Connected.Components/Components/DropZone/DropContainer.razor.cs

// Copyright (c) MudBlazor 2021
// MudBlazor licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using Connected.Annotations;
using Connected.Utilities;
using Microsoft.AspNetCore.Components;

namespace Connected.Components;

public class DragAndDropIndexChangedEventArgs : EventArgs
{
	public DragAndDropIndexChangedEventArgs(string zoneIdentifier, string oldZoneIdentifier, int index)
	{
		ZoneIdentifier = zoneIdentifier;
		Index = index;
		OldZoneIdentifier = oldZoneIdentifier;
	}

	public string ZoneIdentifier { get; }
	public int Index { get; }
	public string OldZoneIdentifier { get; }
}

/// <summary>
/// Used to encapsulate data for a drag and drop transaction
/// </summary>
/// <typeparam name="T"></typeparam>
public class DragAndDropItemTransaction<T>
{
	private Func<Task> _commitCallback;
	private Func<Task> _cancelCallback;

	/// <summary>
	/// The Item that is dragged during the transaction
	/// </summary>
	public T Item { get; init; }

	/// <summary>
	/// The index of the item in the current drop zone
	/// </summary>
	public int Index { get; private set; }

	/// <summary>
	/// The index of the item when the transaction started
	/// </summary>
	public int SourceIndex { get; private set; }

	/// <summary>
	/// Identifier for drop zone where the transaction started
	/// </summary>
	public string SourceZoneIdentifier { get; init; }

	public string CurrentZone { get; private set; }

	/// <summary>
	/// create a new instance of a drag and drop transaction encapsulating the item and source
	/// </summary>
	/// <param name="item">The item of this transaction</param>
	/// <param name="identifier">The identifier of the drop zone, where the transaction started</param>
	/// <param name="index">The source index</param>
	/// <param name="commitCallback">A callback that is invokde when the transaction has been successful</param>
	/// <param name="cancelCallback">A callback that is inviked when the transaction has been cancelled</param>
	public DragAndDropItemTransaction(T item, string identifier, int index, Func<Task> commitCallback, Func<Task> cancelCallback)
	{
		Item = item;
		SourceZoneIdentifier = identifier;
		CurrentZone = identifier;
		Index = index;
		SourceIndex = index;

		_commitCallback = commitCallback;
		_cancelCallback = cancelCallback;
	}

	/// <summary>
	/// Cancel the transaction 
	/// </summary>
	/// <returns></returns>
	public async Task Cancel() => await _cancelCallback.Invoke();

	/// <summary>
	/// Commit this transaction as succesful
	/// </summary>
	/// <returns></returns>
	public async Task Commit() => await _commitCallback.Invoke();

	internal bool UpdateIndex(int index)
	{
		if (Index == index) { return false; }

		Index = index;
		return true;
	}

	internal bool UpdateZone(string idenfifer)
	{
		if (CurrentZone == idenfifer) { return false; }

		CurrentZone = idenfifer;
		Index = -1;
		return true;
	}
}

/// <summary>
/// Record encaplusalting data regaring a completed transaction
/// </summary>
/// <typeparam name="T">Type of dragged item</typeparam>
/// <param name="Item">The dragged item during the transaction</param>
/// <param name="DropzoneIdentifier">Identifier of the zone where the transaction started</param>
/// <param name="IndexInZone">The index of the item within in the dropzone</param>
public record ItemDropInfo<T>(T Item, string DropzoneIdentifier, int IndexInZone);

public class DragAndDropTransactionFinishedEventArgs<T> : EventArgs
{
	public DragAndDropTransactionFinishedEventArgs(DragAndDropItemTransaction<T> transaction) :
		this(string.Empty, false, transaction)
	{

	}

	public DragAndDropTransactionFinishedEventArgs(string destinationDropzoneIdentifier, bool success, DragAndDropItemTransaction<T> transaction)
	{
		Item = transaction.Item;
		Success = success;
		OriginatedDropzoneIdentifier = transaction.SourceZoneIdentifier;
		DestinationDropzoneIdentifier = destinationDropzoneIdentifier;
		OriginIndex = transaction.SourceIndex;
		DestinationIndex = transaction.Index;
	}

	public T Item { get; }
	public bool Success { get; }
	public string OriginatedDropzoneIdentifier { get; }
	public string DestinationDropzoneIdentifier { get; }
	public int OriginIndex { get; }
	public int DestinationIndex { get; }
}


/// <summary>
/// The container of a drag and drop zones
/// </summary>
/// <typeparam name="T">Datetype of items</typeparam>
public partial class DropContainer<T> : UIComponent
{
	private DragAndDropItemTransaction<T> _transaction;

	protected string Classname =>
	new CssBuilder("mud-drop-container")
		.AddClass(Class)
		.Build();

	/// <summary>
	/// Child content of component. This should include the drop zones
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Appearance)]
	public RenderFragment ChildContent { get; set; }

	/// <summary>
	/// The items that can be drag and dropped within the container
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Items)]
	public IEnumerable<T> Items { get; set; }

	/// <summary>
	/// The render fragment (template) that should be used to render the items within a drop zone
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Items)]
	public RenderFragment<T> ItemRenderer { get; set; }

	/// <summary>
	/// The method is used to determinate if an item can be dropped within a drop zone
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Items)]
	public Func<T, string, bool> ItemsSelector { get; set; }

	/// <summary>
	/// Callback that indicates that an item has been dropped on a drop zone. Should be used to update the "status" of the data item
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Items)]
	public EventCallback<ItemDropInfo<T>> ItemDropped { get; set; }

	/// <summary>
	/// The method is used to determinate if an item can be dropped within a drop zone
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DropRules)]
	public Func<T, string, bool> CanDrop { get; set; }

	/// <summary>
	/// The CSS class(es), that is applied to drop zones that are a valid target for drag and drop transaction
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DropRules)]
	public string CanDropClass { get; set; }

	/// <summary>
	/// The CSS class(es), that is applied to drop zones that are NOT valid target for drag and drop transaction
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DropRules)]
	public string NoDropClass { get; set; }

	/// <summary>
	/// If true, drop classes CanDropClass <see cref="CanDropClass"/>  or NoDropClass <see cref="NoDropClass"/> or applied as soon, as a transaction has started
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DropRules)]
	public bool ApplyDropClassesOnDragStarted { get; set; } = false;

	/// <summary>
	/// The method is used to determinate if an item should be disabled for dragging. Defaults to allow all items
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Disabled)]
	public Func<T, bool> ItemIsDisabled { get; set; }

	/// <summary>
	/// If a drop item is disabled (determinate by <see cref="ItemIsDisabled"/>). This class is applied to the element
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.Disabled)]
	public string DisabledClass { get; set; } = "disabled";

	/// <summary>
	/// An additional class that is applied to the drop zone where a drag operation started
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DraggingClass)]
	public string DraggingClass { get; set; }

	/// <summary>
	/// An additional class that is applied to an drop item, when it is dragged
	/// </summary>
	[Parameter]
	[Category(CategoryTypes.DropZone.DraggingClass)]
	public string ItemDraggingClass { get; set; }

	public event EventHandler<DragAndDropItemTransaction<T>> TransactionStarted;
	public event EventHandler<DragAndDropIndexChangedEventArgs> TransactionIndexChanged;

	public event EventHandler<DragAndDropTransactionFinishedEventArgs<T>> TransactionEnded;
	public event EventHandler RefreshRequested;

	public void StartTransaction(T item, string identifier, int index, Func<Task> commitCallback, Func<Task> cancelCallback)
	{
		_transaction = new DragAndDropItemTransaction<T>(item, identifier, index, commitCallback, cancelCallback);
		TransactionStarted?.Invoke(this, _transaction);
	}

	public T GetTransactionItem() => _transaction.Item;

	public bool TransactionInProgress() => _transaction != null;
	public string GetTransactionOrignZoneIdentiifer() => _transaction?.SourceZoneIdentifier ?? string.Empty;
	public string GetTransactionCurrentZoneIdentiifer() => _transaction?.CurrentZone ?? string.Empty;
	public bool IsTransactionOriginatedFromInside(string identifier) => _transaction.SourceZoneIdentifier == identifier;

	public int GetTransactionIndex() => _transaction?.Index ?? -1;
	public bool IsItemMovedDownwards() => _transaction.Index > _transaction.SourceIndex;
	public bool HasTransactionIndexChanged()
	{
		if (_transaction == null)
		{
			return false;
		}

		if (_transaction.CurrentZone != _transaction.SourceZoneIdentifier)
		{
			return true;
		}

		return _transaction.Index != _transaction.SourceIndex;
	}

	public bool IsOrign(int index, string identifier)
	{
		if (_transaction == null)
		{
			return false;
		}

		if (identifier != _transaction.SourceZoneIdentifier)
		{
			return false;
		}

		return _transaction.SourceIndex == index || _transaction.SourceIndex - 1 == index;
	}

	public async Task CommitTransaction(string dropzoneIdentifier, bool reorderIsAllowed)
	{
		await _transaction.Commit();
		var index = -1;
		if (reorderIsAllowed == true)
		{
			index = GetTransactionIndex() + 1;
			if (_transaction.SourceZoneIdentifier == _transaction.CurrentZone && IsItemMovedDownwards() == true)
			{
				index -= 1;
			}
		}

		await ItemDropped.InvokeAsync(new ItemDropInfo<T>(_transaction.Item, dropzoneIdentifier, index));
		var transactionFinishedEventArgs = new DragAndDropTransactionFinishedEventArgs<T>(dropzoneIdentifier, true, _transaction);
		_transaction = null;
		TransactionEnded?.Invoke(this, transactionFinishedEventArgs);
	}

	public async Task CancelTransaction()
	{
		await _transaction.Cancel();
		var transactionFinishedEventArgs = new DragAndDropTransactionFinishedEventArgs<T>(_transaction);
		_transaction = null;
		TransactionEnded?.Invoke(this, transactionFinishedEventArgs);
	}

	public void UpdateTransactionIndex(int index)
	{
		var changed = _transaction.UpdateIndex(index);
		if (changed == false) { return; }

		TransactionIndexChanged?.Invoke(this, new DragAndDropIndexChangedEventArgs(_transaction.CurrentZone, _transaction.CurrentZone, _transaction.Index));
	}

	internal void UpdateTransactionZone(string identifier)
	{
		var oldValue = _transaction.CurrentZone;
		var changed = _transaction.UpdateZone(identifier);
		if (changed == false) { return; }

		TransactionIndexChanged?.Invoke(this, new DragAndDropIndexChangedEventArgs(_transaction.CurrentZone, oldValue, _transaction.Index));
	}


	/// <summary>
	/// Refreshes the dropzone and all items within. This is neded in case of adding items to the collection or changed values of items
	/// </summary>
	public void Refresh() => RefreshRequested?.Invoke(this, EventArgs.Empty);


}