namespace WaitingRoom;

/// <summary>
///     A queue implementation which can be used to represents the waiting queue of
///     patients at a doctor's office.
/// </summary>
public sealed class PatientQueue
{
    private Node? _head;

    /// <summary>
    ///     Gets the number of patients currently waiting in this queue
    /// </summary>
    public int Size { get; private set; }

    /// <summary>
    ///     Adds a new patient to the queue.
    ///     Patients are ordered by arrival time.
    /// </summary>
    /// <param name="patient">Patient to add to the queue</param>
    public void Enqueue(Patient patient)
    {
        var newNode = new Node(patient);
        
        if (_head == null || patient.Arrival < _head.Data.Arrival)
        {
            newNode.Next = _head;
            _head = newNode;
            Size++;
            return;
        }

        var current = _head;
        while (current.Next != null && current.Next.Data.Arrival <= patient.Arrival)
        {
            current = current.Next;
        }
        
        newNode.Next = current.Next;
        current.Next = newNode;
        Size++;
    }

    /// <summary>
    ///     Removes the next patient from the queue.
    /// </summary>
    /// <returns>The next patient to be treated; null if no patient is waiting</returns>
    public Patient? Dequeue()
    {
        if (_head == null)
        {
            return null;
        }

        var patient = _head.Data;
        _head = _head.Next;
        Size--;
        return patient;
    }

    /// <summary>
    ///     Removes the supplied patient from the queue.
    ///     Only patients actually waiting in this queue can be removed.
    /// </summary>
    /// <param name="patient">The patient to remove from the queue</param>
    /// <returns>True if the patient could be removed; false otherwise</returns>
    public bool Remove(Patient patient)
    {
        if (_head == null)
        {
            return false;
        }

        if (_head.Data == patient)
        {
            _head = _head.Next;
            Size--;
            return true;
        }

        var current = _head;
        while (current.Next != null && current.Next.Data != patient)
        {
            current = current.Next;
        }

        if (current.Next == null)
        {
            return false;
        }

        current.Next = current.Next.Next;
        Size--;
        return true;
    }
}