ex-col-04-training/exam_cal_mgmt/ExamCalendar/ExamList.cs

namespace ExamCalendar;

/// <summary>
///     Represents a linked list of exams
/// </summary>
public sealed class ExamList
{
    private Node? _head;

    /// <summary>
    ///     Gets the number of exams currently stored in the list
    /// </summary>
    public int Count { get; private set; }

    /// <summary>
    ///     Insert a new exam into the list. Exams are stored sorted by their date.
    ///     Exams cannot occur on weekends, must have a subject and cannot be null.
    ///     There also cannot be two exams at the same day.
    /// </summary>
    /// <param name="exam">Exam to add</param>
    /// <returns>True if the exam could be added; false otherwise</returns>
    public bool Insert(Exam? exam)
    {
        if (exam == null || string.IsNullOrEmpty(exam.Subject) || 
            exam.Date.DayOfWeek == DayOfWeek.Saturday || exam.Date.DayOfWeek == DayOfWeek.Sunday)
        {
            return false;
        }

        var newNode = new Node(exam);
        
        if (_head == null || _head.Data.Date > exam.Date)
        {
            newNode.Next = _head;
            _head = newNode;
            Count++;
            return true;
        }

        var current = _head;
        while (current != null)
        {
            if (current.Data.Date == exam.Date)
            {
                return false;
            }

            if (current.Next == null || current.Next.Data.Date > exam.Date)
            {
                newNode.Next = current.Next;
                current.Next = newNode;
                Count++;
                return true;
            }
            current = current.Next;
        }
        
        return false;
    }

    /// <summary>
    ///     Returns the exam at the specified position if there is any
    /// </summary>
    /// <param name="position">Index of the exam in the list</param>
    /// <returns>The exam at this position or null if there is none</returns>
    public Exam? GetAt(int position)
    {
        if (position < 0 || position >= Count)
        {
            return null;
        }

        var current = _head;
        for (int i = 0; i < position && current != null; i++)
        {
            current = current.Next;
        }
        
        return current?.Data;
    }

    /// <summary>
    ///     Returns an array containing the exams stored in this list.
    ///     This array contains the references, not copies.
    /// </summary>
    /// <returns>An array containing the elements of the list</returns>
    public Exam[] ToArray()
    {
        var array = new Exam[Count];
        var current = _head;
        int index = 0;
        
        while (current != null)
        {
            array[index++] = current.Data;
            current = current.Next;
        }
        
        return array;
    }

    /// <summary>
    ///     Returns exams within the specified time frame
    /// </summary>
    /// <param name="from">Inclusive lower bound</param>
    /// <param name="to">Inclusive upper bound</param>
    /// <returns>An array of exams which are planned in the specified time frame</returns>
    public Exam[] GetTestsInInterval(DateTime from, DateTime to)
    {
        int count = 0;
        var counter = _head;
        while (counter != null && counter.Data.Date <= to)
        {
            if (counter.Data.Date >= from)
            {
                count++;
            }

            counter = counter.Next;
        }

        var results = new Exam[count];
        var current = _head;
        int index = 0;
        
        while (current != null && index < count)
        {
            if (current.Data.Date >= from && current.Data.Date <= to)
            {
                results[index++] = current.Data;
            }

            current = current.Next;
        }
        
        return results;
    }

    /// <summary>
    ///     Removes and returns the exam which is planned at the specified date from the list.
    ///     Exam can only be removed if it exists.
    /// </summary>
    /// <param name="removeDate">Date of the exam which to remove</param>
    /// <param name="removedTest">Reference to the removed exam, if any</param>
    /// <returns>True if the exam could be removed; false otherwise</returns>
    public bool Remove(DateTime removeDate, out Exam? removedTest)
    {
        removedTest = null;

        if (_head == null)
        {
            return false;
        }

        if (_head.Data.Date == removeDate)
        {
            removedTest = _head.Data;
            _head = _head.Next;
            Count--;
            return true;
        }

        var current = _head;

        while (current.Next != null)
        {
            if (current.Next.Data.Date == removeDate)
            {
                removedTest = current.Next.Data;
                current.Next = current.Next.Next;
                Count--;
                return true;
            }
            
            current = current.Next;
        }
        
        return false;
    }
}