GridViewSorter.cs

using System;
using System.Collections.Generic;
using Eto.Forms;

namespace GW2Scratch.ArcdpsLogManager
{
	public class GridViewSorter<T> where T : class
	{
		private readonly GridView<T> gridView;
		private readonly IReadOnlyDictionary<GridColumn, Comparison<T>> customSorts;
		private bool sortedAscending = false;
		private GridColumn sortColumn = null;

		/// <summary>
		/// Create a new <see cref="GridView"/> sorter.
		/// </summary>
		/// <remarks>If the <see cref="GridView.DataStore"/> is changed, <see cref="UpdateDataStore"/> has to be called
		/// to apply the sort.</remarks>
		/// <param name="gridView">A <see cref="GridView"/> that will be sorted.</param>
		/// <param name="customSorts">Optional custom sorting logic for specified columns.</param>
		public GridViewSorter(GridView<T> gridView, IReadOnlyDictionary<GridColumn, Comparison<T>> customSorts = null)
		{
			this.gridView = gridView;
			this.customSorts = customSorts;
		}

		/// <summary>
		/// Has to be called if the <see cref="GridView.DataStore"/> changes to apply the sort again.
		/// </summary>
		public void UpdateDataStore()
		{
			ApplySort();
		}

		/// <summary>
		/// Enable sorting on the <see cref="GridView"/>. Registers handlers for clicks on the column headers.
		/// </summary>
		public void EnableSorting()
		{
			foreach (var gridColumn in gridView.Columns)
			{
				gridColumn.Sortable = true;
			}

			gridView.ColumnHeaderClick += (sender, args) => { ClickColumn(args.Column); };
		}

		/// <summary>
		/// Sort the <see cref="GridView"/> by the provided column in ascending order.
		/// </summary>
		/// <param name="column">A column in the <see cref="GridView"/>.</param>
		public void SortByAscending(GridColumn column) => SortBy(column, true);

		/// <summary>
		/// Sort the <see cref="GridView"/> by the provided column in descending order.
		/// </summary>
		/// <param name="column">A column in the <see cref="GridView"/>.</param>
		public void SortByDescending(GridColumn column) => SortBy(column, false);

		private void SortBy(GridColumn column, bool ascending)
		{
			if (sortColumn != null)
			{
				sortColumn.Style = "sort-hidden";
			}

			sortColumn = column;
			sortedAscending = ascending;
			
			sortColumn.Style = sortedAscending ? "sort-ascending" : "sort-descending";
			ApplySort();
		}

		private void ClickColumn(GridColumn column)
		{
			bool ascending;
			if (sortColumn == column)
			{
				ascending = !sortedAscending;
			}
			else
			{
				ascending = true;
			}
			
			SortBy(column, ascending);
		}

		private void ApplySort()
		{
			if (sortColumn == null)
			{
				// No sort has been applied yet.
				return;
			}

			if (gridView.DataStore == null)
			{
				return;
			}

			if (!(gridView.DataStore is FilterCollection<T> collection))
			{
				throw new NotSupportedException("Only FilterCollections can be sorted.");
			}

			Comparison<T> sort = null;
			customSorts?.TryGetValue(sortColumn, out sort);

			if (sort == null && sortColumn.DataCell is TextBoxCell textBoxCell)
			{
				sort = GetTextComparison(textBoxCell);
			}

			if (sort == null)
			{
				// If we don't know how to sort out the current column, we keep the old sort.
				return;
			}

			if (!sortedAscending)
			{
				var sortToReverse = sort; // This copy is required
				sort = (x, y) => -sortToReverse(x, y);
			}

			collection.Sort = sort;
		}

		private Comparison<T> GetTextComparison(TextBoxCell textBoxCell)
		{
			return (first, second) =>
			{
				string property1 = textBoxCell.Binding.GetValue(first);
				string property2 = textBoxCell.Binding.GetValue(second);

				// Try to compare as numbers if possible. Many columns will only contain numbers.
				if (long.TryParse(property1, out long value1) &&
				    long.TryParse(property2, out long value2))
				{
					return value1.CompareTo(value2);
				}

				return String.Compare(property1, property2, StringComparison.Ordinal);
			};
		}
	}
}