/* This file is part of the dynarmic project.
 * Copyright (c) 2016 MerryMage
 * This software may be used and distributed according to the terms of the GNU
 * General Public License version 2 or any later version.
 */

#pragma once

#include <iterator>
#include <memory>
#include <type_traits>

#include "common/assert.h"
#include "common/common_types.h"

namespace Dynarmic {
namespace Common {

template <typename T> class IntrusiveList;
template <typename T> class IntrusiveListIterator;

template <typename T>
class IntrusiveListNode {
public:
    void UnlinkFromList() {
        prev->next = next;
        next->prev = prev;
#if !defined(NDEBUG)
        next = prev = nullptr;
#endif
    }

private:
    friend class IntrusiveList<T>;
    friend class IntrusiveListIterator<T>;
    friend class IntrusiveListIterator<const T>;

    IntrusiveListNode* next = this;
    IntrusiveListNode* prev = this;
};

template <typename T>
class IntrusiveListIterator {
public:
    using iterator_category = std::bidirectional_iterator_tag;
    using difference_type   = std::ptrdiff_t;
    using value_type        = T;
    using pointer           = value_type*;
    using const_pointer     = const value_type*;
    using reference         = value_type&;
    using const_reference   = const value_type&;

    // If value_type is const, we want "const IntrusiveListNode<value_type>", not "const IntrusiveListNode<const value_type>"
    using node_type         = std::conditional_t<std::is_const<value_type>::value,
                                                 const IntrusiveListNode<std::remove_const_t<value_type>>,
                                                 IntrusiveListNode<value_type>>;
    using node_pointer      = node_type*;
    using node_reference    = node_type&;

    IntrusiveListIterator() = default;
    IntrusiveListIterator(const IntrusiveListIterator& other) = default;
    IntrusiveListIterator& operator=(const IntrusiveListIterator& other) = default;

    IntrusiveListIterator(node_pointer list_root, node_pointer node) : root(list_root), node(node) {
    }

    IntrusiveListIterator& operator++() {
        node = node == root ? node : node->next;
        return *this;
    }
    IntrusiveListIterator operator++(int) {
        IntrusiveListIterator it(*this);
        node = node == root ? node : node->next;
        return it;
    }
    IntrusiveListIterator& operator--() {
        node = node->prev == root ? node : node->prev;
        return *this;
    }
    IntrusiveListIterator operator--(int) {
        IntrusiveListIterator it(*this);
        node = node->prev == root ? node : node->prev;
        return it;
    }

    bool operator==(const IntrusiveListIterator& other) const {
        DEBUG_ASSERT(root == other.root);
        return node == other.node;
    }
    bool operator!=(const IntrusiveListIterator& other) const {
        return !(*this == other);
    }

    reference operator*() const {
        DEBUG_ASSERT(node != root);
        return static_cast<T&>(*node);
    }
    pointer operator->() const {
        DEBUG_ASSERT(node != root);
        return std::addressof(operator*());
    }

    node_pointer AsNodePointer() const {
        return node;
    }

private:
    friend class IntrusiveList<T>;
    node_pointer root = nullptr;
    node_pointer node = nullptr;
};

template <typename T>
class IntrusiveList {
public:
    using difference_type        = std::ptrdiff_t;
    using size_type              = std::size_t;
    using value_type             = T;
    using pointer                = value_type*;
    using const_pointer          = const value_type*;
    using reference              = value_type&;
    using const_reference        = const value_type&;
    using iterator               = IntrusiveListIterator<value_type>;
    using const_iterator         = IntrusiveListIterator<const value_type>;
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    /**
     * Inserts a node at the given location indicated by an iterator.
     *
     * @param location The location to insert the node.
     * @param new_node The node to add.
     */
    iterator insert(iterator location, pointer new_node) {
        return insert_before(location, new_node);
    }

    /**
     * Inserts a node at the given location, moving the previous
     * node occupant ahead of the one inserted.
     *
     * @param location The location to insert the new node.
     * @param new_node The node to insert into the list.
     */
    iterator insert_before(iterator location, pointer new_node) {
        auto existing_node = location.AsNodePointer();

        new_node->next = existing_node;
        new_node->prev = existing_node->prev;
        existing_node->prev->next = new_node;
        existing_node->prev = new_node;

        return iterator(root.get(), new_node);
    }

    /**
     * Inserts a new node into the list ahead of the position indicated.
     *
     * @param position Location to insert the node in front of.
     * @param new_node The node to be inserted into the list.
     */
    iterator insert_after(iterator position, pointer new_node) {
        if (empty())
            return insert(begin(), new_node);

        return insert(++position, new_node);
    }

    /**
     * Add an entry to the start of the list.
     * @param node Node to add to the list.
     */
    void push_front(pointer node) {
        insert(begin(), node);
    }

    /**
     * Add an entry to the end of the list
     * @param node Node to add to the list.
     */
    void push_back(pointer node) {
        insert(end(), node);
    }

    /**
     * Erases the node at the front of the list.
     * @note Must not be called on an empty list.
     */
    void pop_front() {
        DEBUG_ASSERT(!empty());
        erase(begin());
    }

    /**
     * Erases the node at the back of the list.
     * @note Must not be called on an empty list.
     */
    void pop_back() {
        DEBUG_ASSERT(!empty());
        erase(--end());
    }

    /**
     * Removes node from list
     * @param node Node to remove from list.
     */
    void remove(reference node) {
        node.UnlinkFromList();
    }

    /**
     * Is this list empty?
     * @returns true if there are no nodes in this list.
     */
    bool empty() const {
        return root->next == root.get();
    }

    /**
     * Gets the total number of elements within this list.
     * @return the number of elements in this list.
     */
    size_type size() const {
        return static_cast<size_type>(std::distance(begin(), end()));
    }

    /**
     * Retrieves a reference to the node at the front of the list.
     * @note Must not be called on an empty list.
     */
    reference front() {
        DEBUG_ASSERT(!empty());
        return *begin();
    }

    /**
     * Retrieves a constant reference to the node at the front of the list.
     * @note Must not be called on an empty list.
     */
    const_reference front() const {
        DEBUG_ASSERT(!empty());
        return *begin();
    }

    /**
     * Retrieves a reference to the node at the back of the list.
     * @note Must not be called on an empty list.
     */
    reference back() {
        DEBUG_ASSERT(!empty());
        return *--end();
    }

    /**
     * Retrieves a constant reference to the node at the back of the list.
     * @note Must not be called on an empty list.
     */
    const_reference back() const {
        DEBUG_ASSERT(!empty());
        return *--end();
    }

    // Iterator interface
    iterator               begin()         { return iterator(root.get(), root->next);       }
    const_iterator         begin()   const { return const_iterator(root.get(), root->next); }
    const_iterator         cbegin()  const { return begin();                                }

    iterator               end()           { return iterator(root.get(), root.get());       }
    const_iterator         end()     const { return const_iterator(root.get(), root.get()); }
    const_iterator         cend()    const { return end();                                  }

    reverse_iterator       rbegin()        { return reverse_iterator(end());                }
    const_reverse_iterator rbegin()  const { return const_reverse_iterator(end());          }
    const_reverse_iterator crbegin() const { return rbegin();                               }

    reverse_iterator       rend()          { return reverse_iterator(begin());              }
    const_reverse_iterator rend()    const { return const_reverse_iterator(begin());        }
    const_reverse_iterator crend()   const { return rend();                                 }

    iterator       iterator_to(reference item)       { return iterator(root.get(), &item);       }
    const_iterator iterator_to(reference item) const { return const_iterator(root.get(), &item); }

    iterator erase(iterator it) {
        DEBUG_ASSERT(it.root == root.get() && it.node != it.root);
        IntrusiveListNode<T>* to_remove = it.node;
        ++it;
        to_remove->UnlinkFromList();
        return it;
    }

    /**
     * Exchanges contents of this list with another list instance.
     * @param other The other list to swap with.
     */
    void swap(IntrusiveList& other) {
        root.swap(other.root);
    }

private:
    std::shared_ptr<IntrusiveListNode<T>> root = std::make_shared<IntrusiveListNode<T>>();
};

/**
 * Exchanges contents of an intrusive list with another intrusive list.
 * @tparam T The type of data being kept track of by the lists.
 * @param lhs The first list.
 * @param rhs The second list.
 */
template <typename T>
void swap(IntrusiveList<T>& lhs, IntrusiveList<T>& rhs) {
    lhs.swap(rhs);
}

} // namespace Common
} // namespace Dynarmic