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// A sample program demonstrating using Google C++ testing framework.

#ifndef GTEST_SAMPLES_SAMPLE3_INL_H_
#define GTEST_SAMPLES_SAMPLE3_INL_H_

#include <stddef.h>

// Queue is a simple queue implemented as a singled-linked list.
//
// The element type must support copy constructor.
template<typename E> // E is the element type
class Queue;

// QueueNode is a node in a Queue, which consists of an element of
// type E and a pointer to the next node.
template<typename E> // E is the element type
class QueueNode
{
    friend class Queue<E>;

public:
    // Gets the element in this node.
    const E &element() const { return element_; }

    // Gets the next node in the queue.
    QueueNode *next() { return next_; }
    const QueueNode *next() const { return next_; }

private:
    // Creates a node with a given element value.  The next pointer is
    // set to NULL.
    explicit QueueNode(const E &an_element)
        : element_(an_element)
        , next_(nullptr)
    {
    }

    // We disable the default assignment operator and copy c'tor.
    const QueueNode &operator=(const QueueNode &);
    QueueNode(const QueueNode &);

    E element_;
    QueueNode *next_;
};

template<typename E> // E is the element type.
class Queue
{
public:
    // Creates an empty queue.
    Queue()
        : head_(nullptr)
        , last_(nullptr)
        , size_(0)
    {
    }

    // D'tor.  Clears the queue.
    ~Queue() { Clear(); }

    // Clears the queue.
    void Clear()
    {
        if (size_ > 0) {
            // 1. Deletes every node.
            QueueNode<E> *node = head_;
            QueueNode<E> *next = node->next();
            for (;;) {
                delete node;
                node = next;
                if (node == nullptr)
                    break;
                next = node->next();
            }

            // 2. Resets the member variables.
            head_ = last_ = nullptr;
            size_ = 0;
        }
    }

    // Gets the number of elements.
    size_t Size() const { return size_; }

    // Gets the first element of the queue, or NULL if the queue is empty.
    QueueNode<E> *Head() { return head_; }
    const QueueNode<E> *Head() const { return head_; }

    // Gets the last element of the queue, or NULL if the queue is empty.
    QueueNode<E> *Last() { return last_; }
    const QueueNode<E> *Last() const { return last_; }

    // Adds an element to the end of the queue.  A copy of the element is
    // created using the copy constructor, and then stored in the queue.
    // Changes made to the element in the queue doesn't affect the source
    // object, and vice versa.
    void Enqueue(const E &element)
    {
        QueueNode<E> *new_node = new QueueNode<E>(element);

        if (size_ == 0) {
            head_ = last_ = new_node;
            size_ = 1;
        } else {
            last_->next_ = new_node;
            last_ = new_node;
            size_++;
        }
    }

    // Removes the head of the queue and returns it.  Returns NULL if
    // the queue is empty.
    E *Dequeue()
    {
        if (size_ == 0) {
            return nullptr;
        }

        const QueueNode<E> *const old_head = head_;
        head_ = head_->next_;
        size_--;
        if (size_ == 0) {
            last_ = nullptr;
        }

        E *element = new E(old_head->element());
        delete old_head;

        return element;
    }

    // Applies a function/functor on each element of the queue, and
    // returns the result in a new queue.  The original queue is not
    // affected.
    template<typename F>
    Queue *Map(F function) const
    {
        Queue *new_queue = new Queue();
        for (const QueueNode<E> *node = head_; node != nullptr;
             node = node->next_) {
            new_queue->Enqueue(function(node->element()));
        }

        return new_queue;
    }

private:
    QueueNode<E> *head_; // The first node of the queue.
    QueueNode<E> *last_; // The last node of the queue.
    size_t size_; // The number of elements in the queue.

    // We disallow copying a queue.
    Queue(const Queue &);
    const Queue &operator=(const Queue &);
};

#endif // GTEST_SAMPLES_SAMPLE3_INL_H_
