using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using Pf2e.Database;
using Pf2e.Database.Model.Base;
using Pf2e.Database.Model.Enum;
using Pf2e.Scrapper.WPF.EntityViewer.Stores;
using Pf2e.WPF.EntityViewer.Stores;

namespace Pf2e.WPF.EntityViewer.ViewModel;

internal class EntityListViewModel : ViewModelBase
{
    public Pf2eDbContext Context { get; }
    public SelectedEntityTypeStore SelectedEntityTypeStore { get; }
    public SelectedEntityStore SelectedEntityStore { get; }

    private EntityType? SelectedEntityType => SelectedEntityTypeStore.SelectedEntityType;

    public Entity? SelectedEntity
    {
        get => SelectedEntityStore.SelectedEntity;
        set => SelectedEntityStore.SelectedEntity = value;
    }

    public int Page
    {
        get => _page;
        set
        {
            _page = Math.Clamp(value, 1, PageCount);
            OnPropertyChanged();
            OnPropertyChanged(nameof(HasPrevious));
            OnPropertyChanged(nameof(HasNext));
            Reload();
        }
    }
    private int _page = 1;

    public int EntitiesCount
    {
        get => _entitiesCount;
        set
        {
            _entitiesCount = value;
            OnPropertyChanged();
            OnPropertyChanged(nameof(PageCount));
            OnPropertyChanged(nameof(HasPrevious));
            OnPropertyChanged(nameof(HasNext));
        }
    }
    private int _entitiesCount = 1;

    public int PerPage
    {
        get => _perPage;
        set
        {
            _perPage = value;
            OnPropertyChanged();
            OnPropertyChanged(nameof(PageCount));
            Reload();
        }
    }
    private int _perPage = 30;

    public string Search
    {
        get => _search;
        set
        {
            _search = value;
            OnPropertyChanged();
            Reload();
        }
    }
    private string _search = "";

    public int PageCount => Convert.ToInt32(Math.Ceiling(1.0 * EntitiesCount / PerPage));

    public IEnumerable<Entity> Entities
    {
        get => _entities;
        set
        {
            _entities = [.. value];
            SelectedEntity = Entities.FirstOrDefault();
            OnPropertyChanged();
        }
    }
    private ObservableCollection<Entity> _entities = [];

    public EntityListViewModel(
        Pf2eDbContext context,
        SelectedEntityTypeStore selectedEntityTypeStore,
        SelectedEntityStore selectedEntityStore
    )
    {
        Context = context;
        SelectedEntityTypeStore = selectedEntityTypeStore;
        SelectedEntityStore = selectedEntityStore;

        SelectedEntityTypeStore.SelectedEntityTypeChanged +=
            SelectedEntityTypeStore_SelectedEntityTypeChanged;
    }

    ~EntityListViewModel()
    {
        SelectedEntityTypeStore.SelectedEntityTypeChanged -=
            SelectedEntityTypeStore_SelectedEntityTypeChanged;
    }

    private void SelectedEntityTypeStore_SelectedEntityTypeChanged(EntityType? entityType)
    {
        if (entityType is null)
        {
            Page = 1;
            EntitiesCount = 1;
            Entities = [];
            return;
        }

        Page = 1;
        Reload();
    }

    #region "Методы кнопок"

    private PageNavigationCommand? _firstPageCommand;
    public PageNavigationCommand FirstPageCommand
    {
        get
        {
            return _firstPageCommand ??= new PageNavigationCommand(() =>
            {
                Page = 1;
            });
        }
    }

    private PageNavigationCommand? _previousPageCommand;
    public PageNavigationCommand PreviousPageCommand
    {
        get
        {
            return _previousPageCommand ??= new PageNavigationCommand(() =>
            {
                Page--;
            });
        }
    }

    private PageNavigationCommand? _nextPageCommand;
    public PageNavigationCommand NextPageCommand
    {
        get
        {
            return _nextPageCommand ??= new PageNavigationCommand(() =>
            {
                Page++;
            });
        }
    }

    private PageNavigationCommand? _lastPageCommand;
    public PageNavigationCommand LastPageCommand
    {
        get
        {
            return _lastPageCommand ??= new PageNavigationCommand(() =>
            {
                Page = PageCount;
            });
        }
    }

    public bool HasPrevious => Page != 1;

    public bool HasNext => Page != PageCount;

    #endregion

    #region "Запросы"

    /// <summary>
    /// Выполняет запрос к базе данных и обрабатывает результаты.
    /// </summary>
    public void Reload()
    {
        Pf2eDbContext dbContext = new();

        IQueryable<Entity> query =
            Search == ""
                ? dbContext.Entities.Where(e => e.Type == SelectedEntityType)
                :
                // ReSharper disable once EntityFramework.UnsupportedServerSideFunctionCall
                dbContext.Entities.Where(e =>
                    e.Type == SelectedEntityType && Pf2eDbContext.LocaleSearch(e.Name, Search)
                );

        EntitiesCount = query.Count();
        Entities = [.. query.OrderBy(e => e.Id).Skip((Page - 1) * PerPage).Take(PerPage).ToList()];
    }

    #endregion
}

/// <summary>
/// Команда для навигации по страницам.
/// </summary>
/// <param name="action">Действие, выполняемое при выполнении команды.</param>
public class PageNavigationCommand(Action action) : System.Windows.Input.ICommand
{
    /// <summary>
    /// Действие, выполняемое при выполнении команды.
    /// </summary>
    public Action Action { get; } = action;

    /// <summary>
    /// Событие, вызываемое при изменении возможности выполнения команды.
    /// </summary>
    public event EventHandler? CanExecuteChanged;

    /// <summary>
    /// Проверяет, может ли команда быть выполнена с указанным параметром.
    /// </summary>
    /// <param name="parameter">Параметр команды.</param>
    /// <returns>Флаг, указывающий, может ли команда быть выполнена.</returns>
    public bool CanExecute(object? parameter)
    {
        return true;
    }

    /// <summary>
    /// Выполняет команду с указанным параметром.
    /// </summary>
    /// <param name="parameter">Параметр команды.</param>
    public void Execute(object? parameter)
    {
        Action.Invoke();
    }
}