using System.Collections.Generic;
using System.Linq;
using TINK.Model;

namespace TINK.ViewModel.Map
{
	/// <summary> Helper functionality. </summary>
	/// <remarks> Former name: MapPageFilterFactory</remarks>
	public static class GroupFilterMapPageHelper
	{
		/// <summary> Verifies that filters available are always consistent with filter configuration from settings page/ user group. </summary>
		/// <param name="mapPageFilterDictionary">Last filter from map page. Might have to be updated.</param>
		/// <param name="settingsAndUserFilter">Filter from settings page/ user group.</param>
		public static IGroupFilterMapPage CreateUpdated(
			this IGroupFilterMapPage mapPageFilterDictionary,
			IEnumerable<string> settingsAndUserFilter)
		{
			if (settingsAndUserFilter == null)
			{
				// All filters are null filters no update has to be performed.
				return mapPageFilterDictionary;
			}

			if (mapPageFilterDictionary == null || mapPageFilterDictionary.Count <= 0)
			{
				return new GroupFilterMapPage();
			}

			// Filter dictionary by enumeration.
			var updatedMapPageFilterDictionary = new Dictionary<string, FilterState>(mapPageFilterDictionary).Where(x => settingsAndUserFilter.Contains(x.Key)).ToDictionary(x => x.Key, x => x.Value);

			// Get key of activated filter if there is still one.
			var activatedFilter = updatedMapPageFilterDictionary.FirstOrDefault(x => x.Value == FilterState.On).Key
				?? string.Empty;

			// Add entries which have become available.
			var filterState = FilterState.On; // Set first filter added to on.
			var filtersToAdd = settingsAndUserFilter.Except(updatedMapPageFilterDictionary.Select(x => x.Key));
			foreach (var l_oEntry in filtersToAdd)
			{
				updatedMapPageFilterDictionary.Add(l_oEntry, filterState);
				filterState = FilterState.Off;
			}

			if (updatedMapPageFilterDictionary.Count <= 0)
			{
				return new GroupFilterMapPage(updatedMapPageFilterDictionary);
			}

			// Ensure that there is at least one element on.
			if (updatedMapPageFilterDictionary.Where(x => x.Value == FilterState.On).Count() == 0)
			{
				// No element is active. Set one element active.
				updatedMapPageFilterDictionary[updatedMapPageFilterDictionary.ToArray()[0].Key] = FilterState.On;
				return new GroupFilterMapPage(updatedMapPageFilterDictionary);
			}

			// Ensure that there is only one selected element.
			if (updatedMapPageFilterDictionary.Where(x => x.Value == FilterState.On).Count() > 1)
			{
				// More than one element is active. Set element inactive.
				if (updatedMapPageFilterDictionary.ContainsKey(activatedFilter))
				{
					// Turn filter off.
					updatedMapPageFilterDictionary[activatedFilter] = FilterState.Off;
				}

				return new GroupFilterMapPage(updatedMapPageFilterDictionary);
			}

			return new GroupFilterMapPage(updatedMapPageFilterDictionary);
		}
	}
}