using System.Collections.ObjectModel;
using Avalonia.Threading;

namespace AtomUI.Desktop.Controls;

public sealed class CalendarBlackoutDatesCollection : ObservableCollection<CalendarDateRange>
{
   /// <summary>
   /// The Calendar whose dates this object represents.
   /// </summary>
   private readonly Calendar _owner;

   /// <summary>
   /// Initializes a new instance of the
   /// <see cref="T:Avalonia.Controls.Primitives.CalendarBlackoutDatesCollection" />
   /// class.
   /// </summary>
   /// <param name="owner">
   /// The <see cref="T:Avalonia.Controls.Calendar" /> whose dates
   /// this object represents.
   /// </param>
   public CalendarBlackoutDatesCollection(Calendar owner)
    {
        _owner = owner ?? throw new ArgumentNullException(nameof(owner));
    }

   /// <summary>
   /// Adds all dates before <see cref="P:System.DateTime.Today" /> to the
   /// collection.
   /// </summary>
   public void AddDatesInPast()
    {
        Add(new CalendarDateRange(DateTime.MinValue, DateTime.Today.AddDays(-1)));
    }

   /// <summary>
   /// Returns a value that represents whether this collection contains the
   /// specified date.
   /// </summary>
   /// <param name="date">The date to search for.</param>
   /// <returns>
   /// True if the collection contains the specified date; otherwise,
   /// false.
   /// </returns>
   public bool Contains(DateTime date)
    {
        var count = Count;
        for (var i = 0; i < count; i++)
        {
            if (DateTimeHelper.InRange(date, this[i]))
            {
                return true;
            }
        }

        return false;
    }

   /// <summary>
   /// Returns a value that represents whether this collection contains the
   /// specified range of dates.
   /// </summary>
   /// <param name="start">The start of the date range.</param>
   /// <param name="end">The end of the date range.</param>
   /// <returns>
   /// True if all dates in the range are contained in the collection;
   /// otherwise, false.
   /// </returns>
   public bool Contains(DateTime start, DateTime end)
    {
        DateTime rangeStart;
        DateTime rangeEnd;

        if (DateTime.Compare(end, start) > -1)
        {
            rangeStart = DateTimeHelper.DiscardTime(start);
            rangeEnd   = DateTimeHelper.DiscardTime(end);
        }
        else
        {
            rangeStart = DateTimeHelper.DiscardTime(end);
            rangeEnd   = DateTimeHelper.DiscardTime(start);
        }

        var count = Count;
        for (var i = 0; i < count; i++)
        {
            var range = this[i];
            if (DateTime.Compare(range.Start, rangeStart) == 0 && DateTime.Compare(range.End, rangeEnd) == 0)
            {
                return true;
            }
        }

        return false;
    }

   /// <summary>
   /// Returns a value that represents whether this collection contains any
   /// date in the specified range.
   /// </summary>
   /// <param name="range">The range of dates to search for.</param>
   /// <returns>
   /// True if any date in the range is contained in the collection;
   /// otherwise, false.
   /// </returns>
   public bool ContainsAny(CalendarDateRange range)
    {
        return this.Any(r => r.ContainsAny(range));
    }

   /// <summary>
   /// Removes all items from the collection.
   /// </summary>
   /// <remarks>
   /// This implementation raises the CollectionChanged event.
   /// </remarks>
   protected override void ClearItems()
    {
        EnsureValidThread();

        base.ClearItems();
        _owner.UpdateMonths();
    }

   /// <summary>
   /// Inserts an item into the collection at the specified index.
   /// </summary>
   /// <param name="index">
   /// The zero-based index at which item should be inserted.
   /// </param>
   /// <param name="item">The object to insert.</param>
   /// <remarks>
   /// This implementation raises the CollectionChanged event.
   /// </remarks>
   protected override void InsertItem(int index, CalendarDateRange item)
    {
        EnsureValidThread();

        if (!IsValid(item))
        {
            throw new ArgumentOutOfRangeException(nameof(item), "Value is not valid.");
        }

        base.InsertItem(index, item);
        _owner.UpdateMonths();
    }

   /// <summary>
   /// Removes the item at the specified index of the collection.
   /// </summary>
   /// <param name="index">
   /// The zero-based index of the element to remove.
   /// </param>
   /// <remarks>
   /// This implementation raises the CollectionChanged event.
   /// </remarks>
   protected override void RemoveItem(int index)
    {
        EnsureValidThread();

        base.RemoveItem(index);
        _owner.UpdateMonths();
    }

   /// <summary>
   /// Replaces the element at the specified index.
   /// </summary>
   /// <param name="index">
   /// The zero-based index of the element to replace.
   /// </param>
   /// <param name="item">
   /// The new value for the element at the specified index.
   /// </param>
   /// <remarks>
   /// This implementation raises the CollectionChanged event.
   /// </remarks>
   protected override void SetItem(int index, CalendarDateRange item)
    {
        EnsureValidThread();

        if (!IsValid(item))
        {
            throw new ArgumentOutOfRangeException(nameof(item), "Value is not valid.");
        }

        base.SetItem(index, item);
        _owner.UpdateMonths();
    }

    private bool IsValid(CalendarDateRange item)
    {
        foreach (var day in _owner.SelectedDates)
        {
            if (DateTimeHelper.InRange(day, item))
            {
                return false;
            }
        }

        return true;
    }

    private static void EnsureValidThread()
    {
        Dispatcher.UIThread.VerifyAccess();
    }
}