LehrerApp/LehrerApp.Desktop/ViewModels/Groups/GroupRolloverViewModel.cs

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

namespace LehrerApp.Desktop.ViewModels.Groups;

public partial class GroupRolloverDialogViewModel : ObservableObject
{
    private readonly LearningGroup _source;
    private readonly GroupRolloverService _rollover;
    private readonly SchoolYearService _schoolYears;

    [ObservableProperty] private string _name;
    [ObservableProperty] private string _targetSchoolYear;
    [ObservableProperty] private int _gradeLevel;
    [ObservableProperty] private bool _copyGradingScheme;
    [ObservableProperty] private bool _archiveSource = true;
    [ObservableProperty] private string _nameError = "";
    [ObservableProperty] private string _schoolYearError = "";
    [ObservableProperty] private string _selectionError = "";
    [ObservableProperty] private string _generalError = "";

    public string SourceSummary => $"{_source.Name} · {_source.SchoolYear} · Stufe {_source.GradeLevel}";
    public bool HasGradingScheme { get; }
    public int SelectedCount => Students.Count(s => s.IsSelected);
    public string SelectedCountText => $"{SelectedCount} von {Students.Count} Schülern ausgewählt";
    public ObservableCollection<GroupRolloverStudentItem> Students { get; } = [];
    public LearningGroup? Result { get; private set; }

    public GroupRolloverDialogViewModel(LearningGroup source,
        IStudentRepository students, IGroupMembershipRepository memberships,
        IGradingSchemeRepository gradingSchemes, SchoolYearService schoolYears,
        GroupRolloverService rollover)
    {
        _source = source;
        _rollover = rollover;
        _schoolYears = schoolYears;
        _name = source.Name;
        _targetSchoolYear = NextSchoolYear(source.SchoolYear, schoolYears);
        _gradeLevel = Math.Min(13, source.GradeLevel + 1);
        HasGradingScheme = gradingSchemes.GetByGroup(source.Id) is not null;
        _copyGradingScheme = HasGradingScheme;

        var sourceEnd = schoolYears.SchoolYearEnd(source.SchoolYear);
        foreach (var membership in memberships.GetByGroup(source.Id)
                     .Select(m => (Membership: m, Student: students.GetById(m.StudentId)))
                     .Where(x => x.Student is not null)
                     .OrderBy(x => x.Student!.LastName).ThenBy(x => x.Student!.FirstName))
        {
            var canSelect = membership.Student!.IsActive;
            var isPreselected = canSelect
                                && GroupMembershipService.IsActiveOn(membership.Membership, sourceEnd);
            var item = new GroupRolloverStudentItem(
                membership.Student, membership.Membership, isPreselected, canSelect);
            item.PropertyChanged += (_, e) =>
            {
                if (e.PropertyName != nameof(GroupRolloverStudentItem.IsSelected)) return;
                SelectionError = "";
                OnPropertyChanged(nameof(SelectedCount));
                OnPropertyChanged(nameof(SelectedCountText));
            };
            Students.Add(item);
        }
    }

    [RelayCommand]
    private void Save()
    {
        NameError = "";
        SchoolYearError = "";
        SelectionError = "";
        GeneralError = "";
        var valid = true;

        if (string.IsNullOrWhiteSpace(Name))
        {
            NameError = "Gruppenname erforderlich.";
            valid = false;
        }
        try
        {
            var targetText = TargetSchoolYear.Trim();
            var targetStart = _schoolYears.SchoolYearStart(targetText);
            if (targetText != _schoolYears.FormatSchoolYear(targetStart.Year))
            {
                SchoolYearError = "Format JJJJ/JJ, z.B. 2027/28.";
                valid = false;
            }
            else if (targetStart <= _schoolYears.SchoolYearStart(_source.SchoolYear))
            {
                SchoolYearError = "Das Zielschuljahr muss nach dem bisherigen liegen.";
                valid = false;
            }
        }
        catch (Exception ex) when (ex is FormatException or ArgumentOutOfRangeException or IndexOutOfRangeException)
        {
            SchoolYearError = "Format JJJJ/JJ, z.B. 2027/28.";
            valid = false;
        }
        if (SelectedCount == 0)
        {
            SelectionError = "Bitte mindestens einen Schüler auswählen.";
            valid = false;
        }
        if (!valid) return;

        try
        {
            Result = _rollover.RollOver(_source, new GroupRolloverRequest(
                Name, TargetSchoolYear.Trim(), GradeLevel,
                Students.Where(s => s.IsSelected).Select(s => s.MembershipId).ToList(),
                CopyGradingScheme, ArchiveSource));
        }
        catch (Exception ex) when (ex is InvalidOperationException or FormatException or ArgumentOutOfRangeException)
        {
            GeneralError = ex.Message;
        }
    }

    private static string NextSchoolYear(string source, SchoolYearService schoolYears)
    {
        var start = schoolYears.SchoolYearStart(source);
        return schoolYears.FormatSchoolYear(start.Year + 1);
    }
}

public partial class GroupRolloverStudentItem : ObservableObject
{
    [ObservableProperty] private bool _isSelected;

    public Guid MembershipId { get; }
    public string FullName { get; }
    public string NiveauText { get; }
    public string MembershipStatus { get; }
    public bool CanSelect { get; }

    public GroupRolloverStudentItem(Student student, GroupMembership membership,
        bool isSelected, bool canSelect)
    {
        MembershipId = membership.Id;
        FullName = student.FullName;
        NiveauText = membership.Niveau?.ToString() ?? "–";
        CanSelect = canSelect;
        _isSelected = isSelected;
        MembershipStatus = BuildStatus(student, membership, isSelected);
    }

    partial void OnIsSelectedChanged(bool value)
    {
        if (!CanSelect && value) IsSelected = false;
    }

    private static string BuildStatus(Student student, GroupMembership membership, bool isPreselected)
    {
        if (!student.IsActive) return "Schüler inaktiv · nicht übernehmbar";
        if (isPreselected) return "Bis Schuljahresende aktiv · vorausgewählt";
        if (membership.LeftAt is { } leftAt) return $"Ausgetreten am {leftAt:dd.MM.yyyy} · nicht vorausgewählt";
        if (membership.Period == MembershipPeriod.H1Only) return "Nur 1. Halbjahr · nicht vorausgewählt";
        return "Am Schuljahresende nicht aktiv · nicht vorausgewählt";
    }
}