using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using System.Collections.ObjectModel;
using System.Globalization;

namespace LehrerApp.Desktop.ViewModels.Workload;

// ── Anzeige-Hilfen für die Enums (6.1) ──────────────────────────────────────

public static class WorkTaskStatusDisplay
{
    public static string Label(WorkTaskStatus s) => s switch
    {
        WorkTaskStatus.Open       => "Offen",
        WorkTaskStatus.InProgress => "In Bearbeitung",
        WorkTaskStatus.Done       => "Erledigt",
        _                         => s.ToString(),
    };

    public static string ColorHex(WorkTaskStatus s) => s switch
    {
        WorkTaskStatus.Open       => "#9E9E9E",
        WorkTaskStatus.InProgress => "#1976D2",
        WorkTaskStatus.Done       => "#43A047",
        _                         => "#9E9E9E",
    };

    // Klick auf die Status-Kachel wechselt reihum (6.1.3).
    public static WorkTaskStatus Next(WorkTaskStatus s) => s switch
    {
        WorkTaskStatus.Open       => WorkTaskStatus.InProgress,
        WorkTaskStatus.InProgress => WorkTaskStatus.Done,
        _                         => WorkTaskStatus.Open,
    };
}

public static class TaskCategoryDisplay
{
    public static string Label(TaskCategory c) => c switch
    {
        TaskCategory.Correction  => "Korrektur",
        TaskCategory.Preparation => "Vorbereitung",
        TaskCategory.Admin       => "Verwaltung",
        TaskCategory.Meeting     => "Besprechung",
        TaskCategory.Other       => "Sonstiges",
        _                        => c.ToString(),
    };

    public static string[] Options { get; } = Enum.GetValues<TaskCategory>().Select(Label).ToArray();

    public static TaskCategory FromLabel(string? label) =>
        Enum.GetValues<TaskCategory>().FirstOrDefault(c => Label(c) == label, TaskCategory.Other);
}

// ── Aufgabenliste (6.1.1, 6.1.3) ─────────────────────────────────────────────

public partial class WorkTaskListViewModel : ObservableObject
{
    private readonly IWorkTaskRepository _tasks;
    private readonly IGroupRepository _groups;

    public const string AllFilter = "Alle";
    public const string ActiveFilter = "Offene Aufgaben";
    public const string DoneFilter = "Erledigt";
    public const string NoGroupFilter = "Ohne Gruppe";

    [ObservableProperty] private string _statusFilter = ActiveFilter;
    [ObservableProperty] private string _categoryFilter = AllFilter;
    [ObservableProperty] private string _groupFilter = AllFilter;

    public List<string> StatusFilterOptions { get; } = [ActiveFilter, AllFilter, DoneFilter];
    public List<string> CategoryFilterOptions { get; } = [AllFilter, .. TaskCategoryDisplay.Options];
    public ObservableCollection<string> GroupFilterOptions { get; } = [AllFilter, NoGroupFilter];

    public ObservableCollection<WorkTaskListItem> Tasks { get; } = [];
    public string CountSummary => $"{Tasks.Count} Aufgabe(n)";

    public Func<WorkTask?, Task<WorkTask?>>? OnEditTask { get; set; }

    private Dictionary<Guid, string> _groupNames = [];

    public WorkTaskListViewModel(IWorkTaskRepository tasks, IGroupRepository groups)
    {
        _tasks = tasks;
        _groups = groups;
        Load();
    }

    partial void OnStatusFilterChanged(string value) => Refresh();
    partial void OnCategoryFilterChanged(string value) => Refresh();
    partial void OnGroupFilterChanged(string value) => Refresh();

    public void Load()
    {
        var groups = _groups.GetAll(includeInactive: true);
        _groupNames = groups.ToDictionary(g => g.Id, g => g.Name);

        GroupFilterOptions.Clear();
        GroupFilterOptions.Add(AllFilter);
        GroupFilterOptions.Add(NoGroupFilter);
        foreach (var name in groups.Select(g => g.Name).OrderBy(n => n))
            GroupFilterOptions.Add(name);

        Refresh();
    }

    private void Refresh()
    {
        Tasks.Clear();
        var all = _tasks.GetAll().AsEnumerable();

        all = StatusFilter switch
        {
            ActiveFilter => all.Where(t => t.Status != WorkTaskStatus.Done),
            DoneFilter   => all.Where(t => t.Status == WorkTaskStatus.Done),
            _            => all,
        };

        if (CategoryFilter != AllFilter)
        {
            var category = TaskCategoryDisplay.FromLabel(CategoryFilter);
            all = all.Where(t => t.Category == category);
        }

        if (GroupFilter == NoGroupFilter)
            all = all.Where(t => t.GroupId is null);
        else if (GroupFilter != AllFilter)
            all = all.Where(t => t.GroupId.HasValue && _groupNames.GetValueOrDefault(t.GroupId.Value) == GroupFilter);

        // Fälligkeit: fällige zuerst, unbefristete ans Ende (6.1.1).
        foreach (var t in all.OrderBy(t => t.DueDate ?? DateOnly.MaxValue).ThenBy(t => t.Title))
            Tasks.Add(new WorkTaskListItem(t, _groupNames.GetValueOrDefault(t.GroupId ?? Guid.Empty)));

        OnPropertyChanged(nameof(CountSummary));
    }

    [RelayCommand]
    private async Task AddTask()
    {
        if (OnEditTask is null) return;
        var result = await OnEditTask(null);
        if (result is null) return;
        _tasks.Save(result);
        Refresh();
    }

    [RelayCommand]
    private async Task EditTask(WorkTaskListItem? item)
    {
        if (item is null || OnEditTask is null) return;
        var result = await OnEditTask(item.Model);
        if (result is null) return;
        _tasks.Save(result);
        Refresh();
    }

    [RelayCommand]
    private void CycleStatus(WorkTaskListItem? item)
    {
        if (item is null) return;
        item.Model.Status = WorkTaskStatusDisplay.Next(item.Model.Status);
        _tasks.Save(item.Model);
        Refresh();
    }

    [RelayCommand]
    private void DeleteTask(WorkTaskListItem? item)
    {
        if (item is null) return;
        _tasks.Delete(item.Model.Id);
        Refresh();
    }
}

public class WorkTaskListItem(WorkTask model, string? groupName)
{
    public WorkTask Model { get; } = model;
    public string Title => Model.Title;
    public string CategoryLabel => TaskCategoryDisplay.Label(Model.Category);
    public string GroupName => groupName ?? "";
    public string DueDateDisplay => Model.DueDate?.ToString("dd.MM.yyyy", CultureInfo.InvariantCulture) ?? "";
    public bool IsOverdue => Model.DueDate is { } d && d < DateOnly.FromDateTime(DateTime.Today)
        && Model.Status != WorkTaskStatus.Done;
    public string DueDateColorHex => IsOverdue ? "#D32F2F" : "#9E9E9E";
    public string StatusLabel => WorkTaskStatusDisplay.Label(Model.Status);
    public string StatusColorHex => WorkTaskStatusDisplay.ColorHex(Model.Status);
    public string EstimatedMinutesDisplay => Model.EstimatedMinutes is { } m ? $"{m} min" : "";
}

// ── Dialog: Aufgabe anlegen/bearbeiten (6.1.2) ───────────────────────────────

public partial class AddEditWorkTaskDialogViewModel : ObservableObject
{
    private readonly WorkTask? _source;

    [ObservableProperty] private string _title = "";
    [ObservableProperty] private string _selectedCategory = TaskCategoryDisplay.Options[0];
    [ObservableProperty] private LearningGroup? _selectedGroup;
    [ObservableProperty] private string _dueDateText = "";
    [ObservableProperty] private string _estimatedMinutesText = "";
    [ObservableProperty] private string _notes = "";
    [ObservableProperty] private string _titleError = "";
    [ObservableProperty] private string _dueDateError = "";
    [ObservableProperty] private string _estimatedMinutesError = "";

    public string DialogTitle => _source is null ? "Aufgabe anlegen" : "Aufgabe bearbeiten";
    public List<string> CategoryOptions { get; } = [.. TaskCategoryDisplay.Options];
    public List<LearningGroup> Groups { get; }
    public WorkTask? Result { get; private set; }

    public AddEditWorkTaskDialogViewModel(WorkTask? source, List<LearningGroup> groups)
    {
        _source = source;
        Groups = groups;
        if (source is null) return;

        Title = source.Title;
        SelectedCategory = TaskCategoryDisplay.Label(source.Category);
        SelectedGroup = source.GroupId is { } id ? groups.FirstOrDefault(g => g.Id == id) : null;
        DueDateText = source.DueDate?.ToString("dd.MM.yyyy", CultureInfo.InvariantCulture) ?? "";
        EstimatedMinutesText = source.EstimatedMinutes?.ToString(CultureInfo.InvariantCulture) ?? "";
        Notes = source.Notes ?? "";
    }

    [RelayCommand]
    private void Save()
    {
        TitleError = ""; DueDateError = ""; EstimatedMinutesError = "";
        var valid = true;

        if (string.IsNullOrWhiteSpace(Title)) { TitleError = "Titel erforderlich."; valid = false; }

        DateOnly? dueDate = null;
        if (!string.IsNullOrWhiteSpace(DueDateText))
        {
            if (!DateOnly.TryParseExact(DueDateText, "dd.MM.yyyy", null, DateTimeStyles.None, out var d))
            { DueDateError = "Format TT.MM.JJJJ."; valid = false; }
            else dueDate = d;
        }

        int? estimatedMinutes = null;
        if (!string.IsNullOrWhiteSpace(EstimatedMinutesText))
        {
            if (!int.TryParse(EstimatedMinutesText, out var m) || m <= 0)
            { EstimatedMinutesError = "Ganze Zahl > 0 erwartet."; valid = false; }
            else estimatedMinutes = m;
        }

        if (!valid) return;

        Result = new WorkTask
        {
            Id               = _source?.Id ?? Guid.NewGuid(),
            Title            = Title.Trim(),
            Category         = TaskCategoryDisplay.FromLabel(SelectedCategory),
            GroupId          = SelectedGroup?.Id,
            DueDate          = dueDate,
            EstimatedMinutes = estimatedMinutes,
            Status           = _source?.Status ?? WorkTaskStatus.Open,
            Notes            = string.IsNullOrWhiteSpace(Notes) ? null : Notes.Trim(),
            CreatedAt        = _source?.CreatedAt ?? DateTime.UtcNow,
        };
    }
}