<T>& obj);
+  void PushBack(const RefPtr<T>& obj);
+
+  RefPtr<T> PopFront();
+  RefPtr<T> PopBack();
+
+  RefPtr<T> PeekFront() { return front_; }
+  RefPtr<T> PeekBack() { return back_; }
+
+  uint64_t size() { return size_; }
+
+ private:
+  RefPtr<T> front_;
+  RefPtr<T> back_;
+
+  uint64_t size_ = 0;
+};
+
+template <typename T>
+void IntrusiveList<T>::PushFront(const RefPtr<T>& obj) {
+  // FIXME: Check to make sure obj next and prev aren't set.
+  size_++;
+  obj->next_ = front_;
+  obj->prev_ = nullptr;
+  if (front_ == nullptr) {
+    front_ = obj;
+    back_ = obj;
+    return;
+  }
+
+  front_->prev_ = obj;
+  front_ = obj;
+}
+
+template <typename T>
+void IntrusiveList<T>::PushBack(const RefPtr<T>& obj) {
+  if (front_ == nullptr) {
+    PushFront(obj);
+    return;
+  }
+  size_++;
+  back_->next_ = obj;
+  obj->prev_ = back_;
+  obj->next_ = nullptr;
+  back_ = obj;
+}
+
+template <typename T>
+RefPtr<T> IntrusiveList<T>::PopFront() {
+  if (front_ == nullptr) {
+    return nullptr;
+  }
+  size_--;
+  if (front_ == back_) {
+    RefPtr<T> ptr = front_;
+    front_ = nullptr;
+    back_ = nullptr;
+    return ptr;
+  }
+  RefPtr<T> ptr = front_;
+  front_ = front_->next_;
+  front_->prev_ = nullptr;
+  ptr->next_ = nullptr;
+  return ptr;
+}
+
+template <typename T>
+RefPtr<T> IntrusiveList<T>::PopBack() {
+  if (back_ == nullptr) {
+    return nullptr;
+  }
+  if (front_ == back_) {
+    return PopFront();
+  }
+  size_--;
+  RefPtr<T> ptr = back_;
+  back_ = back_->prev_;
+  back_->next_ = nullptr;
+  ptr->prev_ = nullptr;
+  return ptr;
+}
+
+}  // namespace glcr